Crystal facet effect of WO<sub>3</sub> in heterogeneous catalysis

Crystal facet effect of WO₃ in heterogeneous catalysis

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Miao ZHANG¹, Huixiang WANG¹^,²^,^*, Huipeng LI²^,³, Deshun ZHANG²^,³, Jingwen XU¹, Duojia REN¹, Wei ZHANG¹, Shoufeng XUE¹, Baoliang LÜ¹^,²^,^*

Journal of Fuel Chemistry and Technology | 2026, 54(8) : 20250325-1530 - 20250325-1548

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Journal of Fuel Chemistry and Technology | 2026, 54(8): 20250325-1530-20250325-1548

• REVIEW •

Crystal facet effect of WO₃ in heterogeneous catalysis

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Miao ZHANG¹, Huixiang WANG¹^,²^,^*, Huipeng LI²^,³, Deshun ZHANG²^,³, Jingwen XU¹, Duojia REN¹, Wei ZHANG¹, Shoufeng XUE¹, Baoliang LÜ¹^,²^,^*

Affiliations

¹School of Chemistry and Chemical Engineering, Shanxi Normal University, Taiyuan 030031, China

²Shanxi Key Laboratory of Coal-based Synthetic Oil Product Testing, Changzhi 046000, China

³Shanxi Lu’an Coal-based Clean Energy Limited Liability Company, Changzhi 046200, China

Published: 2026-08-10 doi: 10.1016/S1872-5813(26)60684-6

Outline

Abstract

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As an important transition metal oxide, tungsten trioxide (WO₃) has become one of the most attractive materials in the current field of heterogeneous catalysis due to its comprehensive merits in environmental friendliness, cost-effectiveness and electrical properties. Different crystal facets of WO₃ exhibit significant differences in key catalytic physicochemical properties such as charge separation efficiency, reactant adsorption capacity, and redox activity, which stems from the inherent differences in their atomic arrangement, electronic structure, and surface energy. Relevant studies have confirmed that, influenced by the distinct facet effect, the catalytic performance of WO₃ strongly depends on the exposed facet states determined by its geometric morphology. This finding provides an important direction for mechanism research of modern heterogeneous catalysis. This paper reviews the facet effect of WO₃ as a heterogeneous catalyst in various application fields in recent years, including photocatalysis, electrocatalysis, photoelectrocatalysis, and thermal catalysis process. Meanwhile, combined with theoretical calculations, it explains the intrinsic mechanism underlying the facet effect from the perspective of the atomic structure essence of WO₃ crystal facets. Finally, the paper summarizes the general rules of the WO₃ facet effect across the aforementioned application scenarios, deeply discusses the shortcomings in the current research on the facet effect of WO₃, and prospects the future development direction of this field.

Key words

WO₃ / crystal facet effect / heterogeneous catalysis

Cite this Article

张苗, 王会香, 李慧鹏, 张德顺, 徐静文, 任多佳, 张未, 薛首峰, 吕宝亮. WO₃在多相催化反应中的晶面效应. 燃料化学学报（中英文）, 2026 , 54 (8) : 20250325-1530 -20250325-1548 . DOI: 10.1016/S1872-5813(26)60684-6

Miao ZHANG, Huixiang WANG, Huipeng LI, Deshun ZHANG, Jingwen XU, Duojia REN, Wei ZHANG, Shoufeng XUE, Baoliang LÜ. Crystal facet effect of WO₃ in heterogeneous catalysis[J]. Journal of Fuel Chemistry and Technology, 2026 , 54 (8) : 20250325-1530 -20250325-1548 . DOI: 10.1016/S1872-5813(26)60684-6

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Catalysis plays a vital role in the fields of industrial production, energy conversion and environmental protection^[1−5], such as petroleum refining^[6], synthesis of fiber, plastic^[7], clean utilization of coal^[8] and exhaust gas denitrification^[9]. Therefore, catalysis has evolved into a central discipline in chemistry, and in catalytic processes, heterogeneous catalysis is a core technology due to its advantages of easy separation and recovery, and suitability for continuous production^[10].

The performance of a heterogeneous catalyst largely depends on its specific surface area. Therefore, researches on heterogeneous catalysis commonly adopt strategies such as constructing porous structures (e.g., materials with micropores, mesopores and even macropores), fabricating nanomaterials (e.g., nanoparticles, nanowires, nanosheets, nanoflowers), and engineering hierarchical structures (e.g., complex morphologies including core-shell, hollow, urchin-like and flower-like ones) to boost the specific surface area of heterogeneous catalysts. However, the irregularity and complexity of the aforementioned structures hinder the elucidation of reaction mechanisms at the molecular level and restrict the targeted design of catalysts with high activity, selectivity, and stability.

Since the mid-1950s, metal oxide catalysts have demonstrated irreplaceable roles in areas such as petroleum chemical processing, specialty chemicals synthesis, and environmental remediation, owing to their unique electronic structures and surface chemical properties^[11]. Notably, the catalytic performance of these materials is not only correlated with chemical composition and crystal size, but also strongly associated with crystal morphology^[12−13]. Specifically, by tailoring the morphology of catalysts to achieve selective exposure of specific crystal facets can significantly optimize their catalytic performance^[14−15]. The underlying reason lies in the anisotropic nature of different crystals. Different crystal facets exhibit inherent differences in atomic arrangement, electronic structure and surface energy, which directly influence key catalytic properties such as reactant adsorption, charge separation, and redox activity^[16−17]. This facet-dependent catalytic behavior provides a novel perspective for heterogeneous catalysis research and has made morphology-controlled nanocrystals a focal point of interest in the field of catalytic materials^[18].

WO₃ is an outstanding n-type semiconductor metal oxide, with a high melting point, high strength, and excellent chemical stability^[19−21]. It is not only extensively used in industrial scenarios such as high-melting-point alloys^[22], hard alloys^[23], fire-resistant materials^[24], shielding materials^[25], and ceramic colorants^[26], but has also been practically applied in energy and sensing fields, including lithium-ion batteries, gas sensors, and supercapacitors^[27]. Moreover, WO₃ has a visible-light-responsive bandgap of E_g (2.4–2.8 eV) and a high oxidation potential (>2.5 eV), so it also exhibits significant application value in photocatalysis and electrocatalysis^[28]. Meanwhile, WO₃ features a high oxidation state and excellent thermal stability, thus exhibiting outstanding performance in thermocatalysis.

Over the past two decades, researchers have achieved groundbreaking progress in the study of WO₃ morphology control and facet effect in catalysis, and successfully synthesized WO₃ nanomaterials with exposed specific facets using multiple synthesis strategies, including vapor-phase, liquid-phase, and solid-phase methods^[29−31]. For instance, Zheng et al.^[32] prepared WO₃ thin film dominated by (002) facet on fluorine-doped tin oxide (FTO) glass substrates; Using a hydrothermal method with sodium tungstate as the tungsten source and acetic acid for pH adjustment, Li’s team^[28] synthesized WO₃ nanosheets and nanowires that exposed the (001) and (110) facet, respectively; Lee et al.^[33] prepared WO₃ nanorods exposing the (001) facet using ammonium tungstate, while WO₃ nanorods exposing the (100) and (010) facets were synthesized with sodium tungstate as precursor. These studies have laid a solid material foundation for the systematic investigation of the facet effect of WO₃. Nevertheless, there remains a lack of systematic summaries regarding the structure-activity relationships, underlying mechanisms, and universal laws of the facet effect of WO₃ in diverse heterogeneous catalytic systems. Additionally, related research still confronts numerous scientific challenges and technical bottlenecks.

