NOVELTY - A unitary sliding vane type compressor-expander (12) comprises a compressor portion (102) with compressor inlet and outlet, expander portion (104) with expander inlet and outlet, integral condenser-humidifier disposed in fluid communication with the expander outlet for condensing water out of the expanded gas and returning the condensed water directly to the expander outlet.    USE - For use in conjunction with a proton exchange membrane fuel cell.    ADVANTAGE - The inventive compressor-expander is compact, simple and lightweight. It includes integral condenser-humidifier that provides condensed water for providing lubrication and sealing the unitary vane compressor-expander and humidities the fuel cell, thus improving the efficiency of both compressor-expander and fuel cell.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for:    (a) a fuel cell electrical generation system comprising unitary sliding vane type compressor-expander, fuel cell, and motor; and    (b) improving the efficiency of a fuel cell electrical generation system comprising providing a fuel cell for generating output electrical power, connecting a unitary vane type compressor-expander to the fuel cell, driving the unitary compressor expander with a motor powered by electricity derived from fuel cell electrical generation system, compressing air drawn from the compressor inlet on in the compressor side of the compressor-expander, supplying the compressed air to an oxidant inlet of the fuel cell for reacting with fuel introduced through the fuel inlet, and expanding the spent oxidant gas from the fuel cell across the expander side of the compressor expander.    DESCRIPTION OF DRAWING(S) - The drawings show a cross-sectional view of the inventive unitary sliding vane type compressor-expander, and a schematic drawing of the electrical generation system.    Unitary sliding vane type compressor-expander (12)    Vanes (40)    Compression chamber (50)    Stationary magnets (82)    Compressor portion (102)    Expander portion (104)