Electrocatalytic CO₂ Reduction to Methanol on Pt(111) Modified with a Pd Monolayer

Electrochemical carbon dioxide (CO₂) conversion to value-added, highly reduced chemicals such as methanol (CH₃OH) is a promising possibility for producing renewable fuel and simultaneous CO₂ recycling. However, this process remains a challenge, with only a few selective electrocatalysts known. Here, we present a study of a palladium monolayer on a platinum (111) single crystal (Pd_ML/Pt(111)) as an electrocatalyst for CO₂ conversion to CH₃OH. A custom-made setup was employed in order to detect and quantify gaseous and liquid CO₂ reduction products in sufficient concentrations despite the limitations of working with a single-crystalline electrode. Under ambient reaction conditions, a Faradaic efficiency (FE) of 1.5% at -0.9 V vs reversible hydrogen electrode (RHE) was obtained while using CO₂ as the reactant. Other reaction intermediates, carbon monoxide (CO) and formaldehyde (HCHO) were subsequently used as reactants, leading to FEs of 1.8 and 2.5%, respectively, whereas formic acid is not reduced. The corresponding mechanism concluded from our work is compared to the literature. The electrocatalyst introduced here, with a highly well-defined structure for CO₂ conversion to CH₃OH, opens up possibilities for further catalytic explorations.