Latest ArticlesElectrocatalytic reduction of NO (NORR) is an effective method for NH3 synthesis, due to low bonding energy of NO bond. In this work, we have investigated many CrS2 based catalysts, including pristine CrS2, CrS2 with one S vacancy (v-CrS2), and Ti doped CrS2 (Ti@CrS2). The results have shown that the pristine CrS2 exhibits inert character for NO activation. However, v-CrS2 and Ti@CrS2 can exhibit enhanced interaction with NO, due to increased charge transfer between NO and substrates (0.52–0.75 e) and enhanced adsorption energies of NO on the catalysts (-0.96~-1.64 eV), compared to the situation of CrS2 (0.065 e/-0.30 eV). From the free energy profiles of NO electro-reduction to NH3, we can see that the v-CrS2 and Ti@CrS2 all exhibit ultralow limiting potentials of -0.03~-0.47 V, following both *NOH and *NHO mechanisms. Therefore, introducing vacancy and doping are all promising modification strategies for NORR catalysts. The results have provided a new idea for the search of catalysts for efficient electrocatalytic reduction of NO.
A binary-mixed electron transport layer (ETL) has been reported for constructing solution-processable near-infrared organic light-emitting diodes (NIR OLEDs). Relative to the single-component ETL, the binary-mixed ETL composed of PDINN:TPBi can enhance the carrier transport capacity, reduce device impedance, and weaken fluorescence quenching of the emitting layer. By carefully selecting an appropriate luminescent material Y5 (a nonfullerene electron acceptor in organic solar cells) and precisely fine-tuning the molecular aggregation in active layer using a mixed solvent, the morphology is optimized and luminescence performance is enhanced, resulting in efficient NIR OLEDs with an emission peak at 890 nm. The experiment showcases a Y5-based near-infrared OLED with a maximum radiance of 34.9 W sr-1 m-2 and a maximum external quantum efficiency of 0.50%, which is among the highest values reported for non-doped fluorescent NIR OLEDs with an emission peak over 850 nm.
Unraveling the essence of electronic structure effected by d-d orbital coupling of transition metal and methanol oxidation reaction (MOR) performance can fundamentally guide high efficient catalyst design. Herein, density functional theory (DFT) calculations were performed at first to study the d–d orbital interaction of metallic PtPdCu, revealing that the incorporation of Pd and Cu atoms into Pt system can enhance d-d electron interaction via capturing antibonding orbital electrons of Pt to fill the surrounding Pd and Cu atoms. Under the theoretical guidance, PtPdCu medium entropy alloy aerogels (PtPdCu MEAAs) catalysts have been designed and systematically screened for MOR under acid, alkaline and neutral electrolyte. Furthermore, DFT calculation and in-situ fourier transform infrared spectroscopy analysis indicate that PtPdCu MEAAs follow the direct pathway via formate as the reactive intermediate to be directly oxidized to CO2. For practical direct methanol fuel cells (DMFCs), the PtPdCu MEAAs-integrated ultra-thin catalyst layer (4–5 µm thickness) as anode exhibits higher peak power density of 35 mW/cm2 than commercial Pt/C of 20 mW/cm2 (~40 µm thickness) under the similar noble metal loading and an impressive stability retention at a 50-mA/cm2 constant current for 10 h. This work clearly proves that optimizing the intermediate adsorption capacity via d-d orbital coupling is an effective strategy to design highly efficient catalysts for DMFCs.
Carbon materials are considered as prospective anode candidates for potassium ion batteries (PIBs). However, the low-rate capability is hampered by slow K+ diffusion kinetics and obstructed electron transport of carbon-based anodes. In this work, calcium d-gluconate derived mesoporous carbon nanosheets (CGC) were interpenetrated into the architecture of reduced graphene oxides (RGO) to form the composites of two-dimensional (2D)/2D graphene/mesoporous carbon nanosheets (RGO@CGC). CGC as a rigid skeleton can prevent the graphene layers from restacking and maintain the structural stability of the 2D/2D carbon composites of RGO@CGC. The mesopores in CGC can shorten the path of ion diffusion and facilitate the penetration of electrolytes. RGO possesses the high surface-to-volume ratio and superior electron transport capability in the honeycomb-like 2D network consisting of sp2-hybridized carbon atoms. Especially, the π-π stacking interaction between CGC and RGO enhances stable composite structure formation, expedites interlayer-electron transfer, and establishes three-dimensional (3D) ion transportation pathways. Owing to these unique structure, RGO@CGC exhibits fast and stable potassium storage capability. Furthermore, the effects of binders and electrolytes on the electrochemical performance of RGO@CGC were investigated. Finally, Prussian blue was synthesized as a positive electrode to explore the possibility of RGO@CGC as a full battery application.
Designing carbon materials with ideal stable hierarchical porous structures and flexible functional properties for efficient and sustainable Zn2+ ion storage still faces great challenges. Herein, the three-dimensional carbon superstructures with spherical nanoflower-like structures were tailor-made by the self-assembly strategy. Specifically, organic polymer units (i.e., organic motifs) were formed by tetrachloro-p-benzoquinone (TBQ) and 2, 6-diamino anthraquinone (DAQ) via a noble-metal-free catalyzed coupling reaction. Subsequently, the organic motifs assemble into spherical nanoflower-like superstructures induced by intermolecular hydrogen bonding and aromatic π-π stacking interactions. Well-designed carbon superstructures can provide a stable backbone that effectively blocks structural stacking and collapse. Meanwhile, the hierarchical porous structures in 3D carbon superstructures provide continuous charge transport pathways to greatly shorten the ion diffusion distance, and as a result, the carbon superstructures-based zinc-ion hybrid capacitors (ZIHCs) provide a capacity of 245 mAh/g at 0.5 A/g, a high energy density of 152 Wh/kg and an ultra-long life of 300, 000 cycles at 20 A/g. The excellent electrochemical performance is also attributed to the corresponding charge storage mechanism, i.e., the alternate binding of Zn2+/CF3SO3− ions. Besides, the high-level N/O motifs improve the surface properties of the carbon superstructures and reduce the ion migration barriers for more efficient charge storage. This paper provides insights into the design of advanced carbon-based cathodes and presents a fundamental understanding of their charge storage mechanisms.
