Splitting water effectively to produce hydrogen (H-2) requires the development of non-noble-metal electrocatalysts that are able to make this reaction feasible and energy efficient. Herein, we present a novel "structure upgrading" synthetic approach for the design and synthesis of bio-inspired hydrogen-evolving electrocatalysts based on earth-abundant elements. Using g-C-3 N-4 - an inexpensive inorganic polymer material - as a host material for copper ions, novel Cu-doped g-C3N4 materials with supramolecular structure, efficient electrocatalytic activity and modest overpotentials for hydrogen evolution reaction (HER) are synthesized. Compared with most single-molecule analogs of hydrogenases that work only in organic media, the supramolecular Cu-doped g-C3N4 materials can serve as heterogeneous electrocatalysts with greater stability and good catalytic activity for HER in aqueous media. The materials afford a current density as high as 10 mA cm(-2) at an overpotential as low as 390 mV, and work well in acidic media for, at least, 43 h. (C) 2015 Elsevier B.V. All rights reserved.