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

P-TiOn-VOm nanowires were grown on nickel foam (NF) by one-pot hydrothermal and further vapor deposition/phosphorization method. It is found low valence states of titanium oxide and deficient-oxygen coexist in P-TiOn-VOm/NF. Furthermore, (TiO1.25)3.07 (denoted as TiOn) and VO (denoted as VOm) possess similar structures and matched facets, their epitaxial growth leads to the formation of TiOn/VOm heterostructure with a formation energy of -1.59 eV. P-TiOn-VOm/NF possesses good electron conductivity, and electrons can be transferred from Ti to V centers, as evidenced by DFT calculations and XPS spectra. As a result, the specific capacity of P-TiOn-VOm/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 VOm/NF, P-VOm/NF and P-TiO2-VOm/NF. On the other hand, the TiOn/VOm heterostructure also favors for the separation and transfer of photoinduced electrons and holes, and P-TiOn-VOm/NF exhibits visible-light-driven photoresponse. Under the visible light illumination, the specific capacity of P-TiOn-VOm/NF is increased 6.2 % relative to that in dark. Furthermore, the P-TiOn-VOm/NF//activated carbon (/ AC) asymmetric supercapacitor (ASC) shows an energy density of 37.2 Wh kg-1 at power density of 1 kW kg-1, and excellent cycling performance with 93.6 % capacity retention after 10000 cycles at 5 A g−1, which is comparable to and even superior to those of titanium oxides and vanadium oxides. It is proposed a promising achievement to improve the energy storage performance of P-TiOn-VOm through the P-functionalization and O-deficiency in this work.