An oxygen concentrator is disclosed for generating a flow of oxygen by electrolysis of atmospheric humidity. It comprises a cathode 24 and an anode 26 contacting opposite sides of a proton-conducting membrane 12. A catalytic apparatus 14 comprises a diffusion layer 28 which spaces a catalyst 30 from the cathode. The cathode and the catalytic apparatus are contained within a cathode chamber which comprises a ventilation means 44 for allowing a controlled flow of air to the catalyst. In operation water is electrolysed and hydrogen generated at the cathode flows through the diffusion layer to the catalyst, where it reacts with atmospheric oxygen to form water which flows back to the proton-conducting membrane for further electrolysis.
