Soluble viologen polymers as carbohydrate oxidation catalysts for alkaline carbohydrate fuel cells

Monomeric dialkyl and monoalkyl viologens rapidly catalyze O2-oxidation of carbohydrates in alkaline solution to form carbonate and formate at pH >11. Optimization of these catalytic reactions is important for alkaline carbohydrate fuel cell applications. Use of these monomeric viologens is not optimal because they exit the fuel cell with the reaction products and would need to be recovered and recycled for continued use. Polymeric or immobilized viologens would reduce or avoid these recovery problems. Here, we report the evaluation of water-soluble polymeric viologens as potential fuel-cell-catalysts and show that they rapidly catalyze O2-oxidation of carbohydrates to carbonate and formate at high efficiency. The rates of reduction of polymeric viologens by carbohydrates were rapid and found to be first order in carbohydrate and one-half order in polymer concentration. An unusual feature of the reduction reaction is that the rate of polymer reduction is two-fold faster if carbohydrate is equilibrated with the buffer prior to addition of the catalyst rather than adding the carbohydrate in the presence of the catalyst. Advantages and disadvantages of polymeric viologens as fuel cell catalysts are discussed.