Electrochemical conversion of CO₂ offers a sustainable route for producing fuels and chemicals. Pd-based catalysts are effective for converting CO₂ into formate at low overpotentials and CO/H₂ at high overpotentials, while undergoing poorly understood morphology and phase structure transformations under reaction conditions that impact performance. Herein, in-situ liquid-phase transmission electron microscopy and select area diffraction measurements are applied to track the morphology and Pd/PdH_x phase interconversion under reaction conditions as a function of electrode potential. These studies identify the degradation mechanisms, including poisoning and physical structure changes, occurring in PdH_x/Pd electrodes. Constant potential density functional theory calculations are used to probe the reaction mechanisms occurring on the PdH_x structures observed under reaction conditions. Microkinetic modeling reveals that the intercalation of *H into Pd is essential for formate production. However, the change in electrochemical CO₂ conversion selectivity away from formate and towards CO/H₂ at increasing overpotentials is due to electrode potential dependent changes in the reaction energetics and not a consequence of morphology or phase structure changes.

CO2 的电化学转化为生产燃料和化学品提供了一条可持续的途径。钯基催化剂可有效在低过电位下将 CO₂ 转化为甲酸盐，在高过电位下将 CO/H₂ 转化为甲酸盐，同时在影响性能的反应条件下发生知之甚少的形态和相结构转变。在本文中，应用原位液相透射电子显微镜和选择区域衍射测量来跟踪反应条件下的形态和 Pd/PdH_x 相互转化作为电极电位的函数。这些研究确定了 PdH_x/Pd 电极中发生的降解机制，包括中毒和物理结构变化。恒电位密度泛函理论计算用于探测在反应条件下观察到的 PdH_x 结构上发生的反应机理。微动力学模型表明，将 *H 嵌入 Pd 中对于甲酸盐的产生至关重要。然而，在过电位增加时，电化学 CO₂ 转化选择性从甲酸盐向 CO/H₂ 的变化是由于反应能量学中的电极电位依赖性变化，而不是形态或相结构变化的结果。