(Digital Presentation) Electrocatalytic Ammonia Oxidation Coupled with Hydrogen Production - Moving Towards a Carbon Neutral Water Treatment Cycle

Abstract

Ammonia is a common pollutant, present in municipal wastewater streams. With the continuous shift of people moving to cities and the growing world’s population, the overall wastewater amount is rising. Current ammonia treatment processes in wastewater treatment plants include biological nitrification. Here the ammonia is converted to nitrate or nitrogen. Unfortunately, the capital and operational expenditure costs of such processing are high and the ammonia is converted to products that have no value. Ammonia is a carbon-free energy carrier. Recently, technological solutions have been introduced to strip ammonia from wastewater [1]. The recovered ammonia can be electrochemically oxidised to benign nitrogen in an electrolyser, which can offer a cost-efficient technology to couple wastewater remediation at an anode with the production of a valuable by-product at the cathode, hydrogen. Currently, the commercialisation of the ammonia electrolyser technology is hindered by slow reactions at the anode and the cathode as well as the deactivation or degradation of the catalysts over time [2,3]. Consequently, the development of inexpensive, efficient anode material is imperative to reduce costs associated with ammonia destruction and electrochemical hydrogen production. This study focuses on a non-noble metal NiCu catalyst as a durable anode for alkaline ammonia electrolysis. We report that nickel-copper catalysts can oxidise ammonia to nitrogen at room temperature, see figure below. During electrolysis experiments, gas chromatography of the off-gases confirmed that both, nitrogen at the anode and hydrogen at the cathode, are generated with high faradaic efficiencies. Anode morphology and structure before and after electrolysis was investigated by X-ray diffraction (XRD), X-ray fluorescence (XRF), X-ray Photoelectron Spectroscopy (XPS), and scanning electron microscopy (SEM). To monitor possible intermediates produced by electrolysis, the electrolyte was analysed for NOx regularly by cuvette test and the electrode off-gasses were continuously monitored by GC-TCD. Overall, the electrode showed stability after continuous electrolysis in ammonia for over 30 hours. Further results will be presented at the conference. References: [1] L. Kinidi, I.A.W. Tan, N.B. Abdul Wahab, K.F.B. Tamrin, C.N. Hipolito, S.F. Salleh, Recent Development in Ammonia Stripping Process for Industrial Wastewater Treatment, International Journal of Chemical Engineering. 2018 (2018) 1–14. https://doi.org/10.1155/2018/3181087. [2] B. Zhou, N. Zhang, Y. Wu, W. Yang, Y. Lu, Y. Wang, S. Wang, An option for green and sustainable future: Electrochemical conversion of ammonia into nitrogen, Journal of Energy Chemistry. 60 (2021) 384–402. https://doi.org/10.1016/j.jechem.2021.01.011. [3] N.M. Adli, H. Zhang, S. Mukherjee, G. Wu, Review—Ammonia Oxidation Electrocatalysis for Hydrogen Generation and Fuel Cells, J. Electrochem. Soc. 165 (2018) J3130–J3147. https://doi.org/10.1149/2.0191815jes. Figure 1