Fundamental Insight into the Degradation Mechanism of an rGO-Fe3O4 Supercapacitor and Improving Its Capacity Behavior via Adding an Electrolyte Additive

Reduced graphene oxide (rGO)-Fe3O4 nanosized composites containing various concentrations of reduced graphene oxide (rGO) were synthesized by the hydrothermal method. rGO nanosheet provides a solid framework for Fe3O4, improving the overall conductivity as well as reducing agglomeration of Fe3O4 nanoparticles. rGO-Fe3O4 exhibits a specific surface area of 207.2 m3·g–1 with a total pore volume of 0.203 cm3 g–1. Fabricated into electrode, rGO-Fe3O4 demonstrates a specific capacitance of 182.2 F·g–1 at a current density of 1.25 A·g–1 with a retention rate maintaining at 92.4% after 1000 cycles. Material degradation of the electrode inevitably changes the solid electrolyte interface (SEI) and causes capacitance loss during long-cycle tests. In this regard, advanced surface analysis techniques were applied to better understand the degradation mechanism and reveal possible reactions occurring at the electrode interface after various cycling stages. Strategically, iron molybdate (FeMoO4) has been added as an electrolyte additive in the experiment where molybdenum disulfide (MoS2) formed on the electrode surface and remarkably rejuvenated the capacity with maximum values rising to 186.6, 171.8, and 153.4 F·g–1 at the current densities of 1.25, 2.50, and 3.75 A·g–1 respectively. The notable recovery of capacitance achieved by adding FeMoO4 provides a practical method for solving the problem of material degradation and rejuvenating rGO-Fe3O4 electrode performance in the Na2SO3-based electrolyte.