Abstract
Chemically regenerative redox cathode (CRRC) polymer electrolyte fuel cells (PEFCs) avoid many of the long standing technical problems that plague conventional PEFCs. The circulation of a liquid catalyst, or catholtye, reduces oxygen indirectly and external to the cathode within a gas-liquid contact reactor called the ‘Regenerator’. The cathode catholyte reduction reaction is relatively facile and occurs at carbon without the need for platinum. Not only does this present a major cost advantage but it also avoids many of the major degradation mechanisms effecting durability. The circulation of an aqueous catholyte solution, of relatively high specific heat capacity, also allows easy of heat management. Heat can be removed from the catholyte whilst external of the fuel cell using a simple inline heat exchange, thus, eliminating the need for complex internal coolant channels. The catholyte presence also ensure hydration of the polymer electrolyte membrane without the added complications of fuel gas humidification. The elimination of oxygen from the cathode also prevents internal cell conflagrations and associated damage. Hence, the multiple advantages of CRRC PEFCs make them and attractive technology for study. This investigation now considers the impact of catholyte concentration and temperature on CRRC PEFC system performance with regards two promising polyoxometalate-based catholytes: H7PV4Mo8O40 and Na4H3PV4Mo8O40 (empirical formulae). The results suggest 80oC and a catholyte concentration of 0.3 M provide the optimum performance for both catholytes (at ambient pressure operation).