Abstract <p>Electrochemical hydrogen compression technology is a promising alternative for hydrogen compression due to its simultaneous compression and purification, high efficiency, and simple design. One of the main problems in electrochemical hydrogen compressors is to improve the properties of membranes such as proton conductivity, mechanical strength, low hydrogen crossover. Here we report the properties of sulfonated poly(ether ether ketone) composite membranes reinforced with cellulose nanocrystals (CNCs) for the electrochemical compression systems. The physicochemical properties, including the morphology of composite membranes, water uptake, mechanical strength, ion exchange capacity and proton conductivity were evaluated. The mechanical strength of composite membrane with 3 wt % CNCs showed high tensile strength of 26.0 MPa, and proton conductivity was highest among evaluated membranes as 0.209 S/cm at 90°C. The performance of electrochemical hydrogen compressors was tested for voltage, compression time, and energy efficiency at pressures up to 50 bar. As a result, the composite membrane reinforced with CNCs showed improved energy efficiency and lower hydrogen crossover in electrochemical hydrogen compressor systems.</p>