Highly Active Binder Free Plasma Sprayed Non-Noble Metal Electrodes for Anion Exchange Membrane Electrolysis at Different Reduced KOH Concentrations

Abstract

The production of hydrogen by the water electrolysis technique to provide a fossil fuel alternative energy source has attracted a plethora of attention among the other different methods in the context of sustainability, renewable energy source utilization and green technology.[1] Conventional alkaline water electrolyzer (AWE) offers many advantages compared with other systems. One of the major advantages of AWE over proton exchange membrane water electrolyser (PEMWE) is the replacement of conventional noble metal electrocatalysts with active, stable and relatively low-cost transition metal catalysts. However, AWE electrolyzers suffer from lower operational current density compared with their PEMWE counterpart. Like AWE, anion exchange membrane (AEM) electrolyzer does not require noble metal catalysts, which makes this technology much less expensive than PEMWE, while possessing the advantage of PEMWE. However, the electrochemical water splitting performance of AEM water electrolysis is still much lower than that of PEMWE. Focusing on this issue, the presented work aims at improving the performance of AWE and AEM electrolysers by developing cost effective non-noble electrodes on macro-porous transport layer (MPL) using the air plasma spray deposition method.[2] MPLs were fabricated by depositing Ni-graphite on porous substrates. Graphite was removed during particle in-flight forming a controlled porous layer. Electrodes were developed by plasma spraying of NiMoAl for cathode and NiAl for anode on top of the MPL followed by activation in which Al was partially leached out from layers of both electrodes using an alkaline solution. Electrochemical tests were conducted on half-cell in 6M KOH solution and then in the full cells for AWE and AEM in 6M and 0.3M KOH, respectively. The electrochemical performance is recorded via over-potential measurements, electrochemical impedance spectroscopy (EIS), cyclic voltammetery and polarization curve. With optimal combination of MPL and electrodes, current density of 0.5 Acm-2 at 1.80 V was recorded as the initial performance in 6M solutions for AWE using Zirfon separator and the current density of 0.31 Acm-2 at 1.80 V was recorded for AEM electrolyzer with more dilute KOH solution (0.3M) using an anion exchange membrane. 64 days of abusive testing was conducted for the AWE without measurable degradation in the performance in 6M KOH. The catalysts developed in this work will be promising in supporting the pursuit of cheap, affordable and ideal eco-friendly hydrogen fuel. [1] F. Razmjooei, K.P. Singh, D.S. Yang, et al., Acs Catalysis, 2017, 7, 2381-2391. [2] A.S. Gago, S.A. Ansar, B. Saruhan, et al., J Power Sources, 2016, 307, 815-825.