Low‐Temperature Electrochemical Synthesis of Cubic Carbon Nitride via Co‐Oxidation in Molten LiCl–KCl

Carbon nitride materials, predicted to rival diamond in hardness and exhibit wide bandgaps, have long eluded direct synthesis in bulk crystalline form. We demonstrate the low‐temperature electrochemical synthesis of cubic carbon nitride (c‐C ₃ N ₄ ) via co‐oxidation of carbide (C ₂ ²⁻ ) and nitride (N ³⁻ ) ions in molten LiCl–KCl at 450 °C. Using CaC ₂ and Li ₃ N as stable precursors, we investigate the thermodynamic and electrochemical windows for C─N bond formation on nickel and platinum electrodes. Cyclic voltammetry, potentiostatic, and pulsed electrolysis reveal that co‐oxidation enables the nucleation of C─N bonded phases, with substrate selection critically influencing phase composition and crystallinity. X‐ray diffraction (XRD) revealed reflections consistent with a cubic C ₃ N ₄ candidate phase on Pt electrodes under pulsed conditions, while scanning electron microscopy/energy‐dispersive X‐ray spectroscopy, Raman spectroscopy, and nanoindentation supported the formation of a dense carbon nitride‐containing layer with hardness values up to 9.56 GPa. These findings show that molten‐salt electrochemistry provides a low‐temperature route to carbon nitride‐containing deposits with XRD reflections consistent with a c‑C ₃ N ₄ candidate phase at 450 °C, a temperature substantially lower than those required in conventional high‐pressure or vapor‐phase approaches.