Theoretical Investigation For The Methodology Of Designing The Best Catalysts For Important Proton-coupled Electron Transfer Electrocatalytical Reactions

Fuel cells are one of the most important directions to solve the current energy crisis.In order to produce an efficient and environmental-friendly fuel cell,it is necessary to find a highly efficient catalyst for the electrode reaction.This paper divides the method for designing high-efficiency catalyst into three steps:(1)Understanding the mecha-nism of the reaction under different external conditions(such as temperature,pH,etc.)(2)Calculating the reaction rate according to the mechanism.The pre-exponential fac-tors and activation energies are needed for all elementary steps.(3)Establishing a re-lationship between the reaction rate and some physical quantities in order to obtain a"descriptor".The quantitative study on these descriptors is carried out to obtain the physical factors that can affect the descriptor,and the corresponding methods for quan-titative control are given.Only by doing all these three things together can we really establish a methodology for designing catalysts for electrocatalytic reactions from a first-principle principle.This paper has carried out preliminary research through the specific system around the three problems mentioned above.The corresponding re-search work and the preliminary conclusions obtained will be summarized in below:1.Interaction between adsorbed H atom and the temperature effect on Hydro-gen evolution on Pt(111)in acid mediaBy analyzing the temperature-dependent voltammogram of the hydrogen evolu-tion reaction on the Pt(111)electrode in the acidic solution and the theoretical calculation results,the interaction between the adsorbed hydrogen atoms and the activation energy of the hydrogen evolution reaction and the pre-exponential fac-tor were studied.It was found that on Pt(111),there was a slight repulsion interac-tion between the adsorbed hydrogen atoms.The theoretically simulated isotherm adsorption line of the adsorbed hydrogen atoms was obtained by using the Grand Canonical Monte Carlo simulation method.According to the Tafel slope,it can be stated that the hydrogen evolution reaction follows the Volmer-Tafel mecha-nism and the Tafel process is the rate-determining step.According to the voltam-mograms at different temperatures and the theoretical calculations from DFT,the Tafel reaction was verified as the rate-determining step of the hydrogen evolution reaction.2.Theoretical Study on Hydrogen Atom Adsorption on Pt(110)-(1×1)Crystal Surface and Tafel Step Kinetics First,a stable adsorption configuration of three H atoms was obtained by placing a single H atom on the Pt(110)-(1×1)crystal plane(hereinafter referred to as Pt(110)crystal plane).The interaction between the adsorbed hydrogen atoms between these three sites was then investigated.Then,by increasing the number of hydrogen atoms adsorbed on the surface,the differential adsorption curves of hydrogen adsorbed at the top and bridge sites were studied.Subsequently,the reaction path of the Tafel process on the Pt(110)crystal plane was studied.Five different cases were assumed,and the reaction path and activation energy in each case were calculated by the transition state theory.Since the activation energy of the obtained Tafel process is similar to that of Pt(111),it can be judged that the rate of hydrogen evolution reaction on these two surfaces is also relatively the same,as confirmed by Markovic’s experiment.3.The effect of solvation energy on finding the optimal catalyst for oxygen re-ductionConstant solvation used in previous literature calculations was found by selecting nine Pt-based near-surface alloys and calculating the adsorption energy and sol-vation energy of OHads and OOHads on nine surfaces.It is unreasonable to be able to make this assumption.The reason is that the adsorption energy of OHads in Pt(111)is only 0.1 eV from the apex according to the volcanic curve of oxygen reduction,and the difference of solvation energy on different surfaces when con-sidering solvation energy can be up to 0.2 eV.If the solvation energy is assumed to be the same,an error of more than 0.2 eV is introduced,then finding the best catalysts cannot be accurately performed at the apex of the volcano.Therefore,in the future,when searching for the optimal catalyst,it is necessary to calculate the corresponding solvation energy according to the specific system,so as to ensure the accuracy of the calculation.4.On the effect of solvation energy on Scaling Relation between OHads and OOHads adsorption energiesThe effect of solvation on scaling relation was studied on two adsorbents of OHads and OOHads at two different supercells.The nature of adsorption pro-cess(such as the partition between ionic and colvalent interactions)are analyzed by DFT method.Then the adsorption of single water molecule is studied.After that the structure of adsorbed water bilayer and the solvation structure for OHads and OOHads are also calculated.Since the solvation effect depends on the lattice constant of the surface,after considering the solvation effect,the slope of scaling relation will change.This would provide new insights in designing new catalysts.5.Pre-Exponential Factors in ElectrochemistryBy reviewing the current theoretical and experimental works on pre-exponential factors in electrochemistry,the importance of pre-exponential factors for under-standing electrochemical processes is elucidated.The possible methods for cal-culating pre-exponential factor are reviewed.Then through the experiments of the outer-sphere reaction and the temperature effect in the electrocatalytic reac-tion,it is pointed out that some contradictions and difficulties in deriving the pre-exponential factor of the reaction are experimentally.Future directions on how to study the pre-factors in the future are discussed.6.A new descriptor for understanding adsorption phenomenaIn order to accurately find the optimal catalyst for different reactions,it is neces-sary to find descriptors directly related to the adsorption energy.Then use "d band center"(εcd)as a descriptor for studying adsorption energy.But this descriptor it-self does not include all the interactions in the adsorption process,and it is not possible to make quantitative refinements.So it is very important to find a new type of descriptor that solves the above two problems.The adsorption energy of O atoms on these systems and the change of the density of projected states were investigated by four artificial surface structures.A new type of descriptor(EOS,Energy of Stablization)is proposed.The relationship between the descriptor and the adsorption energy of the O atom and the relationship between the energy of the O-band and the center of the d-band are studied.It is found that the adsorp-tion energy of the adsorbate is better described by the EOS energy than the d-band center.Finally,the error analysis of EOS is carried out and its future development prospects are proposed.