Anode recirculation and purge strategies for PEM fuel cell operation with diluted hydrogen feed gas

Commercial polymer electrolyte membrane (PEM) fuel cell systems require pure hydrogen feed gas (ISO 14687-2), otherwise impurities and inert gases would accumulate. Inert gases are difficult to remove, but do not hazard the fuel cell stack itself. Therefore, two purge strategies are introduced and experimentally investigated which enable fuel cell operation with up to 30 vol.% nitrogen content in the feed gas. Both strategies use a commercial on-line hydrogen sensor at the stack outlet either to trigger a discontinuous purge or to control the purge valve continuously. The experimental results show that the discontinuous purge strategy can be applied up to 10 vol.% nitrogen content in the feed gas. The continuous purge strategy was successfully operated with up to 30 vol.% nitrogen content and achieved the theoretical maximum fuel efficiency between 80 and 100%. The influence of nitrogen crossover on fuel efficiency and operating performance was investigated and found negligible. To sum up, the new continuous purge strategy offers an efficient, easy-to-implement, and robust solution to operate polymer electrolyte membrane fuel cell systems with up to 30 vol.% nitrogen content in the feed gas.