Theoretical Study On The Carbon Dioxide Reduction And Hydrogen Evolution Reaction By The Au Grain Boundaries

In the domain of electrocatalysis,the electrocatalytic properties of transition-metal are related to their structure and electron distribution,making it difficult for further promotion.In this paper,the existence of grain boundaries could improve the catalyst structure and change their own distribution of electron to achieve the purpose of improving the electrocatalytic properties.This paper focuses on the influence of the Au grain boundaries on the carbon dioxide reduction and the hydrogen evolution reaction.The interaction between the structure and the properties is revealed by using the density functional theory(DFT)calculations.The following conclusions are obtained:(1)In this paper,the Au grain boundary model is taken as the research object.By means of density functional theory calculation,the Gibbs free energies of the adsorbed intermediates on different structures are calculated.It is found that Au(110)surface catalytic properties better than Au(100).The grain boundaries made the Gibbs free energy of CO2 to CO decrease,indicating this step in the catalytic reaction would be more prone to occur.(2)Gibbs free energy change of adsorption intermediates from CO2 to CO in the model of Au(110)grain boundary is found to be the strongest adsorptive energy source for Au(110),which makes it difficult to desorb CO.The reaction of the two adsorption intermediates * CHO and * OCH3 for the subsequent reaction and the calculation of the adsorption energy of O indicate that the Au(110)grain boundary is more likely to be CH3 OH selective.Through the comparison with Cu(211),the Gibbs free energies of *COOH and *CO on Au grain boundaries are lower than that of Cu(211)and the catalytic performance is better,and the barrier of *OCH3 to methanol is equal to Cu.(3)The free energy change of *H intermediates on the Au(110)is much lower than that on Au(110)bulk,indicating that the Au grain boundaries have a great improvement on the HER performance of Au.The Gibbs free energy at grain boundary sites was reduced by 0.4 eV-0.6 eV from the calculation of the site activity at the grain boundary,which lead to a huge increase in HER performance at sites with similar performance compared to Pt(111).By controlling the proportion of grain boundaries on Au,we found that 0.01% grain boundary can double the catalytic capacity.(4)We attribute the change of GBs property to the unique unsaturated coordination at the grain boundaries.By calculating the generalized coordination numbers of active sites at the Au(110),we found that there is a certain linear relationship between U_L and (?).At the same time,the d-band center theory is used to determine the shift of the d-band at the grain boundary.Such offset is in agreement with that reported in the earlier literature.At the same time,we found that there is a linear relationship between d band center and UL.Then we can establish a certain linear relationship between d band and (?) by U_L.