Doping-induced metal–N active sites and bandgap engineering in graphitic carbon nitride for enhancing photocatalytic H2 evolution performance

Durable and inexpensive graphitic carbon nitride (g-C3N4) demonstrates great potential for achieving efficient photocatalytic hydrogen evolution reduction (HER). To further improve its activity, g-C3N4 was subjected to atomic-level structural engineering by doping with transition metals (M = Fe, Co, or Ni), which simultaneously induced the formation of metal–N active sites in the g-C3N4 framework and modulated the bandgap of g-C3N4. Experiments and density functional theory calculations further verified that the as-formed metal–N bonds in M-doped g-C3N4 acted as an “electron transfer bridge”, where the migration of photo-generated electrons along the bridge enhanced the efficiency of separation of the photogenerated charges, and the optimized bandgap of g-C3N4 afforded stronger reduction ability and wider light absorption. As a result, doping with either Fe, Co, or Ni had a positive effect on the HER activity, where Co-doped g-C3N4 exhibited the highest performance. The findings illustrate that this atomic-level structural engineering could efficiently improve the HER activity and inspire the design of powerful photocatalysts.