Visible light active black TiO2 nanostructures and its RGO based nanocomposite for enhanced hydrogen generation and electrochemical potency

•Black TiO2/RGO has been synthesised by low pressure vacuum annealing process.•Existence of oxygen vacancies / Ti3+ and RGO promote solar light absorption range.•Conducive transfer of electrons to RGO authenticate augmented hydrogen generation.•Black TiO2/RGO exhibit higher specific capacitance (924.1F/g) at 5 mV/s.•Efficiency of black – nitrogen doped TiO2 is limited due to N-O moiety. Hydrogen is considered to be a sustainable, clean form of energy and a fundamental pillar to combat global warming. Hence, it is necessary to develop an eco – friendly, efficient energy storage device for future generations. Herein, we have developed an effective, vacuum annealing synthetic protocol to prepare black TiO2 (BT), black-nitrogen doped TiO2 (BNT) and RGO composited black TiO2 (BTG) in the presence of ethanol for an efficient photocatalytic hydrogen generation. Change in the optical and electronic properties of black nanocomposites are examined by UV-vis and PL studies. Investigation of FTIR and XPS confirms the reduction of functional groups on the nanocomposites. Meanwhile, low photocatalytic efficiency and capacitance of BNT than expected has been associated with the formation of N-O moiety during the annealing process. Plausible mechanism has been proposed for the low efficiency of BNT to understand the electronic structures of black nanocomposite. [Display omitted]