The present disclosure provides a fuel cell comprising a first sensor comprising a membrane electrode assembly (MEA) comprising a plurality of electrodes 102, 104 and a membrane electrolyte layer disposed between the plurality of electrodes 102, 104, wherein the MEA is disposed between a first substrate 122 and a second substrate 120, wherein the first substrate 122 has at least one opening 112 to provide a gas flow path therethrough to one of the electrodes 104. The fuel cell also comprises an electrical control unit 402 to determine an electrical characteristic of the MEA, wherein the electrical characteristic is indicative of the gas composition of the gas at the one of the electrodes 104 and wherein the electrical control unit 402 will generate an output based on or in response to a change in the electrical characteristic.