Sustainable and Efficient Bicarbonate Electrolysis via Enhanced CO₂ and Cation Availability on a Gas-Water...

The electrochemical conversion of cost-effective bicarbonates into industrially relevant chemicals offers a sustainable, low-carbon-footprint alternative to feedstock production using renewable electricity. However, its performance is limited by low CO₂ concentrations at catalyst surfaces and harsh acidic conditions that promote the hydrogen evolution reaction and catalyst degradation. In this study, we developed a robust ionomer-inorganic nanoparticle (NP) composite coating (5-15 μm Nafion-SiC NPs), positioned between the catalyst and bipolar membrane, enabling efficient dual-permeability of gaseous CO₂ and liquid electrolyte to promote bicarbonate electrolysis over extended operation. Specifically, the Nafion perfluorocarbon chains on the assembled Nafion-SiC NPs interconnect to form a continuous aerophilic network that facilitates CO₂ diffusion. Simultaneously, the interparticle voids between NPs provide hydrophilic pathways that permit efficient electrolyte transport. This prepared stratified electrode increases local CO₂ concentration to 75% saturation and enriches K⁺ availability at electrocatalyst surfaces at cathodic potentials during bicarbonate electrolysis. Experiments validate a high CO₂ permeance of ∼0.008 cm³ cm^-2 s^-1 cmHg^-1 and a low ionic resistance of ∼0.85 Ω cm² for the composite coating under wet conditions. Crucially, the electrically insulating Nafion-SiC NPs resist electric-field-induced K⁺ penetration to ensure long-term hydrophobicity and stable gas transport. This system achieved sustained bicarbonate-to-CO electrolysis over 1100 h with an 84-88% Faradaic efficiency and a 35.8% energy efficiency at 100 mA cm^-2. Extending this gas-liquid dual-permeable coating strategy to Bi- and Sn-based electrodes enhanced bicarbonate-to-formate electroreduction, highlighting the generalizability of this gas-liquid dual-permeable design for advancing heterogeneous electrolysis at triple-phase interfaces.