Hydrogen-storage characteristics of hydrogenated amorphous carbon nitrides

Hydrogenated amorphous carbon nitride (a-CNx:H) materials were prepared using the radio-frequency (RF) magnetron discharge of the mixed gases of hydrocarbons and N2. The starting hydrocarbons were CH4, C2H6, C2H4, C2H2, or C6H6. The stored hydrogen contents of various a-CNx:H materials formed from these starting hydrocarbons were measured by the volumetric analysis. The maximum hydrogen content, 0.78 wt.%, was obtained for the material formed from CH4 at the equilibrium pressure of hydrogen of 11.3 MPa; the other materials gave much smaller hydrogen contents, 0.03–0.11 wt.%. The structures of a-CNx:H materials were analyzed by IR and Raman spectroscopic methods and the near-edge X-ray absorption fine structure (NEXAFS) analysis of carbon K-edge. The correlation between the hydrogen-storage ability and the chemical structure of materials was discussed.