Advanced Bipolar Membranes for Energy and Electrodialysis Technology – APRiCOT

Bipolar membranes dissociate water (H2O à H++OH-) at the interface between a proton and a hydroxide conductor under applied bias. This is being exploited industrially in electrodialysis to produce acid and base, and could be of great value for water and CO2 electrolyzers. Recently, some of us introduced a new BPM assembly and characterization platform, based on membrane electrode assemblies (MEAs), which are used for water electrolyzers and fuel
cells, and which continuously apply pressure over all BPM components during operation. This way, we designed highly active BPMs with record-high current densities of > 3 A·cm-2 – at least 20 times larger than previous results. However, despite this progress, the performance is not yet at levels needed for new applications. For example, the best BPM dissociates water with an overpotential of ~ 500 mV at 2 A·cm-2, but in water electrolysis the total overpotential must
be < 300 mV at 2 A·cm-2, including OER and HER overpotentials. Conversely, we need to better understand the BPM junction, not only for BPM electrolyzers and fuel cells, but also electrodialysis. For the latter, self-supported, free-standing BPMs remain of key significance, as MEAs are too bulky to be used in stacks comprising 50-100 in-series connected BPMs. However, currently, the performance and structural differences between traditional, freestanding BPMs and ones in the MEA are not known. To strengthen scientific exchange and accelerate BPM R&D we need to understand these differences.
In APRiCOT, the German BPM experts at RWTH Aachen (RWTH) and the Fritz Haber Institute (FHI) will leverage the world-expert knowledge in nanoassembly and (2D) materials growth of the French CNRS Centre Interdiciplinaire de Nanoscience de Marseille (CINaM) and the Institut Europeen des Membranes (IEM) to obtain unprecedented control and understanding of the BPM junction. This in turn might lead to high performing small-scale lab
devices that motivate more BPM R&D in the future. More specifically, FHI will leverage the MEA compression and integrate close-packed nanoparticle assemblies and 3D-patterned membranes provided by CINaM and (ion-selective) 2D materials and ALD thin-layers provided by IEM into MEA-BPMs. This way, the impact of junction thickness, morphology, catalyst coverage and ion-selectivity will be studied. This enables FHI and RWTH to develop improved
Multiphysics models alongside experimental results. Then, FHI’s and RWTH’s experimental and simulation results are fed back to IEM and CINaM for further materials optimization. Further, FHI and RWTH will study the structural differences and similarities between MEA- and free-standing BPMs to strengthen scientific exchange and cross-fertilization of ideas between these two platforms. Finally, RWTH will study the water transport and aim at translating FHI’s
recent high current density BPM-MEAs into free-standing BPMs, in particular by exploring selected materials from IEM and CINaM.