(Amazon Catalyst at ECS Grant Winner) Enhancing the Rate of Electrocatalytic Conversion of N2 to NH3 Using Bimetallic Au-Pd Nanoparticles

Abstract

Ammonia is one of the widely produced chemicals in the world, with broad applications in producing nitrogen-based fertilizer, energy, and in the pharmaceutical industry. The current industrial method for ammonia production is energy intensive and heavily relies on fossil fuels, which are responsible for environmental pollution. To meet ammonia demands, it is necessary to develop sustainable and environmentally friendly production methods that consume significantly less energy than the current methods. Here, the use of hollow gold nanocages (AuHNCs) as an effective electrocatalyst is evaluated for electrochemical nitrogen reduction reaction (NRR) under ambient conditions. The electrochemical experiments are carried out at various potentials in 0.5M LiClO4 aqueous solution using AuHNCs, and their catalytic efficiency is determined for the conversion of nitrogen to ammonia [1, 2]. The highest ammonia Faradaic efficiency (30.2%) is achieved at−0.4 V vs. RHE while the highest ammonia yield (3.9 μg cm-2 h-1) is obtained at −0.5 V vs. RHE. The electrocatalytic activity of NRR using AuHNCs is further compared with that of solid Au nanoparticles of various shapes (i.e., rods, spheres or cubes) to elucidate the enhanced rate of the reaction resulting from the increase in surface area and confinement effects. The three-fold enhancement in ammonia Faradaic efficiency is achieved by using the AuHNCs (30.2%) compared to the solid Au nanocubes (11.4%) [1]. It has been demonstrated that electrochemical N2 reduction for NH3 production using Pd nanoparticles requires lower overpotential and results in higher electrocatalytic efficiency for NH3 compared with Au nanoparticles. The use of Pd and hybrid Au-Pd nanoparticles is evaluated for electrochemical nitrogen reduction reaction (NRR) under ambient conditions. The results are further complemented by in-situ surface-enhanced Raman spectroscopy (SERS) and ex-situ 1H NMR to monitor the trace amount of NH3 over the course of the experiment and elucidate the possible differences in the reaction mechanism for electrosynthesis of NH3 on Pd and Au surfaces.