Pulsed CO₂ electroreduction (CO₂RR) has recently emerged as a facile way to in situ tune the product selectivity, in particular toward ethanol, without re-designing the catalytic system. However, in-depth mechanistic understanding requires comprehensive operando time-resolved studies to identify the kinetics and dynamics of the electrocatalytic interface. Here, we track the adsorbates and the catalyst state of pre-reduced Cu₂O nanocubes ( ~ 30 nm) during pulsed CO₂RR using sub-second time-resolved operando Raman spectroscopy. By screening a variety of product-steering pulse length conditions, we unravel the critical role of co-adsorbed OH and CO on the Cu surface next to the oxidative formation of Cu-O_ad or CuO_x/(OH)_y species, impacting the kinetics of CO adsorption and boosting the ethanol selectivity. However, a too low OH_ad coverage following the formation of bulk-like Cu₂O induces a significant increase in the C₁ selectivity, while a too high OH_ad coverage poisons the surface for C-C coupling. Thus, we unveil the importance of co-adsorbed OH on the alcohol formation under CO₂RR conditions and thereby, pave the way for improved catalyst design and operating conditions.

脉冲CO ₂电还原(CO ₂ RR) 最近成为一种简便的方法，可以原位调节产物选择性，特别是对乙醇的选择性，而无需重新设计催化系统。然而，深入的机理理解需要全面的操作时间分辨研究来确定电催化界面的动力学和动力学。在这里，我们使用亚秒时间分辨操作拉曼光谱跟踪脉冲 CO ₂ RR 过程中预还原 Cu ₂ O 纳米立方体 (~ 30 nm) 的吸附物和催化剂状态。通过筛选各种产物引导脉冲长度条件，我们揭示了铜表面上共吸附的 OH 和 CO 在氧化形成 Cu-O _ad或 CuO _x /(OH) _y物种时的关键作用，从而影响了CO 吸附动力学和提高乙醇选择性。然而，在形成块状Cu ₂ O后，过低的OH _ad覆盖率会导致C ₁选择性显着增加，而过高的OH _ad覆盖率会毒害CC偶联的表面。因此，我们揭示了共吸附 OH 对 CO ₂ RR 条件下醇形成的重要性，从而为改进催化剂设计和操作条件铺平了道路。