Facile synthesis of pristine FeS₂ microflowers and hybrid rGO-FeS₂ microsphere electrode materials for high performance symmetric capacitors

Iron pyrite (FeS₂) is an interesting mineral in the transition metal dichalcogenide group due to its high abundance in the earth's crust which can be used for various electrochemical energy storage applications, such as batteries and supercapacitors; however, it suffers from low rate capability and poor cycle performance, which hampers its use from large-scale commercial applications. In the present study, iron disulfide microspheres anchored onto a reduced graphene oxide matrix (rGO-FeS₂ hybrid) were grown using a superficial hydrothermal method. For comparison, rGO-free iron disulfide material was synthesized under the same hydrothermal conditions, and uniformly distributed FeS₂ micro-size flowers were formed. The energy storage capacity of both electroactive materials (FeS₂ and rGO-FeS₂ hybrid material) was tested for supercapacitor applications in a symmetric cell configuration. The pristine FeS₂ microflower electrode exhibited an areal capacitance of 70.98 mF cm⁻² at 5 mV s⁻¹. On the other hand, the rGO-FeS₂ hybrid microsphere electrode exhibited an enhanced areal capacitance of 112.41 mF cm⁻² at the same scan rate with an excellent capacitance retention of 90% over 10,000 cycles. The improved electrochemical performance of the rGO-FeS₂ hybrid material is due mainly to its improved electrical conductivity, high surface area indicating an enhanced electron, and ion transfer mechanism. This study suggests that the rGO-FeS₂ hybrid electrode material has potential applications in energy storage devices.