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%.

Using dual-photoelectrode photoelectrochemical (PEC) devices based on earth-abundant metal oxides for unbiased water splitting is an attractive means of producing green H fuel, but is challenging, owing to low photovoltages generated by PEC cells. This problem can be solved by coupling n-type BiVO with n-type Bi V O to create a virtual p/n junction due to the formation of a hole-inversion layer at the semiconductor interface. Thus, photoelectrodes with high photovoltage outputs were synthesized. The photoelectrodes exhibited features of p- and n-type semiconductors when illuminated under an applied bias, suggesting their use as photoanode and photocathode in a dual-photoelectrode PEC cell. This concept was proved by connecting a 1 mol % W-doped BiVO /Bi V O photoanode with an undoped BiVO /Bi V O photocathode, which produced a high photovoltage of 1.54 V, sufficient to drive stand-alone water splitting with 0.95 % efficiency.

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electrochemical cells for direct conversion of solar energy to electricity (or hydrogen) are one of the most sustainable solutions to meet the increasing worldwide energy demands. in this report, a novel and highly-efficient ternary heterojunction-structured Bi 4 o 7 /Bi 3.33 (Vo 4) 2 o 2 /Bi 46 V 8 o 89 photoelectrode is presented. it is demonstrated that the combination of an inversion layer, induced by holes (or electrons) at the interface of the semiconducting Bi 3.33 (Vo 4) 2 o 2 and Bi 46 V 8 o 89 components, and the rectifying contact between the Bi 4 o 7 and Bi 3.33 (Vo 4) 2 o 2 phases acting afterward as a conventional p-n junction, creates an adjustable virtual p-n-p or n-p-n junction due to self-polarization in the ion-conducting Bi 46 V 8 o 89 constituent. this design approach led to anodic and cathodic photocurrent densities of + 38.41 mA cm-2 (+ 0.76 V RHe) and-2.48 mA cm-2 (0 V RHe), respectively. Accordingly, first, this heterojunction can be used either as photoanode or as photocathode with great performance for artificial photosynthesis, noting, second, that the anodic response reveals exceptionally high: more than 300% superior to excellent values previously reported in the literature. Water splitting by photoelectrochemical cells (PECs) in the presence of light is a sustainable approach to directly convert solar energy into storable chemical energy (H 2 fuel) 1-5. Efforts to solve a number of deficiencies and to gain in performance have included modifying the electronic structure of the materials, constructing favorable surface structures with heterojunction, or controlling the morphology 6,7. The heterojunction concept is actually an excellent alternative for designing materials with improved photocatalytic properties 7 , because promoting a good separation and transport of the photogenerated charges 8,9. This is the case of bismuth vanadate-and bismuth oxide-based heterojunction systems like BiVO 4 /Bi 4 V 2 O 11 10

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