1962 February, “Talking of Trains: Fuel battery locomotives?”, in Modern Railways, page 87:
One of the virtues of the fuel battery is said to be that, unlike all heat engines, it is not limited in theoretical efficiency by the Carnot cycle and its practical efficiency lies in the 60 to 80 per cent range; a point often forgotten, however, is that if hydrogen has to be made, the Carnot cycle efficiency does apply, because this is a heat process.
