Permethyl Cobaltocenium (Cp(*)(2)Co(+)) 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 electrocatalysts 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 [(C(5)Me(5))(2)Co(III)(+) or Cp(*)(2)Co(+)] as an ultra-stable organic cation for polymer HEMs. Compared with the parent cobaltocenium [(C(5)H(5))(2)Co(III)(+) or Cp(2)Co(+)], Cp(*)(2)Co(+) has substantially higher stability and basicity. With polysulfone as an example, we demonstrated the feasibility of covalently linking Cp(*)(2)Co(+) cation to polymer backbone and prepared Cp(*)(2)Co(+)-functionalized membranes as well. The new cation may be useful in designing more durable HEM electrochemical devices.