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

[Display omitted] •MoPO thin film is decorated on MoS2 nanoflakes to enhance its properties.•MoPO/MoS2 has co-existence of adsorption and intercalation capacitance.•KIC exhibits the excellent energy density and outstanding cycle stability. 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 Ω. 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.