Studies Of Hydrogen Evolution,CO₂ Reduction And Their Interaction With Pyridine At Platinum And Copper Electrodes

Electrocatalytic CO2 reduction reaction(CO2RR),to produce hydrocarbon fuel and high value-added carbon-based materials,as one of the most effective means to realize carbon cycle in the ecosystem,has been intensely investigated through both experimental and theoretical studies.However,the reaction mechanism,the variation of the electrochemical interface as well as its influence on the reaction mechanism are all not very clear.Under aqueous conditions,CO2RR and hydrogen evolution reaction(HER)compete with each other and hence decrease the faradaic efficiency for CO2RR.Understanding the effect of CO2 and intermediates during CO2RR process on HER is of fundamental importance to inhibit the HER pathway and realize the optimal conditions for CO2 reduction.Recent studies have demonstrated that pyridine(Pyr)greatly enhance the catalytic efficiency of CO2 reduction to CH3OH and HCOOH,while other researchers argue that pyridine makes no difference to promote CO2RR.To the end,concerning the scientific problems mentioned above,Pt and Cu are employed as working electrodes to carry out investigations.And the main results and conclusions are summarized as follows:1.Investigations on CO2RR and HER on Pt and Cu electrodes with different pH.With rotating disk electrode(RDE),cyclic voltammetry(CV),potential step method and in-situ FTIR,studies in the relationship between CO2RR and HER on Pt electrode with different pH have been carried out.At the potential range of H-UPD and HER,CO2 can be reduced to COad on Pt surface.The yielding rate of COad increased with the coverage of UPD-H,and reached the maximum value at the onset potential of HER.The coverage of COad decreased gradually during HER due to less unoccupied sites and shorter occupied time of Had which was necessary for CO2 adsorption and reduction.Studies have revealed the pH depence of the equilibrium potential in HER and the concentration of H+,and it was found that H2 generation was more dominant even in CO2-saturated solution on Pt electrode.On Cu electrode,difference in the onset potential for CO and CO2 reduction corresponded equally to the potential difference caused by different pH.And COad was always observed at Cu surface,indicating that COad acted as an intermediate in CO2RR.Reaction rate and the main product in the two reactions depended much on the surface structure of the electrodes.2.Investigations on the role of pyridine(Pyr)in CO2RR on Pt and Cu electrodes.Combined electrochemical techniques with in-situ infrared spectroscopy,electrochemical behaviors of pyridine on Pt(111),Pt and Cu thin film electrodes and the effect of pH and the concentration of Pyr were explored.Moreover,the electrode reactions in CO2-saturated solution with pyridine were investigated.It was discovered that the main cathodic reaction in pyridine-containing solution on Pt electrode was still HER.Pyridine,on the one hand,inhibits HER by occupying and poisoning active sites at the electrode surface in the buffer system;on the other hand,acting as buffer in the solution with high pH,generates H2 as the proton source.In the process of CO2 reduction,the presence of pyridine may improve the selectivity of producing COOH-.Finally,comparing data on the three electrodes used,it was found that the electrochemical behaviors of HER and CO2RR in pyridine solution depended strongly on the nature of electrode materials,which may result in different intermediates and reaction mechanism.