Asymmetric chloride-mediated electrochemical process for CO2 removal from oceanwater

Abstract

In recent years, the ocean has come to be recognized as a global-scale reservoir for atmospheric CO₂. The removal of CO₂ from oceanwater is thus considered a compelling approach to reduce ambient CO₂ concentrations, and potentially achieve net-negative emissions. As an effective means of oceanic CO₂ capture, we report an asymmetric electrochemical system employing bismuth and silver electrodes that can capture and release chloride ions by faradaic reactions upon application of appropriate cell voltages. The difference in reaction stoichiometry between the two electrodes enables an electrochemical system architecture for a chloride-mediated electrochemical pH swing, which can be leveraged for effective removal of CO₂ from oceanwater without costly bipolar membranes. With two silver–bismuth systems operating in tandem in a cyclic process, one acidifying the ocean water, and the other regenerating the electrodes through alkalization of the treated stream, CO₂ can be continuously removed from simulated oceanwater with a relatively low energy consumption of 122 kJ mol⁻¹, and high electron efficiency.