P-Functionalized and O-deficient TiOn/VOm nanoparticles grown on Ni foam as an electrode for supercapacitors: epitaxial grown heterojunction and visible-light-driven photoresponse

Abstract

P–TiO_n–VO_m nanowires were grown on nickel foam (NF) via a one-pot hydrothermal method and by further vapor deposition/phosphorization method. It was found that low valence states of titanium oxide and deficient-oxygen coexist in P–TiO_n–VO_m/NF. Furthermore, (TiO_1.25)_3.07 (denoted as TiO_n) and VO (denoted as VO_m) possess similar structures and matched facets, and their epitaxial growth leads to the formation of TiO_n/VO_m heterostructure with a formation energy of −1.59 eV. P–TiO_n–VO_m/NF possesses good electron conductivity and electrons can be transferred from Ti to V centers, as evidenced by the DFT calculations and the XPS spectra. As a result, the specific capacity of P–TiO_n–VO_m/NF can reach 785 C g⁻¹ at 1 A g⁻¹ in the potential range of 0–0.55 V vs. Hg/HgO, which is much larger than those of VO_m/NF, P–VO_m/NF, and P–TiO₂–VO_m/NF. On the other hand, the TiO_n/VO_m heterostructure also favors the separation and transfer of photoinduced electrons and holes, and P–TiO_n–VO_m/NF exhibits visible-light-driven photoresponse. Under visible light illumination, the specific capacity of P–TiO_n–VO_m/NF is increased by 6.2% relative to that in the dark. Furthermore, the P–TiO_n–VO_m/NF//activated carbon (AC) asymmetric supercapacitor (ASC) shows an energy density of 37.2 W h kg⁻¹ at a power density of 1 kW kg⁻¹ and excellent cycling performance with 93.6% capacity retention after 10 000 cycles at 5 A g⁻¹, which is comparable to and even superior to those of titanium oxides and vanadium oxides. A promising achievement has been proposed to improve the energy storage performance of P–TiO_n–VO_m through P-functionalization and O-deficiency in this work.