a recirculating assembly is provided for a fuel cell system having an electrochemical conversion unit which receives a combustible fluid at an inlet , and supplies electric energy at an electrical output , surplus combustible fluid at a first fluid outlet , and a waste fluid at a second fluid outlet . the recirculating assembly has a compressor for increasing the pressure of the surplus combustible fluid not used by the conversion unit , so as to make it once more available to the conversion unit . the drive is powered by residual energy of the waste fluid to drive the compressor .