Preparation Of Ruthenium/Iridium-based Metal Oxides And Their Performance Toward Acidic Oxygen Evolution Reaction

The efficient and sustainable production of hydrogen works as an essential section to promot the wide application of hydrogen power.Proton exchange membrane（PEM）water electrolysis driven by the renewable power is considered as the most promising strategy for hydrogen production and has received intense attention.However,the anodic oxygen evolution reaction（OER）in PEM electrolysis limits the overall efficiency of hydrogen production due to the sluggish kinetics and high energy barrier.Besides,the local acidic environment and the high anode potential during electrolysis will severely erode the stability of anode catalysts.Therefore,developing acidic OER catalysts with both high activity and strong stability can facilitate the development of PEM electrolysis.Ru and Ir-based materials currently acts as the major acidic OER catalysts,however,the insufficient activity of Ir-based materials and the poor stability of Ru-based materials have impeded their application.In this thesis,the activity of Ir-based catalysts and the stability Ru-based catalysts were optimized by designing core-shell nanostructures and regulating material components,respectively.The main studies are as follows.1.Ru@Ir-O nanocatalysts with a core-shell structure were prepared by an impregnation method based on the difference in the sublimation heats of Ru and Ir metals.The core-shell structure consists of a metallic Ru core and an Ir shell with trace O atoms incorporated,and the incorporation of O atoms leads to the tensile strain of the Ir shell.X-ray spectroscopy implied the charge redistribution between the Ru core and the Ir shell.Ru@Ir-O showed an overpotential of 238 m V at 10 m A cm^-2 in 0.5 mol L^-1 H₂SO₄,which is much better than that of commercial IrO₂.It also achieved a mass current density of1169.0 m A mg^-1_metal at the potential of 1.55 V,which was 78 times higher than that of commercial IrO₂.Ru@Ir-O delivered a turnover frequency of 0.91 s^-1,showing excellent intrinsic catalytic activity.Theoretical calculations reveal that the core-shell interaction and tensile strain in Ru@Ir-O jointly lead to the electron enrichment and energy band upward shift of the surface Ir shell,which optimized the energy barrier of rate determined step of O*to HOO*conversion on the surface Ir sites,thus enhancing the intrinsic catalytic activity of Ir.2.Ta-doped RuO₂ nanosheets were prepared by coordination assembly synthesis assisted with roasting in air.The catalysts showed a folded sheets morphology and Ta atoms were uniformly introduced into the nanosheets.The electronic structure characterization showed that the Ta doping reduced the density of electronic states near the Ru center and formed a Ru-O-Ta coordination structure,which was beneficial to the enhanced activity and stability.The representative Ta_0.1Ru_0.9O_2-x exhibited an overpotential of 234 m V at 10 m A cm^-2 in 0.5 mol L^-1 H₂SO₄,which is much lower than that of commercial RuO₂.The mass current density and conversion frequency of Ta_0.1Ru_0.9O_2-x are 20.7 and 17 times higher than those of commercial RuO₂ at the potential of 1.55 V,respectively,showing a high intrinsic activity.Meanwhile,the incorporation of Ta significantly improved the stability of the catalyst,which could be operated at 100m A cm^-2 for more than 300 h in the PEM electrolyzer without visible degradation.