Feasibility study of an electrochemical hydrogen looping system for indirect ocean capture

Abstract

Electrochemical hydrogen looping is a recently developed, sustainable technology to address decentralized anthropogenic carbon dioxide emissions by indirectly retrieving CO₂ from oceans. However, various economic and technical challenges such as efficiency and scalability remain, currently inhibiting industrial implementation. Moreover, salt management will be of particular importance as a consequence of the alkaline hydrogen evolution reaction in combination with the ionic seawater content, causing precipitations. This work explored and improved the feasibility of the electrochemical hydrogen looping system by benchmarking the performance using synthetic seawater and, for the first time, realistic seawater, comparing cell voltage, capture efficiency, and electrochemical energy consumption. Using synthetic seawater, a record-low electrochemical energy consumption of 77.5 kJ mol⁻¹ CO₂, was obtained. Transitioning to realistic seawater, enabled us to uncover challenges such as Mg(OH)₂ and Ca(OH)₂ salt precipitation on the cathode and membranes, resulting in a continuously rising cell voltage, impeding long-term operation. Introducing an in situ acidic wash step (0.5 M HCl, 45 mL min⁻¹) reduced the voltage increase over a 4-hour operation by 13%, improving long-term stability. Despite membrane scaling challenges, a record-low electrochemical energy consumption of 100.8 kJ mol⁻¹ CO₂ was achieved employing realistic seawater.