燃料化学学报（中英文）

界面调控提升CuBi₂O₄光阴极光电化学性能

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江姗姗 , 刘大博 , 肖梦媛 , 范晓星 ^*

燃料化学学报（中英文） | 2026,54(4): 20250224-691-20250224-699

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燃料化学学报（中英文） 2026 , 54 (4) : 20250224-691 -20250224-699

界面调控提升CuBi₂O₄光阴极光电化学性能

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江姗姗, 刘大博, 肖梦媛, 范晓星^*

作者信息

辽宁大学物理学院, 辽宁沈阳 110036

通讯作者:

范晓星

Interface regulation for enhanced photoelectrochemical performance of CuBi₂O₄ photocathodes

Shanshan JIANG, Dabo LIU, Mengyuan XIAO, Xiaoxing FAN^*

Affiliations

School of Physics, Liaoning University, Shenyang 110036, China

Corresponding Author:

Tel: 18640064965, E-mail: xxfan@lnu.edu.cn

出版时间: 2026-04-10 doi: 10.1016/S1872-5813(26)60647-0

文章导航

摘要

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光电化学(PEC)水分解是一种将太阳能直接转化为清洁氢燃料的有效途径。铋酸铜(CuBi₂O₄)作为可见光响应的p型半导体，具有合适的带隙与稳定性。然而，其性能受限于较高的界面电阻以及严重的载流子复合。本研究在FTO与CuBi₂O₄之间引入CuO中间层，构筑CuO/CuBi₂O₄光阴极，以改善界面电荷转移。结果表明，CuO/CuBi₂O₄-200在0 V vs. RHE下的光电流密度达−1.71 mA/cm²，是CuBi₂O₄的3.5倍以上；在365 nm处的IPCE提升至~13%，最大ABPE达0.17%。水分解实验显示其氢气产量为2.05 μmol/cm²，显著优于未修饰电极。性能提升表明，CuO层构建了有利的能带匹配，促进了空穴向FTO的传输，并有效抑制了界面载流子复合。本研究提出了一种简便高效的界面调控工程策略，为高性能半导体PEC光电极的设计与开发提供了新的思路与指导。

关键词

光电化学 / CuBi₂O₄光阴极 / 界面 / 分解水

Abstract

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Photoelectrochemical (PEC) water splitting is an effective approach to directly convert solar energy into clean hydrogen fuel. As a visible-light-responsive p-type semiconductor, CuBi₂O₄ possesses a suitable bandgap and good stability. However, its performance is inhibited by high interfacial resistance and severe charge carrier recombination. In this study, a CuO interlayer was introduced between fluorine-doped tin oxide (FTO) and CuBi₂O₄ to construct CuO/CuBi₂O₄ photocathodes, aiming to improve interfacial charge transfer. The results showed that CuO/CuBi₂O₄-200 exhibited a photocurrent density of −1.71 mA/cm² at 0 V vs. RHE, which was more than 3.5 times higher than that of bare CuBi₂O₄. The incident photon-to-current efficiency (IPCE) at 365 nm was enhanced to ~13% and the maximum applied bias photon-to-current efficiency (ABPE) reached 0.17%. Water splitting experiments revealed a hydrogen yield of 2.05 μmol/cm², significantly surpassing that of the unmodified photoelectrode. The enhanced PEC performance indicated that the CuO layer established a favorable band alignment, promoted hole transport toward the FTO substrate and effectively suppressed interfacial carrier recombination. This work demonstrated a simple and efficient interfacial engineering strategy, offering new insights and guidance for the design and development of high-performance semiconductor-based PEC photoelectrodes.

