DFT Calculation Of Hydrogen Evolution Reaction/Hydrogen Oxidation Reaction On Metal-metal Oxide Composite Catalysts

The degradation of environment and the limited reserves of fossil fuels make it imperative to develop environmental friendly,clean and renewable energy storage equipment and new energy.As a storable,non-pollution and renewable new energy,Hydrogen is considered to be an ideal alternative to fossil fuels and has attracted worldwide attention.Water electrolysis converts electrical energy into chemical energy,and hydrogen fuel cells convert chemical energy into electrical energy so that hydrogen can be recycled.However the high energy consumption,high cost and corrosion induced by large overpotential of hydrogen evolution reaction?HER?which is the cathodic reaction in the water electrolysis hindered the practical widespread application of water electrolysis.Besides,the hydrogen-oxidation reaction?HOR?which is the anodic reaction in fuel cells also impeded the development of fuel cell for its low reaction rate,high cost and low stability of its catalysts.Based on the above reasons,and for the purpose of searching a highly efficient,stable and inexpensive HER/HOR catalyst,we studied the HER/HOR activities of metal-metal oxide composite catalysts and explored the essential reasons for the enhanced activities by using density functional theory?DFT?based first principle calculation.This work can serve as a theoretical guidance for the further development and design of highly active catalysts.This article mainly includes the following two aspects:Firstly,we constructed five composite catalyst modles?MO/Ni?001?,M=Ti,Mn,Fe,Co,and Zn?,and explored the interaction between metal oxides and metals,and the effect of oxides and transition metal species on HER catalytic activities of MO/Ni?001?catalysts.The geometric and electronic structures of MO/Ni?001?denote that,the interface Ni-Ni bond expands,and the interface Ni loses electrons while O obtains electrons after the oxide interacts with the Ni substrate.The calculation of HER activity shows that the H adsorption energy on the Ni atoms close to the interface is obviously weakened when compared with that on pure Ni surface.Among the five composite catalysts,TiO/Ni?001?surface has the strongest H adsorption energy,while the ZnO/Ni?001?surface has the weakest H adsorption energy.When Ni interact with TiO,Ni has the minimum charge transfer and moderate E_ads.Hence,the hydrogen adsorption free energy(?G_H*)is the closest to 0,resulting in the best activity.It was confirmed that the metal oxide can be used to adjust the electronic structure of the metal surface and further to moderate the?G_H*.Consequently the catalytic activity of the metal can be affected by metal oxide.This work provides theoretical guidance for the design and development of high activity,high stability HER catalysts.Secondly,we constructed four catalysts modles,including Ru₅/TiO₂,Ru,RuO₂ and Ru₄/RuO₂.And the density functional theory calculations were employed to reveal the role of TiO₂ in enhancing the HOR activity of Ru-based catalysts.The geometric and electronic structures calculations denote that when Ru clusters are supported on metal oxides?TiO₂,RuO₂?,the Ru-Ru bonds in Ru clusters shrink,and Ru clusters transfer electrons to O and metals?Ti,Ru?in the metal oxides,which result in the positive charged of Ru cluster and the downshift of d-band center of the Ru.Besides,we calculated the adsorption energy of different species?H,OH,H₂O?and found that:Ru surface has the strongest H adsorption energy and OH adsorption energy,while the RuO₂ surface has the weakest H adsorption energy and OH adsorption energy.Ru surface has the weakest H₂O adsorption energy,while the RuO₂ surface has the strongest H₂O adsorption energy.This means that the adsorption energies of all three species on Ru₅/TiO₂ and Ru₄/RuO₂ are between that on Ru and that on RuO₂.HOR activity calculations found that:Ru₄/RuO₂ catalyst has the best HOR activity.The analysis of oxidation resistance shows that the oxidation resistance of Ru₅/TiO₂composite catalysts is stronger than that of Ru catalyst.In summary,the Ru₅/TiO₂ and Ru₄/RuO₂ composite catalysts exhibits better oxidation resistance and HOR catalytic activity than that of Ru due to their moderate Bader charge and d-band center value.The both function together can improve the HOR catalytic activity and stability of the catalyst.This provides us with a certain theoretical basis for the design and synthesis of new HOR catalysts.