A hydrogen fuel cell unit comprising, in order (i) a first bipolar plate having a front face and a rear face, the rear face being an anode in the unit, (ii) a first membrane electrode assembly, (iii) a second bipolar plate having a front face and a rear face, the front face being a cathode in the unit and the rear face being an anode in the unit, wherein the first membrane electrode assembly is between the first and second bipolar plates, and a flow path is provided between the rear face of the first bipolar plate and the first membrane electrode assembly for flow of hydrogen, and a flow path is provided between the front face of the second bipolar plate and the first membrane electrode assembly for flow of oxygen, (iv) a second membrane electrode assembly, and (v) a third bipolar plate having a front face and a rear face, the front face being a cathode in the unit, wherein the second membrane electrode assembly is between the second and third bipolar plates, and a flow path is provided between the rear face of the second bipolar plate and the second membrane electrode assembly for flow of hydrogen, and a flow path is provided between the front face of the third bipolar plate and the second membrane electrode assembly for flow of oxygen, wherein the bipolar plates comprise channels for flow of oxygen and wherein the oxygen flow channels of adjacent plates repeatedly diverge and converge across the plate, wherein the bipolar plates further comprise channels for flow of hydrogen and wherein the hydrogen and oxygen flow channels are substantially transverse to each other, and wherein the oxygen flow channels are formed by an indentation in the bipolar plate and transverse hydrogen flow channels comprise a notch in the indentation that forms the oxygen flow channels, or vice versa, i.e. wherein hydrogen flow channels are formed by an indentation in the bipolar plate and transverse oxygen flow channels comprise a notch in the indentation that forms the hydrogen flow channels. (i) a first bipolar plate having a front face and a rear face, the rear face being an anode in the unit, (ii) a first membrane electrode assembly, (iii) a second bipolar plate having a front face and a rear face, the front face being a cathode in the unit and the rear face being an anode in the unit, wherein the first membrane electrode assembly is between the first and second bipolar plates, and a flow path is provided between the rear face of the first bipolar plate and the first membrane electrode assembly for flow of hydrogen, and a flow path is provided between the front face of the second bipolar plate and the first membrane electrode assembly for flow of oxygen, (iv) a second membrane electrode assembly, and (v) a third bipolar plate having a front face and a rear face, the front face being a cathode in the unit, wherein the second membrane electrode assembly is between the second and third bipolar plates, and a flow path is provided between the rear face of the second bipolar plate and the second membrane electrode assembly for flow of hydrogen, and a flow path is provided between the front face of the third bipolar plate and the second membrane electrode assembly for flow of oxygen, wherein the bipolar plates comprise channels for flow of oxygen and wherein the oxygen flow channels of adjacent plates repeatedly diverge and converge across the plate, wherein the bipolar plates further comprise channels for flow of hydrogen and wherein the hydrogen and oxygen flow channels are substantially transverse to each other, and wherein the oxygen flow channels are formed by an indentation in the bipolar plate and transverse hydrogen flow channels comprise a notch in the indentation that forms the oxygen flow channels, or vice versa, i.e. wherein hydrogen flow channels are formed by an indentation in the bipolar plate and transverse oxygen flow channels comprise a notch in the indentation that forms the hydrogen flow channels.