(Invited) Optimal Morphology of Cu-Based Catalyst for Efficient Electrochemical Synthesis of NH3 By Direct Reduction of N2 and H2o at Ambient Conditions

Abstract

The electrochemical synthesis of ammonia (NH3) by direct reduction of N2 in an aqueous medium under ambient conditions is a sustainable alternative to the energy intensive Haber-Bosch process. The major challenges in the electrochemical synthesis of NH3 are due to lower yield, lower faradaic efficiency (FE), and higher H2 production. To overcome these issues, an efficient and selective electrocatalyst that promotes nitrogen reduction reaction (NRR) and suppresses hydrogen evolution reaction (HER) is required. Here we show polycrystalline Cu is an active catalyst for NRR and it also suppresses H2 formation at lower overpotentials. The objective of this study is to evaluate the effect different morphological forms of Cu such as planar, nanoparticles, nanowires, nanocubes, and porous foam on the activity and FE of NH3. These catalysts are supported on a carbon-based gas diffusion electrode (GDE) and evaluated in a flow-through electrochemical cell for effective mass-transfer of N2. The gaseous product- H2 is quantified using in situ gas chromatography and the liquid product- NH3 is quantified using Nessler’s reagent. The FE and yield of NH3 for Cu-based catalysts are comparable to Fe-based and other noble metal-based catalysts. The optimal Cu-based catalyst structure and electrolyte composition will be presented for electrochemical synthesis of NH3.