Design Of Noble Metal-based Catalysts Reduced By Si-H Bond And Investigation Of Their Electrocatalyst Properties

The extensive use of fossil energy and the increasingly serious environmental pollution make it urgent to develop new sustainable energy.Among them,fuel cell technology stands out,providing new ideas for exploring the road of new energy.Fuel cell has the characteristics of stable power,convenient transportation,less pollution and high specific energy.The reaction kinetics of the cathode reaction oxygen reduction reaction(ORR)of the battery is extremely slow,and the efficiency of the whole fuel cells is limited.Therefore,it is urgent to find efficient ORR catalysts for fuel cells.At present,noble metal catalysts platinum(Pt)are widely used and highly efficient,but their small reserves and high price seriously hinder the development of fuel cells.In order to reduce the usage of Pt and improve its electrochemical activity,people began to design catalysts with low cost,high catalytic activity and good stability.Among them,palladium(Pd)is a catalyst with high ORR catalytic activity except Pt,which even exceeds Pt in alkaline solution.In recent years,the design and development of Pd-based catalysts has become the direction of a large number of researchers.And researchers designed and synthesized binary or ternary Pd-based catalysts.In addition to developing new energy,environmental and energy problems can also be solved by dealing with the combustion products of fossil energy.Carbon dioxide(CO2),the product of fuel combustion,is the main source of greenhouse effect.The reduction of CO2 by electrochemical methods can be completed at room temperature and pressure,and the reaction products are easy to adjust.However,the activation step in the carbon dioxide reduction reaction(CO2RR)requires a high overpotential.Like ORR,the reaction kinetics of CO2RR is slow,so it is necessary to find a catalyst with high catalytic activity and high selectivity to efficiently reduce carbon dioxide to the desired product.In this paper,through the structural design of the catalyst,the catalytic activity of electrocatalysis is improved by using the synergy between non-noble metals or semiconductors and noble metals and the support effect.The specific work is as follows:(1)The catalyst with PdCu bimetallic particles uniformly supported on carbon black was designed and synthesized by Si-H bond reduction.And the relationship between ORR electrocatalytic performance of PdCu bimetallic catalyst and the synergistic effect between Cu and Pd was explored.The transmission diagram shows the existence of Pd and Cu bimetallic structures.An interesting self-activation phenomenon was found in the test of electrocatalytic ORR.The half wave potential(E1/2)moves forward from 0.840 V vs.RHE to 0.880 V vs.RHE.This interesting phenomenon is that the dissolution of Cu during cyclic scanning leads to the selfactivation of the catalyst.The electrochemical active area of Pd increases from 21.79 m2 g-1 to 28.69 m2 g-1.After 500 cycles,the content of Cu decreases by 50%.The optimum E1/2 and E0 of the catalyst are 0.880 V vs.RHE and 1.010 V vs.RHE,respectively,the E1/2 is 40 mV higher than the initial value.When the catalyst is used as the cathode catalyst of zinc-air battery,it shows a high peak power density of 219 mW cm-2 and an open circuit voltage of 1.43 V.(2)A diluted Si modified Pd catalyst DS-Pd NPs was designed for electrocatalysis by Si-H bond reduction.The effect of small-sized semiconductor Si nanoclusters on the catalyst band gap was investigated to probe its influence on the catalytic performance of ORR and its resistance to poisoning.The strong interaction between Si nanoclusters and noble metal Pd effectively stabilizes the catalytic activity.The E0and E1/2of the catalyst are 1.010 V vs.RHE and 0.892 V vs.RHE,respectively.Interestingly,DS-Pd NPs also has strong methanol resistance,which is 35.60 times higher than commercial 10%Pd/C.This excellent methanol resistance is due to the synergy between more oxyphilic and less methylophilic silicon nanoclusters and smaller Pd nanoparticles.(3)Ag nanoparticles supported on silicon nanowires(SiNWs)were prepared by Si-H bond reduction.Three kinds of carbon points(CDs)modified catalysts were used to explore the effect of CDs on the performance of electrocatalytic CO2RR.Electrochemical test and gas chromatography analysis showe that Ag-SiNWsfluorescent CDs has higher selectivity of 84.3%at-0.1 V potential compared with other catalysts,and the onset reaction potential was also low.The modification of fluorescent CDs promotes the catalytic activity and selectivity of Ag-SiNWs.The above three works point out that Si has the functions of support,reduction and modification,which provides a new idea for the synthesis and structure regulation of catalysts.