(62b) Electronic Structure Tuning of Cu-Free Intermetallic Electrocatalysts for CO Reduction

The electrochemical reduction of CO₂ is a potential means for producing carbon-neutral fuels and chemicals using intermittent renewable electricity. However, monometallic Cu is the only available electrocatalyst for the reaction and it is not active or selective enough to make the process economically viable. Unfortunately, research efforts aimed at discovering superior electrocatalysts have failed to even identify alternative materials capable of catalyzing the reaction. The unique reactivity observed over Cu has been attributed to its moderate CO adsorption energy, which is a direct result of its unique d-band structure. Thus, if the d-band structure of another metal could be modified to resemble Cu then it might also exhibit similar reactivity during CO₂ reduction. Intermetallic bonding between electronically dissimilar metals can induce such electronic modifications via a ligand effect. In fact, Cu-free intermetallic catalysts have been shown to exhibit Cu-like reactivity for other reactions, such as methanol steam reforming.

In this presentation, we will explore the hypothesis that the unique d-band structure of Cu enables it to catalyze the reduction of CO₂ to hydrocarbons and alcohols by synthesizing Cu-free intermetallic alloys with nearly identical d-band structures. We will demonstrate the extent to which the d-band structure of Pd can be modified by intermetallic bonding. However, we will also demonstrate that significant composition gradients form in the near-surface region of such intermetallic alloys nearly instantaneously upon air exposure. This observation provides a potential explanation for the poor CO₂ reduction activity reported over similar Cu-free intermetallic electrocatalysts in the recent literature. To address this issue, we propose and validate a generic methodology that prevents the formation of these near-surface composition gradients by protecting the intermetallic surface with a sacrificial passivating overlayer. Finally, we will systematically demonstrate the impact of d-band structure on the CO reduction activity of these Cu-free Pd-based intermetallic electrocatalysts.