Modification of the surface chemistry of nanocrystalline VN yields a new class of supercapacitors that deliver an impressive specific capacitance. The creation of surface nanolayers of VOx (poor electronic conductivity) on the electronically conductive nanocrystalline VN shown in the figure-and on the cover gives rise to a series of reversible redox reactions that are thought to be responsible for the high capacitance. Application of the concept to other transition metals is expected to broaden the scope of supercapacitor materials.