Synthesis And Applications Of Nickel-based Electro-catalyst For Hydrogen Oxidation Reaction In Fuel Cell

In recent years,the development of clean,efficient,and decarbonized renewable energy has become a widespread research focus.Hydrogen energy is an ideal solution for large-scale utilization of renewable energy,promoting low-carbon transformation of the energy structure,and achieving carbon neutrality and emission peak goals.In the hydrogen energy ecosystem,renewable energy such as wind power,photovoltaic,and hydropower can achieve"hydrogen electricity coupling"with hydrogen energy,achieving optimal energy allocation across regions and seasons,which is conducive to achieving"peak shaving and valley filling of electricity"in the process of energy grid connection,thereby building a smart grid.Fuel cells are an ideal way to utilize hydrogen energy,which can directly convert chemical energy stored in hydrogen energy into electrical energy.They have advantages such as high-power generation efficiency,pollution-free emissions,fast load response,and low operating noise.However,fuel cell catalysts typically face highly corrosive environments and can only use expensive precious metals as catalysts;the activity and stability of existing non-noble metal catalysts still lag far behind those of noble metals.Fuel cell has many technical feasibilities and serving as a promising energy conversion approch,but also faces the problem of high prices.In order to efficiently utilize hydrogen energy,it is urgent to develop a new generation of low-cost high-performance fuel cell technology.This dissertation combines theory with experiment to deeply understand the impact of catalyst electrode interfaces and chemical zones on electrocatalytic processes,search the key descriptors to enhance electrode activity,optimize and innovate the electrode/electrolyte interface,and design and prepare a series of electrocatalysts that work in acidic and alkaline environments.Using single cell devices to evaluate the performance of the synthesized catalyst under fuel cell working conditions,therefore provides theoretical basis and experimental exploration for reducing the cost of fuel cell electrocatalysts.This paper mainly includes the following three aspects of work:（1）Carbon-coated nickel（Ni@C）was prepared by controlling the near-surface electrolyte microenvironment of Ni metals through spherical shell coating and encapsulation strategies.Ni@C catalysts can catalyze HOR.The coated carbon shell has proton permeability and reactant permeability,providing a non-corrosive environment for Ni,and realizing the application of non-noble metals in acidic environments.The electrochemical experimental results show that carbon shells have excellent hydrogen/proton conductivity characteristics,which can hinder the attack of OH_ad and free acids,thereby enabling Ni@C to work for a long time in environments with high oxidation,corrosion,and anode voltage.The material exhibits constant HOR/HER activity in the full p H range of 0～13.Electrochemical in situ infrared spectroscopy（in situ ATR-SEIRAS）shows that Ni core was exposed to a non-harsh electrode interface environment in the p H range of 0 to 13.Ni@C PEMFC exhibits a peak power density of 51 mW cm^–2 and a maximum current density output of 200m A cm^–2,which shows an advanced performance compared to Ni/C.（2）Preparation of carbon nitrogen coated nickel（Ni@NC）HOR catalyst by solid phase gel calcination method.Using molecular confinement principle and coating protection strategy,Ni@NC exhibts highly effective anti-poisoning performance and excellent electrochemical stability.It is capable of working in alkaline exchange membrane fuel cells（AEMFCs）using H₂/CO mixture as fuel.XAFS shows that the carbon nitrogen shell is closely coordinated with the Ni metal core.N-doping effectively regulates the defect degree of the graphite shell,making the shell have unique molecular selective permeability.The structure allows the efficient penetration of small molecules of H₂ into the surface of Ni metal core,while exhibiting excellent anti-poisoning properties for large molecules of toxic species(such as CO,S^2-,SCN^-)or oxidized species（such as O₂）.CO stripping,in situ ATR-SEIRAS,and CO temperature programmed desorption experiments jointly reveal the basic principle of anti-poisoning performance is that the adsorption of CO_ad on the Ni surface becomes less and the strength becomes weaker.In the HOR test,the j_{k@50m V} Ni@NC reaching1.92 m A cm_disk^-2,which is 10.6 times of Ni@C;the intrinsic activity（j₀）of Ni@NC reaches 35μA cm_Ni^-2.Ni@NC can maintain 65%of the HOR performance during 30000 cycles of long-term testing.92%,100%,and 92%of HOR activity were maintained in the 100 ppm CO,1 ppm S^2-,and 1 ppm SCN^-poisoning experiment,respectively.In AEMFC,the peak power density of Ni@NC reaches 66 mW cm^-2,and the maximum current density exceeds 150m A cm^-2.It can stably operate at 0.7 V for 210 hours.Its performance in 100ppm CO/H₂ fuel exceeds that of commercial Pt/C.It has considerable anti-poisoning stability,showing a good application prospect in crude hydrogen.（3）A Ni-based alloy HOR catalyst modified with Cr（NiCu Cr/C）was prepared by impregnation method,and combined with a non-noble Ag/C catalyst,a high-performance noble metal AEMFC was assembled.The Volmer step is the main rate control step in alkaline HOR electrode kinetics.Due to the high adsorption energy of H_ad on Ni,the energy barrier of the Volmer step is too high,which is not conducive to the improvement of the HOR activity.In order to promote the Volmer step,a high-performance alkaline HOR catalyst was constructed based on the apparent hydrogen binding energy(HBE_app)theory and a dual strategy of regulating electrode composition and optimizing the hydrogen bond network at the electrode interface.The introduction of Cu,which is weaker in HBE,effectively reduces the d-band center of the Ni electrode,enabling the Ni alloy to have appropriate HBE and oxidation resistance,optimizing the intrinsic activity of the electrode;using Cr element to modify the electrode,in situ ATR-SEIRAS demonstrated that Cr established a richer hydrogen bond network near the electrode surface,accelerating the transfer rate of Had from the Helmholtz layer to the electrolyte.NiCu Cr/C has a mass activity of 72.6 A g _M^-1,13.5 times that of Ni/C.It showed better stability than Ni/C during 25000cycles of aging scanning and 100 ppm CO/H₂ testing.In AEMFC test,NiCu Cr/C reached to 577 mW cm^-2 in peak power density,and a current density of more than 1150 m A cm^-2.It can stably operate at 0.7 V for 156 hours.The assembled PGM-free MEA（cathode Ag/C）has a peak power density of 335mW cm^-2,providing a promising solution for reducing fuel cell prime costs.