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

• MoPO thin film is decorated on MoS 2 nanoflakes to enhance its properties. • MoPO/MoS 2 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 MoS 2 nanoflakes to form integrated hybrid architecture via electrodeposition-process assisted hydrothermal method. Benefitting from its unique structure, MoPO/MoS 2 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/MoS 2 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/MoS 2 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 MoS 2 //MoS 2 device. Amazingly, the MoPO/MoS 2 //MoPO/MoS 2 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.