Semiconductor properties and redox responses at a-C:N thin film electrochemical electrodes

The semiconductor capacitances of the nitrogen-doped amorphous carbon (a-C:N) materials with different sp3/sp2 C ratios were studied as a function of electrode potential in a-C:N/aqueous electrolyte systems. This dependence of capacitance on electrode potential in aqueous 0.1 M NaOH shows that the investigated a-C:N materials are intrinsic semiconductors. The space-charge layers inside the a-C:N electrodes behave similar to a Helmholtz layer because of the presence of surface states when the electrolytes contain O2 or anions other than OH−. The lower density and mobility of carriers of materials with a higher sp3 C fraction within the a-C:N material causes a suppression of redox reactions, and the lower density of carriers contributes to a lower capacitance.