The Bipolar/Flow field plate is a vital component of Polymer Electrolyte Membrane Water Electrolysers (PEMWE) which enables electronic conduction, provide mechanical support to the cell and facilitates mass transport of liquid water and produced gases to and from the electrocatalyst surface. From a mass transport viewpoint, especially at high current density operation, optimizing the dimensions and configuration of the flow field plate is crucial to reducing mass transport limitation and achieve improved cell performance. This work investigates the effect of channel depth of the anode flow field plate on performance of a PEM Water Electrolyser using polarization curve and Electrochemical Impedance Spectroscopy technique. A single electrolyser cell with flow field plate having a single straight channel was employed having the channel depth varied from 3.0 mm to 8.0 mm and the cell performance was studied at current densities up to 2 A/cm². The impedance spectroscopy results show that the effect of channel depth on cell performance is negligible at low and medium current densities, but significant at high current densities. The result indicate that the two-phase flow liquid/gas interactions in the flow channel and the flow regime of operation have a direct influence on mass transport losses and overall performance in the PEM Water Electrolyser. Furthermore, the impedance spectroscopy result at high current densities shows that, generally, deeper channels show better performance than shallower channels which suggests that the effective mass transfer area at the surface of the gas diffusion layer increases with increase in channel depth thus yielding improved mass transport. However, the best performance was observed at 4.5 mm depth which suggests that there exist an optimal channel depth where an increase or decrease in depth would lead to loss of performance. This is attributed to the trade-off between reduced liquid flow velocity and reduced surface coverage of gas bubble/slug in the channel with increasing channel depth in the PEMWE flow field.

Fig 1: Effect of channel depth on cell performance at (a) low, (b) medium and (c) high current density at water flow rate of 40 mL/min and inlet water temperature of 80°C.