Impact of hydrogen concentration for CO₂ reduction on PdH_x: A combination study of cluster expansion and kinetics analysis

Pd hydride has shown better electrochemical CO₂ reduction reaction (CO₂RR) performance compared to metal Pd implying that H in the PdH_𝑥 surface plays a vital role in affecting the performance. Using density functional theory (DFT) calculations in combination with active learning cluster expansion and Monte Carlo simulated annealing we identify 12 stable PdH_𝑥(111) configurations on the DFT convex hull and investigate the binding energies of intermediates in the CO₂RR and the competing hydrogen evolution reaction. Through analysis of intermediate binding energies and a microkinetic model, we identify the atomic structures of the PdH_𝑥 phase most likely to produce syngas. The high activity of the PdH_0.6 surface can be attributed to the fact that H segregation in the PdH_𝑥(111) surface breaks the linear relation between HOCO* and CO* adsorbates.