Binder-free honeycomb-like FeMoO₄ nanosheet arrays with dual properties of both battery-type and pseudocapacitive-type performances for supercapacitor applications

In order to enhance the energy density of a hybrid supercapacitor, it is urgently required to develop unique positive and negative electroactive materials. Metal molybdates nanostructures hold great promise as high-performance electrode materials for next-generation energy storage devices. Herein, iron molybdate honeycomb-like nanosheet arrays (FeMoO₄ HNSAs) are successfully grown on nickel foam via a one-step chemical bath deposition approach, which can be effectively used as binder-free positive and negative electrode material. The morphological, composition and structural properties of FeMoO₄ FNSAs are examined by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction measurements. The honeycomb-like structure composed of interconnected ultrathin nanosheets and the large space between interconnected nanosheets can serve as an ion reservoir, which provides abundant active sites for redox reactions and promotes the rapid diffusion of electrolyte ions. The electrochemical measurements of the FeMoO₄ HNSAs are investigated in positive and negative potential regions using a three-electrode setup. The cyclic voltammetry and galvanostatic charge/discharge measurements envisage both battery-type and pseudocapacitive behavior of FeMoO₄ HNSAs electrode. As a battery-type material, the FeMoO₄ HNSAs electrode exhibits superior electrochemical performances with a high specific capacity (~158.39 mA h g⁻¹ at 2 A g⁻¹), excellent rate capability (~88.08% retains even at 8 A g⁻¹), and outstanding cycling life (~90.76% at 6 A g⁻¹ over 4000 cycles), respectively. Interestingly, the FeMoO₄ HNSAs electrode tested in negative potential region, as a pseudocapacitive electrode material, the FeMoO₄ HNSAs achieves a high specific capacitance of 477.47 F g⁻¹ at 2 A g⁻¹, excellent rate capability of 95.54% even at 8 A g⁻¹, and superior cycling stability with 92.37% capacity retention after 4000 cycles at 6 A g⁻¹. This work demonstrates that the FeMoO₄ HNSAs electrode provides a promising positive and negative electrode material for the energy storage applications in the future.