Key words

photoelectrochemistry / CuBi₂O₄ photocathode / interface / water splitting

引用本文

江姗姗, 刘大博, 肖梦媛, 范晓星. 界面调控提升CuBi₂O₄光阴极光电化学性能. 燃料化学学报（中英文）, 2026 , 54 (4) : 20250224-691 -20250224-699 . DOI: 10.1016/S1872-5813(26)60647-0

Shanshan JIANG, Dabo LIU, Mengyuan XIAO, Xiaoxing FAN. Interface regulation for enhanced photoelectrochemical performance of CuBi₂O₄ photocathodes[J]. Journal of Fuel Chemistry and Technology, 2026 , 54 (4) : 20250224-691 -20250224-699 . DOI: 10.1016/S1872-5813(26)60647-0

正文

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The global transition toward carbon-neutral energy systems has intensified the search for clean and sustainable technologies to replace fossil fuels^[1−2]. Among the emerging energy carriers, hydrogen (H₂), with its high gravimetric energy density and low environmental impact, is widely regarded as an ideal clean energy carrier^[3−4]. To enable large-scale hydrogen production in an environmentally benign manner, solar-driven PEC water splitting has gained significant attention as a promising and scalable route for converting abundant solar energy directly into green hydrogen^[5−7].

In a PEC system, the photocathode plays a crucial role in driving the hydrogen evolution reaction, which directly determines the overall PEC conversion efficiency^[8−10]. Among various materials, p-type CuBi₂O₄ semiconductors, with a narrow band gap (1.5−1.8 eV), strong visible-light absorption and good chemical stability, have emerged as a highly attractive photocathode candidate^[11−12]. Compared with conventional photocathode materials such as Cu₂O^[13] and Si^[14], CuBi₂O₄ exhibits superior resistance to photocorrosion and more favorable band-edge alignment for solar-driven water splitting^[15−16]. Despite these advantages, the practical application of CuBi₂O₄ remains hindered by severe photogenerated carrier recombination, limited charge-transport efficiency, and high interfacial resistance at the interface of electrode and substrate^[17]. Therefore, some strategies are urgently needed to regulate carrier dynamics and accelerate interfacial charge-transfer, thereby exploiting the potential of CuBi₂O₄ photocathodes for efficient solar driven H₂ production.

Various strategies have been developed to enhance the PEC performance of CuBi₂O₄ photocathodes, including elemental doping, surface catalyst loading, heterostructure construction, and band-structure engineering^[18−20]. For example, Hu et al.^[21] improved the carrier concentration of CuBi₂O₄ photocathodes by introducing strontium dopants. The surface-enriched SrCO₃ effectively passivated surface trap states, inhibited interfacial recombination and enhanced band bending within the bulk material. Most previous efforts have primarily focused on modifying the photoactive layer or the electrode surface, less research has paid attention to the interface charge transfer between the photoelectrode and the conductive substrate^[22]. However, the interface remains a key factor limiting the overall device efficiency^[23]. Therefore, improving interface charge-transport between CuBi₂O₄ and FTO substrate is a potential strategy for boosting PEC efficiency.

In this study, a CuO interlayer was introduced between the FTO conductive glass and the CuBi₂O₄ photocathode via an electrochemical deposition method. As a p-type semiconductor, CuO exhibits excellent hole-transport properties and a suitable band structure that is well matched with that of CuBi₂O₄. Additionally, the CuO interlayer alleviated interfacial defects between CuBi₂O₄ and FTO, reduced the interfacial resistance and improved charge-transport kinetics. As a result, the CuO/CuBi₂O₄ photocathode exhibited notable improvements in both photocurrent response and stability. Furthermore, the optimized CuO/CuBi₂O₄-200 photocathode can be successfully coupled with a BiVO₄ photoanode to construct a tandem device that enables overall water splitting under bias-free conditions, demonstrating its excellent potential for practical PEC device integration.

