Rectification of charges on r-TiO2via Pd-cocatalysts and Schottky junctions to produce H2 for green energy systems†

Abstract

For a long-term and sustainable energy system, hydrogen has been considered as one of the ideal and carbon-free fuels. A significant advantage is that it exists abundantly in the form of water, natural gas and biomass. However, the drawback is that it exists in the form of compounds and is not available in a free state. Current study was designed to produce hydrogen via catalytic water-splitting reactions. The advantage of the catalytic water-splitting approach is that it is an economical, controllable and more feasible technology. The efficiency of water-splitting reactions can be enhanced by various factors, such as (i) the use of more selective and effective catalysts, (ii) extending the photon absorption capability, (iii) optimizing or predicting the ideal conditions where hydrogen production rates should be maximum, (iv) controlling the charge transfer and (v) increasing the surface active sites by employing metal cocatalysts. For this purpose, stable metal oxides, such as TiO₂, were used as semiconductor supports to promote catalytic hydrogen generation. TiO₂ surfaces were tuned with Pd-cocatalysts via controlled hydrothermal reactions, followed by chemical reduction. Catalysts synthesized by this method were found to be more effective in term of water-splitting. The structural and optical properties of the catalysts were assessed via XRD, UV-Vis/DRS, SEM, TEM, AFM, Raman, FTIR, PL, and EIS analytical tools. The phase purity and elemental compositions of the catalysts were confirmed by EDX and XPS techniques. Under similar conditions, photoreactions were performed in a quartz reactor (MICQ/US-150 mL). Hydrogen evolution activities and catalytic performances revealed that the Pd/r-TiO₂ catalyst delivers almost ten times higher hydrogen (i.e., 23.19 mmol g⁻¹ h⁻¹) compared to pristine r-TiO₂, which delivers only 2.15 mmol g⁻¹ h⁻¹ of hydrogen. The higher catalytic performance of Pd/r-TiO₂ were attributed to the development of Schottky junctions that escalate and rectify the charge transfer on active sites (i.e., Pd-cocatalysts). Based on the results, it is concluded that the catalysts reported herein hold potential to replace the conventional catalysts used in hydrogen generation technologies.