The synergetic effect of graphene on Cu<sub>2</sub>O nanowire arrays as a highly efficient hydrogen evolution photocathode in water splitting

Dubale, Amare Aregahegn; Su, Wei‐Nien; Tamirat, Andebet Gedamu; Pan, Chun‐Jern; Aragaw, Belete Asefa; Chen, Hongming; Chen, Ching‐Hsiang; Hwang, Bing‐Joe

doi:10.1039/c4ta03464c

Cited by 272 publications

(164 citation statements)

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“…Cu 2 O thin films are attracting increasing attention as solar-cell materials, [1][2][3][4][5] photocathodes, [6][7][8][9] and photocatalysts [10][11][12] for, for example, water splitting. Among thin-film fabrication methods, electrodeposition from an aqueous solution has advantages over conventional methods, such as chemical vapor deposition, because of its low cost and low environmental burden.…”

mentioning

confidence: 99%

Identification of Copper(II)–Lactate Complexes in Cu₂O Electrodeposition Baths: Deprotonation of the α-Hydroxyl Group in Highly Concentrated Alkaline Solution

Chen

Kitada

Seki

et al. 2018

J. Electrochem. Soc.

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Unveiling dissolved species in electrodeposition baths helps our understanding of electrodeposition behavior, such as growth orientation. A highly concentrated aqueous alkaline copper(II)-lactate solution is used for the electrodeposition of copper(I) oxide (Cu 2 O) thin films with <111> orientations; the semiconductor properties of these films facilitate their use in solar-cell materials, photocathodes, and photocatalysts. However, the dissolved species, presumably copper(II)-lactate complexes, cannot be deduced on the basis of known thermodynamic data, and have not been convincingly determined yet. In this work, we determine these cupric complexes by pH titration, ultraviolet-visible spectroscopy, and electrospray-ionization mass spectrometry (ESI-MS), including probe-ESI-MS (PESI-MS). Using PESI-MS, we successfully analyzed a highly concentrated solution without sample dilution. The determined complexes are Cu(H -1 L)L -and Cu(H -1 L) 2 2-, where the H -1 L 2-(CH 3 CH(O -)COO -) is a lactate ion with a deprotonated α-hydroxyl group. As far as we know, this is the first direct experimental observation of H -1 L 2-ions in a highly concentrated aqueous alkaline copper(II)-lactate solution. We also propose that H -1 L 2-is stabilized by the high concentration and through coordination to copper(II) ions. Cuprous oxide (Cu 2 O) is a p-type semiconductor that is inexpensive and of low toxicity. Cu 2 O thin films are attracting increasing attention as solar-cell materials, 1-5 photocathodes, 6-9 and photocatalysts 10-12 for, for example, water splitting. Among thin-film fabrication methods, electrodeposition from an aqueous solution has advantages over conventional methods, such as chemical vapor deposition, because of its low cost and low environmental burden. Moreover, it is easy to obtain cubic Cu 2 O with the preferential <111> orientation by tuning the pH of the electrodeposition bath;13-17 this orientation relaxes lattice misfit with hexagonal ZnO, which is favorable for Cu 2 O-ZnO solar cells.Since the pioneering work of Rakhshani et al., 13 highly concentrated aqueous alkaline solutions have commonly been used for Cu 2 O electrodeposition;13-16 these solutions contain 0.4 M of a copper(II) salt and 3.0 M lactic acid (HL; CH 3 CH(OH)COOH) as the complexing agent, and the pH is adjusted to be in the 9.0-12.5 range. [13][14][15][16] The crystal orientation of the electrodeposited Cu 2 O is pH dependent; i.e. it is <100> at pH values of 9.0 and 9.5, and <111> at pH values of 12.0 and 12.5. [13][14][15][16][17] The pH dependence of the crystal orientation during Cu 2 O electrodeposition may be ascribable to changes in the dissolved copper(II)-lactate complexes. 6,15,16 Unfortunately, to the best of our knowledge, there are no available thermodynamic data for these copper(II)-lactate complexes under these alkaline conditions, especially for such concentrated solutions. Two previous reports have indicated the presence of dissolved copper(II)-lactate complexes in such concentrated alkaline solutions; Leopold et al. a...

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mentioning

confidence: 99%

Identification of Copper(II)–Lactate Complexes in Cu₂O Electrodeposition Baths: Deprotonation of the α-Hydroxyl Group in Highly Concentrated Alkaline Solution

Chen

Kitada

Seki

et al. 2018

J. Electrochem. Soc.

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“…The stability was analyzed by a chronoamperometry under chopped-light illumination with an applied potential of 0 V vs. RHE (Fig. S4), we can see the photocurrent density decreases from −2.75 to − 0.3 mA·cm −2 quickly during 1000 s. Compared to the results in references [12,13], we think that the interaction of Cu(OH) 2 and carbon source is crucial for stabilizing the unstable Cu 2 O photocathodes.…”

