Sustainable Nitrogen Fixation to Produce Ammonia by Electroreduction of Plasma-Generated Nitrite

Abstract

One-step electrocatalytic N2 fixation is of emerging interest but is retarded due to the tough dissociation of the N2 triple bond and low NH3 selectivity. Here, a plasma-electrocatalytic integrated strategy is reported to be effective to circumvent this dilemma and realize high-performance N2 fixation via decoupling the reaction to two steps with NOx– serving as an intermediary: (i) non-thermal plasma (NTP) drives air activation into highly active NOx– intermediates, and (ii) subsequent electroreduction of the resultant NOx– into NH3. A gliding arc–microwave conjunction plasma mode was found to be preferred to achieve an optimal NO2–-N concentration of 2844.31 μg mL–1, adopting 0.5 M KOH as the absorption solution in the first step. For the next ENO2–RR step, plasma-treated 0.5 M KOH was directly used as electrolyte, with well-designed Cu2Pd nanodots anchored on carbonized bacterial cellulose (Cu2Pd/CBC) as electrocatalyst. An exceptional ENO2–RR performance, including a superior RNH3 of 1956.65 μg h–1 mg–1, highest FE of 93.79%, and long time stability of 30 h, was attained for Cu2Pd/CBC, outperforming the counterparts Cu/CBC and Pd/CBC. The synergism of CuPd bifunctional catalytic sites is the key to the greatly enhanced electrocatalytic activity via improving the adsorption of NO2– and the related intermediates while simultaneously supplying sufficient protons. This work provides an alternative strategy toward sustainable and distributed on-site ammonia synthesis.