Maricite (NaMn1/3Ni1/3Co1/3PO4)/Activated Carbon: Hybrid Capacitor

A hybrid capacitor comprising mixed transition-metal sodium phosphate/activated carbon (AC) with sodium hydroxide electrolyte is reported for the first time. The sodium phosphate (maricite, NaMn1/3Ni1/3Co1/3PO4) positive material was prepared by both urea-assisted combustion and polyvinyl pyrrolidone (PVP)-assisted sol-gel syntheses. The electrochemical behavior of maricite and AC was characterized by cyclic voltammetry (CV) and charge-discharge methods. The reaction mechanism at the maricite electrode in NaOH(aq) electrolyte appears to be reversible, involving a faradaic process, while the AC shows capacitive behavior involving a non-faradaic process. The aqueous hybrid capacitor, maricite (as the cathode), and AC (as the anode) studied by galvanostatic (charge-discharge) cycling in the range of 0-1.6 V at 0.5 A g(-1) exhibited a specific discharge capacitance of 45 F g(-1) stable over 1000 cycles.