No abstract

Although four decades of efforts have gone into solar water splitting (SWS), still success eludes and there is no big breakthrough till date. While huge importance is given either individually...

Maximizing light absorption throughout the thin film and effective charge carrier utilization helped improve H2 yield by an order of magnitude.

Shape-controlled Pt nanoparticles (cubic, tetrahedral, and cuboctahedral) are synthesized using stabilizers and capping agents. The nanoparticles are cleaned thoroughly and electrochemically characterized in acidic (0.5 M H2SO4 and 0.1 M HClO4) and alkaline (0.1 M NaOH) electrolytes, and their features are compared to that of polycrystalline Pt. Even with less than 100% shape-selectivity and with the truncation at the edges and corners as shown by the ex-situ TEM analysis, the voltammetric features of the shape-controlled nanoparticles correlate very well with that of the respective single-crystal surfaces, particularly the voltammograms of shape-controlled nanoparticles of relatively larger size. Shape-controlled nanoparticles of smaller size show somewhat higher contributions from the other orientations as well because of the unavoidable contribution from the truncation at the edges and corners. The Cu stripping voltammograms qualitatively correlate with the TEM analysis and the voltammograms. The fractions of low-index crystallographic orientations are estimated through the irreversible adsorption of Ge and Bi. Pt-nanocubes with dominant {100} facets are the most active toward oxygen reduction reaction (ORR) in strongly adsorbing H2SO4 electrolytes, while Pt-tetrahedral with dominant {111} facets is the most active in 0.1 M HClO4 and 0.1 M NaOH electrolytes. The difference in ORR activity is attributed to both the structure-sensitivity of the catalyst and the inhibiting effect of the anions present in the electrolytes. Moreover, the percentage of peroxide generation is 1.5-5% in weakly adsorbing (0.1 M HClO4) electrolytes and 5-12% in strongly adsorbing (0.5 M H2SO4 and 0.1 M NaOH) electrolytes.

In the present work, we have synthesized noble bimetallic nanoparticles (Au–Pd NPs) on a carbon-based support and integrated with titania to obtain Au–Pd/C/TiO2 and Au–Pd/rGO/TiO2 nanocomposites using an ecofriendly hydrothermal method. Here, a 1:1 (w/w) Au–Pd bimetallic composition was dispersed on (a) high-surface-area (3000 m2 g–1) activated carbon (Au–Pd/C), prepared from a locally available plant source (in Assam, India), and (b) reduced graphene oxide (rGO) (Au–Pd/rGO); subsequently, they were integrated with TiO2. The shift observed in Raman spectroscopy demonstrates the electronic integration of the bimetal with titania. The photocatalytic activity of the above materials for the hydrogen evolution reaction was studied under 1 sun conditions using methanol as a sacrificial agent in a powder form. The photocatalysts were also employed to prepare a thin film by the drop-casting method. Au–Pd/rGO/TiO2 exhibits 43 times higher hydrogen (H2) yield in the thin film form (21.50 mmol h–1 g–1) compared to the powder form (0.50 mmol h–1 g–1). On the other hand, Au–Pd/C/TiO2 shows 13 times higher hydrogen (H2) yield in the thin film form (6.42 mmol h–1 g–1) compared to the powder form (0.48 mmol h–1 g–1). While powder forms of both catalysts show comparable activity, the Au–Pd/rGO/TiO2 thin film shows 3.4 times higher activity than that of Au–Pd/C/TiO2. This can be ascribed to (a) an effective separation of photogenerated electron–hole pairs at the interface of Au–Pd/rGO/TiO2 and (b) the better field effect due to plasmon resonance of the bimetal in the thin film form. The catalytic influence of the carbon-based support is highly pronounced due to synergistic binding interaction of bimetallic nanoparticles. Further, a large amount of hydrogen evolution in the film form with both catalysts (Au–Pd/C/TiO2 and Au–Pd/rGO/TiO2) reiterates that charge utilization should be better compared to that in powder catalysts.

The inherent property of palladium to form hydride is effectively exploited for the removal of adsorbed stabilizer and capping agents. Formation of hydride on exposure of Pd nanoparticles to sodium-borohydride weakens the metal's interaction with the adsorbed-impurities and thus enables their easy removal without compromising the shape, size and dispersion.

A series of non‐noble Cu–Ni bimetallic catalysts is prepared with different molar proportions of metals. Of these bimetallic catalysts, 1 wt% is subsequently integrated with titania P25. The catalysts are evaluated for solar hydrogen generation under 1 sun condition in both the powder and thin film forms. All the photocatalysts in the thin film exhibit an 8–24 times higher hydrogen yield (HY) compared with the corresponding particulate counterpart. The highest HY (41.7 mmol h−1 g−1) is demonstrated for the photocatalyst Cu–Ni/TiO2 (CNT; 1:1 = Cu:Ni) in the thin film form, which is 24 times higher than that with its powder counterpart (1.75 mmol h−1 g−1) and exceeds the performance of other Cu–Ni/TiO2 compositions. This enhanced activity in the thin film can be ascribed to improved absorption of visible light and an effective separation of photogenerated charge carriers at the interface of Cu–Ni/TiO2 leading to better charge carrier utilization.

The synthesis of mesoporous TiO 2 by a solution-based assembly process and Ag/TiO 2 nanocomposites is provided. The efficacy of Ag/TiO 2 nanocomposite as photocatalyst in thin-film form is demonstrated for solar hydrogen generation in sunlight. Integration of Ag with TiO 2 dramatically enhanced the H 2 production: with 1 wt% Ag on TiO 2 (TiAg-1), the H 2 yield was observed to be 4.59 mmol h À1 g À1 , which is 2.3 (30) times larger than 0.5 wt% Ag on TiO 2 . TiAg-1 shows 4.3 times higher activity in film form compared with its powder counterpart. High photocatalytic efficiency is attributed to the surface plasmon resonance effect of Ag, electronic integration of Ag with TiO 2 , and subsequent valence band broadening, large distribution of Ag nanoparticles and abundant Ag-TiO 2 Schottky junctions, and the later minimizes electron-hole recombination. Interparticle mesoporous network increases necking and the high surface area offers easy accessibility of the reactants to a large number of active sites.