Section: Morphology and Optical Absorption Propertymentioning

confidence: 95%

“…The carbon layer protected Cu 2 O NWAs exhibited a high photocurrent density of −3.95 mA·cm −2 at 0 V vs. RHE, moreover, the thin protective carbon layer can improve the photostability of Cu 2 O NWAs, 87% of the initial photocurrent density had been reserved after 20 min measurement. Similarly, Dubale et al [13] covered Cu(OH) 2 NWAs with graphene, followed by annealing at 500°C in N 2 atmosphere to form graphene/Cu 2 O composite, which provided an improved photocurrent density of −4.8 mA·cm −2 at 0 V vs. RHE, and 83% of the initial photocurrent density was retained after 20 min reaction. However, the prior electrochemical anodization of Cu to Cu(OH) 2 is an energy-consuming, contaminative and comparatively complex process, and the same problems also exist in other preparation …”

Section: Introductionmentioning

confidence: 95%

Thermal conversion synthesis of Cu2O photocathode and the promoting effects of carbon coating

Zhang

Chen

et al. 2015

Catalysis Communications

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“…8 Copper oxide is considered as a promising and attractive material for solar-driven hydrogen production due to its relatively narrow band gap (2.0-2.2 eV), which makes it effective in harvesting visible light, with a sufficiently more negative conduction band, which provides ease of the water reduction reaction within this narrow band gap. 10,11 Copper oxide is attractive as a selective solar absorber, since it has high solar absorbency and a low thermal emittance. 12 Owing to the existence of copper vacancies in the structure, it exhibits native p-type conductivity.…”

Section: Introductionmentioning

confidence: 99%

“…15,16 Copper oxide is cheap, readily available, nontoxic, and environmentally benign and can be produced from inexpensive materials involving a hazardous free manufacturing process. 10 The natural abundance of copper in the earth's crust makes the large-scale fabrication of a copper oxide photoelectrode possible. For these potential applications, copper oxide micro-or nano-wires have been synthesised by various techniques.…”

Section: Introductionmentioning

confidence: 99%

Hydrogen evolution from solar water splitting on nanostructured copper oxide photocathodes

Momeni

Nazari

2016

Materials Research Innovations

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Copper oxide has received much attention as a photocatalyst for solar water splitting, since it has a band gap of ∼2.0 eV with favourable energy band positions for water cleavage; it is abundant and environmentally friendly. In this paper, we report the preparation of copper oxide thin films on copper substrate with different morphology by a solution route in large scales. The method was simple, low cost, and can be completed in the absence of any surfactant. Copper oxide films were characterised by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), Fourier transform-infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). The XRD analysis and FT-IR analysis confirm the formation of copper oxide films. SEM images show gradual development of hierarchical structures of copper oxide with different morphology. The films were successfully tested as photocathodes in a photoelectrochemical cell, and their photocatalytic activity was evaluated by testing the solar water splitting. The photocatalytic activity of these films was found to be size-dependent and films with smaller dimensions demonstrated a significant increase in photocatalytic activities during solar water splitting process. Based on the above discussion, we believe that these samples are attractive candidates as a visible-light-driven photocatalyst.

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The synergetic effect of graphene on Cu₂O nanowire arrays as a highly efficient hydrogen evolution photocathode in water splitting

Abstract: The graphene modified Cu2O nanowire array demonstrates improved photocurrent density and photostability, attributed to the synergetic effect of graphene.

Cited by 272 publications

References 75 publications

Identification of Copper(II)–Lactate Complexes in Cu₂O Electrodeposition Baths: Deprotonation of the α-Hydroxyl Group in Highly Concentrated Alkaline Solution

Identification of Copper(II)–Lactate Complexes in Cu₂O Electrodeposition Baths: Deprotonation of the α-Hydroxyl Group in Highly Concentrated Alkaline Solution

Thermal conversion synthesis of Cu2O photocathode and the promoting effects of carbon coating

Hydrogen evolution from solar water splitting on nanostructured copper oxide photocathodes

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The synergetic effect of graphene on Cu2O nanowire arrays as a highly efficient hydrogen evolution photocathode in water splitting

Abstract: The graphene modified Cu2O nanowire array demonstrates improved photocurrent density and photostability, attributed to the synergetic effect of graphene.

Cited by 272 publications

References 75 publications

Identification of Copper(II)–Lactate Complexes in Cu2O Electrodeposition Baths: Deprotonation of the α-Hydroxyl Group in Highly Concentrated Alkaline Solution

Identification of Copper(II)–Lactate Complexes in Cu2O Electrodeposition Baths: Deprotonation of the α-Hydroxyl Group in Highly Concentrated Alkaline Solution

Thermal conversion synthesis of Cu2O photocathode and the promoting effects of carbon coating

Hydrogen evolution from solar water splitting on nanostructured copper oxide photocathodes

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The synergetic effect of graphene on Cu₂O nanowire arrays as a highly efficient hydrogen evolution photocathode in water splitting

Identification of Copper(II)–Lactate Complexes in Cu₂O Electrodeposition Baths: Deprotonation of the α-Hydroxyl Group in Highly Concentrated Alkaline Solution

Identification of Copper(II)–Lactate Complexes in Cu₂O Electrodeposition Baths: Deprotonation of the α-Hydroxyl Group in Highly Concentrated Alkaline Solution