(62n) Modeling Adsorbate-Induced Restructuring of Cu Surface in Electro-Reduction Conditions

Rearrangement of Cu surfaces under electrochemical conditions has been demonstrated to play a key role in the surface activation for major electrocatalytic reactions. Despite the extensive experimental insights from surface-sensitive spectroscopic and microscopic methods, their spatial and temporal resolution are far from ideal. Theoretical investigations have also been challenged by the diversity of restructuring configurations, surface stoichiometry, adsorbate configurations, and the effect of electrode potential.

Here, we tackle the complexity of electrochemical restructuring of Cu by a combination of grand canonical DFT and global optimization techniques, which explores the chemical space of Cu rearrangement as well as coverage and configuration of relevant adsorbates. We show that electroreduction condition can induce row-shifting rearrangement on Cu(100), induced by H adsorption. The simulated STM images of the calculated reconstructed structures agree with experimental in situ STM images, which validates our model. The found shifted-row configuration is initiated and stabilized only at a high H coverage since this weakens the Cu-Cu bonds between top- and sub-layer and fills the created 3-fold hollow sites with H adsorbates. Different statistical models are used to study the potential- and pH-dependence of the surface phase diagram. The kinetics and dynamics of surface atoms are studied with BOMD simulations, and their dependence on H coverage and initial configuration is discussed. Then, we further investigate the effects of mixed coverage of H and CO, with corresponds to the conditions of CO₂ reduction reaction. Significant vertical displacement of surface Cu atoms is observed in the regime of intermediate and mixed CO and H coverage. This regime, while predicted to be thermodynamically inaccessible, is kinetically controlled, presenting a tough challenge for theory. To investigate the kinetic trapping effects, we develop a quasi-kinetic Monte Carlo simulation to track the evolution of the system during a simulated cathodic scan. The simulation reveals the path that the system takes across the coverage space and the metastable structures that the system evolves into along the way. Chemical bonding analysis is performed on the metastable structures with elevated Cu*CO species to understand its formation mechanism. By molecular dynamics simulations and free energy calculations, the surface chemistry of the Cu*CO species is explored, and we identifies potential mechanisms via which the Cu*CO species may diffuse or dimerize.

This collection of works provides rich atomistic insights into the surface restructuring phenomena on Cu and the structure of the involved surface phases and species. It also features generalizable methods to explore the chemical space of restructuring surfaces with mixed adsorbates, and its non-equilibrium evolution.