Thin Cation-Exchange Layers Enable High-Current-Density Bipolar Membrane Electrolyzers via Improved Water Transport

With suitable water dissociation (WD) catalysts, bipolar membranes (BPMs) can efficiently dissociate water into H+ and OH- at the junction between anion- and cation-exchange layers (AEL and CEL, respectively). First, however, water must be transported through the AEL or CEL and thus against the outward flow of hydrated H+ and OH-. This is a challenge intrinsic to the BPM architecture and limits operation to current densities typically less than similar to 0.5 A.cm(-2). Here we explore how water transport affects durability and performance in reference alkaline and acidic membrane electrolyzers, and we use the insight gained to design BPMs with improved water transport. We demonstrate a thin-CEL BPM (2-mu m Nafion CEL vertical bar, similar to 200 nm TiO2 vertical bar, similar to 200 nm NiO+ ionomer vertical bar 50 mu m Sustainion AEL) which maintains a pH difference of , similar to 14 units between the anode and cathode for current densities of up to 3.4 A.cm(-2) with a total water electrolysis voltage of similar to 4 V and an estimated WD overpotential of similar to 1.5V. Such high-current-density operation is crucial for key emerging BPM applications, including in water and carbon-dioxide electrolyzers and in (regenerative) fuel cells.

Automated summary

With appropriate water dissociation catalysts, bipolar membranes can efficiently split water molecules into H+ and OH-. However, the challenge lies in transporting water through the membranes against the outward flow of hydrated ions, limiting current densities to around 0.5 A.cm(-2). Efforts are being made to improve water transport in order to achieve high-current-density operation for various applications.