Co₃O₄ Nanoparticles Embedded in Mesoporous Carbon for Supercapacitor\nApplications

Abstract

Metal\noxides are of great interest for supercapacitor application;\nhowever, they suffer from capacity fading during cycling and limited\ncycle life. In this work, a one-pot bottom-up approach is proposed\nto design cobalt oxide (Co₃O₄) nanoparticles\nconfined in a mesoporous carbon. This involved the coassembly of a\nphenolic resin, a surfactant, and a cobalt salt followed by a high\ntemperature pyrolysis (600–800 °C) and a subsequent low\ntemperature oxidation (190–240 °C) step. Very small Co₃O₄ particle size (2.3–7.4 nm) could be achieved\nfor high loadings of Co₃O₄ (up to 59%) in the\ncarbon network. Both the pyrolysis and oxidation temperature increase\nled to an increase of nanoparticle size, porosity and electronic conductivity.\nAt low temperatures, i.e., 600 and 650 °C, and despite the low\nparticle size, the performances are poor and limited by the carbon\nlow electronic conductivity. At high temperature (800 °C), the\nconductivity is improved translating in a higher capacitance, but\nthe larger and more aggregated nanoparticles induced low rate capability.\nThe best compromise to maintain high capacitance and rate capability\nwas observed at 700 and 750 °C and thus for composite materials\ncombining simultaneously dispersed nanoparticles, high porosity, and\ngood electronic conductivity. In particular, the material treated\nat 750 °C presents, in a 2 electrode system using 2 M KOH, a\ncapacitance of 54 F g^–1 at 0.1 A g^–1, a very high rate capability of 48.7% at 10 A g^–1, and a superior rate performance of 82% after 10000 cycles.