Aqueous-phase electrocatalytic hydrogenation of benzaldehyde on Cu leads not only to benzyl alcohol (the carbonyl hydrogenation product), but Cu also catalyzes carbon–carbon coupling to hydrobenzoin. In the absence of an organic substrate, H₂ evolution proceeds via the Volmer–Tafel mechanism on Cu/C, with the Tafel step being rate-determining. In the presence of benzaldehyde, the catalyst surface is primarily covered with the organic substrate, while H* coverage is low. Mechanistically, the first H addition to the carbonyl O of an adsorbed benzaldehyde molecule leads to a surface-bound hydroxy intermediate. The hydroxy intermediate then undergoes a second and rate-determining H addition to its α-C to form benzyl alcohol. The H additions occur predominantly via the proton-coupled electron transfer mechanism. In a parallel reaction, the radical α-C of the hydroxy intermediate attacks the electrophilic carbonyl C of a physisorbed benzaldehyde molecule to form the C–C bond, which is rate-determining. The C–C coupling is accompanied by the protonation of the formed alkoxy radical intermediate, coupled with electron transfer from the surface of Cu, to form hydrobenzoin.

中文翻译：

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Cu 上电催化析氢、羰基氢化和碳碳偶联的机理


苯甲醛在 Cu 上的水相电催化氢化不仅产生苯甲醇（羰基氢化产物），而且 Cu 还催化碳-碳偶联生成氢安息香。在没有有机底物的情况下，H ₂ 的演化通过 Cu/C 上的 Volmer-Tafel 机制进行，其中 Tafel 步骤是速率决定的。在苯甲醛存在下，催化剂表面主要被有机基质覆盖，而H*覆盖率较低。从机理上讲，吸附的苯甲醛分子的羰基 O 上的第一个 H 加成会产生表面结合的羟基中间体。然后，羟基中间体在其 α-C 上进行第二次决定速率的 H 加成，形成苯甲醇。 H的添加主要通过质子耦合电子转移机制发生。在平行反应中，羟基中间体的自由基 α-C 攻击物理吸附的苯甲醛分子的亲电子羰基 C，形成 C-C 键，这是决定速率的。 C-C偶联伴随着所形成的烷氧基中间体的质子化，再加上Cu表面的电子转移，形成氢苯偶姻。