Effective silicon nanowire arrays/WO₃ core/shell photoelectrode for neutral pH water splitting

Abstract

We report the first demonstration of a high-efficiency photoelectrochemical (PEC) water splitting reaction using a novel Si NWs/WO 3 core/shell photoanode prepared by a mild and inexpensive metal-catalyzed electroless etching process followed by dip-coating, airing and annealing methods. The dense and vertically aligned Si NWs/WO 3 core/shell nanostructure were characterized by scanning electron microscopy, transmission electron microscopy and x-ray diffraction. In comparison to planar n-Si, Si NWs and planar Si/WO 3 , the Si NWs/WO 3 samples showed significantly enhanced photocurrent over the entire potential sweep range. More significantly, the Si NWs/WO 3 samples have an exceptionally low photocurrent onset potential of −0.6393 V versus reversible hydrogen electrode (RHE), indicating very efficient charge separation and charge transportation processes. The as-prepared electrode also has a photocurrent density of 2.7 mA cm −2 at 0.6107 V versus RHE in 0.5 M Na 2 SO 4 solution under simulated solar light irradiation (100 mW cm −2 from 300 W Xenon lamp coupled with an AM 1.5 G filter). An optimal solar-to-hydrogen efficiency of about 1.9% was achieved at 0.2676 V versus RHE. Electrochemical impedance spectroscopy was conducted to investigate the properties of the charge transfer process, and the results indicated that the enhanced PEC performance may due to the increased charge separation. The x-ray photoelectron spectroscopy measurements indicated the chemical composition of the Si NWs/WO 3 nanostructure. Our work has provided an efficient strategy to improve the energy conversion efficiency and photocurrent of water splitting materials.Supplementary material for this article is available online

Physical and Chemical Defects in WO3 Thin Films and Their Impact on Photoelectrochemical Water Splitting

“…Several studies have focused on overcoming these issues, such as selective doping of metal and nonmetal semiconductors, 19,20 addition of cocatalysts, like CoO x or Co-Pi, to improve the water oxidation kinetics, 21,22 forming a heterojunction via introduction of another semi-conductor layer, like BiVO 4 , Bi 2 S 3 , and Cu 2 O, to enhance the electron transport properties, 23−25 or using nano/microstructured substrates. 26,27 Various thin film deposition techniques have been used to achieve improved film structures, including a hydrothermal method, 28 sputtering, 29 pulsed laser deposition (PLD), 30 and atomic layer deposition (ALD). 14 Another important aspect that has not received enough attention yet is that the quality of the thin film can significantly affect the PEC properties.…”

Water Splitting Performance Enhancement of the TiO2 Nanorod Array Electrode with Ultrathin Black Phosphorus Nanosheets

“…It is clear, that the R 1 values of BP/TiO 2 NR photoelectrodes is smaller than the TiO 2 NR photoelectrode. This suggests more effective separation of electron‐hole pair and/or faster charge transfer in BP/TiO 2 NR photoelectrode …”

Strategies for improving photoelectrochemical water splitting performance of Si‐based electrodes

“…24 Although Si semiconductor can absorb almost the entire solar spectrum, the planar Si displays strong light reflection. Therefore, it is necessary to construct the specific surface structures to enhance light absorption, such as Si microstructures (micropyramids, [28][29][30][31][32] microwires, [33][34][35] microporous Si 36,37 ) and nanostructures (nanopyramids, 38,39 nanowires, [40][41][42][43][44][45][46][47][48] nanopillars, [49][50][51] nanorods, 52,53 nanospheres, 54 etc.). Both the micro-and nano-structures can increase light harvesting via the multiple reflections and scattering.…”