Architecting hierarchical channels in MOF-derived carbon aerogels to boost ion diffusion for efficient ammonia electrosynthesis from nitrate

Abstract

Metal-organic framework (MOF)-derived carbons have emerged as promising electrocatalysts for the sustainable electrochemical nitrate reduction reaction (NO3RR). However, a significant bottleneck remains because these derivatives inevitably suffer from severe self-aggregation and dense stacking during pyrolysis, which would severely restrict the diffusion flux of NO3− ions, leading to insufficient reactant supply and sluggish reaction kinetics. In this work, we report a generalizable strategy to synthesize MOF-derived carbon aerogels featuring 3D interconnected hierarchical channels, specifically engineered to overcome these diffusion limitations. The optimized cobalt-based carbon aerogel exhibits exceptional electrocatalytic performance, delivering a maximal NH3 yield rate of 323.9 mg h−1 mg−1 and a near-unity Faradaic efficiency of 99.9%. Comprehensive kinetic analyses reveal that this hierarchical design increases the apparent nitrate diffusion coefficient by over 30-fold compared to the bulk counterpart, which effectively lowers the apparent activation energy. Furthermore, in situ spectroscopic investigations confirm a smooth deep-reduction pathway enabled by the rapid reactant supply. A rechargeable Zn-nitrate battery assembled with this carbon aerogel cathode achieves a peak power density of 11.76 mW cm−2, realizing efficient coproduction of electricity and ammonia.