Construction Of Self-Supporting NiFe-Based Metal Oxide Array Electrode And Its Surface Structure Evolution

The use of traditional fuel vehicles has brought about energy shortage and environmental pollution problems,and the development of new-energy vehicles is an effective way to solve these problems.The existing new-energy vehicles use lithium-ion batteries as power suppliers,which have the low energy density and power density,resulting in the problems of short service life and slow start-up speed of new energy vehicles.Fuel cells with clean hydrogen as energy source have attracted wide attention due to their high conversion efficiency,high energy density,high safety,long-term continuous power supply,and environmental friendliness.At present,hydrogen mainly comes from petrochemical smelting process,but the hydrogen obtained from petrochemical industry contains a small amount of carbon impurities,which can easily cause platinum-based catalyst poisoning and deactivation,leading to the performance of fuel cells is greatly reduced.Electrolytic water is an important means for the efficient and rapid preparation of high purity hydrogen.However,the low rate of oxygen evolution reaction in the process of electrolytic water is the key to restrict the efficient electrochemical hydrogen production.Noble metal-based oxygen evolution reaction?OER?catalysts represented by iridium oxide have high catalytic activity,but their reserves are low and development costs are high,which limits the large-scale application of electrolytic pools.The cheap,efficient and stable non-noble metal oxygen evolution catalyst is very important for the large-scale production of hydrogen from electrolytic water.Among the existing non-noble metal catalysts,phosphides,sulfides and hydroxides with iron-nickel bimetals as catalytic active centers exhibit the excellent OER kinetics.The key is the excellent electronic structure of metal active centers,which can obtain optimized"active site-oxygen evolution reaction transition state"binding energy.However,at present,there are few metal active sites,small electrochemical active area and unstable structure of active sites in iron-nickel-based electrocatalysts,which lead to the improvement of their activity and stability.In view of the above problems,the following research work has been carried out in this paper in order to obtain efficient and stable transition metal-based oxygen evolution catalytic electrode:?1?In view of the problems of the existing Nickel-iron-based phosphide powder electrocatalysts,such as the small number of active sites,the low electrochemical active area,and the influence of a large number of oxide intermediates on the structure of active sites in the electrochemical environment,a self-supporting nano-flake nickel-iron phosphide NiFeP_x electrode was constructed by hydrothermal method.Compared with the porous electrode constructed by powder NiFeP_x,the oxygen evolution activity of self-supporting NiFeP_x electrode was studied.Significant improvement was achieved.In addition,NiFeP_x electrode is affected by oxygen evolution intermediates?oxygen free radicals,hydroxyl free radicals,etc.?in the process of long-term catalytic oxygen evolution reaction.The metal phosphide on the electrode surface eventually transforms into metal oxides or hydroxides,and the catalytic electrode shows good activity and stability.?2?In order to solve the problem that the oxygen evolution activity of nano-sheet Ni-Fe phosphide electrode is still not high,NiCo₂O₄ nano-cone electrode with good conductivity was used as carrier to load shell-structured Ni_nFe_1-nO_x nanoparticles on the surface of nano-cone,and a composite material with high oxygen evolution catalysis was obtained.On this basis,we regulated the composition of Ni_nFe_1-nO_x metal elements and pyrolysis temperature,and finally obtained NiCo₂O₄@Ni₈Fe₂O_x with the best oxygen evolution activity,and the self-supporting electrode had a stable oxygen evolution catalytic activity.Furthermore,self-supporting NiCo₂O₄@FeO_x composite electrode was obtained by using self-supporting NiCo₂O₄ nanocone electrode as carrier and loading FeO_x on its surface.NiCo₂O₄@NiFeO_x self-supporting electrode with higher activity and better stability was obtained by using the migration principle of bulk Ni element of NiCo₂O₄ carrier to surface FeO_x in electrolysis process.Compared with the chemically synthesized NiCo₂O₄@Ni₈Fe₂O_x self-supporting electrode,the activity and stability of the self-supporting NiCo₂O₄@FeO_x composite electrode have been significantly improved.The basic reason for the improvement of the catalytic active electrode is that the bulk nickel element gradually migrates to the surface phase during the electrolysis process,and is doped with the surface iron oxide,and finally the optimized ratio of nickel-iron element is reached in the electrochemical process.Finally,we phosphated the self-supporting NiCo₂O₄@FeO_x composite electrode and obtained the best catalytic electrode NiCoP_x@NiFeP_x for oxygen evolution with both activity and stability.