1　Experimental

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1.1　Preparation of CuO photocathode

CuO layers were fabricated on FTO substrates via electrodeposition, following a method similar to previously reported protocols^[24]. A solution of 0.43 g of copper(II) chloride dihydrate (CuCl₂·2H₂O) and 0.15 g of potassium chloride (KCl) was dissolved in 50 mL of distilled water, followed by 20 min of magnetic stirring to form the electrodeposition electrolyte. The CuO films were prepared using a three-electrode system, where FTO conductive glass served as the working electrode, a platinum sheet as the counter electrode, and an Ag/AgCl (saturated KCl) electrode as the reference. Electrodeposition was performed at a constant potential of −0.5 V (vs. Ag/AgCl) for durations of 150, 200, 250 and 300 s. After deposition, the FTO electrode was rinsed with deionized water and air-dried to obtain a red copper film. The samples were then annealed in a muffle furnace at 450 °C for 2 h, transforming the copper film into a CuO film.

1.2　Preparation of CuO/CuBi₂O₄ photocathode

CuO/CuBi₂O₄ photocathodes were fabricated on FTO/CuO substrates via electrodeposition. To prepare the copper precursor solution, 0.02 g of copper(II) nitrate trihydrate (Cu(NO₃)₂·3H₂O) was dissolved in 20 mL of distilled water and magnetically stirred for 20 min. Subsequently, 0.08 g of bismuth(III) nitrate pentahydrate (Bi(NO₃)₃·5H₂O) was dissolved in 20 mL of distilled water and stirred for an additional 20 min. To promote the dissolution of the bismuth salt, 10 mL of a 10% nitric acid (HNO₃) solution was added to the mixture, yielding the bismuth precursor solution. The combined solution was then sonicated for 30 min to ensure uniform dispersion, resulting in the electrodeposition precursor solution. The electrodeposition of the Bi-Cu film followed the same procedure as for the Cu film, using a three-electrode system with FTO/CuO as the working electrode, a platinum sheet as the counter electrode, and an Ag/AgCl (saturated KCl) electrode as the reference. Electrodeposition was conducted at a constant potential of −0.4 V (vs. Ag/AgCl) for 10 min, resulting in a co-deposited Bi-Cu film. After electrodeposition, the sample was removed, dried at room temperature, and then calcined in a muffle furnace at 550 °C for 2 h to obtain the CuO/CuBi₂O₄ photocathode. The composite photoanodes prepared with different CuO electrodeposition durations (100, 150, 200 and 250 s) were denoted as CuO/CuBi₂O₄-100, CuO/CuBi₂O₄-150, CuO/CuBi₂O₄-200 and CuO/CuBi₂O₄-250, respectively. For comparison, the CuBi₂O₄ sample was prepared using the same method, except without the CuO interlayer step.

The experimental reagents, material characterization, PEC testing, and designed formulas involved in this study can be found in the supplementary materials.

2　Results and discussion

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2.1　Morphology and structure characterization

The phase structure of the samples was characterized by X-ray diffraction (XRD). As shown in Figure 1, for CuBi₂O₄, diffraction peaks appeared at 20.92°, 28.09°, 33.36° and 46.80° can be indexed to the (200), (211), (310) and (411) planes, respectively, in good agreement with the standard JCPDS No. 79-1810^[25]. For CuO, the peaks located at 32.52°, 35.57°, 37.53° and 38.77° correspond to the (022), (311), (−222) and (440) planes, respectively, matching well with the standard JCPDS No. 80-1268^[26]. Furthermore, the XRD patterns of CuO/CuBi₂O₄-150, CuO/CuBi₂O₄-200, CuO/CuBi₂O₄-250 and CuO/CuBi₂O₄-300 clearly showed an increase in the intensity of CuO-related peaks with increasing CuO content, which is consistent with the experimental expectations. These results confirmed the successful introduction of CuO layer.

The surface and cross-sectional morphologies of the films were characterized using scanning electron microscopy (SEM). As shown in Figure 2(a), the CuO film electrodeposited onto the FTO substrate exhibited an irregular, block-like structure. In contrast, the CuBi₂O₄ film (Figure 2(b)) presented a uniformly distributed, worm-like morphology. Upon deposition of CuBi₂O₄ onto the FTO/CuO substrate, a dense and homogeneous CuBi₂O₄ layer is formed that uniformly covers the CuO surface, confirming the successful construction of the CuO/CuBi₂O₄ photocathode (Figure 2(c)). Cross-sectional SEM images further revealed that the CuO layer is completely covered by CuBi₂O₄, resulting in a compact and well-integrated composite structure (Figure 2(d)−(f)).

Transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) were employed to examine the interfacial structure between CuO and CuBi₂O₄. The TEM images revealed a distinct and well-defined junction between the two phases (Figure 2(g)). Clear lattice fringes with spacings of 0.246 and 0.289 nm are observed, corresponding to the (–111) plane of CuO and the (002) plane of CuBi₂O₄, respectively, consistent with the standard PDF cards for CuO (#80-1268) and CuBi₂O₄ (#79-1810) (Figure 2(h)). The presence of locally disordered lattice fringes at the interface further confirmed the good contact between CuO and CuBi₂O₄. Moreover, energy-dispersive X-ray spectroscopy (EDS) analysis verifies the coexistence of Cu, O and Bi within the CuO/CuBi₂O₄ film, indicating the successful synthesis of the heterostructured photocathode (Figure 2(i)).

X-ray photoelectron spectroscopy (XPS) was employed to analyze the composition of the films. As shown in Figure 3, the XPS spectra of the pristine CuBi₂O₄ and the CuO/CuBi₂O₄ film were compared. In the Bi 4f spectra (Figure 3(a)), the Bi 4f_7/2 and Bi 4f_5/2 peaks of the pristine CuBi₂O₄ were located at approximately 159 and 164 eV, respectively, corresponding to the typical oxidation state of Bi³⁺. In contrast, the peaks in the composite sample underwent a negative shift of about 0.10−0.20 eV, indicating an increase in the electron cloud density around Bi due to the presence of CuO and suggesting a redistribution of charge at the interface^[27]. In the Cu 2p spectra (Figure 3(b)), the Cu 2p_3/2 peak of the pristine CuBi₂O₄ film was centered at 933−934 eV, accompanied by a pronounced satellite peak (~942 eV), which is characteristic of Cu²⁺ species. For the composite sample, the main peak shifted positively by approximately 0.20−0.30 eV, while the intensity of the satellite peak is significantly reduced. This indicated that the local electronic environment of Cu was modified upon the introduction of CuO, which was consistent with the role of CuO as a hole transport layer that facilitated interfacial charge transfer^[28]. In the O 1s spectra (Figure 3(c)), the main peak for the pristine CuBi₂O₄ appeared at 529.5 eV (lattice oxygen). In the composite sample, a notable increase in peak intensity was observed at approximately 531 eV, which was attributed to surface-adsorbed hydrogen species. This suggested that the CuO interlayer promoted the surface passivation of oxygen, thereby enhancing the stability and interfacial properties^[29]. Overall, the XPS results confirmed the formation of a stable interface interaction between CuO and CuBi₂O₄, which facilitated charge redistribution and separation. Furthermore, these results provided further validation of the role of CuO as an effective hole transport layer in the FTO/CuBi₂O₄ system.

2.2　PEC properties evaluation

The PEC performance of CuBi₂O₄ and CuO/CuBi₂O₄ composite films was evaluated using a three-electrode electrochemical analysis system. As shown in Figure 4(a), the photocathodes of CuBi₂O₄, CuO/CuBi₂O₄-150, CuO/CuBi₂O₄-200, CuO/CuBi₂O₄-250 and CuO/CuBi₂O₄-300 achieved photocurrent densities of approximately −0.49, −1.12, −1.71, −1.22 and −1.01 mA/cm², respectively, at 0 V vs. RHE. Notably, CuO/CuBi₂O₄-200 exhibited the highest photocurrent density among all samples, which is ~3.5 fold higher than that of pristine CuBi₂O₄. Further analysis using transient photocurrent (I−t) curves (Figure 4(b)) revealed that all photocathodes exhibited typical photoresponse behavior, and CuO/CuBi₂O₄-200 maintained stable output over multiple on/off cycles. These results indicated a significant reduction in interfacial charge recombination, with more efficient charge separation and transfer processes.

