Nanomorphology-Enhanced Gas-Evolution Intensifies CO₂ Reduction Electrochemistry

Nanostructured CO₂ reduction catalysts now achieve near-unity reaction selectivity at increasingly improved Tafel slopes and low overpotentials. With excellent surface reaction kinetics, these catalysts encounter CO₂ mass transport limitations at current densities ca. 20 mA cm^-2. We show here that - in addition to influencing reaction rates and local reactant concentration - the morphology of nanostructured electrodes enhances long-range CO₂ transport via their influence on gas-evolution. Sharper needle morphologies can nucleate and release bubbles as small as 20 μm, leading to a 4-fold increase in the limiting current density compared to a nanoparticle-based catalyst alone. By extending this observation into a diffusion model that accounts for bubble-induced mass transport near the electrode's surface, diffusive transport can be directly linked to current densities and operating conditions, identifying efficient routes to >100 mA cm^-2 production. We further extend this model to study the influence of mass transport on achieving simultaneously high selectivity and current density of C2 reduction products, identifying precise control of the local fluid environment as a crucial step necessary for producing C2 over C1 products.