Abstract: The efficient production of gaseous oxygen used in many branches of industry to provide human life in anaerobic environments and in medicine (e.g., in the case of acute respiratory failure as one of COVID-19 complications) is challenging nowadays. The electrochemical oxygen pump (concentrator) with a solid polymer electrolyte representing an electrolyzer with air cathode depolarization is a very promising device, which provides the portable, safe, and efficient in situ production of highly pure oxygen at a twice lower energy consumption as compared to the water electrolyzer with a solid polymer electrolyte. The effect produced by the hydrophobization of a nanostructured oxygen reduction catalyst on the oxygen pump characteristics and the endurance of a cathode catalytic layer to flooding has been considered. The modification of a carbon support with polytetrafluoroethylene particles improves the removal of excessive water from the catalytic layer and increases the limiting current characterizing the appearance of transport limitations. The operational parameters (air temperature, flow rate, and pressure) also have an essential effect on the oxygen pump performance and must be optimized to improve water transport in catalytic layers, increase the operating current densities, and reduce the energy consumption in oxygen production.