Bifunctional iron disulfide nanoellipsoids for high energy density supercapacitor and electrocatalytic oxygen evolution applications Electronic supplementary information (ESI) available. See DOI: 10.1039/c8qi01230j

To solve the problem of low energy density in supercapacitor devices, enhancing the specific capacity of the anode is essential and urgent. FeS2 nanoellipsoids have been prepared using a rapid microwave-assisted method as an anode for supercapacitors. The anode possesses a wide working potential (-1.2 to 0 V), and a high specific capacity (515 C g(-1) at 1 A g(-1)) in 2 M KOH, showing obvious improvement over conventional carbon materials used for supercapacitors. As a consequence, the maximum energy density reached 64 W h kg(-1) at 271.2 W kg(-1) thanks to the high specific capacity of the FeS2 anode, and the asfabricated brand new device was able to retain 91% of its initial capacitance after 5000 cycles. Moreover, the as-prepared FeS2 ellipsoids also exhibit efficient electrocatalytic oxygen evolution in 1 M KOH with an overpotential of 370 mV at 10 mA cm(-2) (vs. RHE). Therefore, the as-prepared FeS2 electrode holds huge potential for use in energy storage and conversion applications in the future.