Controllable Synthesis Of Non-Noble Metal-Based Electrocatalysts For Efficient Hydrogen Oxidation Reaction

As a kind of clean energy conversion equipment without CO₂ emission,hydrogen fuel cell exhibits great application prospects in the future thanks to its high energy conversion efficiency,high reliability and sustainability,and absenses of chemical and noise pollutions as well.Nowadays,both acidic membrane fuel cell(PEMFC)and alkaline membrane fuel cell(AEMFC)necessitate a large amount of noble metal-based catalysts to operate in rigorous strong acid or alkaline environment,resulting in extremely high energy production costs which become a major obstacles hindering its wide industrial applications.Therefore,it is of great significance and importance to develop non-noble metal-based anode catalysts with high-efficiency,low cost,stable and acid-alkaline resistance.However,so far,there are still limited numbers of reports on the efficient non-noble metal-based hydrogen electrocatalytic oxidation(HOR)catalysts,and the performances and stabilities of the reported non-noble metal-based catalysts are still far behind the commercialized Pt/C.In this thesis,non-precious metals-based electrocatalysts with high HOR catalytic activity have been developed by loading active nanoparticles on the heteroatom-doped carbon substrates,heterogeneous metal doping in single catalytic metals,and nano-alloying of binary metals methods.Effective regulation of electronic structure,controllable construction of abundant defects and catalytically active sites,and the influences of doping and alloying on the morphology,chemical state of the catalysts have been studied in-depth.The main research contents are summarized as follows:1.Until now,the W-based catalysts show poor HOR activities and stabilities.Herein,a heteroatom doping strategy has been proposed to modify the carbon substrate,modulate electronic structure and elevate HOR performances of the catalyst.A simple one-step calcination method was used to prepare about 3 nm-sized W₂C particles wrapped in N,P-doped carbon layer,froming a nanocomposite catalyst(W₂C@N,P-C,WNPC).WNPC shows excellent HOR performance and stability under acidic,alkaline or even neutral conditions,which can be ascribed to the high charge transfer capability under a wide range of p H conditions,large specific surface area and increased HOR catalytic active sites,which was attributed to the interactions among various elements in the catalyst and the modulated chemical valence state of the catalyst.2.Based on the research results in the above chapter,Mo has been doped into Ni by a calcination method to prepare HOR electrocatalyst by loading Mo-doped Ni Mo nanoalloy on N-doped carbon rod(NMNC).The doping of Mo induces the distortion of Ni lattice,modifies the electronic structure and elevates the reducibility of Ni,thus regulates the degree of graphitization of C in the catalyst,and balances the conductivity and defect concentration of the catalyst.The N-doped carbon rod as a carrier provides anchor positions for nano-particles,which is beneficial to the dispersion of the nano-particles and exposure of more catalytic active sites.Therefore,the prepared NMNC catalyst exhibits high HOR performance,featuring a current density of 3.23 m A cm^-2 at 0.10 V vs.RHE.The catalyst also shows excellent stability and high resistance to CO poisoning.3.The above two systems necessitate high temperature treatments.Herein,W-doped Cu particles of about 5 nm have been in-situ deposited on carbon paper(CP)by a one-step electrodeposition method.Cu W exhibits high HOR electrocatalytic performance(current density at 0.05 V vs.RHE is 1.86 m A cm^-2),high HOR stability and excellent anti-CO activity.The structure-activity relationship of the catalyst has also been investigated.This research provides a highly convenient and efficient way to design and prepare non-noble metal-based high-efficiency HOR catalysts with favorable surface morphology and chemical state for alkaline fuel cells.4.Based on the conclusions and ideas of above work,Ni W nano-alloy with a cauliflower-like structure and in the form of inter-doped lattice has been prepared by electrodeposition method.Alloying effectively improves the electronic structure and this catalyst exhibits high HOR activity,excellent stability and anti-CO ability under alkaline conditions,which shows a current density of as high as 1.64 m A cm^-2 at 0.05V vs.RHE.Through first-principles calculations of thermodynamics and kinetics,it is proved that when Ni is alloyed with W,the adsorption energy of H₂ will be increased greatly,while the free energy of H* and the energy barrier of oxidation of H* to H₂O will be decreased substantially.At the same time,possible HOR kinetic reaction pathway catalyzed by Ni W catalyst has been proposed.This study reveals a novel nano-alloying and non-noble catalyst electrode with high HOR performance and stability.In summary,this thesis presents the varied doping/alloying strategies for the controlled preparation of non-noble metal-based hydrogen oxidation catalysts of excellent electrode catalytic performances.The electronic structure of the catalyst is adjusted by doping and alloying,and corresponding influences on the morphology,structure,and performances of the catalysts have been explored in a comprehensive manner.This thesis provides a sound theoretical and practical basis for the design,preparation and even the future application of non-precious metal-based element-doped/alloyed hydrogen oxidation catalysts,and hopefully favors the cost reduction of hydrogen fuel cells.