To evaluate the energy conversion capabilities of the photoelectrodes, IPCE and ABPE were measured. As shown in Figure 4(c), pristine CuBi₂O₄ exhibited an IPCE of only ~3.5% at 365 nm, whereas CuO/CuBi₂O₄-200 delivered a markedly enhanced value of ~13%, corresponding to a ~3.7 fold improvement. In comparison, the IPCE value of CuO/CuBi₂O₄-150, CuO/CuBi₂O₄-250 and CuO/CuBi₂O₄-300 is 4.2%, 7.1% and 4.5%, respectively.

The ABPE curves (Figure 4(d)) reveal that the maximum value of CuBi₂O₄ is 0.075%, while it increases to 0.17% for CuO/CuBi₂O₄-200. These results confirm again that CuO modification layer significantly enhanced the overall energy conversion performance of CuBi₂O₄ photocathodes.

In addition, photoelectrochemical impedance spectroscopy (PEIS) was employed to probe the charge-transport kinetics within the photocathodes and across the interface between semiconductor and electrolyte (Figure 4(e)). The equivalent circuit fitting (Table S1) revealed that the optimized CuO interlayer significantly reduced the interfacial charge transfer resistance, thereby facilitating the efficient transport of photogenerated holes to the FTO substrate and effectively inhibiting bulk charge recombination in CuBi₂O₄. Further analysis of the carrier separation (ƞ_sep) and injection (ƞ_inj) efficiencies (Figure 4(f)) demonstrated that the introduction of CuO as a hole transport layer substantially improved bulk carrier separation and reduced surface recombination, thereby enhancing the overall PEC performance.

2.3　PEC water splitting test

To further assess the hydrogen-production capability of the photocathodes, the H₂ and O₂ evolution rates of CuBi₂O₄ and CuO/CuBi₂O₄-200 photocathodes under AM 1.5 G (100 mW/cm²) illumination were quantitatively analyzed. As shown in Figure 5(a) and (c), both photocathodes exhibited a stable increase in H₂ and O₂ production over time. Within 1 h, the CuBi₂O₄ photocathode produced 0.93 μmol/cm² of H₂ and 0.45 μmol/cm² of O₂, whereas the CuO/CuBi₂O₄-200 photocathode achieved significantly higher yields of 2.05 and 0.96 μmol/cm², respectively (Figure 5(b) and (d)). Additionally, the CuO/CuBi₂O₄-150, CuO/CuBi₂O₄-250 and CuO/CuBi₂O₄-300 photocathodes also exhibited enhanced water-splitting activity relative to bare CuBi₂O₄ (Figure S1). These results were in agreement with the photocurrent and efficiency measurements, further indicating that the introduction of an optimized CuO interlayer between the FTO substrate and CuBi₂O₄ significantly enhanced interfacial charge separation and transfer, thereby effectively promoting the utilization of photogenerated carriers and improving PEC water-splitting performance.

Given its high H₂ evolution capability, the CuO/CuBi₂O₄-200 photocathode was further integrated in series with a BiVO₄ photoanode to construct a bias-free tandem water-splitting device (Figure 6(a)). The preparation method and structural characterization of the BiVO₄ photoanode were provided in the Supporting Information (Figure S2 and S3). The BiVO₄ photoanode supplied photogenerated carriers, while FeOOH used as a co-catalyst improved charge separation and transfer efficiency. In addition, FeOOH promoted the oxygen evolution reaction, enhancing the catalytic efficiency of the photoanode. When combined with the CuO/CuBi₂O₄-200 photocathode, the tandem system delivered a maximum photocurrent density of 0.56 mA/cm² under solar illumination (Figure 6(b)), demonstrating its capability to drive overall water splitting under completely bias-free conditions.

