AbstractThe manufacture of composite materials can improve the properties of proton-conducting polymers as membranes in PEM fuel cells. We have investigated composite membranes obtained by dispersion of nanodiamond particles in a sulfonated PolyEtherEtherKetone (SPEEK) matrix. SPEEK is a major proton-conducting aromatic polymer. Nanodiamond has been studied for various applications and can be functionalized with different surface groups. For use in proton-conducting membranes, surface functionalization with proton-donating groups is a promising approach. In this preliminary work, we have studied the properties of membranes made using pristine nanodiamond from diverse origins for a first assessment of the potential properties. The composites were analysed by various techniques, including Thermogravimetric Analysis, water vapor uptake and mechanical tensile tests.