On the role of porous transport layer thickness in polymer electrolyte water electrolysis

The reduction of capital and operational expenditure in polymer electrolyte water electrolysis (PEWE) is of crucial importance for materializing the hydrogen economy. Optimizing the components and design of PEWE cells is a major contribution to this goal. In this study, we have analyzed the impact of reducing the anodic porous transport layer (PTL) thickness by over one order of magnitude from 2 mm to 0.16 mm while keeping other parameters in the PTL constant for a systematic comparison. PTL morphology and its impact on cell performance have been correlated by X-ray tomographic microscopy (XTM) and overpotential breakdown analysis. We found that varying PTL thicknesses in this range can contribute to up to 120 mV overpotential at 4 A/cm² which can be attributed to water transport limitations below the flow field land in thin PTLs. Furthermore, the results indicate that there is an optimal thickness in dependency of the flow field design. For the investigated class of materials, this is corresponding to roughly half of the flow field land size. Subsequently, a guideline was deduced for the optimal relation of PTL thickness and flow field characteristics.