Meeting near-term targets for the price of hydrogen produced by electrolysis requires reductions in the cost of materials and manufacturing as well as increases in the efficiency of converting electricity and water to hydrogen. Central to achieving these goals is engineering electrolyzers with significant increases in current density at efficient cell voltages while simultaneously lowering the loading of precious metals, such as iridium and other platinum group metals (PGMs). The first half of this presentation will introduce the dominant transport mechanisms in PEM water electrolyzers. Here we will highlight the material properties that meter the transport rates and generate the overpotentials that reduce efficiency and increase capital cost. We will then describe the fundamental upper bound of the realistically possible transport rates in the context of the upper limits of PEM electrolyzer performance.

The second half of this presentation will describe the development and application of advanced experimental, imaging, and simulation tools in evaluating the present state-of-the-art PEM electrolyzer materials and components. We will highlight emerging operando diagnostics for evaluating water reactant transport rates and anode dry-out at the catalyst, porous transport layer (PTL), and membrane electrode assembly (MEA)-scale. We will also present diagnostics for uncovering the overpotential due to proton transport in the anode catalyst layer, including those for ionomer-free anode concepts. Our talk will also feature the use of ultra-high resolution 3D imaging of electrolyzer electrodes in evaluating the impact of catalyst and processing on the electrode morphology and catalyst utilization and efficacy. The imaging methods employed include nano-scale resolution X-ray computed tomography (nano-CT), plasma-focused ion beam cross-sectioning for scanning electron microscopy (pFIB-SEM), and micro-CT. Finally, we will present the use of continuum and image-based pore-scale simulations of PEM electrolyzers to develop a pathway towards the fundamental upper limits of PEM electrolyzer performance and cost reductions.