Driven by the political and societal endeavors to drastically reduce CO₂ emissions in several sectors within the next decades, such as in the transport or the industrial production sectors, the substitution of fossil fuels by “green” hydrogen is widely considered. Electrochemical splitting of water inside polymer electrolyte membrane water electrolyzers (PEMWEs) is one possibility for efficient and sustained production of “green” hydrogen. However, its efficiency is still limited by the coupled kinetics of flow and reaction that occur at the anodic side of the PEMWEs. Especially the microstructure inside the anodic porous transport layer (PTL) plays a major role in the counter-current transport of the feedstock water and the product oxygen.

In this work, a prototype model of a novel microfluidic PEMWE cell for experimental examination of the two-phase flow inside the anodic PTL is presented. The cell is made of transparent PMMA (Poly-Methyl-Methacrylate) to allow monitoring of the fluid flow. The anodic PTL is represented by a quasi 2D pore network with uniformly distributed pore sizes, similar to previous work [1, 2]. However, in contrast to previous works, the microfluidic device is realized as a complete electrochemical cell. Thus, the gas phase is not injected at a discrete point but generated at an electrically activated catalyst coated membrane with iridium ruthenium oxide on the anode side and carbon-supported platinum on the cathode side. Platinum meshes were used as current collectors on both sides.

The microfluidic electrochemical cell is used to study the correlation of gas-liquid invasion patterns in-dependence of the pore network structure and the applied current densities and stoichiometry of flow rates. In contrast to more advanced measurements, like operando neutron imaging [3], the simplified quasi 2D structure allows studying the invasion profiles directly. In addition to that, very easy comparison of the experimentally recorded profiles to simulation results, e.g., from Lattice Boltzmann simulation [4], is possible via simple image processing algorithms.

Keywords: microfluidic PEMWE cell; anodic porous transport layer (PTL); counter-current transport; invasion regimes; current density; pore-scale physics, Lattice Boltzmann simulation.

References

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[3] J.K. Lee, C.H. Lee, K.F. Fahy, P.J. Kim, J.M. LaManna, E. Baltic, D.L. Jacobson, D.S. Hussey, S. Stiber, A.S. Gago, K.A. Friedrich, A. Bazylak, Spatially graded porous transport layers for gas evolving electrochemical energy conversion: High performance polymer electrolyte membrane electrolyzers, Energy Convers. Manag. 226 (2020) 113545. https://doi.org/10.1016/j.enconman.2020.113545.

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