Redox supercapacitor performance of nanocrystalline molybdenum nitrides obtained by ammonolysis of chloride- and amide-derived precursors

• Hexagonal δ1-MoN < 500 °C or cubic γ-Mo2N > 600 °C from a MoCl5-derived polymer.
• High double layer capacitance in aqueous electrolyte with good cycling stability.
• Phase behaviour of molybdenum nitride from a Mo(NMe2)4-derived polymer.
• Good capacitance and stable cycling in relatively low surface area materials.
• Redox peaks in the electrochemical data suggesting a largely redox-based process.

Reactions of MoCl5 or Mo(NMe2)4 with ammonia result in cubic γ-Mo2N or hexagonal δ1-MoN depending on reaction time and temperature. At moderate temperatures the cubic product from Mo(NMe2)4 exhibits lattice distortions. Fairly high surface areas are observed in the porous particles of the chloride-derived materials and high capacitances of up to 275 F g−1 are observed when electrodes made from them are cycled in aqueous H2SO4 or K2SO4 electrolytes. The cyclic voltammograms suggest charge is largely stored in the electrochemical double layer at the surface of these materials. Amide-derived molybdenum nitrides have relatively low surface areas and smaller capacitances, but do exhibit strong redox features in their cyclic voltammograms, suggesting that redox capacitance is responsible for a significant proportion of the charge stored.