2.4　Optical characteristics

Figure 7 presents the optical absorption characteristics and corresponding bandgap calculations for CuBi₂O₄ and CuO/CuBi₂O₄-200 photocathodes. As shown in the UV-vis diffuse reflectance spectra (UV-vis DRS) (Figure 7(a)), all electrodes exhibited prominent absorption features in the visible light range (300−900 nm). Notably, CuO/CuBi₂O₄-200 shows significantly higher absorption intensity compared to CuBi₂O₄, indicating that the CuO layer effectively enhances light-harvesting capability. Further analysis of the Tauc plot (Figure 7(b)) was performed to determine the optical bandgap. CuBi₂O₄ exhibited a bandgap of approximately 1.79 eV, while that of CuO/CuBi₂O₄-200 showed a slightly reduced value of 1.76 eV. This reduction of the bandgap facilitated light absorption in the visible region, thereby enhancing the excitation efficiency of photogenerated carriers.

2.5　Charge transfer mechanism

To further elucidate the role of the CuO interlayer in the charge transfer process, the band structure of the composite photocathodes was analyzed using UV-vis and Mott-Schottky (M-S) testing. The UV-vis results indicated that the bandgap of CuBi₂O₄ was approximately 1.79 eV, while that of CuO is 1.81 eV (Figure S4). Additionally, the flat-band potential from the Mott-Schottky curves was used to estimate the Fermi levels (E_f) of CuBi₂O₄ and CuO (Figure 8(a) and (b)). Based on these results, the band structure diagram for the CuO/CuBi₂O₄ photocathode was constructed (Figure 8(c)). Based on the band structure, a mechanism for photogenerated charge carrier separation and transmission was proposed. Under illumination, CuBi₂O₄ generated photogenerated electrons and holes. However, its intrinsic band structure led to significant bulk and interfacial recombination, limiting the PEC efficiency. The introduction of the CuO interlayer provided a favorable energy-level alignment that facilitated the rapid extraction of photogenerated holes from CuBi₂O₄ into CuO, effectively inhibiting the recombination at the CuBi₂O₄ interface. These holes were subsequently transported through the FTO substrate to the counter electrode, where they participated in oxidation reactions. Simultaneously, the reduced recombination within the CuBi₂O₄ bulk allowed a greater number of electrons to migrate to the electrode surface and drive the hydrogen-evolution reaction. Thus, in the CuO/CuBi₂O₄ photocathode, CuO served as an efficient interfacial “bridge,” lowering the charge-transfer barrier and inhibiting electron-hole recombination. This synergistic interfacial modulation significantly improved carrier separation efficiency and enhanced the overall PEC performance of the photocathode.

3　Conclusion

收起

In this study, a high-performance CuO/CuBi₂O₄ photocathode was successfully constructed by introducing a CuO interlayer between the FTO substrate and CuBi₂O₄. Systematic structural characterization revealed that the CuO layer not only improved the surface morphology and interfacial adhesion of CuBi₂O₄ but also established favorable band alignment. As a result, the optimized CuO/CuBi₂O₄-200 photocathode delivered a photocurrent density of −1.71 mA/cm² at 0 V vs. RHE, more than 3.5 times that of the pristine CuBi₂O₄, along with an enhanced IPCE of ~13% at 365 nm and a maximum ABPE of 0.17%. Furthermore, when coupled with a classical BiVO₄ photoanode, the CuO/CuBi₂O₄-200 photocathode successfully enabled bias-free overall water splitting, demonstrating strong potential for practical PEC applications. Mechanistic investigations further verified that the CuO interlayer functioned as an effective hole-transport layer, reducing interfacial resistance and improving charge separation and injection efficiencies, thereby enhancing both PEC activity and operational stability. This work provided a simple yet effective interface-engineering strategy and offered valuable insights for the rational design of high-performance PEC photocathodes.

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2026年第54卷第4期

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doi: 10.1016/S1872-5813(26)60647-0

接收时间：2025-09-08
首发时间：2026-09-23
出版时间：2026-04-10

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收稿日期：2025-09-08
修回日期：2025-10-14
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辽宁大学物理学院, 辽宁沈阳 110036

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2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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