Photo-assisted water oxidation with cobalt-based catalyst formed from thin-film cobalt metal on silicon photoanodes

Young, Elizabeth R.; Costi, Ronny; Paydavosi, Sarah; Nocera, Daniel G.; Bulović, Vladimir

doi:10.1039/c1ee01209f

Cited by 110 publications

(92 citation statements)

References 18 publications

(24 reference statements)

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“…These catalysts model the oxygen-evolving complex of Photosystem II (14) because they: (i) self-assemble under mild conditions (11)(12)(13)15); (ii) exhibit high activity in pH 7-9 water at room temperature (11,12); (iii) are functional in a variety of water sources (12,15); (iv) are comprised of inexpensive, terrestrially abundant materials (11,12); and (v) self-heal by reversing catalyst corrosion at open circuit upon application of a potential (16,17). Their ability to be interfaced easily with light-absorbing and charge-separating materials (18)(19)(20)(21)(22)(23)(24) has permitted the construction of a buried junction PEC device (25,26). In the wireless configuration, the buried junction device captures many of the functional elements of the water-splitting chemistry of a leaf (27,28).…”

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confidence: 99%

Interplay of oxygen-evolution kinetics and photovoltaic power curves on the construction of artificial leaves

Surendranath

Bediako

Nocera

2012

Proc. Natl. Acad. Sci. U.S.A.

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An artificial leaf can perform direct solar-to-fuels conversion. The construction of an efficient artificial leaf or other photovoltaic (PV)-photoelectrochemical device requires that the power curve of the PV material and load curve of water splitting, composed of the catalyst Tafel behavior and cell resistances, be well-matched near the thermodynamic potential for water splitting. For such a condition, we show here that the current density-voltage characteristic of the catalyst is a key determinant of the solar-to-fuels efficiency (SFE). Oxidic Co and Ni borate (Co-B i and Ni-B i ) thin films electrodeposited from solution yield oxygen-evolving catalysts with Tafel slopes of 52 mV∕decade and 30 mV∕decade, respectively. The consequence of the disparate Tafel behavior on the SFE is modeled using the idealized behavior of a triple-junction Si PV cell. For PV cells exhibiting similar solar power-conversion efficiencies, those displaying low open circuit voltages are better matched to catalysts with low Tafel slopes and high exchange current densities. In contrast, PV cells possessing high open circuit voltages are largely insensitive to the catalyst's current density-voltage characteristics but sacrifice overall SFE because of less efficient utilization of the solar spectrum. The analysis presented herein highlights the importance of matching the electrochemical load of water-splitting to the onset of maximum current of the PV component, drawing a clear link between the kinetic profile of the water-splitting catalyst and the SFE efficiency of devices such as the artificial leaf.energy storage | solar energy | solar fuel | buried junction W ater splitting is the central chemistry that underlies the storage of solar energy in the form of chemical fuels because it delivers hydrogen from a renewable source (1-3). Direct solarto-fuels conversion can be achieved by interfacing suitable catalysts that carry out two separate half-reactions of water splittingthe four electron-four proton oxidation of water to O 2 and the two electron two-proton reduction of the produced protons to H 2 -to a photovoltaic (PV) material. Numerous device configurations have been proposed for photoelectrochemical (PEC) water splitting (4-10), and they can be broadly categorized into those devices wherein the photovoltaic material makes a rectifying junction with solution as opposed to those in which the rectifying junctions are protected from solution or "buried." Fig. 1 schematically depicts the latter with a double-junction configuration of absorber materials with progressively larger band gaps that are connected in series using thin-film ohmic contacts to generate open circuit voltages (V oc ) that are large enough to drive water splitting. Thin-film ohmic contacts at the termini of this stack serve both to protect the semiconductor from the chemistries occurring in solution and to enable efficient charge transfer to catalyst overlayers, which execute the oxygen-evolution reaction (OER) and hydrogen-evolution reaction (HER). Whereas waterspli...

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confidence: 99%

Interplay of oxygen-evolution kinetics and photovoltaic power curves on the construction of artificial leaves

Surendranath

Bediako

Nocera

2012

Proc. Natl. Acad. Sci. U.S.A.

