Unraveling the precise location and nature of active sites is of paramount significance for the understanding of the catalytic mechanism and the rational design of efficient electrocatalysts. Here, we use well-defined crystalline cobalt oxyhydroxides CoOOH nanorods and nanosheets as model catalysts to investigate the geometric catalytic active sites. The morphology-dependent analysis reveals a ~50 times higher specific activity of CoOOH nanorods than that of CoOOH nanosheets. Furthermore, we disclose a linear correlation of catalytic activities with their lateral surface areas, suggesting that the active sites are exclusively located at lateral facets rather than basal facets. Theoretical calculations show that the coordinatively unsaturated cobalt sites of lateral facets upshift the O 2p-band center closer to the Fermi level, thereby enhancing the covalency of Co-O bonds to yield the reactivity. This work elucidates the geometrical catalytic active sites and enlightens the design strategy of surface engineering for efficient OER catalysts.

揭示活性位点的精确位置和性质对于理解催化机理和合理设计高效电催化剂具有重要意义。在这里，我们使用定义明确的结晶羟基氧化钴 CoOOH 纳米棒和纳米片作为模型催化剂来研究几何催化活性位点。与形态相关的分析表明，CoOOH 纳米棒的比活性比 CoOOH 纳米片高约 50 倍。此外，我们揭示了催化活性与其侧表面积的线性相关性，表明活性位点仅位于侧面而不是基面。理论计算表明，侧面的配位不饱和钴位点使 O 2p上移带中心更接近费米能级，从而增强 Co-O 键的共价性以产生反应性。这项工作阐明了几何催化活性位点，并启发了高效 OER 催化剂的表面工程设计策略。