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-IL_EMB) 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-IL_EMB’s enzymatic transformation of NO₂^– to NH₃. Herein, Pd₂Ag-BNs not only promoted the electrocatalytic conversion of NO₃^– to NO₂^– but also immobilized CPO-IL_EMB via electrostatic interaction. In an electroenzymatic cascade catalysis system, Pd₂Ag-BNs boosted the reduction efficiency of NO₃^– to NO₂^–, and CPO-IL_EMB 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·mg_cat^–1 for NO₃RR in a neutral solution.\