| 1. |
- Jian, Jingxin, et al.
(author)
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A nanostructured NiO/cubic SiC p-n heterojunction photoanode for enhanced solar water splitting
- 2019
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In: Journal of Materials Chemistry A. - : ROYAL SOC CHEMISTRY. - 2050-7488 .- 2050-7496. ; 7:9, s. 4721-4728
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Journal article (peer-reviewed)abstract
- Photoelectrochemical (PEC) water-splitting offers a promising method to convert the intermittent solar energy into renewable and storable chemical energy. However, the most studied semiconductors generally exhibit a poor PEC performance including low photocurrent, small photovoltage, and/or large onset potential. In this work, we demonstrate a significant enhancement of photovoltage and photocurrent together with a substantial decrease of onset potential by introducing electrocatalytic and p-type NiO nanoclusters on an n-type cubic silicon carbide (3C-SiC) photoanode. Under AM1.5G 100 mW cm(-2) illumination, the NiO-coated 3C-SiC photoanode exhibits a photocurrent density of 1.01 mA cm(-2) at 0.55 V versus reversible hydrogen electrode (V-RHE), a very low onset potential of 0.20 V-RHE and a high fill factor of 57% for PEC water splitting. Moreover, the 3C-SiC/NiO photoanode shows a high photovoltage of 1.0 V, which is the highest value among reported photovoltages. The faradaic efficiency measurements demonstrate that NiO also protects the 3C-SiC surface against photo-corrosion. The impedance measurements evidence that the 3C-SiC/NiO photoanode facilitates the charge transfer for water oxidation. The valence-band position measurements confirm the formation of the 3C-SiC/NiO p-n heterojunction, which promotes the separation of the photogenerated carriers and reduces carrier recombination, thus resulting in enhanced solar water-splitting.
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| 2. |
- Jian, Jingxin, et al.
(author)
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A Review of Recent Progress on Silicon Carbide for Photoelectrochemical Water Splitting
- 2020
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In: Solar RRL. - : WILEY-V C H VERLAG GMBH. - 2367-198X. ; 4:7
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Research review (peer-reviewed)abstract
- Solar water splitting based on semiconductor photoelectrodes is a promising route to convert solar energy into renewable hydrogen fuel. Since the pioneering work of photoelectrochemical (PEC) systems in 1972, a large variety of semiconductors such as oxides, sulfides, phosphides, and silicon have been studied in the context of PEC water splitting configuration. Among them, silicon carbide (SiC) exhibits an excellent energy band structure that straddles the water redox potentials. In particular, cubic SiC (3C-SiC), with a suitable bandgap of 2.36 eV, is favorable for visible sunlight absorption. Recently, 3C-SiC has attracted much interest in PEC water splitting. In this review, the progress, challenges, and prospects of using SiC for PEC water splitting are summarized.
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| 3. |
- Jian, Jingxin, et al.
(author)
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Cu2O/ZnO p-n Junction Decorated with NiOx as a Protective Layer and Cocatalyst for Enhanced Photoelectrochemical Water Splitting
- 2020
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In: ACS Applied Energy Materials. - : AMER CHEMICAL SOC. - 2574-0962. ; 3:11, s. 10408-10414
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Journal article (peer-reviewed)abstract
- Cuprous oxide (Cu2O) has attracted much interest as a photocathode for photoelectrochemical (PEC) water splitting because of its elemental abundance and the favorable band gap, but its poor stability in aqueous solutions hinders the practical PEC application. Compared to the mostly used TiO2 and noble metal cocatalysts for coating the Cu2O photocathode, this work demonstrates a strategy to fabricate a noble metal-free photocathode. We construct a Cu2O/ZnO p-n junction photocathode decorated with the NiOx layer as both the protective layer and the hydrogen evolution reaction (HER) cocatalyst. The NiOx cocatalyst exhibits a small Tafel slope of 35.9 mV/dec and a very low overpotential of 115 mV to drive a current of 10 mA/cm(2), which are very close to the HER activity of the noble metal platinum. With decorated NiOx the Cu2O/ZnO/NiOx photocathode exhibits significantly improved stability and photocurrent density with a Faradaic efficiency of H-2 gas evolution of 95 +/- 4%, distinctly outperforming the Cu2O, Cu2O/ZnO, and Cu2O/ZnO/TiO2 photocathodes. Moreover, electrochemical impedance analysis evidenced that NiOx as a cocatalyst also facilitates the transfer of photogenerated electrons across the electrode/electrolyte interface for water reduction. This work demonstrates that NiOx is not only a stable protective layer against corrosion but also a highly active H-2 evolution cocatalyst. These findings provide new insights for the design of noble metal-free photocathodes toward solar fuel development.
