Several types of fuel cells suitable for different energy applications at varying scales have been developed, but all share the basic design of two electrodes (anode and cathode) separated by a solid or liquid electrolyte or a membrane (Fig. 2). Hydrogen (or a hydrogen-containing fuel) and air are fed into the anode and cathode of the fuel cell, and the electrochemical reactions assisted by catalysts take place at the electrodes. The electrolyte enables transport of ions between the electrodes while the excess electrons flow through an external circuit to provide electrical power