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.