S-scheme heterojunction has been extensively investigated for hydrogen evolution and environmental pollution issues. In this study, a monoclinic WO₃/hydrothermally treated red phosphorus (HRP) S-scheme composite was prepared by hydrothermal method. XPS and EPR characterization confirmed that the monoclinic WO₃/HRP composite formed S-scheme heterojunction. 5%WO₃/HRP composite displayed the optimal photocatalytic activity under visible light irradiation, and its degradation rate of Rhodamine B (RhB) reached 97.6% after 4 min of visible light irradiation, while its hydrogen evolution rate reached 870.69 μmol·h^-1·g^-1 which was 3.62 times of that of pure HRP. This could be ascribed to the tight interfacial bonding between WO₃ and HRP, and the formation of S-scheme heterostructure, enabling rapid separation of photogenerated carriers and therefore improving the strong redox capacity. This study provided a promising RP-based photocatalyst to meet the demand for clean energy and drinking water.

Bismuth vanadate (BVO) can be used for photoelectrochemical (PEC) water splitting to hydrogen. However, suffering from its high charge-recombination and slow surface catalytic reaction, the PEC performance is far below the expectation, and the modification of the co-catalysts only on the electrode cannot overcome this disadvantage. Here, we report FeNiO_x cocatalyst decorated on the BVO photoanode, which can restrict the onset potential and improve the PEC performance. Moreover, a more effective dual modified-BVO photoanode is formed, with the loading of g-C₃N₄ before decoration of FeNiO_x cocatalyst. The type-II p-n heterojunction composed by g-C₃N₄ nanosheets and BVO, can inhibit recombination of photogenerated charge, and promote the separation of charge effectively at the electrode. Results show that the charge separation efficiency of the electrode reaches 88.2% after the insertion of g-C₃N₄, which is nearly 1.5 times that of BVO/FeNiO_x (60.6%). Moreover, surface charge injection efficiency of the dual-modified BVO/g-C₃N₄/FeNiO_x electrode reaches 90.2%, while the current density reaches 4.63 mA∙cm^-2 at 1.23 V (vs. RHE). This work provides a facile approach to develope high performance photoanodes for PEC water splitting.

Nickel-based electrocatalytic material is considered one of the cost-optimal transition metal catalysts in alkaline water electrolysis due to its accessible industrial-applicability. Nevertheless, slow hydrogen evolution kinetics and low activation are still the grand challenges. Herein, we report a three-dimentional porous cluster structure vanadium oxide implanting into nickel-copper alloy electrocatalyst with phase-separation metallic nickel and copper as the main crystal phase mixed up with amorphous vanadium oxide phase, which is fabricated in situ on nickel foam (NF) by one-step cyclic voltammetry. The tri-hierarchical porous micro-nano structure of VO_x-NiCu/NF was constructed by nanoparticles of whichmicropores were created by clusters. This nickel foam micropores endows the target catalyst with a 28-fold increased electrochemically active surface area (ECSA), comparable to Pt-like catalytic activity towards hydrogen evolution reaction (HER). Encouragingly, VO_x-NiCu/NF needs merely 35 mV (η₁₀) to drive -10 mA·cm^-2 towards HER in alkaline medium. In addition, the as-prepared VO_x-NiCu/NF exhibits excellent long-time stability and durability. These data suggest that the formation of cluster structure, piled by nanoparticles, creates a large number of surface micropores, which greatly enhance the active sites and provide abundant material transfer channels for HER. Formation of NiCu alloy and amorphous V₂O₅ phase synergically boost the intrinsic HER activity to a certain extent. Simultaneously, the ideal composition and unique structural characteristics of VO_x-NiCu/NF contribute to the superior catalytic performance with the structural advantage responsible for the predominant effect. On the basis of kinetic analysis, the HER at VO_x-NiCu/NF proceed via a Volmer-Heyrovsky mechanism, where chemical desorption of hydrogen adsorbed is regarded as the rate-limiting step. Therefore, this study lays a foundation for promotion electrocatalytic hydrogen production.

Oxygen evolution reaction (OER) is the key reaction for water splitting, but its slow kinetics limitsits application. Therefore, rational design and construction of efficient OER catalysts are crucial for water splitting. Here, a Co²⁺ ion doped NiFe layered double hydroxides coupled Ti₆C_3.75 (NiFeCo-LDH-Ti₆C_3.75) catalyst was prepared by a simple one-step hydrothermal method using cobalt nitrate, nickel nitrate, iron nitrate, urea, and Ti₆C_3.75 as raw materials. NiFeCo-LDH-Ti₆C_3.75 catalyst showed a lamellar stacking structure, which is facilitating exposing more active sites. Introduction of Co²⁺ and Ti₆C_3.75 reduced the electronic density of Ni and Fe sites of NiFeCo-LDH-Ti₆C_3.75 catalyst. Benefiting from these features, the NiFeCo-LDH-Ti₆C_3.75 catalyst exhibits excellent OER activity with an overpotential of merely 290 mV at a current density of 20 mA·cm^-2 and a Tafel slope of 87.84 mV·dec^-1 with faster reaction kinetics. NiFeCo-LDH-Ti₆C_3.75 catalyst shows a relatively low charge transfer resistance, which means a fast charge transfer efficiency. Furthermore, after 6000 cycles of accelerated aging test at 20 mA·cm^-2, the overpotential only increased ~7 mV, indicating excellent cycle stability of NiFeCo-LDH-Ti₆C_3.75.

