Correction to Solar Water Splitting Cells

Walter, Michael G.; Warren, Emily L.; McKone, James R.; Boettcher, Shannon W.; Mi, Qixi; Santori, Elizabeth A.; Lewis, Nathan S.

doi:10.1021/cr200102n

Cited by 69 publications

(55 citation statements)

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“…Tungsten oxide possesses a bandgap at around 2.6 eV, has valence band maximum (VBM) edge (vs NHE) sufficiently positive to oxidize H 2 O producing intermediate hydroxyl (·OH) radicals, however, the conduction band minimum (CBM) edge (vs NHE) is insufficiently negative to reduce O 2 to superoxide (O 2 ·) and/or hydroperoxy (HO 2 ·) radicals. This results in low photocatalytic activity for degradation of organic pollutants by oxidation with radicals …”

Section: Introductionmentioning

confidence: 99%

Correlation of Optical Properties, Electronic Structure, and Photocatalytic Activity in Nanostructured Tungsten Oxide

Ling

Blackman

Palgrave

et al. 2017

Adv Materials Inter

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cause a negative effect on the photocatalytic activity by acting as charge-recombination centers. [9] Therefore, controlling the level of V O plays an important role in defect engineering. The amount of V O in tungsten oxide was recently reported to be controlled through air-annealing at various temperatures (300-600 °C) and times (0.5-8 h), giving improvements in photocatalytic activity and electrochemical performance. [11] Recently, we have investigated the growth and properties of chemical vapor deposited (CVD) nanostructured tungsten oxide. [12] The appearance of defects in the direction perpendicular to NR growth was the driving force for formation of the 1D structure via a planar-defect-driven growth mechanism. [13] Herein, we study the growth of tungsten oxide nanorod (NR) array thin films, their 1D nanostructure growth mechanism and the variable concentration of V O , and their influence on the photocatalytic properties of the deposited nanomaterial. We find that as the NR grow, the cross-section increases due to the coalescence of adjacent NRs and a change in the V O concentration is observed. Hence, the V O concentration in 1D tungsten oxide deposited via aerosol assisted chemical vapor deposition (AACVD) is a function of the deposition time. The photocatalytic activity Tungsten trioxide nanorod arrays are deposited using aerosol assisted chemical vapor deposition. The electronic structure, defect chemistry, optical bandgap, and photocatalytic activity are found to vary progressively with nanorod length. Nanorods less than 1 µm in length show a widening of the optical bandgap (up to 3.1 eV), more disorder states within the bandgap, an absence of reduced tungsten cation states, and increased photocatalytic activity for destruction of a test organic pollutant (stearic acid) compared to nanorods of 2 µm length or greater which possessed bandgaps close to the bulk value for tungsten oxide (2.6-2.8 eV), the presence of reduced tungsten states (W 4+ ), and lower photocatalytic activity. The results indicate that for maximum photocatalytic performance in organic pollutant degradation, tungsten oxide should be engineered such that the bandgap is widened relative to bulk WO 3 to a value above 3 eV; although less photons are expected be absorbed, increases in the overpotential for oxidation reactions appear to more than offset this loss. It is also desirable to ensure the material remains defect free, or the defect concentration minimized, to minimize carrier recombination.

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Section: Introductionmentioning

confidence: 99%

Correlation of Optical Properties, Electronic Structure, and Photocatalytic Activity in Nanostructured Tungsten Oxide

Ling

Blackman

Palgrave

et al. 2017

Adv Materials Inter

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“…These formulations, as previously described by Liu et al, 15 contained block copolymer structure directing agents, which have been developed in conjunction with a drying/precipitation and calcination protocol to yield porous metal oxide thin-film samples. Briefly, each Fe-Co-Ni-Ti composition in the library was synthesized by combining four "inks", each with an elemental precursor (FeCl 3 20 , MW = 5800; Sigma Aldrich) was dissolved into 45 mL ethanol. The ink formulation and physicochemical properties have been detailed in.…”

Section: Methodsmentioning

confidence: 99%

“…1,2 The widespread deployment of this technology requires a device fabricated with high-performance, robust materials made from earth-abundant elements. 3 The realization of this device relies on the discovery of new materials, prompting an aggressive high-throughput materials discovery effort within the Joint Center for Artificial Photosynthesis (JCAP, http://solarfuelshub.org/). This effort includes searches for new photoanodes, photocathodes, and catalysts for several solar fuels reactions, of which the oxygen evolution catalyst is discussed in this manuscript.…”

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confidence: 99%

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Combined Catalysis and Optical Screening for High Throughput Discovery of Solar Fuels Catalysts

