A Fundamental Study Of Electrode/Polymer Electrolyte Interface

In the field of modern electrochemical technologies,solid-state electrolytes are widely applied in various devices such as proton-exchange membrane fuel cells(PEMFCs)which typically comprises a perfluorosulfonic acid electrolyte.In electrochemical devices mentioned above,reactions typically occur at the electrode/solid polymer electrolyte interface instead of the conventional electrode/solution interface.Consequently,some concepts in electrochemistry based on classical electrode/solution interface,are facing challenges when employed in the novel electrode/polymer electrolyte interface,considering the distinct difference in ionic transport behavior between solution and polymer electrolyte.To date,the microstructure,structure-activity relationship and dynamic evolution of electrode/polymer electrolyte interface remain unclear due to its complexity and the lack of practical electrochemical methods.In this thesis,some researches on electrode/polymer electrolyte interface have been conducted.The main results are summarized as follows:1.So far,most electrochemical methods used for the research on electrode/polymer electrolyte interface reported in the literatures suffer from the complex design and the leakage of liquid electrolyte.Here,we designed and created a hydrogen reference electrode with a Nafion^?membrane in pure water,which permits the electrochemical measurements in polymer electrolyte system without any solution.Moreover,the method mentioned above is accurate and reliable,which paves a facile way for the research on electrode/polymer electrolyte interface.On this basis,this thesis comprehensively studied the difference in the electrochemical behavior of the polycrystalline Pt electrode between solution and polymer electrolyte,and developed a gas diffusion electrode(GDE)setup for the measurements of catalytic properties and performance under realistic reaction conditions.2.A three-electrode system for the electrochemical measurement was established in this thesis,which allows for the test in alkaline polymer electrolyte(APE)without any solution.By this way,this thesis comprehensively studied the difference in the electrochemical behavior of the polycrystalline Pt electrode between alkaline solution and APE-H₂O system.Furthermore,the method above was used to study the effect of carbonate poisoning of alkaline polymer electrolyte on the kinetics and reaction mechanisms for the HOR/ORR on Pt.As for the effect of carbonate on alkaline polymer electrolyte fuel cell(APEFC),this thesis studied and evaluated the voltage loss of APEFC caused by the carbonation effect from the perspective of membrane potential.3.With the method for electrochemical measurement in APE-H₂O system,this thesis studied three basic types of electrochemical reactions including surface diffusion,bulk diffusion and electrochemical dissolution-deposition reaction.Here,we analyzed the difference of the reactions above between alkaline solution and APE-H₂O system,and discussed the potential of APE membrane for battery applications.4.The high-p H environmental condition of APE makes it not only suitable for various electrocatalytic reactions,but also for electrode reactions with a phase transformation during discharge/charge processes.This thesis discovered and confirmed the zincate-conducting property of APE membrane,and applied it in alkaline Zn-based battery.The variation of[Zn(OH)₄]^2-concentration at the Zn/APE interface can help realize the uniform deposition of zinc and suppress dendrite formation,which permitted a cell without any short on cycling.This finding may pave a facile way to solve the problems associated with dendrites for diverse alkaline Zn-based batteries.5.Compared with conventional electrochemical methods,in-situ spectroscopic techniques deliver new and valuable insights into the electrochemical interface at a molecular level.Here,we designed and built an operando near-ambient pressure X-ray photoelectron spectroscopy(NAP-XPS)technique to track the hydration process of Nafion and the electrochemical reaction at the Pt/Nafion interface.This work may pave a practical way for the operando spectroscopy study of the novel electrode/polymer electrolyte interface.