Tuning Eley-Rideal Mechanism in Electrochemical Acetylene Semi-Hydrogenation

The Eley-Rideal (ER) mechanism is pivotal in heterogeneous catalysis processes such as fuel cells and electrolyzers, which rely heavily on the interaction between solution-phase and surface-phase species. In this study, we examine the semi-hydrogenation of acetylene to ethylene to explore the factors influencing the ER mechanism. We employed the density functional theory (DFT) to calculate the hydrogenation of acetylene on face-centered cubic metals and copper-based alloys. Microkinetic modeling identifies changes in the rate-determining steps of different alloys as electronegativity decreases. We then constructed the volcano plot for the adsorption energy toward C₂H₂ and the reaction rate, which predicted that Cu₃Au is the best candidate alloy for the C₂H₂ semi-hydrogenation. Both extensive prior research and our experimental findings validated our volcano plot. Notably, our work points out the two key determinants of the ER mechanism: atomic activation and steric hindrance. For metals with weaker adsorption, steric hindrance primarily obstructs the ER mechanism, while for metals with stronger adsorption, the ER mechanism is hindered due to the challenge of atomic activation. Therefore, introducing weak adsorption sites into moderately adsorptive metals can improve the overall efficiency of the ER reaction by balancing these two factors.