Against this backdrop, this review aims to systematically summarize the research advances in the facet effects of WO₃ catalysts in heterogeneous catalytic systems (e.g., photocatalysis, electrocatalysis, photoelectrocatalysis and thermal catalysis). Specifically, it focuses on the following aspects: (1) analyzing the structure-activity relationships of different WO₃ facets in various catalytic reactions; (2) elucidating the physicochemical mechanisms underlying the facet effect of distinct crystal facets; (3) summarizing the universal laws governing the facet effect of WO₃ in diverse catalytic systems; (4) discussing the key scientific issues and technical bottlenecks in current research on the WO₃ facet effect; (5) proposing potential breakthrough directions and innovative ideas for future studies in this field. In addition, a brief introduction is also given to the facet effect in the WO₃ sensing process. It is anticipated that this work will provide theoretical support for the rational design and performance optimization for WO₃-based catalytic materials, and offer new perspectives for the expanded application of facet engineering in the field of heterogeneous catalysis.

1　Facet effect of WO₃ in photocatalytic reactions

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WO₃, as a non-toxic, earth-abundant, and low-cost semiconductor, possesses excellent chemical and thermal stability, tunable band gap, high electron mobility, and remarkable visible-light absorption capacity^[34]. These properties make it an ideal candidate material in the field of semiconductor photocatalysis, exhibiting great application potential in scenarios such as photocatalytic water splitting for hydrogen production and pollutant degradation^[35].

Currently, photocatalytic technology has attracted extensive research interest due to its ability to convert solar energy into chemical energy. However, photocatalysts generally suffer from issues like low light utilization efficiency and easy recombination of electron-hole (e⁻-h⁺) pairs^[36]. Crystal facet engineering by regulating the type and ratio of exposed crystal facets of nanomaterials can modify their band structures and atomic arrangements, thereby effectively enhancing photocatalytic performance. Nevertheless, the specific mechanism by which the crystal facets of WO₃ regulate photocatalytic activity remains unclear. In the following sections, the photocatalytic performance and crystal facet effect of WO₃ will be discussed in detail in combination with specific catalytic reactions.

1.1　Water oxidation

Solar-driven water oxidation is an artificial photosynthesis method for clean energy production and storage^[37]. In the study on the Cu₂O/WO₃ series of catalysts, Gong et al.^[38] found that the loading method of Cu₂O over WO₃ exerted a crucial influence on the catalytic performance. Specifically, when the ascorbic acid liquid-phase reduction method was adopted, Cu₂O can be selectively loaded onto the edged (200) and (020) crystal facets of square-like WO₃ (as shown in Figure 1(a), (b)). While when the sodium borohydride liquid-phase reduction method was used, it was randomly distributed on the predominant (002) crystal facet (as shown in Figure 1(c), (d)). After Pt was loaded onto these two catalysts (named Pt@Cu₂O/WO₃ and Cu₂O-Pt/WO₃ for the former and latter, respectively), Figure 1(e) shows the photocatalytic activity under different Cu₂O loadings of the composite catalyst.

At a loading of 1.97%, the photocatalytic O₂ evolution rate of Cu₂O-Pt/WO₃ is only 731.9 μmol/(g·h) (red solid triangle), which is much lower than that of Pt@Cu₂O/WO₃ (1238.6 μmol/(g·h)). The reaction mechanism was proposed as follows. On one hand, square-like WO₃ itself exhibited spatial separation of photogenerated charges between different crystal facets: photogenerated holes (h⁺) tended to migrate preferentially to the (002) facet to form a h⁺-rich region, while photogenerated electrons (e⁻) accumulated on the edge of (200) and (020) facets to form an e⁻-rich region, participating in the photooxidation and photoreduction half-reactions respectively. On the other hand, the catalyst followed the Z-scheme charge transfer mechanism: after WO₃ and Cu₂O were photoexcited, the photogenerated e⁻ in the conduction band (CB) of WO₃ migrated to the edge of (200) and (020) facets and recombined with the photogenerated h⁺ in the valence band (VB) of Cu₂O at the interface. This process not only retained the h⁺ with strong oxidizing ability in the VB of WO₃ but also preserved the e⁻ with strong reducing ability in the CB of Cu₂O. Meanwhile, Pt can efficiently capture the e⁻ from Cu₂O and transfer them to AgNO₃ (serving as the sacrificial agent) to reduce Ag⁺ to Ag. It is precisely the synergy of these effects that significantly improves the catalytic efficiency, enabling Pt@Cu₂O/WO₃ to exhibit excellent photocatalytic O₂ evolution performance (Figure 1(f)).

Wang et al.^[39] designed an unique graphene (GR) hybridized 2D ternary GR/(001)/(100)WO₃ facet junction via a graphene hybridization strategy, which further confirmed the intrinsic difference in the photocatalytic activity of WO₃ with different exposed facets. As shown in Figure 1(g), the photocatalytic oxidation activity of WO₃ with exposed (001) facets was higher compared with that exposed (100) facets. The core design of this catalyst centers on the combination of the advantages of specific crystal facets and the functional properties of graphene: through a facile two-step hydrothermal method, WO₃ with highly exposed (001) facets (denoted as (001) WO₃) was first tightly connected to GR via -C-W- “bridges”. Figure 1(h), (i) showed the corresponding micromorphology, and a proposed sandwich-like configuration was illustrated in Figure 1(j). Graphene, with its dual functions as a “h⁺ trap” and a “co-catalyst”, not only efficiently captured photo-generated h⁺ to reduce charge recombination but also accelerated reaction kinetics. Subsequently, WO₃ with (100) facets (denoted as (100) WO₃) were grown epitaxially on the surface of (001) WO₃, constructing a multi-facet synergistic composite structure (Figure 1(k)). Eventually, the GR/(001)/(100) WO₃ facet junction exhibited excellent water oxidation performance, achieving an apparent quantum efficiency of 26% at 420 nm. The intrinsic origin of its performance advantage lied in the full utilization of the high oxidation activity of the (001) facets of WO₃, as well as the efficient charge transfer and reaction system synergistically constructed by graphene and the facet junction.

1.2　Oxidation of benzyl alcohol

Using clean, renewable solar energy instead of traditional fossil fuels to drive reactions enables efficient conversion of benzyl alcohol into high-value-added chemicals, providing core technical support for green upgrading in the fine chemical industry^[40−41]. Li’s research group^[28] systematically investigated the photocatalytic performance of WO₃ nanowires with exposed (110) facet and WO₃ nanosheets with exposed (001) facet in the selective oxidation of benzyl alcohol to benzaldehyde (Figure 2(a)−(d)). Experimental results demonstrated that the activity of WO₃ with (110) facets for benzyl alcohol oxidation is 2.46 times than that of WO₃ with (001) facets (0.11 mmol/(g·h)).

