Reaction intermediates during operando electrocatalysis identified from full solvent quantum mechanics molecular dynamics

Abstract

Electrocatalysis provides a powerful means to selectively transform molecules, but a serious impediment in making rapid progress is the lack of a molecular-based understanding of the reactive mechanisms or intermediates at the electrode–electrolyte interface (EEI). Recent experimental techniques have been developed for operando identification of reaction intermediates using surface infrared (IR) and Raman spectroscopy. However, large noises in the experimental spectrum pose great challenges in resolving the atomistic structures of reactive intermediates. To provide an interpretation of these experimental studies and target for additional studies, we report the results from quantum mechanics molecular dynamics (QM-MD) with explicit consideration of solvent, electrode–electrolyte interface, and applied potential at 298 K, which conceptually resemble the operando experimental condition, leading to a prototype of operando QM-MD (o-QM-MD). With o-QM-MD, we characterize 22 possible reactive intermediates in carbon dioxide reduction reactions (CO2RRs). Furthermore, we report the vibrational density of states (v-DoSs) of these intermediates from two-phase thermodynamic (2PT) analysis. Accordingly, we identify important intermediates such as chemisorbed CO2 (b-CO2), *HOC-COH, *C-CH, and *C-COH in our o-QM-MD likely to explain the experimental spectrum. Indeed, we assign the experimental peak at 1,191 cm−1 to the mode of C-O stretch in *HOC-COH predicted at 1,189 cm−1 and the experimental peak at 1,584 cm−1 to the mode of C-C stretch in *C-COD predicted at 1,581 cm−1. Interestingly, we find that surface ketene (*C=C=O), arising from *HOC-COH dehydration, also shows signals at around 1,584 cm−1, which indicates a nonelectrochemical pathway of hydrocarbon formation at low overpotential and high pH conditions.

Designing materials for electrochemical carbon dioxide recycling

“…Creating a material where the atoms are arranged to precisely manipulate each step of the reaction, with minimal energy input, is the longstanding goal of efficient catalysis. For CO 2 RR, this will require new spectroscopic tools and enhanced theoretical techniques that together illuminate unknown mechanistic steps 6,[21][22][23][24] , such as the protonation steps that convert bound CO into CH 4 , the singular or multiple C-C bond formation step(s), and the factors that drive selectivity among oxygenates [120][121][122] . Ideally, these tools should operate in situ and operando, providing real-time insight into material evolution along with insight into the chemical origins of CO 2 activation and C-C bond formation.…”

Formation of carbon–nitrogen bonds in carbon monoxide electrolysis

“…Very recently, we started to employ the two-phase thermodynamic (2PT) model to extract entropies and quantum effect. 5 This combination of MD and 2PT analysis allows us to estimate the contributions from ZPE. The predicted free energies with and without ZPE are shown in Supplementary Table 5.…”

Atomistic modeling of electrocatalysis: Are we there yet?

“…(169) To circumvent this issue, the group of Goddard has been relying extensively on pre-equilibration at a reactive force field level of theory(170) before turning to the actual AIMD simulations. (168,171,172) This is only possible if a suitable empirical force fields is available, which is currently only the case for Cu (170) and for dominating noble metal surfaces (169,173). Furthermore, "suitable" is based on the assumption that the equilibration at the force field level brings the system into the vicinity of the DFT equilibrium ensemble, a hypothesis that is difficult to (in-)validate in the absence of rigorous DFT based sampling.…”