Design Of Electrode Structure And Its Application In Gas-involving Electrochemical Reactions

With the development of society and the progress of mankind,the human production is more and more inseparable from chemical raw materials such as coal and petroleum,which are not renewable resources.And a large amount of exhaust gas will damage to the environment.Therefore,the clean and renewable electrochemical energy storage technology has attracted widespread attention.Many advanced clean energy conversion technologies,such as fuel cells,water splitting,metal-air batteries and CO2 reduction,are currently research hotspots.As a clean energy source,hydrogen energy has become the focus of attention because of its large energy density and wide source.As the main source of hydrogen energy,water splitting technology is the most mature method.In the process of water splitting,the catalyst can effectively reduce the activation energy and improve the catalytic efficiency.Noble metal-based catalysts have been widely used for their excellent catalytic performance and good stability.However,the low natural content and high cost of noble metal-based metals have become a major problem and shackle that restricts the development of large-scale electrolytic water hydrogen production technology.In addition,the development of other energy conversion fields is also constrained by the problems of limited reserves and high costs of noble metal-based materials.Alkaline fuel cell is an energy conversion device with high concentration of potassium hydroxide as electrolyte.It has the advantages of fast start-up,high efficiency,high power density and operation under normal temperature and pressure.The oxygen reduction reaction(ORR)at the positive electrode is an important factor that affects the performance of the alkaline fuel cells.In order to improve the electrochemical reaction activity,on the one hand,we can find a more efficient catalyst that can replace Pt,on the other hand,it is possible to increase the specific surface area of the electrode and increase the number of active sites without changing the loading of the noble metal-based catalyst.As a new energy conversion technology,water splitting,fuel cells,etc.all involve gas-involving electrochemical reactions.In order to further study the new energy conversion technology,based on the basic characteristics of the electrochemical gas-involving reaction,this work changes the surface structure of the electrode and improves the gas transmission process,realizing the controllable preparation of high-performance catalytic electrode structure.The specific work and research results are as follows:(1)We have manufactured vertical graphene oxide substrate by freeze drying technology using graphene oxide and Polytetrafluoroethylene(PTFE)as precursor liquid.It can be seen by scanning electron microscope that the vertical graphene oxide substrate has the vertical channel,which produced by freezing temperatures.The pore size will decrease with the decreasing of freezing temperature.Using hydrophilic carbon paper as the current collector,the precursor liquid is directly frozen on the carbon paper to obtain the graphene oxide electrode substrate.The platinum particles were evenly covered on the graphene oxide substrate by vacuum sputtering,then the honeycomb electrode was tested in a 0.1 M KOH solution saturated with oxygen.It was found that when the freezing temperature is-40? and the volume ratio of PTFE solution is 10:1,the honeycomb electrode has the best the oxygen reduction reaction(ORR).The potential is-0.1 V(vs.SCE).The current density can reach 50 mA cm-2 at 1 V.Compared with gas diffusion electrodes and commercial platinum carbon,honeycomb electrodes have the largest current density and superior stability,indicating that the designing electrode structure can improve catalytic performance.Combining freeze drying technology and spin coating,a freeze coating device was manufactured,and a thin film with micro-nano structure pores was obtained by using the device,which opened up new ideas for the practical application of fuel cells in the future.(2)A three-dimensional nickel-molybdenum-iron electrode with high catalytic activity was synthesized by electrodeposition using copper foam as the substrate.By optimizing the electroplating solution pH and electrodeposition time,it was found that Ni-Mo-Fe electrode has high catalytic activity at pH 5.25 and 80 min deposition time,the optimal HER and OER starting potential can reach-0.08 V(vs.RHE)and 1.4 V(vs.RHE).Compared with Pt/C and IrO2/C,Ni-Mo-Fe electrode has a greater current density at the same overpotential.This is because the design of the catalyst structure which has a larger specific surface area and full exposure of the active sites.Through the design of the electrode structure,the active sites are fully exposed and will improve the catalytic activity of the catalyst.Designing the electrode structure provides a new idea for reducing the amount of catalyst.