Low-crystalline iron oxide hydroxide nanoparticle anode for high-performance supercapacitors.

Carbon materials are generally preferred as anodes in supercapacitors; however, their low capacitance limits the attained energy density of supercapacitor devices with aqueous electrolytes. Here, we report a low-crystalline iron oxide hydroxide nanoparticle anode with comprehensive electrochemical performance at a wide potential window. The iron oxide hydroxide nanoparticles present capacitances of 1,066 and 716?F?g(-1) at mass loadings of 1.6 and 9.1?mg?cm(-2), respectively, a rate capability with 74.6% of capacitance retention at 30?A?g(-1), and cycling stability retaining 91% of capacitance after 10,000 cycles. The performance is attributed to a dominant capacitive charge-storage mechanism. An aqueous hybrid supercapacitor based on the iron oxide hydroxide anode shows stability during float voltage test for 450?h and an energy density of 104?Wh?kg(-1) at a power density of 1.27?kW?kg(-1). A packaged device delivers gravimetric and volumetric energy densities of 33.14?Wh?kg(-1) and 17.24?Wh?l(-1), respectively.