Ultrathin 2D graphitic carbon nitride @ metal films: underpotential sodium deposition in adlayers for sodium‐ion batteries

Efficient and low-cost anode materials for the sodium-ion battery are highly desired to enable more economic energy storage. We describe here effects on an ultrathin carbon nitride film deposited on a copper metal electrode, the combination of which show an unusually high capacity to store sodium metal. The g-C 3 N 4 film is as thin as 10 nm and can be fabricated by an efficient, facile, and general chemical-vapor deposition method. A high reversible capacity of formally up to 51 Ah g -1 indicates that the Na is not only stored in the carbon nitride as such, but that carbon nitride activates also the metal for reversible Na-deposition, while forming at the same time an solid electrolyte interface layer avoiding direct contact of the metallic phase with the liquid electrolyte.