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| 4. |
- Jian, Jingxin, et al.
(author)
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Cubic SiC Photoanode Coupling with Ni:FeOOH Oxygen-Evolution Cocatalyst for Sustainable Photoelectrochemical Water Oxidation
- 2020
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In: Solar RRL. - : WILEY-V C H VERLAG GMBH. - 2367-198X. ; 4:1
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Journal article (peer-reviewed)abstract
- As an efficient water oxidation cocatalyst, the Earth-abundant nickel-iron oxyhydroxide (Ni:FeOOH) is introduced to coat on the cubic silicon carbide (3C-SiC) photoanode surface for improving the photoelectrochemical (PEC) water oxidation performance. The FeOOH is prepared on the 3C-SiC photoanode surface by hydrothermal deposition, followed by a photoassisted electrodeposition of NiOOH. It is shown that the Ni:FeOOH layer is composed of the beta-FeOOH nanorods with a conformal coating of the amorphous NiOOH. Under AM1.5G 100 mW cm(-2) illumination, the 3C-SiC/Ni:FeOOH photoanode exhibits a very low onset potential of 0.2 V versus reversible hydrogen electrode (V-RHE) and a high photocurrent density of 1.15 mA cm(-2) at 1.23 V-RHE, distinctly outperforming the 3C-SiC and the 3C-SiC/FeOOH counterparts. Open-circuit potential and impedance spectroscopy results demonstrate that the nanostructured Ni:FeOOH layer on the 3C-SiC surface increases the photovoltage and promotes the charge transfer toward the electrolyte, thus significantly improving the PEC water-splitting performance. These results provide new insights for the development of photoanodes toward efficient solar-fuel generation.
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| 5. |
- Jian, Jingxin, et al.
(author)
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Interface-Engineered Ni-Coated CdTe Heterojunction Photocathode for Enhanced Photoelectrochemical Hydrogen Evolution
- 2023
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In: ACS Applied Materials and Interfaces. - : AMER CHEMICAL SOC. - 1944-8244 .- 1944-8252. ; 15:17, s. 21057-21065
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Journal article (peer-reviewed)abstract
- Photoelectrochemical (PEC) water splitting for hydrogen production using the CdTe photocathode has attracted much interest due to its excellent sunlight absorption property and energy band structure. This work presents a study of engineered interfacial energetics of CdTe photocathodes by deposition of CdS, TiO2, and Ni layers. A heterostructure CdTe/CdS/TiO2/Ni photocathode was fabricated by depositing a 100-nm n-type CdS layer on a p-type CdTe surface, with 50 nm TiO2 as a protective layer and a 10 nm Ni layer as a co-catalyst. The CdTe/CdS/TiO2/ Ni photocathode exhibits a high photocurrent density (Jph) of 8.16 mA/cm2 at 0 V versus reversible hydrogen electrode (VRHE) and a positive-shifted onset potential (Eonset) of 0.70 VRHE for PEC hydrogen evolution under 100 mW/cm2 AM1.5G illumination. We further demonstrate that the CdTe/CdS p-n junction promotes the separation of photogenerated carriers, the TiO2 layer protects the electrode from corrosion, and the Ni catalyst improves the charge transfer across the electrode/electrolyte interface. This work provides new insights for designing noble metal-free photocathodes toward solar hydrogen development.
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| 6. |
- Jian, Jingxin, et al.
