Permethyl Cobaltocenium (Cp*2Co+) As an Ultra-Stable Cation for Polymer Hydroxide Exchange Membranes

Hydroxide (OH⁻) exchange membranes (HEMs) are important polymer electrolytes enabling the use of affordable and earth-abundant catalysts and membranes for electrochemical energy conversion devices such as HEM fuel cells, HEM electrolyzers, and HEM solar hydrogen generators. Many HEM cations exist featuring desirable properties but new cations are still needed to increase chemical stability at elevated temperatures. Here we introduce the permethyl cobaltocenium [(C₅Me₅)₂Co(III)⁺ or Cp^*₂Co⁺] as an ultra-stable cation for HEMs. Compared with the parent cobaltocenium [(C₅H₅)₂Co(III)⁺ or Cp₂Co⁺], Cp^*₂Co⁺ has substantially higher stability and basicity. We also show that Cp^*₂Co⁺-based HEMs possess very high thermal and alkaline stability, which are useful in designing more durable HEM electrochemical devices.