Rational design of a membrane-coated cathode for selective electrochemical hydrogen evolution in chlorate electrolysis

Abstract

The industrial chlorate process has traditionally used chromium(VI) as an electrolyte additive for high Faraday efficiency. However, due to its recognized toxicity and carcinogenic properties, the EU has regulated its usage, prompting the need for alternative approaches. In this study, we propose the adoption of a polymeric membrane-coated cathode (MCC) as a straightforward yet highly efficient solution to enhance the selectivity of the hydrogen evolution reaction (HER) in chlorate electrolysis. Proof-of-concept MCCs were fabricated by coating roughened titanium substrates with cation and anion exchange membrane layers, which function as selective barriers for anodic hypochlorite species. The study revealed that a thin membrane coating on the electrode surface effectively suppressed the permeation of anodic intermediates, without compromising the current density for HER. By optimizing the coating layer thickness and substrate surface properties of MCC, the chlorate electrolysis cell demonstrated an impressive Faradaic efficiency of up to 95% at a current density of 150 mA/cm², while maintaining exceptional stability. The outcome of this study can potentially advance the feasibility of industrial chlorate production in meeting regulatory requirements and effectively mitigating environmental consequences.