Coupled Electrocatalytic-Enzymatic Tandem Reduction for Selective Nitrate-to-Ammonia Conversion

Abstract As a promising strategy for green synthesis, tandem electroenzymatic catalysis has recently emerged. This work designs a tandem electroenzymatic catalysis platform by directionally immobilizing ionic liquid modified chloroperoxidase (CPO-ILEMB) onto silver-loaded reduced graphene oxide (Ag/rGO) modified with polyethyleneimine (PEI), thereby constructing the CPO-ILEMB/Ag/rGO-PEI bioconjugate for NO3– reduction reaction (NO3–RR). Firstly, Ag/rGO-PEI electrocatalytically reduces NO3– to NO2–. Subsequently, CPO-ILEMB converts NO2– to NH4+ with high substrate selectivity and catalytic specificity. PEI covalently immobilizes enzyme molecules via glutaraldehyde, enhancing their stability, and its protonated form provides positive charges to enrich NO3– and the intermediate NO2–. In situ FTIR analysis reveals that the NO2– intermediate is rapidly consumed at the CPO-ILEMB/Ag/rGO-PEI interface, accompanied by the accumulation of NH4+ species, verifying the successful construction of this tandem electroenzymatic system. As a result, the CPO-ILEMB/Ag/rGO-PEI bioconjugate achieves a Faradaic efficiency of 94.97% and an NH4+ yield rate of 4.94 mg h–1 mgcat–1 at –0.56 V vs. RHE, representing an NH4+ yield rate of 19.8-fold increase over Ag/rGO-PEI, and maintains stable performance during 216 h of continuous operation.