Oxygen evolution reaction (OER) suffers from four-electron transfer, sluggish kinetics and high energy requirements, limiting the development of new energy technologies such as hydrogen production from water electrolysis. In recent years, non-noble metal composite catalysts have attracted increasing attention due to their advantages of excellent catalytic activity and cost compared with noble metal-based catalysts. This review summarizes the latest progress in this field. Firstly, the OER mechanism and the evaluation methods of catalytic performance are briefly introduced. Then the non-noble metal/nitrogen-doped carbon composites are further classified into metal/nitrogen-doped carbon composites, metal single atom/nitrogen-doped carbon composites, alloy/nitrogen-doped carbon composites, and metal oxide/nitrogen-doped carbon composites. The research progress of the electrocatalysts is summarized and analyzed based on the synthesis method and catalytic activity, aiming to explore the role of nitrogen-doped carbon materials in catalyst structure and catalyst performance. Finally, perspectives are given out for the current problems and future directions of non-noble metal/nitrogen-doped carbon composites.

Oxygen reduction reaction (ORR) is important for energy and catalytic applications. Therefore, it is significant to develop highly active and selective catalysts to promote ORR. According to the reaction process, ORR can be categorized into two- and four-electrons transfer pathways. In this work, chemically modified graphene sheets with different defects were used as precursors, which were integrated with Ag-7,7,8,8-tetracyanoquinodimethane (Ag-TCNQ) to form hybrid catalysts. The ORR activities of Ag-TCNQ/high defect graphene and Ag-TCNQ/low defect graphene were compared. The results show that the electron transfer number of ORR with Ag-TCNQ/high defect graphene is 2.4. And its corresponding production yield of H₂O₂ is 0.62 mg/h, and Faraday efficiency is 64.45%. In comparison, the electron transfer number of ORR with Ag-TCNQ/low defect graphene is 3.7 and the corresponding half-wave potential is about 0.7 V (vs. RHE). Therefore, high structural defects promote the two-electron process of ORR, while low structural defects facilitate the four-electron process of ORR. In the composites, Ag-TCNQ nanoparticles and graphene have formed a hybrid effect to improve the catalytic activities.

Developing a highly efficient and stable photocatalyst or co-catalyst is one of the important topics in the field of photocatalysis research. In this study, graphene oxide, cobalt chloride and 2-methylimidazole were used as precursors to prepare Co_5.47N-loaded nitrogen-doped reduced graphene oxide (Co_5.47N/N-rGO) co- catalyst by combining liquid phase method and nitridation in flowing NH₃ where Co_5.47N with a crystallite size of 10~20 nm was highly dispersed over N-rGO surface. The Co_5.47N/N-rGO co-catalyst significantly improves the hydrogen evolution performance of commercial nano TiO₂ (P25). When the mass percent of Co_5.47N/N-rGO was 25%, the hydrogen evolution rate of the obtained sample reached 11.71 mmol·h ^-1·g ^-1, which was 90 times higher than that of pure P25 and similar to that loaded noble metal Pt (11.88 mmol·h ^-1·g ^-1). Furthermore, the catalyst also has good stability. The research provides a new idea for the future development of efficient non-precious metal co-catalysts.

Oxygen evolution reaction (OER) plays an important role in solving energy shortage and environmental problems, but it requires a huge overpotential to overcome the slow kinetic barriers, so the development of high- efficiency electrocatalysts has become an indispensable step. In this work, the performance of α-MnO₂(001) and Mo doped α-MnO₂(001) electrocatalytic oxygen evolution reaction were studied by using density functional theory. Gibbs free energy, density of states and differential charge density were calculated according to the reaction path. The research results show that Mo doping can effectively modulate the electronic structure of α-MnO₂(001) surface, improve desorption and adsorption capacity between intermediates and the catalyst, and provide more electrons for OER. Gibbs free energy calculation results indicate that the formation of O₂ from *OOH is the rate-determining step for OER in the Mo doped α-MnO₂(001) system. Mo doping reduces the overpotential to 1.01 V, which presents a good catalytic performance for oxygen evolution.

