Highly hydrophilic polybenzimidazole/Zirconia composite separator with reduced gas crossover for alkaline water electrolysis

Porous separators have been widely used in alkaline water electrolyzers (AWEs). To solve the problem of high gas permeability and stability caused by the large pores and poor compatibility of commercial Zirfon separators, it is important to develop a diaphragm with high OH− conductivity, high bubble point pressure, low area resistance, and low hydrogen permeability for alkaline electrolyzers. Here, we proposed highly hydrophilic polybenzimidazole-type composite porous separators with specific sponge-like pores via nonsolvent-induced phase separation. The high hydrophilicity of poly(2, 2'-(1, 4-naphthalene)-5, 5′-dibenzimidazole) (NPBI) and ZrO2 enhanced the interfacial interaction to prevent filler overflow. Compared to the Zirfon separator, the area resistance and hydrogen permeability of the proposed separators were significantly reduced. The Z60 diaphragm exhibited a higher water absorption rate (62.2%) and KOH liquid absorption rate (23.5%), lower area resistance (0.162 Ω cm2), higher bubble pressure (4.48 bar), and lower hydrogen permeability (2.63 L min−1·cm−2). Moreover, the voltage of the Z60 diaphragm was 2.007 V at 0.5 A/cm2 in 6 M KOH, which is comparable to commercial Zirfon. The Z60 separator used for AWEs with Ni foam catalysts obtained an excellent long-term stability of up to 400 h with a voltage fluctuation of only 55 μV/h. Therefore, the design of the NPBI/ZrO2 porous composite diaphragm provides a new idea for the development of high-performance alkaline water electrolysis.