(186h) Elucidating Selectivity Determining Elementary Steps for Ethanol Electrooxidation on Pt (100) Via Combined Molecular Dynamics and DFT Analysis

Direct ethanol-based fuel cells (DEFC) are a viable source for renewable energy production, with numerous environmentally friendly ethanol feedstocks sources, such as biomass and CO₂ reduction, available. Despite these advantages, DEFC’s require high overpotential and suffer from low selectivity to fully oxidized product CO₂ (12 e^- per ethanol) on pure metal catalyst. To systematically understand these phenomena, and thereby facilitate design of improved DEFC’s, studies have aimed to probe the fundamentals of the reaction chemistry on single crystal surfaces of noble metal catalysts such as Pt. However, the mechanistic details of the reactions are not fully known, and even basic information such as the nature of the rate-limiting step is not understood.

In this work, we consider a detailed analysis to understand the reaction mechanism of ethanol (CH₃CH₂OH) electrooxidation on Pt(100) single crystal surface in the lower (0.2-0.3 V), and higher overpotential regions ( > 0.6 V vs. SHE). We make use of periodic Density Functional Theory as well as Ab-Initio Molecular Dynamics (AIMD) simulations, and combine it with theoretical electrochemistry analyses. We first elucidate the reaction mechanism in the lower potential regime by incorporating various effects such as reactant coverages and solvation, as well as by considering chemical and electrochemical reaction barriers. The barriers are determined using techniques such as explicit proton transfer from water bilayers, potential of mean force simulations using AIMD, and the Climbing Image Nudged Elastic Band (CINEB) algorithm. Then, we probe the state of the surface at higher potentials, and elucidate the effect of high coverages of co-adsorbed surface hydroxyl species on the adsorption energetics of important intermediates. Finally, we discuss the detailed reaction mechanism and shed light on selectivity determining reaction steps.