Cu₂O is an attractive photocathode for CO₂ reduction reaction (CO₂RR). The instability of Cu₂O usually makes it present as a part of composite or multilayer in CO₂RR. The systematic study of pure Cu₂O for CO₂RR is quite rare, resulting in the elusiveness of the origin for the activity and selectivity of CO₂RR under different conditions. Herein, exploration of the factors that influence the product distribution and Faradic efficiency of CO₂RR using pure Cu₂O is carried out, like Cu₂O structure and electrolyte composition. Persistent Cu⁺ is found to be key for selective CO₂RR, especially favoring the formation of C2 product (CH₃COOH). The Cu₂O film thickness, local pH, and the electrolyte cations are revealed to influence the amount of surface Cu⁺. The number of H⁺ and dissolved CO₂ affected by electrolytes also account for the disparity of CO₂RR results. Therefore, by considering both the CO₂RR and the dynamic change of Cu₂O, this work has provided a compositional descriptor to link the structure of Cu₂O and the CO₂RR property, which can be useful for future development of Cu₂O-based catalysts.

Cu _{2 O 是用于 CO 2}还原反应 (CO ₂ RR)的有吸引力的光电阴极。Cu ₂ O的不稳定性使其在CO ₂ RR中通常以复合或多层的形式存在。纯Cu ₂ O对CO ₂ RR的系统研究非常少，导致CO ₂ RR在不同条件下的活性和选择性来源难以捉摸。在此，探索了影响使用纯Cu _{2 O的CO 2} RR的产物分布和法拉第效率的因素，如Cu ₂ O结构和电解质组成。持久性铜⁺被发现是选择性 CO ₂ RR 的关键，特别是有利于 C2 产物 (CH ₃ COOH) 的形成。Cu ₂ O 膜厚度、局部 pH 值和电解质阳离子显示影响表面 Cu ⁺的量。受电解质影响的 H ⁺和溶解的 CO _{2的数量也是导致 CO 2} RR 结果差异的原因。因此，通过同时考虑 CO ₂ RR 和 Cu ₂ O 的动态变化，这项工作提供了一个将 Cu ₂ O 的结构与 CO ₂ RR 性质联系起来的组成描述符，这对于 Cu 的未来发展很有用₂ O基催化剂。