Abstract
The conversion of solar energy into hydrogen fuel by splitting water into photoelectrochemical cells (PEC) is an appealing strategy to store energy and minimize the extensive use of fossil fuels. The key requirement for efficient water splitting is producing a large band bending (photovoltage) at the semiconductor to improve the separation of the photogenerated charge carriers. Therefore, an attractive method consists in creating internal electrical fields inside the PEC to render more favorable band bending for water splitting. Coupling ferroelectric materials exhibiting spontaneous polarization with visible light photoactive semiconductors can be a likely approach to getting higher photovoltage outputs. The spontaneous electric polarization tends to promote the desirable separation of photogenerated electron- hole pairs and can produce photovoltages higher than that obtained from a conventional p-n heterojunction. Herein, we demonstrate that a hole inversion layer induced by a ferroelectric Bi4V2O11 perovskite at the n-type BiVO4 interface creates a virtual p-n junction with high photovoltage, which is suitable for water splitting. The photovoltage output can be boosted by changing the polarization by doping the ferroelectric material with tungsten in order to produce the relatively large photovoltage of 1.39 V, decreasing the surface recombination and enhancing the photocurrent as much as 180%.
Highlights
The strategy based on storing solar energy in the form of chemical energy is the envisaged development of technology in an attempt to prevent or minimize harmful effects on the natural environmental, which has been recognizably accelerated by the large current use of fuels derived from fossil sources
In the more recent years, the n-type BiVO4 semiconductor has been widely studied as a photoanode in water-splitting photoelectrochemical cells (PEC) cells taking into account that it is composed of chemical elements that are relatively abundant on Earth, has a short bandgap energy (2.5 eV), its valence band is suitably positioned towards the water oxidation, and its conduction band is suitably placed close to the H2 evolution potential[13]
The BiVO4/Bi4V2O11 heterojunction prepared through the Pechini method was deposited onto fluorine-doped tin oxide (FTO) glass covered with SnO2 to act as a passivating layer by using the spray pyrolysis method as previously elsewhere reported[32]
Summary
The strategy based on storing solar energy in the form of chemical energy is the envisaged development of technology in an attempt to prevent or minimize harmful effects on the natural environmental, which has been recognizably accelerated by the large current use of fuels derived from fossil sources. Various p-n heterojunctions such as BiOI/BiVO416,17, BiOCl/BiVO418, Bi2O3/BiVO419,20, NiO/BiVO421, Si/BiVO422, CuO/BiVO423, Cu2O/BiVO424, Ag2O/BiVO425, and Co3O4/BiVO426 have been proven to be an efficient method for keeping electron-hole pairs separated due to the built-in potential produced by the heterojunction Those mentioned p-type semiconductors are either unstable in water under oxidizing conditions or unable to absorb a wider visible light range than BiVO4, limiting its application on photoelectrochemical water splitting. When the ferroelectric Bi4V2O11 is coupled to the BiVO4, its spontaneous electrical polarization generates a sufficiently high electric field that produces an inversion layer at the BiVO4/Bi4V2O11 interface (Fig. 1a), resulting in an increased band bending, enhancing the charge generation and the separation efficiency By this approach, BiVO4 is the light-absorbing material for generating the electron-hole pairs, whereas the ferroelectric Bi4V2O11 perovskite plays the role of absorbing light and creating a built-in electric field to separate the photogenerated charges, inducing the carrier transport. The photovoltage and photocurrent were enhanced as much as 83% and 180%, respectively
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