Gregoire

Xiang

Mitrović

et al. 2013

J. Electrochem. Soc.

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Considerable research and development efforts are being devoted to the efficient generation of solar fuels. A solar fuels device couples a solar photoabsorber with catalysts to convert solar energy to chemical energy via reactions such as oxygen evolution (water splitting). Widespread deployment of this technology hinges upon discovery of new materials through efforts such as the high throughput screening of oxygen evolution catalysts, as discussed in this manuscript. We derive an expression for the efficiency of the oxygen evolution catalyst that combines catalytic and optical properties. Using this hybrid efficiency, we screen 5456 samples in a (Fe-Co-Ni-Ti)O x pseudo-quaternary catalyst library using automated, high throughput electrochemical and optical experiments. The observed compositional trends in this catalyst efficiency lead to the discovery of a new high performance composition region. 1,2 The widespread deployment of this technology requires a device fabricated with high-performance, robust materials made from earth-abundant elements. 3 The realization of this device relies on the discovery of new materials, prompting an aggressive high-throughput materials discovery effort within the Joint Center for Artificial Photosynthesis (JCAP, http://solarfuelshub.org/). This effort includes searches for new photoanodes, photocathodes, and catalysts for several solar fuels reactions, of which the oxygen evolution catalyst is discussed in this manuscript.One established solar fuel generator concept combines a solar photoabsorber with an optically inactive heterogeneous catalyst to evolve oxygen (water splitting). 3,4 That is, the oxygen evolution reaction (OER) is mediated by a "dark" catalyst that is coupled to a photoabsorber, which provides the required potential and current for the electrocatalytic reaction through the photovoltaic effect. This anodic reaction balances a fuel-producing cathodic reaction such as hydrogen evolution or CO 2 reduction. Variations within this solar fuel design concept include the use of a tandem absorber containing a coupled photoanode and photocathode instead of a single photoabsorber [5][6][7] or the use of a homogeneous OER catalyst instead of the heterogeneous catalyst. 3,[8][9][10][11] Homogeneous catalysts are not considered in this manuscript, and the general discussion of optimizing the OER catalyst is applicable to any photoabsorber device. Our primary assumptions concerning device architecture are that the OER catalyst coats the photoanode and this anode is exposed to solar illumination. These assumptions are based upon a tandem photoabsorber system in which the photoanode is the top cell and has a larger bandgap than the photocathode.While heterogeneous catalysts are used in a variety of technologies, the OER catalyst in this solar application has a special optical performance requirement. Since the solar radiation impinges the catalyst before reaching the photoabsorber, the catalyst layer must be sufficiently transparent. Since the optical properties of the electroc...

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“…[203][204][205][206] A schematic showing a typical electrochemical, three electrode setup is shown in Figure 3.11. In the case of the majority of electrochemical analysis presented in these experiments, a 3 mm diameter (.070686 cmshell/core nanowires (discussed in Chapters 6 and 7), the nanowires were synthesized and subsequently chemically modified on stainless steel substrates.…”

Section: Electrochemical and Electrocatalytic Characterizationmentioning

confidence: 99%

Phase transformation studies of metal oxides to dichalcogenides in 1-d structures.

Cummins¹,

Ray²

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Recently, the use of materials with nanoscale morphologies has expanded, particularly with applications in energy conversion, catalysis, and energy storage. One drawback to single crystalline nanomaterials, especially 1D nanowires, is the difficulty in synthesizing these compounds, as the material chemistry becomes more complicated.Metal oxide nanowires can be synthesized easily and can be produced in relatively large quantities. However, more complex materials, such as metal chalcogenides, cannot typically be synthesized using facile methods, and currently very few techniques involve scalable methods. Phase transformation of metal oxides nanowires to form metal sulfides and selenides by gas-solid reactions is one viable route to scalable chalcogenide production. However, the transformation of 1D materials from oxides to other compositions using gas-solid reactions has not been well studied and the underlying mechanisms involved with phase transformation are minimally understood. A fundamental understanding of how gas phase reactants interact with nanomaterials is critical to not only making new materials on the nanoscale, but also allowing the engineering and optimization of nanomorphologies for functional applications.v Iron sulfide and molybdenum sulfide nanowires are chosen as the two model materials to investigate crystal phase transformations in 1D systems.In reaction of Fe2O3 single crystal nanowires with H2S gas to form FeS, the formation of a hollow nanotube morphology is observed, caused by unequal diffusion of the cation and anion, resulting in the accumulation of voids. These findings suggest that the reactant (sulfur) does not diffuse into the nanostructure; rather, iron atoms diffuse outward and react on the surface. The resulting FeS compound also has interesting optical absorption properties that could be of use in solar applications.The conversion of MoO3 nanowires in an attempt to form MoS2 nanowires resulted in a MoS2/MoOx shell/core nanowire morphology, with strong diffusion limits in formation of the sulfide shell. In this case, the sulfur diffusion through the MoS2 shell limits the reaction, leading to core-shell morphology.The MoS2/MoOx shell/core architecture shows considerable activity for electrocatalysis of the hydrogen evolution reaction due to the high surface area architecture for edge plane sites. Chemical intercalation of the MoS2 shell shows a further change in the crystal morphology and an improvement in catalytic activity. Reducing agents (hydrazine) are also investigated in attempts to chemically modify the MoS2 surface, changing the surface charge carrier concentrations. This is the first report of the effect of hydrazine in any chalcogenide system and the hydrazine treated MoS2 nanowire architecture shows one of the best electrocatalytic performance to date. The chemical modifications of MoS2 1D structures suggest the electrocatalytic activity can be tuned and corresponding architectures could be synthesized through phase transformation by design. These experiments help to d...

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Correction to Solar Water Splitting Cells

Cited by 69 publications

References 0 publications

Correlation of Optical Properties, Electronic Structure, and Photocatalytic Activity in Nanostructured Tungsten Oxide

Correlation of Optical Properties, Electronic Structure, and Photocatalytic Activity in Nanostructured Tungsten Oxide

Combined Catalysis and Optical Screening for High Throughput Discovery of Solar Fuels Catalysts

Phase transformation studies of metal oxides to dichalcogenides in 1-d structures.

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