Abstract:
Hydroxides are the archetype of layered crystals with metal-oxygen (M-O) octahedron units, which have been widely investigated as oxygen evolution reaction (OER) catalysts. However, the better crystallinity of hydroxide materials, the more perfect octahedral symmetry and atomic ordering, resulting in the less exposed metal sites and limited electrocatalytic activity. Herein, a glassy state hydroxide material featuring with short-range order and long-range disorder structure is developed to achieve high intrinsic activity for OER. Specifically, a rapid freezing point precipitation method is utilized to fabricate amorphous multi-component hydroxide. Owing to the freezing-point crystallization environment and chaotic M-O (M = Ni/Fe/Co/Mn/Cr etc.) structures, the as-fabricated NiFeCoMnCr hydroxide exhibit a highly-disordered glassy structure, as-confirmed by X-ray/electron diffraction, enthalpic response, and pair distribution function analysis. The as-achieved glassy-state hydroxide materials display a low OER overpotential of 269 mV at 20 mA cm-2 with a small Tafel slope of 33.3 mV dec-1, outperform the benchmark noble-metal RuO2 catalyst (341 mV, 84.9 mV dec-1) . Operando Raman and density functional theory studies reveal that the glassy state hydroxide converted into disordered active oxyhydroxide phase with optimized oxygen intermediates adsorption under low OER overpotentials, thus boosting the intrinsic electrocatalytic activity.
摘要:
氢氧化物是具有金属-氧(M-O)八面体单元的层状晶体的原型,已被广泛研究作为析氧反应(OER)催化剂。然而,氢氧化物材料的结晶度越好,更完美的八面体对称性和原子有序,导致较少的暴露金属位点和有限的电催化活性。在这里,开发了具有短程有序和长程无序结构的玻璃态氢氧化物材料以实现OER的高固有活性。具体来说,利用快速冰点沉淀法制备无定形多组分氢氧化物。由于冰点结晶环境和混乱的M-O(M=Ni/Fe/Co/Mn/Cr等)。)结构,制造的NiFeCoMnCr氢氧化物表现出高度无序的玻璃态结构,通过X射线/电子衍射证实,焓响应,和成对分布函数分析。获得的玻璃态氢氧化物材料在20mAcm-2时显示出269mV的低OER超电势,Tafel斜率为33.3mVdec-1,优于基准贵金属RuO2催化剂(341mV,84.9mVdec-1)。操作拉曼和密度泛函理论研究表明,在低OER超电势下,玻璃态氢氧化物以优化的氧中间体吸附转化为无序的活性羟基氧化物相,从而增强内在的电催化活性。