Rational design of organic layer/3D silver foam electrodes for electrochemical CO2 reduction reaction at diluted concentration

Abstract

Electrocatalysts for the electrochemical CO₂ reduction reaction (CO₂RR) have been developed for carbon neutrality by enabling the direct conversion of renewable resources into valuable carbon-based fuels and chemicals. Even electrocatalysts that exhibit high selectivity for CO₂RR at high CO₂ concentrations often suffer from increased competitive hydrogen production at lower CO₂ concentrations, requiring the investigation of catalysts that maintain stable selectivity across a wide concentration range. In this work, we fabricated a highly porous three-dimensional (3D) silver foam on an organic layer-added gas diffusion electrode. The porous 3D Ag foam exhibited the greatest improvement when combined with a benzimidazole organic layer (BI-sf), whose suitable CO₂-affinitive interfacial modifier and release facilitated CO₂ reduction pathways toward CO production on the Ag surface. These phenomena helped to enhance the partial current density (j_CO) and faradaic efficiency (FE) for CO production under diffusion-controlled regions. Compared with Ag nanoparticles (AgNP), the BI-sf electrocatalyst achieved a 4-fold and 2.5-fold increase in maximum j_CO with membrane-electrode-assembly (MEA) under 10% and 100% CO₂ concentration conditions, respectively. Additionally, when the CO₂ concentration decreased within 50–10%, BI-sf maintained relatively higher FE (CO) values compared to when BI was absent, demonstrating the promoting effect of BI under low concentrations of CO₂. These findings suggest that adjusting molecular interactions with CO₂ is particularly important to achieve high product selectivity in CO₂RR under low CO₂ concentrations for practical CO₂ utilization applications.