Modified layered titanates for enhanced photochemical and photoelectrochemical water splitting

The search for sustainable green energy sources is becoming essential due to the rising global energy demands while making use of sunlight and water as benign resources show the most potential. A notable method is the use of the energy of the sun to split water into hydrogen and oxygen. Highlighting its critical role in meeting the world's energy demands as a promising energy carrier, hydrogen, with its zero carbon emissions. Solar-driven photocatalytic and photoelectrochemical water splitting offer a compelling method to produce hydrogen and oxygen. Exfoliation and ion exchange methods were utilized to expose active sites in layered titanates, along with modifications like loading single atoms with photoactive species. The first part of this study involved exfoliating potassium lithium layered titanates (KTLO) and photo-deposition of single atom Sn onto the layer surfaces, as Sn atoms act as co-catalysts. The exfoliation is confirmed by using X-ray diffraction (XRD), showing the expansion of interlayer spaces. Exfoliated titanate showed a distinguished photocatalytic hydrogen evolution reaction (HER) from water and ammonia borane. Adding Sn single atoms to its surface significantly increases the photocatalytic activity, causing roughly a threefold increase in exfoliated titanate. It is also demonstrated that the optimal Sn loading is required for the best HER activity. A thorough investigation demonstrated by photoluminescence spectroscopy (PL) showed that exfoliated titanate showed an improved lifetime for charge carriers. The second part of this study focused on the photocatalytic and photoelectrochemical activities of cetyltrimethylammonium bromide (CTAB) intercalated layered cesium titanate (CsTO). Interlayer spacing served as proof of successful intercalation confirmed by the X-ray diffraction. Interlayer space expansion of CsTO results in morphological changes and a larger surface area, characterized by Scanning Electron Microscopy (SEM). Likely, the treatment with CTAB induced an ion exchange mechanism during the intercalation process, resulting in the removal of Cs+ ions, and this phenomenon was v confirmed through X-ray Photoelectron Spectroscopy (XPS) analysis. As an n-type material, CTAB intercalated CsTO samples are promising candidates to utilize surface electrons for photocatalytic HER, and photogenerated holes are utilized for photoelectrochemical oxygen evolution reaction (OER). Carbon content between interlayers had an impact on charge carrier utilization and served as a conductive layer for photoelectrochemical OER. Consistent with the photocatalytic HER findings, the linear sweep voltammetry (LSV) experiments conducted for the OER revealed a similar trend, indicating enhanced activity with increased CTAB concentrations. Overall, this study highlights the potential of modified layered titanate photocatalysts for effective water splitting driven by solar energy, with implications for HER and OER in the search for renewable energy sources.