Plasma-coupled Electrochemical Ammonia Synthesis Using a Solid Acid Electrochemical Cell

Abstract

Carbon-free synthesis of ammonia is an essential component of a sustainable future. In this work, we develop a reactor utilizing a solid acid electrochemical cell coupled with an atmospheric pressure nitrogen/argon plasma jet for the electrochemical nitrogen reduction reaction. The cell is based on the electrolyte Cs₇(H₄PO₄)(H₂PO₄)₈, which displays high conductivity at temperatures above 90 °C. We show that plasma-activated nitrogen species directly react with protons at the surface of the molybdenum cathode at 140 °C. Under a reducing bias of -2 V across the electrochemical cell and a plasma power consumption of 7.3 W, the plasma-coupled electrochemical route produces ammonia at a rate of 1.2 ± 0.5 nmol/s•cm ². In the absence of the plasma, the purely electrochemical process produces negligible amounts of ammonia, comparable to the background level of 0.05 nmol/s•cm ², underscoring the critical role of the plasma activation.