The extensive use of fossil fuels has significantly raised atmospheric CO₂ levels, leading to serious environmental concerns. Direct electroreduction of captured CO₂ (CO₂ER) into value added chemicals and fuels using renewable electricity is raising great interest as a way to mitigate CO₂ emissions.

Copper (Cu) is one of the most promising electrocatalytsts for converting CO₂ to value-added multicarbon (C₂₊) chemicals and fuels. However, CO₂ER technology is facing various scientific challenges mainly related to (a) the lack of selectivity of cathode Cu electrocatalysts and (b) the lack of in-depth studies in electrolyzers at high current density (i.e. high reaction rates). In this work, we demonstrate that dilute alloys – an underexplored class of electrocatalytic materials – can be tuned to control the selectivity toward C₂₊ products in zero-gap electrolyzers.

Dilute alloys employ trace amounts of a secondary metal (like Pd, Ag) in a primary metal matrix (like Cu or Au), resulting in localized strain and electronic effects that improve selectivity toward C₂₊ products and optimize intermediate binding energies (1).

Preparation methods are crucial in dilute alloys as they dictate the surface composition of as-prepared alloys which can directly influence their catalytic performance (2). Yet the influence of preparation methods on dilute alloys for CO₂ electroreduction is underexplored and underexploited.

In this work, PdCu dilute alloys were prepared via two different wet-chemical methods, namely co-reduction and sequential reduction. In the co-reduction method, Cu and Pd precursors are introduced and reduced simultaneously to obtain PdCu dilute alloy nanoparticles. In the sequential reduction method, Cu nanoparticles are prepared first, and Pd is added via galvanic replacement. A narrow size distribution of ca 4 nm was obtained and the Pd composition was varied and controlled at 2, 4, and 6 at.% for both methods. The dilute alloys were characterized using a combination of techniques such as HR-TEM, XPS, and in situ IR to elucidate the structure of the as-prepared catalysts.

Electrocatalytic tests were carried in zero-gap electrolyzers at high current density (>100 mA cm²). An important finding is that the selectivity for C₂₊ products and notably ethylene is highest for PdCu with 4 at.% Pd. Investigation of the effect of the preparation method and composition on the catalytic activity and selectivity of CuPd dilute alloys will be discussed in details.

This study aims at elucidating the effect of preparation methods on the synergetic effect of Cu-based dilute alloys for CO₂ electroreduction.