To elucidate the underlying mechanism, density functional theory (DFT) calculations were performed, which revealed that the effective mass of photogenerated h⁺ on the (110) facet (0.94 m₀, where m₀ denotes the rest mass of an electron) is significantly lower than that on the (001) facet (1.28 m₀). This difference in h⁺ effective mass directly leads to a distinction in h⁺ mobility between the two facets: the (110) facet exhibits a higher h⁺ mobility of 4.92 cm²/(V·s), whereas the (001) facet shows a lower value of 3.14 cm²/(V·s). Further calculations based on the Einstein equation and h⁺ lifetime data indicate that the h⁺ diffusion length on the (110) facet (74.8 nm) is longer than that on the (001) facet (53.4 nm).

In conclusion, the superior photocatalytic performance of the (110) facet arises from the synergistic effects of h⁺: lower effective mass, higher mobility, and longer diffusion length. Meanwhile, Mott-Schottky measurements and XPS (X-ray Photoelectron Spectroscopy) valence band spectrum elucidate the carrier differences between various crystal facets based on microscopic physical mechanisms (Figure 2(e)−(h)).

1.3　N₂ fixation

Photocatalytic N₂ fixation technology utilizes clean and renewable solar energy as the energy source, featuring mild reaction conditions and environmental friendliness. Replacing the conventional NH₃ production process (Haber-Bosch process) holds great significance for energy utilization and environmental sustainability^[42−43]. Currently, the commonly used catalysts mainly include metal oxides, bismuth oxyhalides, and graphitic carbon nitride^[44]. However, the photoexcited e⁻ on these catalysts tend to recombine with h⁺, making it difficult to activate the stable N≡N triple bond, and the electron accumulation efficiency remains low. Restricted by these issues, the efficiency of existing systems is far from meeting practical application requirements^[45].

To overcome this bottleneck, Xiong et al.^[46] pioneered a unique strategy of “electron pump-enhanced facet engineering”. By synergistically tailoring crystal facets and co-catalysts, they constructed a WO₃/C(CN)₃ composite photocatalytic system for N₂ fixation. This system employed WO₃ nanosheets (WO₃ NS) with exposed (100) facet and WO₃ nanowires (WO₃ NW) with exposed (110) facet as substrates, which were coupled with a novel organic semimetallic cocatalyst C(CN)₃. The core design concept is to regulate the interfacial charge transfer pathway by leveraging the differences in electronic structures between different facets of WO₃. As shown in Figure 3(a), HRTEM image revealed that the predominantly exposed facet of WO₃ NS is the (100) facet, on which C(CN)₃ was preferentially coated, while WO₃ NW interacted with C(CN)₃ via the (110) facet.

The calculated work functions of W_f (WO₃ NS: 6.177 eV, WO₃ NW: 3.223 eV, C(CN)₃: 5.220 eV) provided a theoretical basis for determining the direction of electron transfer (Figure 3(b)). Combined with the effect of the interfacial built-in electric field, the charge transfer behaviors of the two composite systems were finally clarified. In the WO₃ NS/C(CN)₃ system (WsC), the built-in electric field drives photogenerated e⁻ to be directionally “pumped” from the (100) facet of WO₃ into the active sites of C(CN)₃, rendering C(CN)₃ e⁻-enriched and thus enabling efficient activation of N₂; In the WO₃ NW/C(CN)₃ system (WwC), the reversed direction of the built-in electric field leads to electron transfer from C(CN)₃ to the (110) facet of WO₃, resulting in C(CN)₃ becoming electron-deficient and losing its N₂ fixation activity (Figure 3(c)). The results of performance tests further confirm the effectiveness of this strategy. As shown in Figure 3(d), (e), the NH₃ production of pure WO₃ NS and WO₃ NW is relatively low, reaching only 3.4 and 1.6 μmol/(g·h), respectively. After modification with C(CN)₃, the catalytic activity of the WsC composites is significantly enhanced. Among them, the WsC1-1 sample (WsC1-1 represents the ratio of WO₃ NS to C(CN)₃ of 1∶1) achieves an NH₃ production of 20.475 μmol/(g·h), which is 4.7 times that of the WwC.

1.4　CO₂ reduction

Solar-driven reduction of CO₂ to high-value hydrocarbon fuels and CO is recognized as an effective approach to address global warming and energy crisis^[47−48]. Among various tungsten oxides, WO₃ is widely employed in the photocatalytic reduction of CO₂ due to its facile preparation and excellent controllability over structure and morphology^[49].

Xie et al.^[50] successfully synthesized two types of WO₃ crystals by controlling the acid hydrolysis of crystalline WB: quasi-cubic WO₃ with nearly equal proportions of (002), (200) and (020) facets, and rectangular sheet-like WO₃ dominated by (002) facets. Figure 4(a) showed the atomic structure models of the (002), (020) and (200) facets in monoclinic WO₃. When these two WO₃ samples were used for the photocatalytic reduction of CO₂ to CH₄ under the same conditions and a significant difference in performance was observed: the WO₃ nanosheets predominantly exposing (002) facets exhibited an activity of 0.34 μmol/(g·h), while the quasi-cubic WO₃ showed no activity. This result indicated that the (002) facet of WO₃ servers as the key active facet for CO₂ photoreduction.

Zhang et al.^[51] integrated facet engineering with heterojunction construction. They prepared 1D WO₃ nanowires dominated by (110) facets (WO₃-110) and 2D hexagonal WO₃ nanosheets dominated by (001) facets (WO₃-001) via a hydrothermal method (as shown in Figure 4(b)−(f)) and further coupled these two WO₃ samples with CuO nanoparticles respectively to construct p-n heterojunction photocatalysts for CO₂ photoreduction. To compare and analyze the separation-recombination performance of photogenerated e⁻-h⁺ pairs between CuO-WO₃-001 nanosheets and CuO-WO₃-110 nanowires, the measurements of photocurrent, electrochemical impedance spectroscopy (EIS), and photoluminescence (PL) were employed (as shown in Figure 4(h)−(j)). All three methods consistently demonstrate that the CuO-WO₃-110 nanowires outperformed the CuO-WO₃-001 nanosheets in both the separation efficiency of e⁻-h⁺ pairs and the interfacial charge transfer rate (Figure 4(g)). Owing to the fact that the (110) facet is more conductive to charge carrier migration, WO₃-110 exhibited higher activity than WO₃-001, the CO yield of the WO₃-110/CuO composite reached 7.647 μmol/(g·h).

Shi et al.^[52] focused on the activity optimization of the WO₃(001) facet in heterojunction systems. Using FTO as the substrate, they synthesized two types of Cu₂O-modified hexagonal WO₃ nanosheet catalysts via vertical growth: Cu₂O/WO₃-001 (with dominant (001) facets) and Cu₂O/WO₃ (without dominant (001) facets). The photocatalytic CO₂ reduction activities of the two catalysts were evaluated under visible light irradiation. The results showed that the activity of Cu₂O/WO₃-001 was superior to that of pure components and Cu₂O/WO₃. After 24 h of light irradiation, the yields of CO, O₂ and H₂ reach 5.73, 2.79 and 0.34 μmol/(g·h), respectively, and good stability was maintained after 4 cycles (Figure 4(k)−(m)). This confirmed the synergistic effect between the (001) facet and the heterojunction. This study further verified that the (001) facet of WO₃ can serve as an efficient site for CO₂ adsorption and activation, while the heterojunction constructed with Cu₂O can enhance charge separation. The synergistic effect of these two factors endows the catalyst with both high activity and practicality.

