Efficient Solar Water Splitting with a Composite “n-Si/p-CuI/n-i-p a-Si/n-p GaP/RuO2” Semiconductor Electrode

Yamane, Satoshi; Kato, Naoaki; Kojima, Shinji; Imanishi, Akihito; Ogawa, Sachiko; Yoshida, Norimitsu; Nonomura, Shuichi; Nakato, Yoshihiro

doi:10.1021/jp904297v

Cited by 45 publications

(35 citation statements)

References 56 publications

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“…At the current densities necessary for a PV-EC device, earth-abundant catalysts provide OER overpotentials that range from 0.25 to 0.4 V, corresponding to η ec in the range of 75-85%. Lower overpotentials are possible with non-earth-abundant materials such as RuO 2 (4).…”

Section: Resultsmentioning

confidence: 99%

Modeling integrated photovoltaic–electrochemical devices using steady-state equivalent circuits

Winkler¹,

Cox

Nocera

et al. 2013

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

104

118

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We describe a framework for efficiently coupling the power output of a series-connected string of single-band-gap solar cells to an electrochemical process that produces storable fuels. We identify the fundamental efficiency limitations that arise from using solar cells with a single band gap, an arrangement that describes the use of currently economic solar cell technologies such as Si or CdTe. Steady-state equivalent circuit analysis permits modeling of practical systems. For the water-splitting reaction, modeling defines parameters that enable a solar-to-fuels efficiency exceeding 18% using laboratory GaAs cells and 16% using all earth-abundant components, including commercial Si solar cells and Co-or Ni-based oxygen evolving catalysts. Circuit analysis also provides a predictive tool: given the performance of the separate photovoltaic and electrochemical systems, the behavior of the coupled photovoltaic-electrochemical system can be anticipated. This predictive utility is demonstrated in the case of water oxidation at the surface of a Si solar cell, using a Co-borate catalyst. P owering electrochemical reactions with photovoltaic devices to produce fuels provides an appealing solution to the societal need for clean energy (1). Although the deployment of photovoltaic modules has expanded rapidly over the last decade as costs have dropped (2), utilization of solar power is constrained by its local intermittency, thus providing an imperative for storage by the direct conversion of solar energy to chemical fuels. Photosynthetic organisms directly convert solar energy into chemical fuels by splitting water to produce molecular oxygen and hydrogen equivalents, which are fixed by their combination with carbon dioxide to produce carbohydrates. The technological imitation of photosynthesis-an "artificial leaf"-can be realized by integrating oxygen and hydrogen evolution catalysts to a semiconductor in a buried junction configuration (3). Most buried junction devices have relied on expensive solar cell architectures and/or catalysts (4), including those demonstrating solar-to-fuel efficiencies (SFEs) exceeding 18% (5-7). More economical artificial leaves have been realized with earthabundant catalysts and solar cell materials but at reduced SFE (8, 9). We now seek to provide an analytical framework for the construction of higher SFE architectures comprising earthabundant materials.The efficiency of converting solar energy to stored chemical fuel has been considered (10-13) for a variety of configurations, including the specific treatment of buried junction devices (10). A primary result of these analyses is that singlejunction solar cells are limited in powering water splitting with high SFE because solar cell materials that are well matched to the solar spectrum do not produce sufficient voltages to drive water splitting. Multijunction devices overcome this limitation, enabling high SFE by integrating several materials into a single multijunction device (5-7, 12). Despite their higher limiting SFEs, however, multijun...

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Section: Resultsmentioning

confidence: 99%

Modeling integrated photovoltaic–electrochemical devices using steady-state equivalent circuits

Winkler¹,

Cox

Nocera

et al. 2013

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

104

118

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“…Although highly efficient, high costs are associated with the GaInP 2 ∕GaAs tandem cell and the catalysts and device stability is poor (52). Though less efficient (2.5-8% hydrogen production efficiency), Si-based tandem cell concepts (33,(53)(54)(55)(56) have promise of lower cost. These tandem cells typically consist of a stack of amorphous Si and Si-Ge alloys that are operated in basic electrolyte (pH > 13).…”

Section: Resultsmentioning

confidence: 99%

Light-induced water oxidation at silicon electrodes functionalized with a cobalt oxygen-evolving catalyst

