A Bifunctional Catalyst for Green Ammonia Synthesis from Ubiquitous Air and Water.

Abstract

Ammonia (NH₃ ) is essential for modern agriculture and industry, and, due to its high hydrogen density and no carbon emission, it is also expected to be the next-generation of "clean" energy carrier. Herein, directly from air and water, a plasma-electrocatalytic reaction system for NH₃ production, which combines two steps of plasma-air-to-NO_x ^- and electrochemical NO_x ^- reduction reaction (eNO_x RR) with a bifunctional catalyst, is successfully established. Especially, the bifunctional catalyst of CuCo₂ O₄ /Ni can simultaneously promote plasma-air-to-NO_x ^- and eNO_x RR processes. The easy adsorption and activation of O₂ by CuCo₂ O₄ /Ni greatly improve the NO_x ^- production rate at the first step. Further, CuCo₂ O₄ /Ni can also resolve the overbonding of the key intermediate of ^* NO, and thus reduce the energy barrier of the second step of eNO_x RR. Finally, the "green" NH₃ production achieves excellent FE_NH3 (96.8%) and record-high NH₃ yield rate of 145.8 mg h^-1  cm^-2 with large partial current density (1384.7 mA cm^-2 ). Moreover, an enlarged self-made H-type electrolyzer improves the NH₃ yield to 3.6 g h^-1 , and the obtained NH₃ is then rapidly converted to a solid of magnesium ammonium phosphate hexahydrate, which favors the easy storage and transportation of NH₃ .