We demonstrate an extreme test of O2 tolerance for a biological hydrogen-cycling catalyst: the generation of electricity from just 3% H2 released into still, ambient air using an open fuel cell comprising an anode modified with the unusual hydrogenase from Ralstonia metallidurans CH34, that oxidizes trace H2 in atmospheric O2, connected via a film of electrolyte to a cathode modified with the fungal O2 reductase, laccase.