(author)
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Nanoporous Cubic Silicon Carbide Photoanodes for Enhanced Solar Water Splitting
- 2021
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In: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 15:3, s. 5502-5512
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Journal article (peer-reviewed)abstract
- Cubic silicon carbide (3C-SiC) is a promising photoelectrode material for solar water splitting due to its relatively small band gap (2.36 eV) and its ideal energy band positions that straddle the water redox potentials. However, despite various coupled oxygen-evolution-reaction (OER) cocatalysts, it commonly exhibits a much smaller photocurrent (<similar to 1 mA cm(-2)) than the expected value (8 mA cm(-2)) from its band gap under AM1.5G 100 mW cm(-2) illumination. Here, we show that a short carrier diffusion length with respect to the large light penetration depth in 3C-SiC significantly limits the charge separation, thus resulting in a small photocurrent. To overcome this drawback, this work demonstrates a facile anodization method to fabricate nanoporous 3C-SiC photoanodes coupled with Ni:FeOOH cocatalyst that evidently improve the solar water splitting performance. The optimized nanoporous 3C-SiC shows a high photocurrent density of 2.30 mA cm(-2) at 1.23 V versus reversible hydrogen electrode (V-RHE) under AM1.5G 100 mW cm(-2) illumination, which is 3.3 times higher than that of its planar counterpart (0.69 mA cm(-2) at 1.23 V-RHE). We further demonstrate that the optimized nanoporous photoanode exhibits an enhanced light-harvesting efficiency (LHE) of over 93%, a high charge-separation efficiency (Phi(sep)) of 38%, and a high charge-injection efficiency (Phi(ox)) of 91% for water oxidation at 1.23 V-RHE, which are significantly outperforming those its planar counterpart (LHE = 78%, Phi(sep) = 28%, and Phi(ox) = 53% at 1.23 V-RHE). All of these properties of nanoporous 3C-SiC enable a synergetic enhancement of solar water splitting performance. This work also brings insights into the design of other indirect band gap semiconductors for solar energy conversion.
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| 7. |
- Li, Baoying, et al.
(author)
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Nanoporous 6H-SiC Photoanodes with a Conformal Coating of Ni-FeOOH Nanorods for Zero-Onset-Potential Water Splitting
- 2020
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In: ACS Applied Materials and Interfaces. - : AMER CHEMICAL SOC. - 1944-8244 .- 1944-8252. ; 12:6, s. 7038-7046
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Journal article (peer-reviewed)abstract
- A surface-nanostructured semiconductor photoelectrode is highly desirable for photo-electrochemical (PEC) solar-to-fuel production due to its large active surface area, efficient light absorption, and significantly reduced distance for charge transport. Here, we demonstrate a facile approach to fabricate a nanoporous 6H-silicon carbide (6H-SiC) photoanode with a conformal coating of Ni-FeOOH nanorods as a water oxidation cocatalyst. Such a nanoporous photoanode shows significantly enhanced photocurrent density (j(ph)) with a zero-onset potential. A dendritic porous 6H-SiC with densely arranged holes with a size of similar to 40 nm on the surface is fabricated by an anodization method, followed by the hydrothermal deposition of FeOOH nanorods and electrodeposition of NiOOH. Under an illumination of AM1.5G 100 mW/cm(2), the Ni-FeOOH-coated nanoporous 6H-SiC photoanode exhibits an onset potential of 0 V versus the reversible hydrogen electrode (V-RHE) and a high j(ph) of 0.684 mA/cm(2) at 1 V-RHE, which is 342 times higher than that of the Ni-FeOOH-coated planar 6H-SiC photoanode. Moreover, the nanoporous photoanode shows a maximum applied-bias-photon-to-current efficiency (ABPE) of 0.58% at a very low bias of 0.36 V-RHE, distinctly outperforming the planar counterpart. The impedance measurements demonstrate that the nanoporous photoanode possesses a significantly reduced charge-transfer resistance, which explains the dramatically enhanced PEC water-splitting performance. The reported approach here can be widely used to fabricate other nanoporous semiconductors for solar energy conversion.
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| 8. |
- Shtepliuk, Ivan, et al.
(author)
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Silver nanoparticle array on weakly interacting epitaxial graphene substrate as catalyst for hydrogen evolution reaction under neutral conditions
- 2021
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 119:15
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Journal article (peer-reviewed)abstract
- The paucity of research on hydrogen evolution reaction (HER) under neutral conditions, which is a more sustainable way to produce H-2 compared to acidic and alkaline HER, encourages the development of efficient catalytic materials and devices and deeper investigation of the mechanisms behind neutral HER. We present an electrode concept for facilitating HER under neutral conditions. The concept entails the use of annealing-reshaped silver (Ag) nanoparticle array on monolayer epitaxial graphene (MEG) on 4H-SiC. Measurements of HER performance show more positive onset potential of the cathodic HER for Ag-decorated MEG compared to that for pristine MEG, indicating improved water dissociation at Ag/MEG electrodes. Complementary morphological characterization, absorption measurements, and Raman mapping analysis enable us to ascribe the enhanced catalytic performance of electrodes decorated with 2 nm thick annealed Ag on the synergetic effect originating from simultaneous water reduction on circular Ag nanoparticles of 31 nm in diameter and on compressively strained Ag-free graphene regions. The overall results pave the way toward development of stable van der Waals heterostructure electrodes with a tunable metal-carbon interaction for fast HER under neutral conditions. (C) 2021 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
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