The oxygen reduction reaction (ORR) occurs at the cathode and the oxide ions produced are transported via an electrolyte to the anode (Equation ). It is here at the anode site that the oxide ions react with fuel (hydrogen gas) to produce electrons (Equation ). The electrons generated at the interface of the anode and electrolyte are transported to an external circuit for useful work through the anode. The electrons finally arrive at the cathode and continue the process .