Dynamics of photogenerated holes in undoped BiVO<sub>4</sub> photoanodes for solar water oxidation

Ma, Yimeng; Pendlebury, Stephanie R.; Reynal, Anna; Formal, Florian Le; Durrant, James R.

doi:10.1039/c4sc00469h

Cited by 346 publications

(426 citation statements)

References 37 publications

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“…Data were collected as a function of LED excitation intensity at a fixed applied potential at 1.7 VRHE to ensure effective suppression of surface electron/hole recombination. 12,16 Under these conditions BiVO4 holes exhibit a maximum absorption change at 550 nm ( Figure S2), in agreement with our previous studies of analogous films under pulsed laser excitation. 12,29 As we have previously reported, these quasi-steady conditions result in the observation of long-lived holes accumulated at the photoelectrode surface, and thus, measuring the absorption change at 550 nm provides an assay of their reaction kinetics.…”

Section: -28supporting

confidence: 91%

Rate Law Analysis of Water Oxidation and Hole Scavenging on a BiVO₄ Photoanode

Mesa

Pastor

et al. 2016

ACS Energy Lett.

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Spectroelectrochemical studies employing pulsed LED irradiation are used to investigate the kinetics of water oxidation on undoped dense bismuth vanadate (BiVO4) photoanodes under conditions of photoelectrochemical water oxidation and compare to those obtained for oxidation of a simple redox couple. These measurements are employed to determine the quasi-steady-state densities of surface-accumulated holes, p s, and correlate these with photocurrent density as a function of light intensity, allowing a rate law analysis of the water oxidation mechanism. The reaction order in surface hole density is found to be first order for p s < 1 nm–2 and third order for p s > 1 nm–2. The effective turnover frequency of each surface hole is estimated to be 14 s–1 at AM 1.5 conditions. Using a single-electron redox couple, potassium ferrocyanide, as the hole scavenger, only the first-order reaction is observed, with a higher rate constant than that for water oxidation. These results are discussed in terms of catalysis by BiVO4 and implications for material design strategies for efficient water oxidation.

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Section: -28supporting

confidence: 91%

Rate Law Analysis of Water Oxidation and Hole Scavenging on a BiVO₄ Photoanode

Mesa

Pastor

et al. 2016

ACS Energy Lett.

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“…BiVO 4 is known to suffer from poor electron mobility, and photon efficiency is therefore lost relatively easily to electron-hole recombination [33,34]. This phenomenon is reportedly due to the fact that the VO 4 tetrahedra are not connected to each other [35], thus making it hard for photogenerated electrons to flow towards the conducting support.…”

Section: Disadvantages Of Bivo 4 As a Photoanodementioning

confidence: 96%

Recent Advances in the BiVO4 Photocatalyst for Sun-Driven Water Oxidation: Top-Performing Photoanodes and Scale-Up Challenges

2017

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Photoelectrochemical (PEC) water splitting, which is a type of artificial photosynthesis, is a sustainable way of converting solar energy into chemical energy. The water oxidation half-reaction has always represented the bottleneck of this process because of the thermodynamic and kinetic challenges that are involved. Several materials have been explored and studied to address the issues pertaining to solar water oxidation. Significant advances have recently been made in the use of stable and relatively cheap metal oxides, i.e., semiconducting photocatalysts. The use of BiVO 4 for this purpose can be considered advantageous because this catalyst is able to absorb a substantial portion of the solar spectrum and has favourable conduction and valence band edge positions. However, BiVO 4 is also associated with poor electron mobility and slow water oxidation kinetics and these are the problems that are currently being investigated in the ongoing research in this field. This review focuses on the most recent advances in the best-performing BiVO 4 -based photoanodes to date. It summarizes the critical parameters that contribute to the performance of these photoanodes, and highlights so far unresolved critical features related to the scale-up of a BiVO 4 -based PEC water-splitting device.

