N-TiO2 crystal seeds incorporated in amorphous matrix for enhanced solar hydrogen generation: Experimental & first-principles analysis
Abstract
We present here a combined study on the photoelectrochemical activity of highly active Nitrogen doped titanium dioxide thin-film using experiments and First principle density (DFT) based calculation. Hybridization of N 2p with O 2p and localized valence band upshifting leads to the reduction in band-gap of N-TiO2. To validate theoretical findings, the role of nitrogen in TiO2 is revisited with a focus on partial crystallinity. The best-case photoelectrode, nanostructured partially crystalline nitrogen-doped titanium dioxide (PCNDTO) offered photocurrent density of 24.3 mA/cm2 at 1 V versus saturated calomel electrode (SCE). The absence of well-defined peaks and long-range order in XRD pattern and Raman spectrum respectively suggests partially crystallinity. High-resolution transmission electron microscopy (HR-TEM) images confirm the presence of TiO2 crystals in the amorphous matrix. High photoelectrochemical response can be attributed to the abundance of hydroxyl groups, high electrochemical active surface area, reduced charge transfer resistance, and reduced charge carrier recombination rate.
Conclusion
The present study shows the efficient splitting of water into hydrogen and oxygen using PCNDTO material. The photocurrent density of 24.3 mA/cm2 was obtained at 1 V vs. SCE in NaOH electrolyte (pH 13) in partially crystalline form and results were compared with the highly crystalline form of TiO2. The incorporation of N in TiO2 during the calcination process resulted in partial amorphization of TiO2 as well as generation of oxygen vacancy which accounts for its high photoelectrochemical response. DFT calculations were attempted apparently for the first time in PEC studies for electronic structure (band structure) of PCNDTO that explains the reduction in bandgap which agrees well with experimental findings. The role of crystallinity on the PEC activity of metal oxide has been systematically studied by annealing films in different calcination environments and high temperatures. Present work, therefore, provides insight into the role of crystallinity on the PEC response.
To be cited as:
N. K. Biswas, A. Srivastav, S. Saxena, A. Verma, R. Runjhun Dutta , M. Srivastava, S. Upadhyay, V.R. Satsangi, R. Shrivastav, S. Dass, N–TiO2 crystal seeds incorporated in amorphous matrix for enhanced solar hydrogen generation: Experimental & first-principles analysis, International Journal of Hydrogen Energy, Volume 47, Issue 53, 2022, Pages 22415-22429, ISSN 0360-3199, https://doi.org/10.1016/j.ijhydene.2022.05.064 .