الفهرس 
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Abstract
Hydrogen generation via photoelectrochemical water splitting is considered a promising method
of clean and renewable energy to deal with the energy crisis in the world. Efficient visible light harvesting of photoelectrochemical water splitting with bare TiO2, the most popular semiconductor photoanode, is still challenging. Sulfur-doped titanium oxide on the surface of sulfur-doped reduced graphene oxide nanocomposites (S-TiO2/S-RGO) were successfully synthesized for the first time through a simple low cost solvothermal reaction process. The sulfur doping was detected in both TiO2 matrix and carbon framework structure of reduced graphene oxide using X-ray photoelectron spectroscopy (XPS) and Energy-dispersive X-ray spectroscopy (EDX). Cross-sectional atomic force microscopy (AFM) analysis of S-RGO nanosheets reveals a thickness of 0.51 nm which is much thinner than those previously reported of heteroatom doped-RGO, confirming the single-layer feature. When the as-prepared (S-TiO2/S-RGO) nanocomposites are utilized as photoanodes for photoelectrochemical (PEC) water splitting, they exhibited an enhanced photoelectrochemical performance and long-term stability. The photocurrent density of S-TiO2/S-RGO(0.2) photoanode revealed 3.36 mA/cm2 at 1 V vs Ag/AgCl which is considered 3 times enhancement compared to bare synthesized TiO2. This enhancement in the photocurrent density was attributed to the increased separation rate of photogenerated electrons and holes and efficient visible light harvesting as a result of the successful combination of the S-TiO2 and the S-RGO in the same nanocomposite photoanode.
Extending to this work reported on synthesis of the S-TiO2/S-RGO nanocomposites, the synthesis of the N-TiO2/N-RGO and N,S-TiO2/N,S-RGO nanocomposites was demonstrated for the first time through a low-cost and efficient solvothermal approach for photoelectrochemical water splitting. The biphasic N,S-TiO2/N,S-RGO nanocomposites samples combined the merits of the N and S doping in both TiO2 lattice and in the same time in the carbon framework structure of RGO and the synergistic effect resulting between the anatase-brookite phases. The highest photocurrent density was achieved for the N,S-TiO2/N,S-RGO(0.1) nanocomposite photoanode which is 6 times enhancement greater than bare TiO2 photoanode. These are considered significant promising results in comparison with S-TiO2/S-RGO nanocomposite photoanodes presented in our previous work which revealed only 3 times enhancement in photocurrent density than bare TiO2. The N,S-TiO2/N,S-RGO nanocomposites contributed to easier water oxidation and better PEC properties than the N-TiO2/N-RGO nanocomposites samples. This promising result presents a new approach for the synthesis of high-efficient future metal-free photoelectrocatalysts.