Understanding the cell performance along the channel for industrial PEM water electrolysis operation

Proton exchange membrane (PEM) water electrolysis cells can be operated very flexibly and at high current densities. Increasing the current density above today’s industrial standard, in combination with low loadings of the catalyst layer, is necessary to become more economical and resource-saving. The water consumption and gas evolution rate are proportional to the current density, leading to a significant difference in the volumetric water-to-gas ratio over the active cell area when operating at high current densities and low water flow rates. This study analyzes industrial-relevant PEM water electrolysis operation at high current densities of up to 7 A·cm–², measured in a segmented along the channel test cell with a 30 cm channel length. We present locally resolved measurements of current density, temperature, and impedance spectra and discuss variations of operating parameters and porous transport layer microstructure for low-loading catalyst-coated membranes. To achieve a deeper understanding of the observed phenomena, we compare conventional voltage breakdown analysis, done by subtracting ohmic overpotentials through high-frequency resistance measurements, and kinetic overpotential using Tafel analysis with distribution of relaxation times (DRT) and equivalent circuit modeling. At industrially relevant operation with water stoichiometries greater than 50, no relevant mass transport losses or membrane drying effects are observed along the channel. In cases of low stoichiometries, combined with the high heat dissipation of the reaction at high current densities, a significant temperature increase of more than 8 K and a high-frequency resistance reduction along the channel are observed. Investigations using low-loading catalyst-coated membranes and different porous transport layers reveal a high sensitivity of local clamping pressure on the polarization processes but less impact on the high-frequency resistance