Current density mapping and optical flow visualisation of a polymer electrolyte membrane water electrolyser

•Current mapping of a water electrolyser demonstrated for the first time.•Optical visualisation allows flow and current density to be reconciled.•Transition from bubbly to slug flow associated with enhanced current density.

A polymer electrolyte membrane water electrolyser (PEMWE) employing a segmented current collector made from a printed circuit board (PCB) with optical access to the channel has been demonstrated for the first time. The cell allows the local current density, flow regime and bubble formation dynamics to be studied in real time. Transition is observed from a flow of discrete bubbles at the start of the channel to long bullet shaped bubbles towards the end of the channel associated with a significant increase in local current density.

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