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“…[15][16][17][18][19][20][21] In this reaction, the primary role of CoPi is to facilitate the photogenerated hole transfers via an intervalency cycle of Co(II), Co(III), and Co(IV). However, the electrodeposition grows the CoPi very rapidly, forming a thick layer that fully covers the underlying semiconductor particles.…”

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confidence: 99%

Photoelectrochemical Water Oxidation Using ZnO Nanorods Coupled with Cobalt-Based Catalysts

Jeon¹,

Choi²,

Jeong³

et al. 2011

Journal of Electrochemical Science and Technology

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Photoelectrochemical performances of ZnO electrodes are enhanced by coupling with cobalt-based catalyst (CoPi) in phosphate electrolyte (pH 7). For this study, hexagonal pillar-shaped ZnO nanorods are grown on ZnO electrodes through a chemical bath deposition, onto which CoPi is deposited with different photodeposition times (10-30 min). A scanning electron microscopic study indicates that CoPi deposition does not induce any change of ZnO morphology and an energy-dispersive X-ray spectroscopic analysis shows that inorganic phosphate ions (Pi) exist on ZnO surface. Bare ZnO electrodes generate the current of ca. 0.36 mA/cm 2 at a bias potential of 0.5 V vs. SCE, whereas ZnO/CoPi (deposited for 10 min) has ca. 50%-enhanced current (0.54 mW/cm 2 ) under irradiation of AM 1.5G-light (400 mW/cm 2 ). The excess loading of CoPi on ZnO results in decrease of photocurrents as compared to bare ZnO likely due to limited electrolyte access to ZnO and/or CoPi-mediated recombination of photogenerated charge carriers. The primary role of CoPi is speculated to trap the photogenerated holes and thereby oxidize water into molecular oxygen via an intervalency cycle among Co(II), Co(III), and Co(IV).

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“…Recently, cobalt(II)-phosphate complexes (Co-Pi) have been demonstrated to work effectively as OEC in photoelectrolysis when coupled to ZnO [45] , hematite [46 -48] , WO 3 [49] , BiVO 4 [50 -52] , and Si electrodes [53,54] . In all cases, Co-Pi deposition onto the photoanode surface yielded large cathodic shifts of the onset potentials or enhanced performances for water oxidation.…”

Section: Oxygen Evolution Catalyst (Oec) Loadingmentioning

confidence: 99%

Nanostructure designs for effective solar-to-hydrogen conversion

Shen

Mao

2012

Nanophotonics

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Conversion of energy from photons in sunlight to hydrogen through solar splitting of water is an important technology. The rising signifi cance of producing hydrogen from solar light via water splitting has motivated a surge of developing semiconductor solar-active nanostructures as photocatalysts and photoelectrodes. Traditional strategies have been developed to enhance solar light absorption (e.g., ion doping, solid solution, narrow-band-gap semiconductor or dye sensitization) and improve charge separation/transport to prompt surface reaction kinetics (e.g., semiconductor combination, co-catalyst loading, nanostructure design) for better utilizing solar energy. However, the solar-to-hydrogen effi ciency is still limited. This article provides an overview of recently demonstrated novel concepts of nanostructure designs for efficient solar hydrogen conversion, which include surface engineering, novel nanostructured heterojunctions, and photonic crystals. Those fi rst results outlined in the main text encouragingly point out the prominence and promise of these new concepts principled for designing high-effi ciency electronic and photonic nanostructures that could serve for sustainable solar hydrogen production.

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Photo-assisted water oxidation with cobalt-based catalyst formed from thin-film cobalt metal on silicon photoanodes

Cited by 110 publications

References 18 publications

Interplay of oxygen-evolution kinetics and photovoltaic power curves on the construction of artificial leaves

Interplay of oxygen-evolution kinetics and photovoltaic power curves on the construction of artificial leaves

Photoelectrochemical Water Oxidation Using ZnO Nanorods Coupled with Cobalt-Based Catalysts

Nanostructure designs for effective solar-to-hydrogen conversion

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