The ultra-low potential oxidation of aldehydes is a conspicuous replacement for oxygen evolution reaction due to its efficiency in lowering the energy required for hydrogen production and producing H₂ on dual sides of the electrolyzer. However, the activity origin of catalysts and the reaction mechanism remains unclear. Herein, a formaldehyde oxidation reaction (FOR) with high current density (165 mA cm⁻² at 0.35 V_RHE) is realized on partially reduced CuO on Cu foam (Cu_xO@CF) electrocatalysts. In situ characterizations and density functional theory calculations identified and investigated the existence of Cu⁰ and Cu⁺ and the synergistic effect for FOR and corroborate the reaction pathway. The results reveal that Cu⁰ can facilitate the reaction energy of HOCH₂O^∗ + HO^∗, and Cu⁺ is more favorable for C–H bond cleavage. Meanwhile, H atoms in the produced H₂ are verified to be entirely from HCHO. This work provides theoretical guidance for designing Cu-based electrocatalysts for FOR.

醛类的超低电位氧化是析氧反应的显着替代，因为它可以有效降低电解槽两侧产生氢气和产生 H ₂所需的能量。然而，催化剂的活性来源和反应机理仍不清楚。_{在此，在泡沫铜 (Cu x} O@CF) 电催化剂上实现了部分还原的 CuO 的高电流密度（165 mA cm ^-2在 0.35 V _RHE ）的甲醛氧化反应（FOR） 。原位表征和密度泛函理论计算确定并研究了 Cu ⁰和 Cu ^+的存在以及 FOR 的协同作用，证实了反应途径。结果表明，Cu ^{0可以促进HOCH} ₂ O ^∗  + HO ^∗的反应能，Cu ⁺更有利于C-H键的断裂。同时，证实生成的H ₂中的H原子完全来自HCHO。这项工作为设计用于 FOR 的铜基电催化剂提供了理论指导。