Anionic catalyst binders based on trimethylamine-quaternized poly(2,6-dimethyl-1,4-phenylene oxide) for alkaline electrolyzers

• Trimethylamine-quaternized poly(2,6-dimethyl-1,4-phenylene oxide) (qPPO) was prepared.
• qPPO was tested as a catalyst binder in an alkaline membrane electrolyzer.
• The application of qPPO lead to higher current densities than that of PTFE binder.

Poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) was brominated under the conditions of radical mechanism and subsequently quaternized with trimethylamine. Flat membranes were prepared by casting quaternized PPO (qPPO) dissolved in ethanol or ethanol/dimethylformamide mixture on a Teflon plate followed by solvent evaporation. The membranes were characterized by their degree of swelling in water, ion exchange capacities (IEC) and ionic conductivities. qPPO with a degree of quaternization of 25.5 mol% and with anionic conductivities of 10.09 S/m and 12.34 S/m (at 50 °C and 70 °C, respectively) was tested as an anion-conductive polymer binder in a single cell alkaline laboratory electrolyzer in which the anode and cathode compartments were separated with a heterogeneous anion selective membrane. The cathode contained Pt/carbon catalyst bonded with qPPO so that Pt/qPPO weight ratio was 85/15. The anode contained NiCo2O4 spinel catalyst which was bonded either with qPPO (spinel/qPPO weight ratios 95/5, 90/10 or 75/25) or with a non-conducting PTFE (spinel/PTFE weight ratio 85/15). It was found that the application of the qPPO binder in the anode lead to higher current densities than the application of a non-conductive PTFE binder at all electrolyte KOH concentrations (1–15 wt%). The performance of a laboratory membrane electrolyzer with the anode containing NiCo2O4 spinel catalyst bonded with qPPO (spinel/qPPO weight ratio 75/25) and a 1 wt% KOH electrolyte was similar to that of an industry unit with a 30 wt% KOH electrolyte.