Preparation And Performance Recovery Of Nickel-Molybdenum-based Electrocatalyst For Alkaline Hydrogen Oxidation Reaction

With the intensive implementation of "double carbon" strategy,environmentally friendly hydrogen energy is expected to become a reliable alternative to traditional fossil energy sources.Anion exchange membrane fuel cells(AEMFCs)can directly convert the chemical energy in hydrogen gas into electrical energy,and the alkaline environment allows allows the use of non-noble-metal-based electrocatalysts,effectively keeping the cost at a low level and enabling the large-scale commercialization of the technology.Currently,in the research field of HOR catalysts for AEMFC anode,nickel-based catalysts show excellent catalytic performance in half-cell reactions due to their appropriate binding energy of hydrogen and hydroxyl.However,there are still some problems to be solved in this field for the practical application of AEMFC in the future.On the one hand,the activity of non-noble-metal-based alkaline HOR catalysts still have much room for improvement,and it is necessary to further optimize the design of catalysts,especially to enhance their performance in membrane electrode assemblies(MEAs).On the other hand,non-noble-metal-based catalysts are generally poor in stability and oxidation resistance.In the cases such as AEMFC start-up/shut-down and hydrogen starvation,the HOR catalysts are prone to be oxidized and deactivated,so the design of HOR catalysts with high oxidation resistance is also an urgent issue to be addressed in the development of AEMFCs.Faced with the above challenges,this study aims to design highly active and long-lasting alkaline HOR catalysts.A supported catalyst based on nickel-molybdenum alloy was developed,and we studied its performance recovery,so as to realize the regeneration of the damaged catalyst.The research results of this study are as follows:1.A carbon nanotube-supported nickel-molybdenum alloy(NiMo/OCNT)catalyst was prepared.The nanoparticles in the catalyst are uniformly dispersed,exposing abundant active sites,and the electrochemical surface area is significantly larger than that of nickel-molybdenum alloy without carbon nanotube support.In addition,the charge transfer between the alloy and the support is beneficial to adjust the electronic structure and to optimize the adsorption of reaction intermediates(H,OH).As a result,the catalyst exhibits excellent HOR activity in alkaline media,with an exchange current density of 3.52 mA cm-2,and a kinetic current density of 8.46 mA cm-2 at 30 mV overpotential.These performance indicators are remarkably higher than that of nickel-molybdenum alloy and commercial Pt/C catalysts under the same test conditions.Moreover,thanks to the role of carbon nanotube support,the catalyst shows exceptional stability in accelerated durability tests,retaining 88.4%of the activity after 12,000 cycles of electrochemical scanning.The AEMFC single cell assembled with NiMo/OCNT as anode catalyst achieves a peak power density of 417.6 mW cm-2.This work provides a new strategy for designing and preparing highly active alkaline HOR catalysts based on non-noble metal elements.2.A performance-recoverable alkaline HOR electrocatalyst based on NiMo/OCNT was developed.The novel NiMo/OCNT catalyst is oxidatively damaged at high potential,but the alkaline HOR activity can be restored to nearly the initial levels after electrochemical in-situ recovery.Material structure characterizations and electrochemical tests demonstrate that damage and recovery of catalyst are inextricably linked to changes in OH adsorption strength due to changes in the oxidation state of surface:OH adsorption strength of the catalyst is at its optimum value(near the peak of "volcano" plot)when it is not oxidized.After the catalyst is oxidatively damaged,the adsorption of OH on surface is too strong,resulting in the poisoning of catalytic sites.By holding it at a low potential for a period of time,the catalyst surface is recovered and OH adsorption is re-optimized.Furthermore,for practical AEMFC,the single cell with NiMo/OCNT as anode catalyst also shows good performance recoverability.This work provides a new approach for the development of long-lifetime AEMFC based on non-noble metal catalysts.