In situ–generated PdH x promotes electrochemical CO 2 conversion to CO

Palladium-based catalysts have been recognized to be active for the production of syngas with controlled carbon monoxide (CO)/hydrogen gas ratios via the electrochemical carbon dioxide (CO 2 ) reduction reaction (CO 2 RR); however, the active phase remains the subject of debate. In this work, we have found that the Faradaic efficiency of CO is linearly dependent on the hydride stoichiometry of in situ–generated palladium hydride (PdH x ) for palladium (Pd)–based catalysts, despite their different composition, size, and morphology, as well as the applied potential. The active phase for the production of CO via the CO 2 RR on the surfaces of Pd-based catalysts is revealed to be in situ–generated PdH x . In situ surface-enhanced infrared absorption spectroscopy and electro-optical imaging results demonstrate that in situ–generated PdH x is totally different from chemically synthesized PdH x . Density functional theory calculations demonstrate that the higher stoichiometry of in situ–generated PdH x promotes CO production. Our results provide insights into the rational design of Pd-based catalysts with improved CO 2 RR performance.