Pijpers

Winkler

Surendranath³

et al. 2011

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

199

194

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Integrating a silicon solar cell with a recently developed cobaltbased water-splitting catalyst (Co-Pi) yields a robust, monolithic, photo-assisted anode for the solar fuels process of water splitting to O 2 at neutral pH. Deposition of the Co-Pi catalyst on the Indium Tin Oxide (ITO)-passivated p-side of a np-Si junction enables the majority of the voltage generated by the solar cell to be utilized for driving the water-splitting reaction. Operation under neutral pH conditions fosters enhanced stability of the anode as compared to operation under alkaline conditions (pH 14) for which long-term stability is much more problematic. This demonstration of a simple, robust construct for photo-assisted water splitting is an important step towards the development of inexpensive direct solar-to-fuel energy conversion technologies.photoelectrochemical | hydrogen | solar energy | storage P hotosynthetic organisms convert the energy of sunlight into chemical energy by splitting water, producing molecular oxygen and hydrogen equivalents in the highly conserved enzyme complex photosystem II (PSII) (1). Absorbed photons are transferred to the reaction center of PSII, where a single electron/hole charge separation occurs. The oxidative power of the photo-produced hole in PSII is transferred to the oxygen evolving complex (OEC) where water splitting occurs. The electron is transferred to the adjacent photosystem I (PSI), where it participates in the reduction reaction of NAD þ into NADH, which is ultimately used to fix CO 2 . Crucial in the above configuration is the separation of the functions of light collection and conversion from catalysis. Whereas light collection/conversion generates electron/ hole pairs one at a time, water splitting is a four-electron/hole process (2, 3). Hence, the multielectron catalysts of PSII and PSI, positioned at the terminus of the photosynthetic charge-separating network, are compulsory so that the one photon-one-electron/ hole "wireless current" can be bridged to the four-electron/hole chemistry of water splitting.An artificial photosynthesis can be designed if the one-electron/hole wireless current of a semiconductor can be integrated directly with catalysts to perform the four-electron-four proton catalysis of water splitting. To this end, an important recent advance has been the creation of a cobalt-phosphate (Co-Pi) catalyst (4, 5) that captures the functional elements of the OEC of PSII (6). As in PSII OEC, the Co-Pi catalyst self-assembles upon oxidation of an earth-abundant metal [Co 2þ for Co-Pi vs. Mn 2þ for OEC (7-9)] in phosphate-buffered solutions at neutral pH (4, 10), exhibits high activity in natural water and sea water at room temperature (11), activates water by proton-coupled electron transfer (3) [as does the OEC of PSII (12, 13)], and is self-healing (14) [as is PSII (15-18)]. Moreover, X-ray Absorption Spectroscopy (XAS) studies (19,20) have established that the Co-Pi catalyst is a structural relative of PSII OEC. PSII OEC is a Mn 3 CaO 4 -Mn cubane (21) where the fourth M...

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“…Single crystaln-Si(100) and p-Si(100) wafers with a thickness of 525 ± 25 µm were purchased from Kyodo International Inc. The n-Si(100) and p-Si(100) wafer surfaces were cleaned by a RCA cleaning method [26]. That is, the successive immersions of the wafers in a boiling mixture of 95% sulfuric acid (H 2 SO 4 ) and 30% hydrogen peroxide (H 2 O 2 ) at a volume ratio of 3:1, in a 5% hydrofluoric acid (HF) solution for 5 min, in a boiling mixture of 25% aqueous ammonium (NH 3 ), 30% H 2 O 2 and distilled water at a volume ratio of 1:1:3 for 15 min, again in the 5% HF solution for 5 min, and in a 40% ammonium fluoride (NH 4 F) solution for 5 min [26].…”

Section: Introductionmentioning

confidence: 99%

“…The n-Si(100) and p-Si(100) wafer surfaces were cleaned by a RCA cleaning method [26]. That is, the successive immersions of the wafers in a boiling mixture of 95% sulfuric acid (H 2 SO 4 ) and 30% hydrogen peroxide (H 2 O 2 ) at a volume ratio of 3:1, in a 5% hydrofluoric acid (HF) solution for 5 min, in a boiling mixture of 25% aqueous ammonium (NH 3 ), 30% H 2 O 2 and distilled water at a volume ratio of 1:1:3 for 15 min, again in the 5% HF solution for 5 min, and in a 40% ammonium fluoride (NH 4 F) solution for 5 min [26]. On the cleaned n-Si(100) or p-Si(100) surface, a WO 3 film was deposited by sputtering a W metal target under oxygen (O 2 , 40 SCCM)/argon (Ar, 60 SCCM) gas mixture and 1.5 Pa for 16 min at substrate temperature of 400˚C, using a radio frequency (RF) magnetron sputtering apparatus (Tokuda, Model CFS-8EP).…”

Section: Introductionmentioning

confidence: 99%

Ohmic Hetero-Junction of n-Type Silicon and Tungsten Trioxide for Visible-Light Sensitive Photocatalyst

Yoshimizu¹,

Hotori²,

Irie³

2017

MSCE

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Visible light-sensitive photocatalyst was developed by combining n-type silicon (n-Si) and tungsten trioxide (WO 3 , n-Si/WO 3 ), yielding an ohmic contact in between. In this system, the ohmic contact acted as an electron-and-hole mediator for the transfer of electrons and holes in the conduction band (CB) of WO 3 and in the valence band (VB) of n-Si, respectively. Utilizing thusconstructed n-Si/WO 3 , the decomposition of 2-propanolto CO 2 via acetone was achieved under visible light irradiation, by the contribution of holes in the VB of WO 3 to decompose 2-propanol and the consumption of electrons in the CB of n-Si to reduce O 2 .

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Efficient Solar Water Splitting with a Composite “n-Si/p-CuI/n-i-p a-Si/n-p GaP/RuO₂” Semiconductor Electrode

Cited by 45 publications

References 56 publications

Modeling integrated photovoltaic–electrochemical devices using steady-state equivalent circuits

Modeling integrated photovoltaic–electrochemical devices using steady-state equivalent circuits

Light-induced water oxidation at silicon electrodes functionalized with a cobalt oxygen-evolving catalyst

Ohmic Hetero-Junction of n-Type Silicon and Tungsten Trioxide for Visible-Light Sensitive Photocatalyst

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