The bifunctional mechanism that involves adsorbed hydroxide in the alkaline hydrogen oxidation and evolution reactions, important in hydrogen fuel cells and water electrolysers, is hotly debated. Hydroxide binding has been suggested to impact activity, but the exact role of adsorbed hydroxide in the reaction mechanism is unknown. Here, by selectively decorating steps on a Pt single crystal with other metal atoms, we show that the rate of alkaline hydrogen evolution exhibits a volcano-type relationship with the hydroxide binding strength. We find that Pt decorated with Ru at the step edge is 65 times more active for the hydrogen evolution reaction (HER) than is the bare Pt step. Simulations of electrochemical water dissociation show that the activation energy correlates with the OH* adsorption strength, even when the adsorbed hydroxide is not a product, which leads to a simulated volcano curve that matches the experimental curve. This work not only illustrates the alkaline HER mechanism but also provides a goal for catalyst design in targeting an optimum hydroxide binding strength to yield the highest rate for the alkaline HER. A three-dimensional (H and OH adsorbed species) HER activity volcano and the implications for hydrogen oxidation are discussed.

涉及碱性氢氧化和放出反应中吸附的氢氧化物的双功能机理，在氢燃料电池和水电解槽中很重要。已提出氢氧化物结合会影响活性，但尚不清楚吸附的氢氧化物在反应机理中的确切作用。在这里，通过用其他金属原子选择性装饰Pt单晶上的步骤，我们表明碱性氢的释放速率与氢氧化物结合强度表现出火山型的关系。我们发现，在台阶边缘装饰有Ru的Pt对氢析出反应（HER）的活性是裸Pt台阶的65倍。电化学水离解的模拟表明，活化能与OH *吸附强度相关，即使当吸附的氢氧化物不是产品时，也会导致模拟的火山曲线与实验曲线相匹配。这项工作不仅说明了碱性HER的机理，而且还为催化剂设计提供了一个目标，即以最佳的氢氧化物结合强度为目标，以实现碱性HER的最高转化率。讨论了三维（吸附有H和OH的物质）HER活性火山及其对氢氧化的影响。