Molybdenophosphate thin film decorated on the surface of MoS2 nanoflakes for aqueous K-ion capacitors

The molybdenophosphate (MoPO) thin film was anchored on MoS2 nanoflakes to form integrated hybrid architecture via electrodeposition-process assisted hydrothermal method. Benefitting from its unique structure, MoPO/MoS2 electrode exhibits the excellent electrochemical properties, including a specific capacitance of 552.8 F g(-1) at a current density of 2 A g(-1), rate performance of 83.7% at 10 A g(-1) and low internal resistance of 1.9 Omega. Interestingly, kinetic analysis of MoPO/MoS2 electrode displays adsorption and intercalation capacitance contribution of 59.5% and 40.5% at 10 mV s(-1), respectively. Furthermore, ex-situ energy dispersive X-ray spectroscopy mapping and inductively coupled plasma mass spectroscopy identify the intercalation of K+ distributed in the material. Meanwhile, ex-situ X-ray photoelectron spectroscopy demonstrates that the valence states of P, Mo and S elements are changed after intercalating K+. Moreover, the aqueous symmetrical K-ion capacitor (KIC) assembled by MoPO/MoS2 electrodes manifests a high energy density of 52.6 Wh kg(-1) at a power density of 746.9 W kg(-1), four times higher than that of MoS2//MoS2 device. Amazingly, the MoPO/MoS2//MoPO/MoS2 KIC exhibits the super-long cycling stability with 90% capacitance retention after 26,000 cycles at 2 A g(-1). Hence, this work provides a simple and efficient strategy for the application of aqueous KICs in the future.