Nanocellular Organelle Engineering for Optimizing Reaction Microenvironments in Nitrate-to-Ammonia Electrocatalysis

Certain natural catalysts, biological enzymes, tend to be confined within cellular organelles to achieve high catalytic efficiency in small molecule conversion due to the optimized reaction environment within their internal space. Inspired by this, we implement nanocellular organelle engineering using a "ship-in-a-bottle" strategy to encapsulate ZIF-67 with metal-ligand coordination motifs into hollow mesoporous carbon spheres (ZIF-67@HMCS) for catalytic process intensification. As a proof of concept, we employed the electrochemical nitrate reduction reaction (NO₃ ^-RR) as a probe and found that the spatial confinement effect within the hollow mesoporous architecture enriches the intermediate NO₂ ^- and elevates the local pH, thereby constructing a favorable reaction microenvironment that promotes deep reduction while suppressing the competitive hydrogen evolution reaction, ultimately enabling efficient conversion of NO₃ ^- to NH₃. In a neutral electrolyte medium, the ZIF-67@HMCS model electrocatalyst attains the highest Faraday efficiency for NH₃ (FE_NH3) at 97.6%, maintains FE_NH3 above 80% over a wide potential window (∼0.5 V), and delivers over 90% FE_NH3 even at low substrate concentrations (200-5000 ppm). This nanocellular organelle engineering activates the electrocatalytic properties of metal-organic frameworks through a novel spatial confinement effect, while also offering profound insights into nature-inspired reaction microenvironment optimization for targeted small molecule conversions.