Creating Abundant Gas–Solid–Liquid Triple-Phase Interfaces in Hierarchical Porous Structure for Efficient Electrochemical CO₂ Reduction

Gas–solid–liquid triple-phase interfaces are essential for improving the performance of industrial carbon dioxide (CO₂) electrolyzers by facilitating mass transfer process. Yet there still lacks experimental approaches and theoretical understanding in the creation of stable triple-phase interfaces at the catalyst layer in gas diffusion electrodes. Here, hierarchical porous CuS microtubes assembled by interconnected hexagonal nanosheets exposing the highly active (001) facet are developed for efficient electrochemical CO₂ reduction reaction (CO₂RR). We demonstrate how the hierarchical structure of the catalysts aided the creation of triple-phase interfaces by combined experimental and theoretical simulation results. Compared to the nanoparticle-assembled CuS microtube counterpart, the nanosheet-assembled CuS microtubes exhibit superior intrinsic performance toward the production of formate. More importantly, the hierarchical porous structure is found to be essential for the highly selective formate production by creating abundant gas–solid–liquid triple-phase interface. A significant drop in formate selectivity and an increase in mass transfer resistance are observed when breaking the tubular architecture. Simulation results further demonstrate that electrolyte would quickly penetrate into the microtubes due to the capillary force, which promotes the formation of abundant gas–solid–liquid triple-phase interfaces on the mesoporous wall as active sites during CO₂RR.