Synthesis And Properties Of Non-platinum Electrocatalysts For Hydrogen Oxidation In Alkaline Media

Anion exchange membrane fuel cells（AEMFCs）has attracted extensive attention because of its alkaline working environment and low corrosiveness,which is expected to fundamentally get rid of the dependence of fuel cell on precious metal platinum catalyst.However,the slow kinetic process of hydrogen oxidation（HOR）in alkaline medium and the poor activity and stability of non-noble metal catalysts seriously restrict the development of AEMFCs.In this dissertation,low cost nickel（Ni）,ruthenium（Ru）catalysts of both high activity and stability were designed and developed aiming at tackling the above scientific and technological chellenges.By means of electrochemical method,spectroscopy,microscopy,as well as density functional theory（DFT）calculations,the essence of the catalytic behavior towards the anode HOR over the catalysts were insightfully investigated.Futhermore,the AEMFCs single cell was assembled to verify the practicability of the catalyst.The main progresses are as follows:1.In order to solve the problem of low activity and poor stability of Ni based catalyst HOR,ultra-small Ni nanoparticles coated with controllable carbon layer were prepared by confinement strategy.The experimental results show that the thickness of carbon layer can be adjusted by controlling the time of dopamine polymerization,and the electronic structure of Ni surface can be regulated.Compared with the uncoated Ni-based catalyst,Ni@NC/PEI-XC can optimize the adsorption energy of Ni to the intermediate species of HOR.In addition,the ultra-thin carbon layer also plays a role in stabilizing Ni nanoparticles,inhibiting the oxidation of metal Ni,and improving the catalytic stability of HOR.2.To address the problem of excessive adsorption of Had and OHad on Ru-based catalysts,it was predicted by DFT calculation that the amine（NH₂-）ligand regulation could make the d-band center of Ru metal downshifted,leading to weakened adsorption energy of H_ad and OH_ad on Ru nanoclusters,as well as energetically favorable HOR/HER rate-limiting step.Accordingly,a carbon supported Ru nanocluster catalyst（Ru/PEI-XC）with rich Ru-NH₂ interface was prepared by grafting polyethyleneimine（PEI）with rich NH₂ groups onto the surface of carbon support.FTIR and XPS showed that the coordination between Ru nanoclusters and amine groups,and electrons were transferred from the amine ligand to Ru metal,allowing Ru retained enough metal active sites to provide H_adadsorption sites.The mass activity and exchange current density of the optimized Ru/PEI-XC catalyst are1.7 and 3.6 times of that for the commercial Pt/C catalyst,respectively.Moreover,the HER performance of the optimized Ru/PEI-XC catalyst is better than that of Pt/C catalyst in a wide p H range.The potentiostatic and accelerated aging experiments show that Ru/PEI-XC has a good long-term stability in catalyzing HOR and HER.When Ru/PEI-XC was used as anode catalyst for AEMFCs,the peak power density of Ru/PEI-XC reached 1.4 W mg^-1_PGM.In addition,Ru/PEI-XC can also be used as a cathode to drive a rechargeable Mg-seawater battery with a maximum discharge power density of 18.9 m W cm^-2.3.To address the problem that Ni and Ru metals are easily passivated in the HOR potential interval,a nano-twins catalyst（Ni_xRu_x/C）with rich Ni-Ru heterogeneous interface was prepared by spontaneous electrodisplacement reaction.Experimental and theoretical studies show that the electron transfer from Ni to Ru at the Ni/Ru interface makes the Ru surface more electron rich and provides the H_ad adsorption site,while the electron loss on Ni surface becomes the main OH_ad adsorption site.The synergistic effect of the two optimizes the binding energy of H_ad and OH_ad intermediates.So that HOR/HER can be carried out at a lower reaction energy barrier.The optimized Ni₁Ru₁/C catalyst showed good activity and stability in both half and full batteries.