Selective oxidation of olefin to epoxides is an important reaction in industry, however, developing heterogeneous catalysts to achieve the effective catalysis for this reaction under O2 atmosphere at room temperature is challenging but highly desired. In this work, two novel 2D cobalt metal-organic complexes, namely [Co(L)(5-HIP)]·2H2O (Co-MOC-1) and [Co(L)(BTEC)0.5]·H2O (Co-MOC-2) (L = (E)-4,4′-(ethene-1,2-diyl)bis(N-(pyridin-3-yl)benzamide; 5-H2HIP = 5-hydroxyisophthalic acid; H4BTEC = pyromellitic acid) were designed and synthesized through hydrothermal method, which exhibited different metal coordination modes (4-coordinate and 5-coordinate, respectively) and 2D layer structures directed by different carboxylates co-ligands. Two Co-MOCs can serve as heterogeneous catalysts for the selective oxidation of olefins to epoxides at room temperature using O2 as oxidant. Furthermore, a higher catalysis activity of Co-MOC-1 than Co-MOC-2 (96.7% vs. 90.2% yield of 1,2-epoxycyclooctane) was observed, which may be attributed to the coordination unsaturated Co centers, the less coordination number and larger interlayer spacing of Co-MOC-1.
Natural hydraulic lime (NHL) has garnered increasing attention for its sustainable and suitable performance in the field of historical building restoration. However, the prolonged hardening time and sluggish hydration rate of NHL influence the workability, strength development, and durability of construction structures in which it is used. In this study, nano-metakaolin (NMK) was applied as a highly reactive supplementary cementitious material (SCM) for NHL-based mortars to enhance their properties with various ratios. Meanwhile, the effects of NMK and its related enhancement mechanism on the physical properties and chemical structures of NHL composites were systematically investigated, mainly involving the modifications in their microstructure, chemical composition, and C-S-H structure. Results demonstrated that NMK-modified samples showed distinct and superior properties to pure NHL sample, such as shorter initial/final setting times (15.1%–49.1%, 27.1%–50.0%), and higher compactness (67.8%–81.4%, 38.1%–44.8%), lower shrinkage (25.0%–56.3%, 12.5%–25.0%), enhanced compressive strength (404.5%–546.0%, 180.8%–354.1%) and flexural strength (227.5%–351.1%, 59.9%–125.7%) for both early and late curing times (7 and 28 days). The inclusion of NMK not only acts as a fine filler, but also promotes NHL's hydrate rate by its super high pozzolanic activity, thus optimizing the pore structures and increasing the content and the average silicate chain length of hydration gel in NHL. Overall, this study can contribute to a deeper understanding of the enhancement mechanism of NMK on the physical properties and chemical structures of NHL from a meso/microscopic perspective, with a view to broadening NHL's potential applications.
Manipulating catalyst structures to control product selectivity while maintaining high activity presents a considerable challenge in CO2 hydrogenation. Combining density functional theory calculations and microkinetic analysis, we proposed that graphene-supported isolated Pt atoms (Pt1/graphene) and Pt2 dimers (Pt2/graphene) exhibited distinct selectivity in CO2 hydrogenation. Pt1/graphene facilitated the conversion of CO2 into formic acid, whereas Pt2/graphene favored methanol generation. The variation in product selectivity arose from the synergistic interaction of Pt2 dimers, which facilitated the migration of H atoms between two Pt atoms and promoted the transformation from *COOH intermediates to *C(OH)2 intermediates, altering the reaction pathways compared to isolated Pt atoms. Additionally, an analysis of the catalytic activities of three Pt1/graphene and three Pt2/graphene structures revealed that the turnover frequencies for formic acid generation on Pt1ⅱ/graphene and methanol generation on Pt2ⅰ/graphene were as high as 744.48 h-1 and 789.48 h-1, respectively. These values rivaled or even surpassed those previously reported in the literature under identical conditions. This study provides valuable insights into optimizing catalyst structures to achieve desired products in CO2 hydrogenation
Exploring the intrinsic reasons for the dynamic reconstruction of catalysts during electrocatalytic reactions and their impact on activity enhancement still face severe challenges. Herein, the bifunctional catalyst Ru/V-CoO/CP with doping strategy and heterostructure was synthesized for overall water splitting. The Ru/V-CoO exhibits excellent activity for HER and OER with low overpotentials of 49, 147 mV at a current density of 10 mA/cm2 in 1.0 mol/L KOH, respectively. The assembled electrolytic cell just needs voltages of 1.47 and 1.71 V to achieve 10 and 350 mA/cm2 current density under the same conditions and delivers an outstanding stability for over 100 h, which is far superior to the commercial RuO2Pt/C cell. Experimental and theoretical results indicate that the doping of V species and the formation of heterostructures lead to charge redistribution. More importantly, the leaching of V species induces electron transfer form Co to O and then Ru through the Co-O-Ru electron bridge, optimizes the adsorption strength of the key intermediate, thereby reducing the free energy barrier of the rate-determining step and improving catalytic activity. This work proposes an effective strategy of using cation dissolution to induce electron transfer through the electron bridge and thus regulate the electronic structure of catalysts, providing new ideas for the design and development of efficient and stable electrocatalysts.
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