Impact of Porous Transport Layer Properties on Performance and Durability of Anion Exchange Membrane (AEM) Electrolyzers

Abstract

Hydrogen, produced from water electrolysis, is a promising resource due to the high energy density, its ability in long term storage, and its ability to transition between electricity and chemical bonds. With decreasing electricity prices, electrolysis has a significant growth opportunity load-following intermittent power and provides a pathway for the increased use of renewable electricity sources.(1) Efficient water splitting for commercial electrolysis devices is predicated on the development of materials such as catalysts and transport layers. In comparison to proton exchange membrane (PEM) systems, anion exchange membrane (AEM) based electrolysis reduces component cost by employing inexpensive, non-precious metal catalysts and transport layers.(2) With recent improvements in the stability and ionic conductivity of membranes, further examination of other individual components including transport layers and catalysts is needed as they can significantly impact AEM cell performance and durability.Porous transport layers (PTLs) have an important functionality in the transport of electrons, heat, and reactants/products; and it is critical that PTLs do not add significantly to voltage, current, thermal, interfacial, and fluidic losses. In a water electrolyzer, the overpotential at the anode creates a much harsher environment that is highly corrosive, making carbon paper unsuitable.(3) In the case of a supporting electrolyte which is often required for AEM electrolysis, a concentrated, alkaline environment can be even harsher for the PTL and titanium based PTLs used for PEM systems can be incompatible as Ti can be soluble at high pH and potential. This renders the need to develop novel materials that can be used as PTLs on the anode side in AEM water electrolysis.In this work, we have screened different anode PTLs and have analyzed the impact of the properties of the PTL on cell-level performance and short-term durability of AEM water electrolysis. The influence of variables like thickness, pore size/morphology and porosity of the PTL are critical towards minimizing ohmic and transport losses within an AEM cell. Moreover, interfacial contact between the catalyst coated membrane and PTL has a significant impact on the initial performance of the cell, and how components are integrated into membrane electrode assemblies was found to have an impact on electrolyzer performance/durability.[1] Q. Xu, S. Z. Oener, G. Lindquist, H. Jiang, C. Li, S. W. Boettcher, ACS Energy Letters, 6 (2021) 305-312.[2] S. Ghoshal, B. S. Pivovar, S. M. Alia, Journal of Power Sources, 488, (2021) 229433.[3] Z. Kang, J. Mo, G. Yang, S. T. Retterer, D. A. Cullen, T. J. Toops, J. B. Green Jr, M. M. Mench, F. Zhang, Energy & Environmental Science, 10 (2017) 166-175.