Boosting Electrocatalytic Nitrate Reduction through Enhanced Mass Transfer in Cu-Bipyridine 2D Covalent Organic Framework Films

Abstract

Electrocatalytic nitrate reduction (NO₃RR) is a promising method for pollutant removal and ammonia synthesis and involves the transfer of eight electrons and nine protons. As such, the rational design of catalytic interfaces with enhanced mass transfer is crucial for achieving high ammonia yield rates and Faradaic efficiency (FE). In this work, we incorporated a Cu-bipyridine catalytic interface and fabricated crystalline 2D covalent organic framework films with significantly exposed catalytic sites, leading to improved FE and ammonia yield (FE=92.7 %, NH₃ yield rate=14.9 mg ⋅ h^-1cm^-2 in 0.5 M nitrate) compared to bulk catalysts and outperforming most reported NO₃RR electrocatalysts. The film-like morphology enhances mass transfer across the Cu-bipyridine interface, resulting in superior catalytic performance. We confirmed the reaction pathway and mechanism through in situ characterizations and theoretical calculations. The Cu sites act as primary centers for adsorption and activation, while the bipyridine sites facilitate water adsorption and dissociation, supplying sufficient H* and accelerating proton-coupled electron transfer kinetics. This study provides a viable strategy to enhance mass transfer at the catalytic interface through rational morphology control, boosting the intrinsic activity of catalysts in the NO₃RR process.

Keywords: Ammonia synthesis; Catalytic interface; Covalent organic frameworks; Electrocatalysis; Nitrate reduction.