1.5　Degradation of organic pollutant

WO₃-based semiconductor photocatalysts can effectively degrade a wide variety of organic dyes, including Methyl Orange (MO), Methylene Blue (MB), Alizarin Red S (ARS) and Rhodamine B (RhB)^[53−54]. The type and proportion of its exposed crystal facets are among the core factors determining its degradation performance, which has been verified by numerous experimental studies and theoretical calculations^[55]. In 2017, Wang et al.^[56] synthesized WO₃ nanorods predominantly exposing (200) facet and WO₃ nanosheets with exposed (002) facet using sodium sulfate and ammonium sulfate as capping agents and under different hydrothermal conditions. They evaluated the photocatalytic activity of these materials using RhB as the target reactant, with the apparent rate constant (K_app) as the evaluation index. As shown in Figure 5(a), the K_app value of WO₃ nanosheets (W3) reaches 0.0115 min⁻¹, while that of WO₃ nanorods (W2) is only 0.0034 min⁻¹. Further analysis indicated that the (002) facet exhibited the best visible-light photocatalytic performance due to its highest surface energy, which was confirmed by DFT calculations.

As shown in Figure 5(c), the surface energy of the WO₃(001) facet (equivalent plane of (002)) is 1.74 J/m², which is higher than that of the (100) and (010) facets (1.69 J/m²). Moreover, the electron transfer efficiency on the electrode surface was characterized by EIS. Generally, the smaller the semicircle arc diameter of the EIS spectrum, the lower the electron transfer resistance, corresponding to higher separation and transport efficiency of photoexcited e⁻-h⁺ pairs^[57]. As shown in Figure 5(b), the arc radius on the EIS Nyquist plot of the W3 sample is the smallest, which proved that the (001) facet is more conducive to the separation of charge carriers. This property, together with the high surface energy, collectively endowed it with excellent photocatalytic performance.

Based on this, Zhang et al.^[58] synthesized WO₃ nanocrystals with different exposure ratios of the (001) facet. They found that when the exposure ratio of the (001) facet was the highest, the K_app of RhB degradation by the material reached 0.526 h⁻¹, which was more than 5 times that of commercial WO₃ (0.060 h⁻¹). The research team attributed this performance advantage to the fact that the high-energy facet could generate reactive oxygen species (ROS) more efficiently and further reduce the recombination rate of photogenerated e⁻-h⁺ pairs. This finally confirmed that the exposure ratio of the (001) facet in orthorhombic WO₃ nanocrystals was positively correlated with their photodegradation efficiency. Lee et al.^[33] prepared a WO_AT@PCN hybrid photocatalyst by combining porous g-C₃N₄ nanosheets (PCN) and WO₃ nanorods with exposed (001) facets WO_AT (WO_AT was synthesized using ammonium tungstate as the precursor), which demonstrated significantly enhanced performance for the degradation of oxytetracycline (OT) and naproxen (NP) pollutants under visible light compared with PCN, WO_AT, and WO_ST (WO_ST was synthesized using sodium tungstate as the precursor) with different exposed facets (Figure 5(d)−(g)). Furthermore, the hybrid catalyst exhibited excellent stability and reusability across multiple test runs. They attributed the remarkable photodegradation performance of this hybrid catalyst to three aspects: first, the (001) facets of WO_AT, inherently possess a high specific surface area and excellent charge separation properties; second, the hybrid system enables enhanced visible light absorption; and third, the S-scheme charge transfer pathway formed at the interface can effectively promote the separation of photoexcited charges and enhance the redox capabilities of the separated photoexcited electrons and holes. Wang et al.^[59] prepared flower-shaped WO₃ architectures weaved up of ultrathin nanobelts with oriented (001) facets. Compared with the hydrothermal counterpart assembled by thick, individual WO₃ nanobelts, this (001) faceted flower-shaped WO₃ exhibited improved photocatalytic activity for the degradation of MO, with the reaction K_app enhanced by 2.1 fold. The separation and migration of photogenerated e⁻-h⁺ pairs were characterized by PL spectroscopy. Generally, a lower PL intensity indicates a lower carrier recombination rate and thus a higher photocatalytic activity^[60]. The sample exhibited the weakest PL intensity, demonstrating more efficient separation and transfer of photogenerated carriers. Combined with the photocurrent response tests, it showed a higher photocurrent density under simulated sunlight and maintained approximately 1.5 times the photocurrent density of the WO₃ thick, individual WO₃ nanorods after cycling. Additionally, it had a smaller arc radius in the EIS Nyquist plot. These results collectively confirmed that the highly active (001) facets in WO₃ can facilitate interfacial charge transfer.

Ding et al.^[61] introduced a synergistic effect by constructing a composite system, and also found the key role of the facet effect. They prepared Ag/WO₃ composite catalysts via in situ photoreduction, where silver nanoparticles (Ag NPs) were selectively deposited on the surface of hexagonal WO₃ nanorods with different exposed facets. The degradation of RhB, MO and other organic pollutants was carried out under visible-light irradiation. The results showed that both the intrinsic charge separation property of the (001) facet on WO₃ nanorods and the surface plasmon resonance (SPR) effect of Ag NPscontributed to enhancing visible-light absorption and reducingthe recombination of photogenerated electron-hole pairs.

Finally, the comparison indicated that the Ag/WO₃-001 composite catalyst with the (001) facet as the dominant exposed facet exhibited significantly better photocatalytic degradation activity than the Ag/WO₃-001 composite catalyst with the (100) and (010) facets as the main exposed facets.

Zhu et al.^[62] focused on the regulation of the crystal orientation of hexagonal WO₃ nanorods, and prepared hexagonal WO₃ nanorods with two crystal orientations: [110] and [001] (Figure 5(h)). Their study reveals that hexagonal WO₃ nanorods grown along specific crystal orientations exhibited significant differences in exposed facets. Among them, the nanorods exposing the (001) facet had much higher adsorption capacities for RhB and MB than those exposing the (100) or (110) facet, which once again highlighted the structural advantage of the (001) facet in interacting with organic dye molecules.

In summary, the photocatalytic performance of WO₃ is directly influenced by its exposed facets, among which the (001) facet exhibits the most prominent superiority in the degradation of organic dyes, primarily attributable to its exceptionally high efficiency in separating photogenerated charge carriers. However, the underlying mechanism responsible for this highly efficient charge separation on the (001) facet has not been fully elucidated. Based on this, we speculate that since the (001) facet serves as the starting point for numerous lattice channels in WO₃, these intrinsic channels may induce differential transport behaviors for electrons and holes, thereby enabling effective spatial separation and consequently enhancing the photocatalytic activity.

2　Facet effect of WO₃ in electrocatalytic reactions

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In the field of electrocatalysis, the (001) crystal facet of WO₃ demonstrates unique advantages. For example, to address the sluggish kinetics of conventional electrocatalytic nitrogen reduction reaction (NRR), Hou’s team^[63] developed a dual-driven nitrate electrocatalytic reduction (NO₃RR) system based on a Cu₁/WO₃ catalyst for sustainable NH₃ synthesis. They innovatively utilized nitrate pollutants (

${\mathrm{NO}}_3^- $

) as the nitrogen source for NH₃ production. The Cu₁/WO₃ catalyst was prepared via a simple wet-chemical method, where Cu single atoms were anchored onto the surface of WO₃ nanosheets predominantly exposing the (001) facet with rich in oxygen vacancies (Ov) (Figure 6(a), (c)). Characterization results revealed that the oxygen vacancies in WO₃ (WO₃-Ov) effectively stabilized the Cu atoms, forming a stable Cu-O-W coordination structure, which preserved the nanosheet morphology and enabled uniform distribution of Cu species (Figure 6(b)).