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“…48 Previous in situ TAS studies of the water oxidation reaction on TiO2 show that the absorption of holes at ~500 nm increases with applied potential, where the population of long-lived holes tracked the current-voltage curve. 49 In the study herein, we focus on the long-lived (millisecond to second) charge carriers responsible for photocatalytic water oxidation on TiO2, 50,51 akin to several other metal oxide surfaces such as BiVO4 45 and α-Fe2O3.…”

Section: Transient Photocurrent and Transient Absorption Spectroscopymentioning

confidence: 99%

Water Oxidation Kinetics of Accumulated Holes on the Surface of a TiO₂ Photoanode: A Rate Law Analysis

et al. 2017

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ABSTRACT. It has been more than 40 years since Fujishima and Honda demonstrated water splitting using TiO2, yet there is still no clear mechanism by which surface holes on TiO2 oxidize water. In this article, we use a range of complementary techniques to study this reaction that provide a unique insight into the reaction mechanism. Using transient photocurrent (TPC) and 2 transient absorption spectroscopy (TAS), we measure both the kinetics of electron extraction (t50% ~200 µs, 1.5 VRHE) and the kinetics of hole oxidation of water (t50% ~100 ms, 1.5 VRHE) as a function of applied potential, demonstrating the water oxidation by TiO2 holes is the kinetic bottleneck in this water splitting system. Photo-induced absorption spectroscopy (PIAS) measurements under 5 s LED irradiation are used to monitor the accumulation of surface TiO2 holes under conditions of photo-electrochemical water oxidation. Under these conditions we find that the surface density of these holes increases non-linearly with photocurrent density. In alkali (pH 13.6), this corresponded to a rate law for water oxidation that is 3 rd order with respect to surface hole density, with a rate constant = 22 ± 2 nm 4 .s -1 . Under neutral (pH = 6.7) and acidic (pH = 0.6) conditions the rate law was 2 nd order with respect to surface hole density, indicative of a change in reaction mechanism. Although a change in reaction order was observed, the rate of reaction did not change significantly over the wide pH range examined (with TOFs per surface hole in the region of 20 -25 s -1 at ~1 sun irradiance). This showed that the rate limiting step does not involve OH -nucleophilic attack and demonstrated the versatility of TiO2 as an active water oxidation photocatalyst over a wide range of pH.TOC graphic

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Dynamics of photogenerated holes in undoped BiVO₄ photoanodes for solar water oxidation

Cited by 346 publications

References 37 publications

Rate Law Analysis of Water Oxidation and Hole Scavenging on a BiVO₄ Photoanode

Rate Law Analysis of Water Oxidation and Hole Scavenging on a BiVO₄ Photoanode

Recent Advances in the BiVO4 Photocatalyst for Sun-Driven Water Oxidation: Top-Performing Photoanodes and Scale-Up Challenges

Water Oxidation Kinetics of Accumulated Holes on the Surface of a TiO₂ Photoanode: A Rate Law Analysis

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Dynamics of photogenerated holes in undoped BiVO4 photoanodes for solar water oxidation

Cited by 346 publications

References 37 publications

Rate Law Analysis of Water Oxidation and Hole Scavenging on a BiVO4 Photoanode

Rate Law Analysis of Water Oxidation and Hole Scavenging on a BiVO4 Photoanode

Recent Advances in the BiVO4 Photocatalyst for Sun-Driven Water Oxidation: Top-Performing Photoanodes and Scale-Up Challenges

Water Oxidation Kinetics of Accumulated Holes on the Surface of a TiO2 Photoanode: A Rate Law Analysis

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Dynamics of photogenerated holes in undoped BiVO₄ photoanodes for solar water oxidation

Rate Law Analysis of Water Oxidation and Hole Scavenging on a BiVO₄ Photoanode

Rate Law Analysis of Water Oxidation and Hole Scavenging on a BiVO₄ Photoanode

Water Oxidation Kinetics of Accumulated Holes on the Surface of a TiO₂ Photoanode: A Rate Law Analysis