Chloroperoxidase Immobilized on Pd₂Ag Nanoparticles for the Electrocatalytic Reduction of Nitrate to Ammonia

Ammonia (NH3) production by the Haber-Bosch method is one of the foremost commercial technologies; however, it suffers serious problems, such as high energy consumption and emission of greenhouse gas. Electrocatalytic nitrate reduction to NH3 (NO3RR) provides a more prospective pathway for NH3 production in terms of environmental problems and energy conversion. In this work, a nanobiohybrid composed by ionic liquid-modified chloroperoxidase (CPO-ILEMB) immobilized on bimetallic Pd2Ag nanodendrites (Pd2Ag-BNs) was proposed for NO3RR through a novel electroenzyme cascade catalytic reaction. The electrocatalytic reduction of nitrate (NO3–) to nitrite (NO2–) was achieved using Pd2Ag-BNs, followed by CPO-ILEMB’s enzymatic transformation of NO2– to NH3. Herein, Pd2Ag-BNs not only promoted the electrocatalytic conversion of NO3– to NO2– but also immobilized CPO-ILEMB via electrostatic interaction. In an electroenzymatic cascade catalysis system, Pd2Ag-BNs boosted the reduction efficiency of NO3– to NO2–, and CPO-ILEMB subsequently transformed NO2– to NH3. This electroenzymatic cascade catalysis system could achieve a high Faraday efficiency of 97.1% and a high NH4+ yield of 109.91 mg·h–1·mgcat–1 for NO3RR in a neutral solution.\