Exploration of efficient water oxidation catalysts (WOCs) is the primary challenge in conversion of renewable energy into fuels. Here we report a molecularly well-defined heterogeneous WOC with Aza-fused, π-conjugated, microporous polymer (Aza-CMP) coordinated single cobalt sites (Aza-CMP-Co). The single cobalt sites in Aza-CMP-Co exhibited superior activity under alkaline and near-neutral conditions. Moreover, the molecular nature of the isolated catalytic sites makes Aza-CMP-Co a reliable model for studying the heterogeneous water oxidation mechanism. By a combination of experimental and theoretical results, a pH-dependent nucleophilic attack pathway for O-O bond formation was proposed. Under alkaline conditions, the intramolecular hydroxyl nucleophilic attack (IHNA) process with which the adjacent -OH group nucleophilically attacks Co⁴⁺=O was identified as the rate-determining step. This process leads to lower activation energy and accelerated kinetics than those of the intermolecular water nucleophilic attack (WNA) pathway. This study provides significant insights into the crucial function of electrolyte pH in water oxidation catalysis and enhancement of water oxidation activity by regulation of the IHNA pathway.

探索高效的水氧化催化剂 (WOC) 是将可再生能源转化为燃料的主要挑战。在这里，我们报告了一种分子定义明确的异质 WOC，它具有氮杂融合、π 共轭、微孔聚合物 (Aza-CMP) 配位的单钴位点 (Aza-CMP-Co)。Aza-CMP-Co 中的单个钴位点在碱性和近中性条件下表现出优异的活性。此外，分离催化位点的分子性质使 Aza-CMP-Co 成为研究非均相水氧化机制的可靠模型。通过实验和理论结果的结合，提出了一种依赖于pH的亲核攻击途径，用于OO键的形成。在碱性条件下，相邻的-OH基团亲核攻击Co的分子内羟基亲核攻击（IHNA）过程⁴⁺ =O 被确定为速率决定步骤。与分子间水亲核攻击 (WNA) 途径相比，该过程导致较低的活化能和加速动力学。本研究为电解质 pH 在水氧化催化中的关键作用以及通过调节 IHNA 途径增强水氧化活性提供了重要的见解。