The core innovation of this system lay in its dual-driven mechanism design (Figure 6(d)): On one hand, WO₃ serves as a proton-driving center, with its (001) facet exhibiting excellent water dissociation capability (with an energy barrier of only 0.51 eV, much lower than 1.45 eV for Cu(111)), thereby continuously supplying protons for the reaction (Figure 6(e)). On the other hand, the electron-deficient Cu₁ sites (d-band center of −1.08 eV, higher than that of metallic Cu at −2.13 eV) act as nitrate activation centers, significantly enhancing the adsorption and activation of

${\mathrm{NO}}_3^- $

and its intermediates (Figure 6(f)).

Performance tests showed that Cu₁/WO₃ achieved an NH₃ production rate of 91 mmol/(g·h) at −0.60 V, with an NH₃ selectivity of 99.2% and a Faradaic efficiency of 93.7%, while generating only minimal nitrite by-products. Its overall performance surpassed that of most reported catalysts. Moreover, the catalyst maintained excellent stability after 2880 min of continuous operation and exhibits good tolerance to common impurity ions and organic compounds in water.

Meanwhile, Li et al.^[64] synthesized ultrathin tungsten trioxide (WO₃) nanosheets for efficient electrocatalytic conversion of methane to ethanol. HRTEM images (Figure 6(g)−(j)) showed lattice spacings of 0.366 and 0.372 nm, corresponding to the (200) and (020) planes of monoclinic WO₃, respectively. While the authors proposed the (010) facet as the predominantly exposed surface, further analysis suggested the (001) facet as the more likely active surface. A series of characterizations confirmed that this facet possesses the highest oxygen vacancy concentration. The WO₃ nanosheets achieved an exceptionally high ethanol production rate of 125.1 mmol/(g·h) with 99.4% selectivity at a low potential of 1.2 V vs. RHE over 8 h.

To elucidate the role of oxygen vacancies, the authors performed DFT calculations on pristine WO₃ (denoted as WO₃) and oxygen vacancy-rich WO₃ (denoted as Ov-WO₃), proposing possible reaction pathways for methane conversion on these surfaces. As shown in Figure 6(k), the CH₄* → CH₃* reaction is the key step in CH₄ oxidation. The presence of Ov lowers the energy barrier for this step by 0.92 eV, indicating that Ov-WO₃ facilitated CH₄ activation and initiation of the methane oxidative coupling (MEO) reaction more easily than WO₃. In the second step (CH₃* → CH₂), the carbon in CH₃* could bind with two low-coordination W atoms around the Ov on the Ov-WO₃ surface, significantly reducing the dehydrogenation energy compared to WO₃ (−0.4 eV for Ov-WO₃ vs. 1.49 eV for WO₃). For Ov-WO₃, the rate-determining step was CH₂* → CH₂OH, with the largest energy change of 1.22 eV; whereas for WO₃, it was CH₄ → CH₃*, with an energy change of 1.5 eV, indicating a lower overall energy barrier for CH₄ oxidation on Ov-WO₃. The CH₂OH* + CH₃* → CH₃CH₂OH* step was exothermic (with exothermicities of −1.4 eV for Ov-WO₃ and −2.34 eV for WO₃), favoring C–C bond coupling. In summary, oxygen vacancies on (001) facet served as key active sites, effectively promoted C–H bond activation and C–C coupling during methane conversion, thereby significantly enhanced electrocatalytic activity and ethanol selectivity. This study provided a constructive strategy for designing highly active and selective electrocatalysts for efficient methane conversion.

3　Facet effect of WO₃ in photoelectrocatalytic reactions

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3.1　Water splitting

Photoelectrochemical (PEC) catalysis, which integrates the dual advantages of photocatalysis and electrocatalysis, has become as a pivotal technology for driving various chemical reactions^[65−67]. Among them, PEC water splitting based on semiconductor photoelectrodes not only serves as an ideal and eco-friendly approach for H₂ production using renewable solar energy but also provides a critical pathway for the large-scale production of sustainable hydrogen fuel^[68]. Over the past five decades, improving the solar-to-hydrogen (STH) conversion efficiency has remained a core objective in this field^[69−71]. Against this backdrop, WO₃ is regarded as a highly promising visible-light-responsive photoanode material for PEC water splitting, owing to its environmental benignity, low cost, moderate hole diffusion length of 150 nm (which ensures efficient charge separation) and electron mobility of 12 cm²/(V·s) (which supports effective charge transport)^[72−73]. However, its E_g (2.6–2.8 eV) results in a narrow light response range and low solar light harvesting efficiency. To overcome this limitation, researchers often optimize its performance through doping, heterojunction construction, or facet modification.

Wang et al.^[74] successfully synthesized WO₃ nanosheets with exposed (200) and (002) facets, respectively, via a two-step hydrothermal method by precisely regulating the reaction time and procedures. As shown in Figure 7(a), among these samples, the WO₃ photoanode with exposed (002) facet (1-step-8 h, one-step hydrothermal method with a reaction time of 8 h) achieves a photocurrent density of 3.1 mA/cm² at 1.23 V vs. reversible hydrogen electrode (RHE), which is significantly higher than that of the sample with exposed (200) facet (2.1 mA/cm², 1-step-16 h, one-step hydrothermal method with a reaction time of 16 h). Meanwhile, the researchers investigated their photoresponsive properties and measured their chopped transient photocurrent density vs. time curves. In Figure 7(b), the performance of the (200)-faceted sample degrades sharply after 400 seconds of intermittent light irradiation, whereas the (002)-faceted sample exhibits superior stability. They also evaluated their incident-photon-to-current conversion efficiencies (IPCE) across different wavelength ranges, as shown in Figure 7(c), the IPCE value of the 1-step-16 h photoanode is much lower than that of the 1-step-8 h photoanode, indicating that the exposed (002) facet of the 1-step-8 h photoanode is more conducive to the separation of photoexcited electron-hole pairs.

Liu et al.^[75] prepared WO₃ with e⁻-rich edge (020)/(200) facet and h⁺-rich (002) facet. They then rationally modified the WO₃ surface with Ag nanoparticles and ZnFe layered double hydroxides (ZnFe-LDHs) to construct an Ag/WO₃/ZnFe-LDH composite photoanode (Figure 7(d)). After 4000 s of continuous illumination, the current density of this photoanode remains stable (Figure 7(e)). It achieves a maximum photocurrent density of 1.18 mA/cm² at 1.23 V vs. RHE, which is 14.4 times higher than that of WO₃ without preferential facet orientation (Figure 7(f)). More importantly, it realized an average H₂ production rate of 38.18 μmol/h in natural seawater splitting and exhibited excellent photoelectrochemical stability. As shown in Figure 7(g), the faradaic efficiency of hydrogen evolution in this system is nearly 100%. This successfully addresses the long-standing issues of poor corrosion resistance and low efficiency of traditional photoelectrodes in seawater.

