The importance of grand-canonical quantum mechanical methods to describe the effect of electrode potential on the stability of intermediates involved in both electrochemical CO2 reduction and hydrogen evolution†

Haochen Zhang, William A. Goddard, Qi Lu, Mu Jeng Cheng

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

The rational design of electrocatalysts to convert CO2 to fuel requires predicting the effect of the electrode potential (U) on the binding and structures of the intermediates involved in CO2 electrochemical reduction (CO2ER). In this study, we used grand-canonical quantum mechanics (GC-QM) to keep the potential constant during the reactions (rather than keeping the charge constant as in standard QM) to investigate the effect of U on adsorption free energies (DGs) of 14 CO2ER intermediates on Cu(111) as well as the intermediates involved in the competitive hydrogen evolution reaction (HER). In contrast to most previous theoretical studies where DGs were calculated under constant charge (= 0, neutral), we calculated DGs under constant potential (U = 0.0, 0.5, 1.0, and 1.5 VSHE). By comparing the DGs calculated under constant U (= 0.0 VSHE) to those calculated under constant charge, we found differences up to 0.22 eV which would change the rates at 298 K by a factor of about 5300. In particular we found that the adsorption of species with a CQO functional group (i.e., *COOH, *CO, and *CHO) strengthened by up to 0.16 eV as U became more negative by 1 V, whereas the adsorption of -O- species (i.e., *OH, *OCH3, *COH, and *CHOH) weakened by up to 0.20 eV. For the (111) index surfaces of Cu, Au, Ag, Ir, Ni, Pd, Pt and Rh, we investigated the effect of U on the reaction free energy (DG) at pH = 0 for the crucial elementary steps for CO2ER (*CO + (H+/e-) - *CHO, DG = (DG*CHO - DG*CO) + eU) and HER (* + (H+/e-) - *H, DG = DG*H + eU. Our results indicated that the influence of U on (DG*CHO - DG*CO) was metal dependent. In contrast, the energy for converting a proton in solution to H* on the surface, DG*H, was barely affected by U (for the studied metals). Overall we found substantial differences (MAD 4 0.18 eV) between the DGs calculated under U = -1.0 VSHE (relevant to experiments) and those calculated under constant charge (= 0, neutral) common to most theoretical investigations. Therefore, we strongly recommend application GC-QM to obtain accurate energetics for CO2ER.

Original languageEnglish
Title of host publicationComputational Molecular Science and Engineering Forum 2018 - Core Programming Area at the 2018 AIChE Annual Meeting
PublisherAIChE
Pages200-208
Number of pages9
ISBN (Electronic)9781510876156
DOIs
Publication statusPublished - 2018
EventComputational Molecular Science and Engineering Forum 2018 - Core Programming Area at the 2018 AIChE Annual Meeting - Pittsburgh, United States
Duration: 2018 Oct 282018 Nov 2

Publication series

NameComputational Molecular Science and Engineering Forum 2018 - Core Programming Area at the 2018 AIChE Annual Meeting

Conference

ConferenceComputational Molecular Science and Engineering Forum 2018 - Core Programming Area at the 2018 AIChE Annual Meeting
CountryUnited States
CityPittsburgh
Period18-10-2818-11-02

All Science Journal Classification (ASJC) codes

  • Chemical Engineering(all)
  • Computer Science Applications
  • Engineering(all)
  • Modelling and Simulation

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    Zhang, H., Goddard, W. A., Lu, Q., & Cheng, M. J. (2018). The importance of grand-canonical quantum mechanical methods to describe the effect of electrode potential on the stability of intermediates involved in both electrochemical CO2 reduction and hydrogen evolution†. In Computational Molecular Science and Engineering Forum 2018 - Core Programming Area at the 2018 AIChE Annual Meeting (pp. 200-208). (Computational Molecular Science and Engineering Forum 2018 - Core Programming Area at the 2018 AIChE Annual Meeting). AIChE. https://doi.org/10.1039/c7cp08153g