Electrochemical hydrogen adsorption and desorption, and the state of adsorbed hydrogen (*H) on metal surfaces are of fundamental interest as well as practical importance for the hydrogen evolution reaction (HER) and electrochemical hydrogenation reactions including CO₂ and CO electroreduction. Here, we report a previously undiscovered phenomenon whereby *H desorbs as H₂ during an anodic potential sweep at potentials anodic of (more positive than) the equilibrium potential of U⁰(H₂/H⁺), hence at potentials where hydrogen desorption would be expected as H⁺. Using electrochemistry – online mass spectrometry, we observe, quantify, and characterize the phenomenon on two different materials in two different environments – Ru(0001) in acid and polycrystalline Cu in alkaline. For both Ru and Cu, the anodic H₂ formation seems to coincide with *OH adsorption, which would be consistent with a displacement mechanism. We propose that a high barrier for the Volmer step causes some of the displaced *H to desorb as H₂ (Tafel step) rather than the thermodynamically more favorable desorption as H⁺ (Volmer step).

中文翻译：

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在Ru和Cu电极上形成阳极分子氢

电化学氢的吸附和解吸以及金属表面上氢的吸附状态（* H）对于氢释放反应（HER）和电化学氢化反应（包括CO ₂和CO电还原）具有重要的现实意义。这里，我们报告一个以前未发现的现象，其中* H解吸以H ₂在电势的阳极（正大于）的平衡电位的阳极电位扫描期间ù ⁰（H ₂ / H ⁺），因此，在电势，其中氢解吸将预期为H ⁺。使用电化学–在线质谱，我们观察，量化和表征在两种不同环境中的两种不同材料上的现象-酸性的Ru（0001）和碱性的多晶Cu。对于Ru和Cu而言，阳极H _2的形成似乎与* OH吸附相吻合，这与置换机理是一致的。我们认为，沃尔默步骤的高阻隔会导致部分置换的* H脱附为H ₂（塔菲尔步骤），而不是热力学上更有利的脱附形式为H ⁺（沃尔默步骤）。