Formic acid (FA) is considered as a new type of hydrogen storage material with great application prospect due to its high hydrogen content and easy recharging as a liquid. Seeking high efficiency catalysts to solve the problem of slow reaction kinetics of hydrogen evolution from FA is vital. In this work, polyethyleneimine modified graphene (PEI-rGO) was used as the catalyst substrate, and PEI-rGO supported AuPd nanocomposite material (Au_0.3Pd_0.7/PEI-rGO) was prepared by wet chemical method. The Au_0.3Pd_0.7/PEI-rGO catalyst exhibits remarkable activity for the hydrogen generation from FA, affording an unprecedented turnover frequency (TOF) of 2357.5 mol_H2∙ mol_catalyst ^-1∙h ^-1 without any additives, which is superior to most heterogeneous catalysts under similar reaction conditions. Its excellent catalytic performance is attributed to the strong interaction between PEI-rGO substrate and AuPd nanoparticles, which regulates the size, dispersion and electronic structure of metal active components. Furthermore, the recycle test result shows that the catalyst has good stability.

In order to exploit energy sources (like photocatalytic water splitting for hydrogen production) and protect environment (like organics degradation), supported noble metal catalysts have made considerable progress in terms of design, fabrication, and theory. Herein, based on the specific morphology and structure of dendritic mesoporous silica nanospheres (DMSNs), TiO₂ nanoparticles (NPs) were introduced into the channels via Sol-Gel method, developing dendritic mesoporous silica&titania nanospheres (DMSTNs). Then, amino groups (-NH₂) were grafted onto DMSTNs surfaces by organic modification technology. Finally, ultrasmall gold (Au) NPs were anchored onto the as-prepared DMSTNs-NH₂ through impregnation method and sodium borohydride (NaBH₄) reduction. DMSTNs supported Au NPs catalysts could be successfully constructed, as verified by different methods. Under simulated sunlight for splitting water, the amount of produced H₂ by the brand-new catalysts and the corresponding rate are 69.08 µmol·g^-1 and 13.82 µmol·g^-1·h^-1, respectively, roughly. seven times of that of the contrast sample (DMSNs supported Au NPs). Without light irradiation, the apparent kinetic constant of p-nitrophenol reduction by the as-prepared catalysts is 6.540×10^-3 s^-1, about 17 times higher than that of the reference (0.372×10^-3 s^-1). ln conclusion, DMSTNs supported Au NPs exhibit good multifunctional catalytic activity.

Bismuth vanadate is one of the most promising photoanodes for photoelectrocatalytic water splitting, however, its photoelectrocatalytic efficiency is still not ideal due to its sluggish kinetic reaction rate. The RhO₂ cocatalyst was loaded on the BiVO₄ thin film photoanode by impregnation method, and the photoelectrochenucal performance of the BiVO₄ photoanode with different RhO₂ loadings was studied. RhO₂ with grain size of 10-25 nm was uniformly loaded on the BiVO₄ film with grain size of 100-250 nm and thickness of 400 nm. The BiVO₄ photoanode with 1.65% RhO₂ (mass percent) showed the best comprehensive performance, of which the visible-light photocurrent density reached 3.81 mA·cm^-2 under 1.23 V (vs. RHE) in 1.0 mol/L Na₂SO₃ (pH8.5) electrolyte, which was 10.58 times higher than that of bare BiVO₄. In the absence of any sacrificial agent, the photoanodes produced hydrogen and oxygen at the same time at the ratio of close to 2 : 1, and the oxygen production rate was 8.22 µmol/(h·cm²). RhO₂ loading effectively improved the surface water oxidation kinetics, so that photogenerated holes could undergo water oxidation reaction more quickly. Meanwhile, the photogenerated carrier recombination was inhibited, significantly improving the photoelectrocatalytic performance. In addition, since holes were more easily extracted from the surface of photoanode into electrolyte solution in the presence of RhO₂ cocatalyst, reducing accumulation on the surface of the photoanode, the BiVO₄/RhO₂ (1.65%) photoanode achieved excellent stability for more than 10 h.

In the photocatalytic hydrogen production reaction, the introduction of cocatalyst to promote the rapid transfer of photogenerated electrons is an effective way to improve the photocatalytic activity. At present, the most efficient cocatalysts are mainly precious metals, greatly restricting the use of this method. In this study, influence of the close interface between non-noble metal cocatalyst CoN and g-C₃N₄ 0D/2D on the performance of photocatalytic hydrogen production was explored. The results showed that the support of non-noble metal cocatalyst CoN can effectively improve the photocatalytic hydrogen production of 2D g-C₃N₄, and the support amount also has an positive effect on its activity. The compact 0D/2D interface is favorable for the rapid transmission of photogenerated electrons. Photocatalytic efficiency of 10% CoN/2D g-C₃N₄ composite reached 403.6 μmol·g^-1·h^-1, 20 times of that of 2D g-C₃N₄ monomer, which was comparable to that of noble metal cocatalyst. As a hydrogen evolution cocatalyst, loaded CoN can significantly promote the charge transfer process, thus greatly improving the activity of photocatalytic hydrogen evolution.