Liu et al.^[76] investigated the underlying mechanism of crystal facet-dependent properties mentioned above. They synthesized four types of WO₃ thin films with different facet orientations (200-WO₃, plate-like WO₃, 002-WO₃ and thin-flake WO₃) and deposited BiVO₄ on their surfaces to construct heterojunctions for PEC water splitting. The results revealed that the Fermi energy of WO₃ exhibits a distinct facet dependence: 200-WO₃ has the highest Fermi energy (5.47 eV), 002-WO₃ the lowest (5.18 eV), while plate-like and thin-flake WO₃ shows intermediate values between these two extremes. This difference directly alters the flat-band potential of the WO₃/BiVO₄ heterojunction—a key parameter influencing the difficulty of initiating PEC reactions. Specifically, the heterojunction constructed with (002)-dominant WO₃ exhibits a more negative flat-band potential due to the lower Fermi energy of (002)-WO₃, leading to a reduced onset potential of 0.868 V vs. RHE in PEC tests. This not only significantly lowers the reaction energy consumption but also improves the energy conversion efficiency of the device, thus clarifying the intrinsic mechanism of facet orientation in regulating heterojunction performance from the perspective of electronic structure.

These studies provide clear insights for the structural design and performance optimization of semiconductor optoelectronic devices and hold great significance for advancing the development of efficient, stable, and practical PEC water splitting technologies.

3.2　Conversion of methane into ethylene glycol

The utilization of methane as a feedstock for the production of value-added chemicals (such as C₂H₆, CH₃OH and HCOOH) represents an important direction in energy catalysis. However, the high stability and inertness of the C–H bond in methane molecules pose significant challenges for its PEC conversion, especially in achieving high selectivity toward C₂₊ products^[77−79]. Xiong’s team^[80] successfully achieved highly efficient PEC methane conversion under mild conditions without external oxidants through facet tuning strategies. Their study first applied DFT calculations to systematically compare the adsorption behaviors of hydroxyl radicals (·OH)—key reactive species—on different facets ((010), (100) and (001)) of monoclinic WO₃. Figure 8(a) shows the lowest-energy adsorption configurations of ·OH on these three facets. The calculated adsorption energies are −1.742, −1.826 and −1.935 eV, respectively. Although ·OH exhibits strong adsorption on all three facets, both its configuration and reactivity demonstrate distinct facet-dependent behaviors: For (100) facet, two adsorbed ·OH are spatially close (1.872 Å) forming hydrogen bond; for (001) facet, ·OH is further converted into H₂O and surface-bound oxygen species; whereas for (010) facet, the vast distance (3.342 Å) effectively suppresses hydrogen bonding and side reactions, thereby preserving the high reactivity of ·OH and facilitating C–H bond activation in methane.

To verify the facet-dependent effects, they designed WO₃ photoanodes with graded (010) facet exposure ratios (nanobars, NB; nanoplates, NP; and nanoflakes, NF), as shown in Figure 8(b), (c). EPR (Electron paramagnetic resonance) measurements using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as a spin-trapping agent were performed to detect ·OH generated on the prepared WO₃ photoanodes. As shown in Figure 8(d), the DMPO-·OH adduct signal intensity follows the order WO₃ NB > WO₃ NP > WO₃ NF, indicating that the ·OH production rate correlates positively with the ratio of (010) facets. Among the tested photoanodes, the WO₃ nanobars with the highest proportion of (010) facets exhibited the best performance in PEC methane conversion. At an applied potential of 1.3 V vs. RHE, the ethylene glycol production rate reaches 0.47 mmol/(cm²·h), with a selectivity of 66% and a Faradaic efficiency of 23.9%—2.5 times higher than that of nanoflakes. At applied potentials of 1.1 and 1.3 V vs. RHE, STF efficiencies of 0.10% and 0.12% are achieved, respectively, with a carbon balance >90% (Figure 8(e), (f)). Furthermore, the system demonstrated high stability over 12 h of PEC methane oxidation. This study highlights the critical role of facet regulation in enhancing radical reactivity and product selectivity, providing new insights for the design of efficient photoanodes for methane conversion.

4　Facet effect of WO₃ in thermocatalytic reactions

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In recent years, the application of WO₃ as an acid catalyst has attracted significant attention, and its catalytic activity is closely related to the distribution of surface acid sites^[81−82]. It has been widely employed in various reactions such as olefin metathesis, epoxidation and isomerization^[83−85], yet investigations into the facet effect have not been conducted in these reactions to date, which constitutes a promising research direction for the future.

Relevant research on the facet effect that has been reported so far is as follows. Gao et al.^[86] investigated the catalytic conversion of furfuryl alcohol (FA) to ethyl levulinate (EL) over WO₃ with different exposed crystal facets (nanosheets with the (001) facet, nanobelts with the (100) facet, and nanoparticles with the (110) facet, see Figure 9(a)−(c) in an ethanol system). WO₃ with the (110) facet achieves an EL production rate of 4.7 mmol/(g·h) at 170 °C, while WO₃ with the (100) and (001) facets mainly converts FA into polymers.

The study pointed out that this difference stems from the varying characteristics of acid sites on different crystal facets. Specifically, the (110) facet not only has a higher total number of atoms and a higher proportion of W atoms but also is rich in high-valence W⁶⁺ species and W=O bonds with high binding energy, which significantly enhances its surface acidity. This facet possesses both strong Brønsted acid sites (BAS) and Lewis acid sites (LAS): the former can provide protons, while the latter promotes the adsorption of reactant molecules. The synergistic effect of these two types of acid sites efficiently facilitates the conversion of FA to EL (Figure 9(d)).

In contrast, the (100) facet has a high proportion of W atoms but a small total number of atoms. Although it is favorable for the formation of LAS, the acid strength is weak. Due to the dominance of strong LAS and the weakness of BAS, it tends to cause FA to form polymers. The (001) facet has a large total number of atoms but a high oxygen proportion and low binding energy of W⁶⁺, which is not only unfavorable for the exposure of W atoms but also inhibits the formation of hydroxyl groups, resulting in only weak LAS and BAS.

In addition, the (110) facet catalyst exhibits better sustainable catalytic performance than the (100) facet catalyst. All the above conclusions were verified by characterization techniques such as FT-IR and NH₃-TPD (Figure 9(e)−(h)).

The facet effect of WO₃ was not only observed in heterogeneous catalytic reactions but also applicable in the field of gas sensing involving chemical conversion. In the field of gas sensing, WO₃-based materials have attracted significant research interest due to their high sensitivity and selectivity^[87−88]. Yin et al.^[89] synthesized thickness-controlled rectangular WO₃ nanosheets predominantly exposing (020) and (200) facets via a low-temperature acid-assisted (hydrochloric acid) hydrothermal method followed by thermal treatment. The resulting samples a1, a2 and a3 had average thicknesses of approximately 110, 70 and 10 nm, respectively, with the (020) facet exposure ratio following the order a3 > a1 > a2. The sensors prepared using samples a1, a2 and a3 are labeled as sensor 1, sensor 2 and sensor 3, respectively. It was found that the gas-sensing response to acetone significantly increased with higher exposure of the (020) facet, demonstrating distinct facet-dependent behavior.

As shown in Figure 10(a)−(c), when tests at their respective optimal operating temperatures toward 1.0×10⁻⁴ of various gases, sensor 3 exhibits superior acetone sensing performance: a high response value of 49.1. As shown in Figure 10(d), at the same gas concentration, sensor 3 exhibits the highest response intensity. Meanwhile, it has a low detection limit of 5.0×10⁻⁷ (Figure 10(e)) and rapid response/recovery times of 7 and 19 s, respectively. The sensing mechanism was further discussed, suggesting that the abundant dangling bonds and localized electric polarization on specific exposed facets may be key factors contributing to the high sensitivity and selectivity toward acetone.

