Investigation of Ionomer and Catalyst (Co₃O₄, Mn₃O₄, or MnO₂) Interactions Using a Polyethylene Midblock Copolymer in Anion Exchange Water Electrolyzers to Understand Performance and Durability

Abstract

An anion exchange membrane water electrolyzer (AEMWE) was studied with three electrocatalysts (Co3O4, Mn2O3, MnO2) for the oxygen evolution reactions at 50˚C in 1M K2CO3 (aq). We employ an optimized robust high performance polymer based on a polyethylene mid-block copolymer, poly(vinylbenzyl-N‑methylpiperidinium carbonate)‑b‑polyethylene‑b‑poly(vinylbenzyl-N‑methylpiperidinium carbonate) as the AEM and the anode ionomer. The cathode utilized a high loading of Pt/C, 1 mg/cm2, to minimize contributions to the kinetics. We tested three catalyst loadings (0.5, 2.5, and 4.5 mg/cm2) with a fixed ionomer loading of 0.5 mg/cm2 to assess ionomer-catalyst interactions. The best-performing catalyst loadings were investigated in a 100 h durability test at 750 mA/cm2. The 2.5 mg/cm2 MnO2 catalyst displayed superior performance, with 2.40 ± 0.02 V at 1 A/cm2. In the 100 h durability test, the Mn2O3 catalyst showed a degradation rate of +269 ± 15 μV/h, whereas Co3O4 and MnO2 showed -800 ± 157 μV/h, -114 ± 15 μV/h, respectively with no membrane thinning indicating a gradual improvement. The MnO2 electrode was further investigated in a 500 h test was conducted, revealing a voltage change rate of -21 μV/h for 24-375 h. Pre and post-test FTIR mapping revealed evolution of micrometer-sized morphology corresponding to templating by the Ni-foam electrode.