Gold nanoparticle-catalysed photosensitized water reduction for hydrogen generation

Abstract

The use of gold nanoparticles (AuNPs) as a catalyst in photosensitized water reduction for hydrogen generation was investigated using conventional three-component systems. Three photosensitizers, ZnPP, ZnTPP and Eosin Y, were utilized to prepare water splitting solutions containing AuNPs (2 nm or 6 nm in diameter), a redox mediator (Rh(bpy) 3 Cl 3 ), a sacrificial electron donor (TEOA) and an amphiphilic diblock copolymer, PAA 52 -b-P4VP 90 , whose micelles can solubilize the hydrophobic ZnPP or ZnTPP. It was found that AuNPs exhibit good catalytic activity comparable to a Pt catalyst (K 2 PtCl 4 ). Under visible light irradiation at room temperature, hydrogen evolution was observed over the investigated period of time up to 10 hours, with the accumulative amount of the gas being influenced by the size of AuNPs (more efficient with 2 nm AuNPs) and the nature of the photosensitizer (comparable performance with ZnPP and Eosin Y, but lower with ZnTPP). Moreover, absorption and emission spectral changes of ZnPP in the water splitting solution were monitored and analysed; an unidentified species formed at the beginning of irradiation appears to not interfere with the photosensitized hydrogen generation process.This study suggests that AuNPs could be used to replace Pt in catalysing the photosensitized water reduction reaction in widely adopted three-component water splitting systems.

Gold-Decorated Silicon Nanowire Photocatalysts for Intracellular Production of Hydrogen Peroxide

“…However, it is possible that surface-adsorbed oxygen or trapped bubbles could result in residual oxygen present. − Another possible mechanism would be the two-electron oxidation of H 2 O to produce H 2 O 2 ; however, given the lower thermodynamic potential of H 2 O oxidation to produce O 2 , this may be less likely . The coupled reduction reaction undertaken by photogenerated electrons is possibly the two-electron reduction of H 2 O to H 2 facilitated by gold (Figure E). , As sustained H 2 O 2 production is observed (Figure E), regardless of the specific mechanism, both charge carriers likely migrate to the silicon surface for the reaction; if only one charge carrier was removed from the SiNW via reaction with the electrolyte, charge accumulation would quickly inhibit the H 2 O 2 production process. Future studies are still required to understand the mechanism for H 2 O 2 production under our conditions.…”

Exploring Multidimensional Chemical Spaces: Instrumentation and Chemical Systems for the Parallelization of Hydrogen Evolving Photocatalytic Reactions

“…82 While colloid production is highly dependent on reaction conditions, these catalysts have demonstrated remarkably high ability, and Pt is used as the yardstick for other tested systems. Heterogeneous reactions in WRR are typically colloidal dispersions for the sake of enhancing the active surface area 164 and enabling added frequency of collisions through Brownian motion of the colloids. Thus, one needs to utilize nanoparticles (NPs) of the catalyst material.…”

High-Throughput Screening of Earth-Abundant Water Reduction Catalysts toward Photocatalytic Hydrogen Evolution

“…The majority of reported photocatalytic systems utilize noble-metal photosensitizers, commonly made from iridium­(III), rhenium­(I), rhodium­(III), ruthenium­(II), and platinum­(II). − While these typically demonstrate high activity and efficiency, the rarity, expense, and toxicity of noble metals necessitate the search for more sustainable alternatives. Luminescent organic dyes, such as Eosin Y (EY) (Figure a), are significantly cheaper than metal-based phosphors and also exhibit photophysics amenable to both synthetic photochemistry , and water reduction. − Co-catalysts with the highest turnover also contain noble metals, especially colloidal platinum and palladium, but they can also be replaced with earth-abundant alternatives, particularly molecular complexes of cobalt, iron, and nickel. , Specifically, there is a great variety in reported cobalt complexes with ligand derivatives that include 2,2′-bipyridine, glyoxime, dithiolene, macrocycles, and Schiff bases . The facile redox chemistry that allows cobalt to transition between its +3 and +1 oxidation states in single-electron steps enables a variety of potential mechanistic pathways; water is reduced either by monomolecular protonation of cobalt­(III or II) hydride or by a bimolecular pathway, where two cobalt­(III) hydrides react to evolve H 2 (Figure b). − Multiple proposed mechanisms for this catalyst moiety are still debated in the literature. ,− Computational work has also provided support for the particular order of reaction intermediates and shed light on potential rate-limiting steps for electrocatalytic water reduction involving cobalt species. , Cobaloxime complexes that contain two bidentate dimethylglyoximes ( GL1 ) and an axial monodentate ligand (commonly pyridine, py), particularly [Co­( GL1 ) 2 pyCl] and the difluoroborylated derivative [Co­( GL1 BF 2 ) 2 pyCl] (Figure c), are robust water reduction co-catalysts known to evolve hydrogen in combination with noble-metal , and organic dye ,, photosensitizers.…”