A CoS2 nanopyramid array with a low mass loading (∼0.625 mg cm−2) fabricated on 3D carbon fiber paper exhibits ultrahigh activity towards acidic hydrogen evolution with a low onset potential (∼61 mV) and a small overpotential (∼140 mV) for driving a current density of ∼100 mA cm−2, ascribed to the one-step solvothermal synthesis, unique 3D nanostructure and intrinsic metallic properties of the electrocatalyst.
