Visible photoelectrochemical water splitting into H ₂ and O ₂ in a dye-sensitized photoelectrosynthesis cell

Abstract

A hybrid strategy for solar water splitting is exploited here based on a dye-sensitized photoelectrosynthesis cell (DSPEC) with a mesoporous SnO 2 /TiO 2 core/shell nanostructured electrode derivatized with a surface-bound Ru(II) polypyridyl-based chromophore-catalyst assembly. The assembly, [(4, H 2 ) 2 bpy) 2 Ru(4-Mebpy-4'-bimpy)Ru (tpy) (OH 2 dye-sensitized photoelectrosynthesis cell | water oxidation | core/shell A lthough promising, significant challenges remain in the search for successful strategies for artificial photosynthesis by water splitting into oxygen and hydrogen or reduction of CO 2 to reduced forms of carbon (1-5). In a dye-sensitized photoelectrosynthesis cell (DSPEC), a wide band gap, nanoparticle oxide film, typically TiO 2 , is derivatized with a surface-bound molecular assembly or assemblies for light absorption and catalysis (6-8). In a DSPEC, visible light is absorbed by a chromophore, initiating a series of events that culminate in water splitting: injection, intraassembly electron transfer, catalyst activation, and electron transfer to a cathode or photocathode for H 2 production. Sun and coworkers have recently demonstrated visible-light-driven water splitting with a coloading approach combining Ru(II) polypyridyl-based light absorbers and catalysts on TiO 2 (9). The efficiency of DSPEC devices is dependent on interfacial dynamics and competing kinetic processes. A major limiting factor is the requirement for accumulating multiple oxidative equivalents at a catalyst site to meet the 4e − /4H + demands for oxidizing water to dioxygen (2H 2 O -4e − -4H + → O 2 ) in competition with back electron transfer of injected electrons to the oxidized assembly.One approach to achieving structural control of local electron transfer dynamics at the oxide interface in dye-sensitized devices is by use of nanostructured core/shell electrodes (10-12). In this approach, a mesoporous network of nanoparticles is uniformly coated with a thin oxide overlayer prepared by atomic layer deposition (ALD). We have used core/shell electrodes to demonstrate benzyl alcohol dehydrogenation (13). This approach has also been used to enhance the efficiency of dye-sensitized solar cells (14,15). Recently, we described the use of a core/shell consisting of an inner core of a nanoparticle transparent conducting oxide, tin-doped indium oxide (nanoITO), and a thin outer shell of TiO 2 for water splitting by visible light (16 Fig. 1A, provided the basis for a photoanode in a DSPEC application with a Pt cathode for H 2 generation with a small applied bias in an acetate buffer at pH 4.6.Application of the core/shell structure led to a greatly enhanced efficiency for water splitting compared with mesoscopic, nanoparticle TiO 2 but the per-photon absorbed efficiency of the resulting DSPEC was relatively low and problems arose from longterm instability due to loss of the assembly from the oxide surface in the acetate buffer at pH 4.6. The latter is problematic because the rate of water oxidation is enhanced by added buffer bases...

Solar photothermochemical alkane reverse combustion

“…At low P H2O , the SPARC reaction may be starved for hydride equivalents, leading to incomplete reduction of the CO 2 . Surprisingly, a number of FTS studies have shown that deliberate addition of water to the feed can be beneficial in terms of shifting the selectivity toward C 5 + products (14)(15)(16)(17), which indicates that the presence of water, in itself, is not detrimental to the hydrocarbon-chain-forming process. It is not yet clear how the selectivity of the SPARC reaction can be tuned toward lessoxygenated products, but the feedstock ratio is likely to be one key factor.…”

“…Hydrogen, carbon monoxide, C 1 hydrocarbons, and syngas are the most commonly produced fuels and are derived from water or water and CO 2 (6,16,17). Hydrogen produced via the water-splitting reaction (WSR, reaction 1) is arguably the easiest to produce and stores the most energy on a mass basis (kJ/kg); however, it is not a particularly attractive replacement fuel for transportation, due to technological issues with low-volume energy density, safe storage, and transportation (18).…”

Dye-Sensitized Photocatalytic Water Splitting and Sacrificial Hydrogen Generation: Current Status and Future Prospects

“…The electrode was prepared with a surface-bound Ru(II) polypyridal-based chromophorephotocatalyst assembly having both a light absorber and water oxidation photocatalyst ( Figure 11) [40]. The chromophore-photocatalyst assembly was stabilized on TiO2 surface via atomic layer deposition of Al2O3 or TiO2 to provide long-term water splitting ability even at pH 7 (in phosphate buffer).…”

“…Alibabaei et al [40] developed a dye-sensitized photo electrosynthesis cell (DSPEC) for solar water splitting utilizing a mesoporous SnO2/TiO2 core/shell nanostructured electrode for solar water splitting. The electrode was prepared with a surface-bound Ru(II) polypyridal-based chromophorephotocatalyst assembly having both a light absorber and water oxidation photocatalyst ( Figure 11) [40].…”

“…Cartoon is representing an atomic layer deposition (ALD) core/shell electrode surface with ALD overlayer stabilization of a surface-bound assembly. Reproduced with permission from [40]. Copyright National Academy of Sciences, 2015.…”