Theoretical Study Of Single Atom Catalysts For Carbon Dioxide Reduction And Oxygen Reduction Reaction

Single-atom catalysts（SACs）have attracted wide attention due to the maximum usage of single atom,novel geometric and electronic configurations and great potential to achieve high activity and selectivity for a variety of reactions in clean energy related applications.Particular for their high activity and selectivity in CO₂ reduction（CO₂RR）and oxygen reduction reaction（ORR）.CO₂RR technology is aim to convert CO₂and H₂ into hydrocarbons and alcohols as high-value-added fuels or commodity chemicals which is timely critical for solving the energy and environmental protection problems.The use of biological materials in vivo can offer a promising approach to tune the biofunctionality of materials with good biocompatibility and biosafety comparing with the using of the foreign（relative to the materials in vivo）materials.Single-atom biological catalysts have received enormous attentions for easy synthesis,high stability and catalytic activity with wide applications in therapeutics and biomedical devices.Therefore,the development and design of biological catalysts with excellent ORR catalytic performance is of great significance for the commercial application of biofuel cells and energy-related devices.1.CO₂RR:the thermoreduction of CO₂ on the Co/Mo S₂ single-atom catalysts is performed using density functional theory including dispersion corrections（DFT-D）.The analysis of electronic structures indicates that the local structure of Co-Mo-3S at the interface plays an important role in CO₂reduction.The simulation of the various reaction pathways shows that CO₂RR likely occurs in the reverse water gas conversion（RWGS）and CO hydrogenation pathway rather than the formate pathway.Additionally,the rate-limiting step is CO hydrogenation into formyl（HCO）reaction,and the entire reaction path can be summarized as*CO₂→*CO→*CHO→*CH₂O→*CH₂OH and*CH₃O→CH₃OH.Furthermore,the rate constant calculations indicating that the Co/Mo S₂ can promote CO₂RR at high temperatures.Therefore,the Co/Mo S₂is an efficient single-atom catalysts for converting CO₂ to methanol.2.ORR:the properties of Fe substituted Ca _II ion in HAP surface（Fe@HAP）and Fe adsorbed over HAP surface（Fe/HAP）,and the detailed kinetic and thermodynamic behaviors of the ORR processes on these substrates have been investigated based on the first-principles study.It is found that Fe dopant by substituted Ca _II atom into HAP surface could be more stably anchored at HAP surface than Fe adsorbate,and the introduced Fe dopant can enormously increase the endogenous ORR catalytic activity of magnetic HAP catalysts.Furthermore,the ORR process on the Fe@HAP prefers to the 4e^-pathway with the small reaction barrier for the rate-limiting step,and the two OH species formed from the hydrogenation of the adsorbed O₂ prefer to further hydrogenate into two H₂O molecules and their self-dehydrogenation is not preferable according to the transition states simulation,which is also confirmed by our Gibbs free energy calculation.Consequently,the Fe@HAP could be an efficient catalyst as cathode material in the applications of the implantable biofuel cells and shed light on the design of SACs based on biomaterials for various applications.