Ultra-fast one-step synthesis and surface engineering of mesoporous 3D α-Fe2O3 hollow nanospheres for high-performance and stable negative electrode for supercapacitors

Abstract Supercapacitors (SCs) have received considerable attention in portable digital devices because of their long life span and high power densities. However, low energy densities of SCs limited their practical applications due to the lack of high-performance negative electrode materials. This work demonstrates the surface engineering of α-Fe2O3 hollow nanospheres (α-Fe2O3-HNS) by controlled crystal growth through hollowing mechanism by the Ostwald ripening approach using facile one-step and low-cost hydrothermal method. The formation of α-Fe2O3-HNS was confirmed by scanning and transmission electron microscopy and further characterized by a variety of analytical methods. To investigate the electrochemical properties of α-Fe2O3-HNS, we systemically tested it in aqueous electrolyte under the extended potential window of −1.2–0.0 V versus Ag/AgCl. Among three samples of α-Fe2O3 nanospheres, the α-Fe2O3-HNS sample manifests a record high specific capacitance of 1041.18 F g−1 while partially hollow and solid α-Fe2O3 nanospheres displayed relatively low specific capacitances of 534.31 and 325.38 F g−1 at 1 A g−1, respectively. The α-Fe2O3-HNS sample demonstrates excellent cycling retention of 98.88% while other samples retained 94.23% and 88.25%, respectively after 10,000 cycles at a high current density of 15 A g−1. The surface engineering of α-Fe2O3-HNS offers not only the high surface area but also allows a large number of electroactive sites at electrode/electrolyte contact. Furthermore, we investigated the quantification of capacitive and diffusion controlled stored charge for high performance charge storage kinetics of as-prepared electrodes, by employing power’s law and impressively α-Fe2O3-HNS sample reveals high capacitive type charge storage of (85% at 10 mV/s). The obtainable results fully exhibit the unique advantage of a hollow structure to fabricate superior negative electrode materials for supercapacitors.