Effects of Electrolyte Buffer Capacity on Surface Reactant Species and the Reaction Rate of CO2 in Electrochemical CO2 Reduction

Effects of Electrolyte Buffer Capacity on Surface Reactant Species and the Reaction Rate of CO2 in Electrochemical CO2 Reduction

TitleEffects of Electrolyte Buffer Capacity on Surface Reactant Species and the Reaction Rate of CO2 in Electrochemical CO2 Reduction
Publication TypeJournal Article
Year of Publication2018
AuthorsHiroshi Haishiba, Lien-Chun Weng, YiKai Chen, Hiroki K Sato, Satoshi Yotsuhashi, Chengxiang Xiang, Adam Z Weber
JournalThe Journal of Physical Chemistry C
Volume122
Issue7
Pagination3719 - 3726
Date Published01/2018
ISSN1932-7447
Abstract

In the aqueous electrochemical reduction of CO2, the choice of electrolyte is responsible for the catalytic activity and selectivity, although there remains a need for more in-depth understanding of electrolyte effects and mechanisms. In this study, using both experimental and simulation approaches, we report how the buffer capacity of the electrolytes affects the kinetics and equilibrium of surface reactant species and the resulting reaction rate of CO2 with varying partial CO2 pressure. Electrolytes investigated include KCl (nonbuffered), KHCO3 (buffered by bicarbonate), and phosphate-buffered electrolytes. Assuming 100% methane production, the simulation successfully explains the experimental trends in maximum CO2 flux in KCl and KHCO3 and also highlights the difference between KHCO3 and phosphate in terms of pKa as well as the impact of the buffer capacity. To examine the electrolyte impact on selectivity, the model is run with a constant total current density. Using this model, several factors are elucidated, including the importance of local pH, which is not in acid/base equilibrium, the impact of buffer identity and kinetics, and the mass-transport boundary-layer thickness. The gained understanding can help to optimize CO2 reduction in aqueous environments.

DOI10.1021/acs.jpcc.7b11316
Short TitleJ. Phys. Chem. C
Refereed DesignationRefereed