Atmospherically Plasma-Sprayed Macro Porous Layers for Anion Exchange Membrane Water Electrolysis Operating with Alkaline Supporting Electrolyte

Green hydrogen produced via water electrolysis plays an important role in the decarbonisation of the global energy economy. Besides reducing electricity prices and increasing electrolyser efficiency, lowering electrolyser investment cost is an important avenue to make electrolysis technology more economically attractive. Anion exchange membrane water electrolysis (AEMWE) combines the advantages of proton exchange membrane water electrolysis (PEMWE), i.e., high current density while maintaining high efficiency and fast dynamic response with the advantages of alkaline water electrolysis (AWE), i.e., low-cost materials. However, an optimised porous transport layer (PTL) component for AEMWE is yet to be developed. Typically, PTLs in commercial electrolysers are metallic foams, felts, meshes, sintered sheets or graphitic fibre laminates, although these structures either perform poorly or they are extremely expensive. Furthermore, a high number of low-resistance contact points at the interface between the catalyst layer and the PTL is required to enable high catalyst utilisation. At the same time, operation at high current densities requires an especially efficient liquid/gas exchange at this interface. Both important functions, good electrical contact and mass transport facilitation, are fulfilled by a macro porous layer (MPL). Stiber et al designed and characterized a titanium/niobium MPL deposited via vacuum plasma spraying (VPS) on a stainless-steel mesh substrate, vastly improving the performance of a PEMWE [1]. Similarly, Razmjooei et al deposited a nickel layer via atmospheric plasma spraying (APS) and demonstrated the performance-increasing effect in AEMWE operating with pure water [2]. In this work, within the frame of the German project AEM-Direkt, a Ni-based MPL was developed to improve high current density operation in AEMWE working with a supporting alkaline electrolyte. For this, a Ni-C composite powder was deposited on a stainless-steel multi-mesh PTL via APS (Fig. a). The carbon acts as a pore forming agent and is subsequently removed by an ex-situ oxidation step in air at 700°C followed by a reduction step in ammonia at 500°C. A highly porous, smooth and flat Ni-MPL is formed. Using the MPL on the anode, the AEMWE single cell achieves 2 V at 3 A cm -2 (Fig. b), which is comparable to the performance of PEMWE. As anode catalyst layer a novel 20 nm thickness sputtered nickel layer designed and manufactured by Siemens-Energy was used, deposited on a DURAION® AEM, manufactured by Evonik Operations GmbH. As cathode, a Pt/C based catalyst coated substrate (CCS) was employed. In continuation of this study, the designed MPL will be further optimised and characterised as cathode MPL as well. Acknowledgement This work is carried out within the project AEM-Direkt (Förderkennzeichen 03HY130) funded by the German Ministry of Science and Education (BMBF). References Stiber S, Sata N, Morawietz T, Ansar SA, Jahnke T, Lee JK, et al. A high-performance, durable and low-cost proton exchange membrane electrolyser with stainless steel components. Energy & Environmental Science. 2022;15(1):109-22. Razmjooei F, Morawietz T, Taghizadeh E, Hadjixenophontos E, Mues L, Gerle M, et al. Increasing the performance of an anion-exchange membrane electrolyzer operating in pure water with a nickel-based microporous layer. Joule. 2021;5(7):1776-99. Figure 1