An APXPS Probe of Cu/Pd Bimetallic Catalyst Surface Chemistry of CO₂ Toward CO in the Presence of H₂O and H₂

The electroreduction of CO₂ represents a promising avenue to convert greenhouse gas into valuable fuels and store energy from intermittent renewable sources. Cu-based bimetallic surfaces constitute high-interest electrocatalysts for this reaction because of the relatively low overpotentials and the tunable selectivity they offer. This work proposes an investigation on the first activation and conversion step of CO₂ at the gas–solid interface of a model bimetallic surface with the goal of bringing understanding on the potential effects of the metal combination on the microscopic phenomenon occurring during the catalytic reaction. A partial monolayer of Cu on a substrate of Pd is studied along with a pure Pd surface and a partially oxidized Cu surface by ambient-pressure X-ray spectroscopy (AP-XPS), as they were exposed to CO_2(g), H₂O_(g), and H_2(g). The evolution of the adsorbed carbon species populations under the various gaseous conditions revealed a dramatic difference of catalytic activity toward the reduction of CO₂ among the surfaces. The Cu surface favored the adsorption of CO₂, while the Pd surface catalyzed its reduction. The observation of both these functions at the bimetallic surface confirmed that bimetallicity can serve as an effective tool for the combination of different catalytic functions at the microscopic level on a single bifunctional surface. Molecular transitions for the reduction of CO₂ to CO on the bimetallic surface were proposed to highlight the diversity of electronic and bifunctional effects that can arise from the bimetallic character of a surface.