On the other hand, addressing the need for detecting toxic, volatile, and flammable triethylamine (TEA) in industrial settings, Wang et al.^[90] prepared a series of WO₃ samples (denoted as C1-400, C2-400, C4-400 and C6-400) using alcohols with different carbon chain lengths (methanol, ethanol, n-butanol, cyclohexanol) as solvents, combined with solvothermal pretreatment at 180  °C and subsequent calcination at 400  °C in air. XRD quantitative analysis of normalized intensity ratios of characteristic facets revealed that the (002) facet intensity ratio of C2-400 was significantly lower than those of other samples. Meanwhile, UPS (Ultraviolet Photo-electron Spectroscopy) characterization combined with W_f (work function) calculations indicated that C2-400 possessed a notably higher W_f (Figure 10(g)−(i)). This phenomenon was attributed to surface electronic restructuring induced by the lowest proportion of the (002) facet. A higher W_f requires more energy to excite electrons for participation in gas-sensing reactions, which correlates well with the optimal operating temperature of C2-400 at 325 °C—significantly higher than those of C1-400 (275 °C) and C4-400 (250 °C). As shown in Figure 10(f), at this temperature, C2-400 exhibits a high response value, excellent selectivity, fast response/recovery (3 s/5 s) to 1.0×10⁻⁶ TEA, and a detection limit as low as 2.0×10⁻⁷, well below the ACGIH threshold of 1.0×10⁻⁶. These results fully demonstrated the critical role of facet structure in regulating electronic properties and gas-sensing behavior.

5　Summary and outlook

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This review systematically elucidates the facet-dependent effects of WO₃ nanocrystals in heterogeneous catalytic systems, including photocatalysis, electrocatalysis, photoelectrocatalysis, and thermal catalysis. In the field of photocatalysis, the interfacial charge separation characteristics and electronic structure differences of WO₃ determine its activity in water oxidation, benzyl alcohol oxidation, N₂ fixation, and CO₂ reduction. DFT calculations revealed that the (110) facet exhibits outstanding performance in benzyl alcohol oxidation due to the synergistic advantages of its lower effective hole mass, higher hole mobility, and longer hole diffusion length. In organic pollutant degradation reactions, the (002) facet demonstrates excellent photogenerated charge carrier separation and transport properties, attributed to its highest surface energy and the minimal electron transfer resistance confirmed by EIS. In electrocatalytic oxygen evolution, the (001) facet shows remarkable performance owing to its high specific surface area and optimized adsorption energy. In photoelectrocatalysis methane conversion, DFT calculations uncover the differences in·OH adsorption behavior across various crystal facets, clarifying the regulating mechanism of facet structure on reaction pathways. In thermal catalysis, the (110) facet achieves superior catalytic efficiency through the synergistic effect of its unique Brønsted and Lewis acid sites. In gas sensing applications, the (020) facet shows high selectivity toward molecules such as triethylamine and acetone, owing to its excellent gas adsorption capacity and redox properties.

However, current research predominantly remains at the level of phenomenological description and fragmented attribution of performance differences among crystal facets. Although various characterization techniques have partially established “structure-property” correlations, studies have yet to deeply elucidate the unified physicochemical mechanisms underlying the facet effects or extract universal structure-activity relationships.

Despite significant progress, several challenges remain in the study of facet effects in WO₃: (1) The controllable synthesis of high-index facets remains challenging; (2) Theoretical understanding of the atomic arrangement, dangling bonds, and electronic structure of different facets is insufficient; (3) The coupling effects of size, facet synergy, and interfacial charge behavior are often overlooked; (4) Research on facet effects in thermal and electrocatalysis is still relatively limited. Future research should focus on developing precise facet control strategies, combining in situ characterization and theoretical calculations to reveal interfacial reaction mechanisms, expanding the application of facet effects to more catalytic systems, and promoting the design of practical catalysts.

Based on literature researches, we have summarized the current representative performance benchmarks across various catalytic fields, providing important reference data for the evaluation of catalytic materials. (1) In the field of photocatalysis, under visible light, the highest oxygen evolution rate for photocatalytic water oxidation can reach 631.33 mmol/(g·h), with an oxygen evolution quantum efficiency of 84% at a wavelength of 400 nm. For the oxidation of benzyl alcohol to benzaldehyde, the optimal catalyst achieves a benzaldehyde production rate of 23.068 mmol/(g·h) and a conversion rate as high as 99%. The highest reported NH₃ production rate for photocatalytic nitrogen fixation is 521.37 μmol/(g·h). For photocatalytic CO₂ reduction, the CO production rate can reach 1.7 × 10⁶ μmol/(g·h). In the field of organic pollutant degradation, the K_app values for the degradation of MO and RhB can be as high as 0.05 min⁻¹. (2) In the field of electrocatalysis, nitrate-to-ammonia synthesis can achieve 100% ammonia selectivity and a Faradaic efficiency exceeding 98%, with an ammonia production rate of 1.18 × 10⁴ mmol/(g·h). (3) In the field of photoelectrocatalysis water splitting, the highest reported photocurrent density reaches 4.8 mA/cm² (at 1.23 V vs. RHE) with excellent stability exceeding 120 h. (4) In thermocatalysis, the production rate of ethyl levulinate (EL) from thermocatalytic conversion of furfuryl alcohol reaches 9.61 mmol/(g·h). Moreover, in electrochemical sensing, the lowest detection limit for acetone is as low as 5.0×10⁻⁸, and for triethylamine, it reaches 1.0×10⁻⁷. Considering the above reference values, the catalytic performance of WO₃ exhibits clear field-specific disparities. In photoelectrocatalytic and electrocatalytic methane conversion systems, the current performance of WO₃ is at a high level, whereas in other catalytic fields, its performance is generally at a medium level. This review primarily emphasizes how the facet effects of WO₃ influence its catalytic behavior from a mechanistic perspective. Therefore, the selected case studies aim to demonstrate how different facet exposures significantly alter catalytic performance trends and selectivity. To further enhance the catalytic performance of WO₃ across various fields in the future, strategies such as doping and modification can be employed to optimize its electronic structure and surface active site properties, providing a reference direction for subsequent performance optimization research.

In summary, the study of facet effects in WO₃ is evolving from macroscopic performance regulation to atomic-level mechanistic understanding. Through multidisciplinary collaboration and advanced characterization techniques, breakthroughs in both fundamental theory and practical applications can be anticipated.

