Ionomer-driven selectivity control in natural sunlight-powered CO₂ electrolysis using Ag electrodes in seawater

Abstract

The increasing concentration of anthropogenic CO2 in the atmosphere is exacerbating global warming, making the need for carbon reduction technologies even more urgent. While photovoltaic cell (PV)-assisted electrochemical carbon dioxide reduction (CO2RR) is a promising approach for converting carbon dioxide into value-added chemicals and fuels, its practical implementation is hindered by the low selectivity and stability of electrocatalysts, particularly in seawater electrolytes. Unlike purified potassium bicarbonate (KHCO3) electrolytes, natural seawater electrolyte presents additional challenges, such as catalyst deactivation due to unwanted metal ions and competitive side reactions, and instability under fluctuating solar irradiation in PV-electrolysis systems. This study explores the role of ionomer selection in silver-based CO2RR under natural solar-driven PV-electrolysis in seawater. Comparing Nafion and Sustainion, we have found that Sustainion significantly enhances carbon monoxide selectivity (>95 % Faradaic efficiency) by suppressing the hydrogen evolution reaction (HER) and facilitating bicarbonate transport, reducing calcite-induced deactivation. Moreover, silver and Sustainion electrodes maintain stable performance under fluctuating sunlight, unlike silver and Nafion, which degrade quickly due to limescale formation. These findings emphasize the importance of optimizing ionomer-catalyst interactions and operational conditions for durable seawater-based carbon dioxide electrolysis. The integration of ionomer-engineered silver catalysts with PV-electrolysis presents a promising approach for scalable and sustainable carbon dioxide conversion.