Abstract
A surface-nanostructured semiconductor photoelectrode is highly desirable for photoelectrochemical (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 (jph) with a zero-onset potential. A dendritic porous 6H-SiC with densely arranged holes with a size of ∼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/cm2, the Ni–FeOOH-coated nanoporous 6H-SiC photoanode exhibits an onset potential of 0 V versus the reversible hydrogen electrode (VRHE) and a high jph of 0.684 mA/cm2 at 1 VRHE, 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 VRHE, 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.
Highlights
The Electrochemical impedance spectroscopy (EIS) results clearly demonstrate that the porous Ni−FeOOH/PSC18 photoanode possesses a significantly reduced charge-transfer resistance, which explains the dramatically enhanced PEC water-splitting performance
Nanoporous 6H-silicon carbide (6H-Silicon carbide (SiC)) with densely arranged holes with a size of ∼40 nm on the surface can be fabricated by an anodization method
The Scanning electron microscopy (SEM), TEM, and X-Ray photoelectron spectroscopy (XPS) results confirm the deposition of Ni−FeOOH nanorods on the 6H-SiC surface and in the dendritic porous structure
Summary
Photoelectrochemical (PEC) water splitting is regarded as a promising approach to convert solar light into a stable, environmentally friendly, renewable, and clean chemical energy, H2.1−4 Since the pioneering PEC work by Fujishima and Honda,[5] semiconductor materials such as TiO2, Fe2O3, ZspnliOtt,inagn.6d−2B1 iVHOow[4] ehvaevre, been widely the inherent studied for PEC drawbacks of the water semiconductor materials including the unfavorable energy band position with respect to water redox potentials, the short carrier diffusion length, and the sluggish oxygen-evolution kinetics hamper the significant progress of PEC water splitting.[22]. The indirect band gap of 6H-SiC has a smaller light absorption coefficient than direct band gap semiconductors This results in larger light penetration depth than the sum of the width of the spacecharge region and the carrier diffusion length. We employ a facile anodization approach to fabricate PSC photoanodes with an optimal depth of the nanoporous layer that matches the light penetration depth. Given the fact that the anodization method can be used to fabricate a porous structure on a variety of semiconductors, this work demonstrates a simple approach to improve the water-splitting efficiency by rational design of the porous photoelectrodes
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