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doi: 10.1016/S1872-5813(26)60684-6

Receive Date：2025-10-30
Online Date：2026-09-23
Published：2026-08-10

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Received：2025-10-30
Revised：2025-12-15
Accepted：2025-12-17

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¹School of Chemistry and Chemical Engineering, Shanxi Normal University, Taiyuan 030031, China

²Shanxi Key Laboratory of Coal-based Synthetic Oil Product Testing, Changzhi 046000, China

³Shanxi Lu’an Coal-based Clean Energy Limited Liability Company, Changzhi 046200, China

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Tel: 0351-2051-294, E-mail: wanghx@sxnu.edu.cn

lvbl@sxnu.edu.cn

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表12种不同金属材料的力学参数

科 Family	属数 Number of genus	种数 Number of species	占总种数比例 Percentage of total species (%)	属 Genus	种数 Number of species	占总种数比例 Percentage of total species (%)
鹅膏菌科Amanitaceae	2	11	5.26	鹅膏菌属 Amanita	10	4.78
小菇科 Mycenaceae	2	12	5.74	丝盖伞属 Inocybe	5	2.39
多孔菌科 Polyporaceae	8	14	6.70	蜡蘑属 Laccaria	5	2.39
红菇科 Russulaceae	3	23	11.00	小皮伞属 Marasmius	6	2.87
				小菇属 Mycena	11	5.26
				光柄菇属 Pluteus	5	2.39
				红菇属 Russula	17	8.13
				栓菌属 Trametes	5	2.39

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Fig.1 (a) TEM and (b) HRTEM images of Cu₂O/WO₃ prepared by ascorbic acid liquid-phase reduction method; (c) TEM and (d) HRTEM images of Cu₂O/WO₃ prepared by sodium borohydride liquid phase reduction; (e) Photocatalytic water oxidation activities of different Cu₂O loadings; (f) Schematic diagram for photoexcited carriers separation processes in Pt@Cu₂O/WO₃ photocatalyst; (g) The rate of O₂ production and AQE (apparent quantum efficiency) on (100) and (001) planes of WO₃; (h) SEM, (i) TEM images and (j) SAED pattern of GR/(001)/(100)WO₃ (its schematic diagram is inset of (j)); (k) The possible mechanism for the enhanced water oxidation on this unique catalyst^[38−39](with permission from Elsevier)

Fig.2 (a) and (b) SEM graph of nanowire and nanosheet (inset TEM graph); (c) and (d) HRTEM graph of nanowire and nanosheet; (e), (f) Mott-Schottky plot of (110) and (001); (g), (h) XPS valence band spectrum of (110) and (001)^[28](with permission from ACS Publications)

Fig.3 (a) FE-SEM, TEM, HRTEM, HAADF and EDS mapping images of WsC1-1 and WwC1-1; (b) Electrostatic potential of C(CN)₃, WO₃ NS (100) and WO₃ NW (110); (c) Synthesis of WsC and WwC composites, and the electrons transfer in built-in electric field under light irradiation; (d) NH₃ yield of the prepared samples (λ > 420 nm); (e) The production rate of NH₃ of the prepared samples^[46](with permission from Elsevier)

Fig.4 (a) Crystalline model of the nanosheet^[50]; (b) Schematic illustration of the preparation procedures of samples; (c), (d) TEM and HRTEM images of CuO-WO₃-001 nanosheets and (e), (f) CuO-WO₃-110 nanowires; (g) Schematic illustration of the charge separation; (h) Photocurrent response, (i) EIS and (j) PL spectra of both samples^[51]; (k) Photocatalytic performance of CO₂ reduction over samples (Cu₂O a; WO₃ b; WO₃-001 c; Cu₂O/WO₃ d; Cu₂O/WO₃-001 e; Cu₂O/WO₃-001-m f); (l) Total yields of the products; (m) Recyclability test of Cu₂O/WO₃-001 catalyst^[52] (with permission from RSC Publications, Elsevier)

Fig.5 (a) The first-order kinetics of RhB photocatalytic degradation over WO₃ photocatalysts and (b) their EIS^[56]; (c) Schematic drawing of the crystal structure and 2D atom arrangement on the (001), (100) and (010) facets^[58]; (d) and (f) Photocatalytic degradation performance comparison of the synthesized samples in terms of the removal of OT and NP; (e) and (g) The corresponding kinetics plots for OT and NP degradation^[33]; (h) Illustration of the growth orientation of the hexagonal single crystal WO₃ nanorods^[62] (with permission from Elsevier, RSC Publications)

Fig.6 (a) Schematic illustration of synthesis procedure for Cu₁/WO₃ catalyst; (b) TEM images of WO₃ and Cu₁/WO₃; (c) HRTEM image of Cu₁/WO₃; (d) Schematic illustration of the dual-driven NO₃RR mechanism; (e) Free energy profiles for water dissociation on Cu(111) and WO₃(002) at pH value 13.2, respectively; (f) Projected density of states (PDOS) for the Cu of Cu(111) and Cu₁/WO₃(002), respectively^[63]; (g)−(j) Morphological and structural characterizations of S200/30 (Reaction time: 200 ℃, 30 h); (k) Reaction path and reaction energy profiles for CH₄ electrocatalytic oxidation to ethanol on the surfaces of WO₃ and Ov-WO₃ respectively^[64] (with permission from John Wiley and Sons, Elsevier)

Fig.7 (a) Photocurrent density vs. applied potential curves and (b) vs. time measured at 1.23 V vs. RHE, (c) IPCE spectra of the 1-step-16 h (black curves), 1-step-8 h (magenta curves) and 2-step-16 h (blue curves) photoanodes; (d) Schematic illustration for the fabrication of Ag/WO₃/ZnFe-LDH NSAs; (e) Photocurrent–potential curves of different samples under illumination; (f) Amperometric I–t curves; (g) Total H₂ production detected by a gas chromatograph^[74−75](with permission from Elsevier)

Fig.8 (a) The atomic structures of ·OH adsorption on twinning W atoms of (010), (100) and (001) facets; (b) SEM images of WO₃ NB, WO₃ NP and WO₃ NF; (c) Schematic illustration for monoclinic WO₃ nanostructures with different (010) facet ratios on substrates; (d) EPR detection of ·OH using DMPO as a spin-trapping agent of WO₃ NB, WO₃ NP and WO₃ NF; (e) Production rate and (f) carbon selectivity of EG produced in PEC CH₄ conversion on WO₃ photoanodes with different (010) facet ratios at a range of potentials under 100 mW/cm² illumination^[80](with permission from John Wiley and Sons)

Fig.9 TEM and HRTEM images of (a1, a2) WO₃ nanosheets, (b1, b2) WO₃ nanobelts, (c1, c2) WO₃ nanoparticles; (d) Relationship between the WO₃ catalyst structure and acid site distribution; (e) FT-IR spectra of furfuryl alcohol, ethyl alcohol, and ethyl levulinate; (f) FT-IR changes in the conversion of furfuryl alcohol to ethyl levulinate at 150 ℃ in N₂ (from top to bottom, the curves correspond to the following reaction times: 5, 10, 15, 20, 25, 30, 32, 35, 38, 40 min); (g) NH₃-TPD spectra of the WO₃ catalysts with different morphologies; (h) Distribution of acidic sites over the WO₃ catalysts with different morphologies obtained by NH₃-TPD^[85](with permission from RSC Publications)

Fig.10 (a)−(c) Responses of the sensors to 1.0×10⁻⁴ various gases; (d) Acetone response plots of the sensors from 5.0×10⁻⁶−1.0×10⁻³ (The inset is an enlarged image of the dashed box part); (e) The corresponding logarithm fit curves^[89] of sensor 1, sensor 2 and sensor 3 with (020) facet increasing; (f) Responses of the sensors based on C1-400, C2-400 (more (002) facet), C4-400 and C6-400 upon exposure to 1.0×10⁻⁴ TEA in different operating temperatures; (g)−(i) UPS spectra of the C1-400, C2-400 and C4-400 samples^[90](with permission from Elsevier)

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