Solid polymer electrolyte electrochemical energy conversion devices that operate under highly alkaline conditions afford faster reaction kinetics and the deployment of inexpensive electrocatalysts compared with their acidic counterparts. The hydroxide anion exchange polymer is a key component of any solid polymer electrolyte device that operates under alkaline conditions. However, durable hydroxide-conducting polymer electrolytes in highly caustic media have proved elusive, because polymers bearing cations are inherently unstable under highly caustic conditions. Here we report a systematic investigation of novel arylimidazolium and bis-arylimidazolium compounds that lead to the rationale design of robust, sterically protected poly(arylimidazolium) hydroxide anion exchange polymers that possess a combination of high ion-exchange capacity and exceptional stability.

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A benchmark hydroxide-conducting polymer is utilized in alkaline hydrogen fuel cell and water electrolyzer devices at 60 °C for >100 hours.

We report on poly(arylene-imidazoliums), which were synthesized by microwave polycondensation of dialdehyde with bisbenzil and quantitatively functionalized by alkylation. This cationic polyelectrolyte is sterically protected around the C2-position and is stable in 10 M KOH aq at 100 °C (t 1/2 of >5000 h). Alkaline stability is rationalized through analyses of model compounds, single crystal X-ray diffraction, and density functional theory. The polyelectrolytes form tough, pliable, transparent, ionically conductive films.