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Bismuth vanadate photoanodes often suffer from poor electron transport, which restricts their photoelectrochemical performance in water oxidation. Here, reduced graphene oxide sheets with excellent electronic conductivity are introduced to bismuth vanadate photoanode films to provide a channel for electron transport. As a result, the charge separation efficiency of the photoanode films increases from 59 to 78 % at 420 nm and 1.23 V (vs. the reversible hydrogen electrode) under back irradiation. In particular, the onset potential for photoelectrochemical water oxidation over reduced graphene oxide-bismuth vanadate photoanode films has a cathodic shift of approximately 120 mV in potassium borate electrolyte compared to bare bismuth vanadate photoanode films. [ABSTRACT FROM AUTHOR]

Summary The photocatalytic and photoelectrochemical reduction of water or CO 2 is an intriguing approach to producing sustainable solar fuels, and has attracted growing and intense interest. Nanostructuring of photocatalysts and photoelectrodes has been proven to be a strong strategy to dramatically improve overall solar-to-fuel conversion efficiencies. Another technological barrier for the practical implementation of solar fuel production is long-term material durability, which has recently been well addressed through use of conformal coatings of protective layers onto the narrow band-gap semiconductors that are suitable for efficient solar-to-fuel conversions but photoelectrochemically unstable. These significant progresses may lead us to the practical implementation of solar fuel production. In this review, we will focus on these exciting progresses achieved using nanostructuring strategies, specifically regarding how the nanostructure influences the charge transport and separation; special attention will be paid to how a nanoscale coating (overlayer) passivates the surface states, thereby reducing the surface electron–hole recombination, and how a nanoscale coating (protective layer) prevents the photocorrosion or photopassivation of the semiconductors with optimal band gaps. We hope that the design strategies using these nanostructures will offer new and greater opportunities for efficient solar fuel production to existing photocatalytic and photoelectrochemical systems. [ABSTRACT FROM AUTHOR]

Ta3N5 is a promising photoanode candidate for photoelectrochemical water splitting, with a band gap of about 2.1 eV and a theoretical solar-to-hydrogen efficiency as high as 15.9 % under AM 1.5 G 100 mW cm−2 irradiation. However, the presently achieved highest photocurrent (ca. 7.5 mA cm−2) on Ta3N5 photoelectrodes under AM 1.5 G 100 mW cm−2 is far from the theoretical maximum (ca. 12.9 mA cm−2), which is possibly due to serious bulk recombination (poor bulk charge transport and charge separation) in Ta3N5 photoelectrodes. In this study, we show that volatilization of intentionally added Ge (5 %) during the synthesis of Ta3N5 promotes the electron transport and thereby improves the charge-separation efficiency in bulk Ta3N5 photoanode, which affords a 320 % increase of the highest photocurrent comparing with that of pure Ta3N5 photoanode under AM 1.5 G 100 mW cm−2 simulated sunlight. [ABSTRACT FROM AUTHOR]

With a theoretical maximum photocurrent of ca. 12.5 mA cm−2 under AM 1.5 G 100 mW cm−2 irradiation, the presently achieved plateau photocurrent of about 0.6 mA cm−2 on bare LaTiO2N photoanodes indicates the presence of serious charge transport limitations. Only recently, a plateau photocurrent of about 4 mA cm−2 was achieved on precious IrO2 modified LaTiO2N photoanodes prepared by a rather expensive and complex method, without discussing the intrinsic mechanism of improved photocurrents. In this study, by establishing highly crystalline porous LaTiO2N particles and superior inter-particle connectivity with reduced density of grain boundaries among the film particles, a record plateau photocurrent of 6.5 mA cm−2 on the Co3O4 modified LaTiO2N photoanodesis demonstrated under AM 1.5 G 100 mW cm−2 simulated sunlight. More broadly, this work shows the intrinsic requirements and significance of constituting (oxy)nitride particles for efficient charge transport and therefore desirable photoelectrochemical performances on the (oxy)nitride photoelectrodes, which have never been noticed and investigated before. With the obtained rules to follow are encouraging to explore the remaining substantial (oxy)nitride semiconductors as potential photoelectrodes for solar energy conversion. [ABSTRACT FROM AUTHOR]

• Progress of non-oxide semiconductors for photoelectrochemical solar fuel production is summarized. • Protection strategies to increase the operational durability of non-oxide photoelectrodes are highlighted. • The effects of interfacial energy diagrams on charge transfer kinetics at various interfaces are presented. • Future perspectives for development of efficient and stable non-oxide solar-fuel photoelectrodes are discussed. Among various artificial photosynthesis routes, photoelectrochemical (PEC) hydrogen (H 2) production via water splitting and hydrocarbon generation via carbon dioxide (CO 2) reduction are particularly intriguing for achieving a sustainable society. A simpler and potentially economical device design for PEC cells, as compared with those containing photovoltaic cells, is using semiconductor–liquid junction (SCLJ) based photoelectrodes to assemble a photoanode–photocathode tandem cell. The SCLJs form immediately upon semiconductor films immersing into electrolytes, which are then used to separate photogenerated electron–hole pairs and drive corresponding redox chemistry. To engineering these SCLJ-based photoanode–photocathode tandem PEC devices to achieving considerable solar energy conversion efficiencies, the key step is to identify suitable semiconductor materials, the core component in most solar energy conversion systems. In addition, applying effective strategies to modify these semiconductors are needed, as they cannot simultaneously meet all the requirements of efficient light absorption, charge separation and extraction, surface reaction, and operational stability at the same time. This article provides a review on promising non-oxide semiconductors for PEC conversion of solar energy into chemical fuels. The efforts to increase charge transport and separation, to accelerate the charge transfer kinetics across various interfaces, and to engender long-term durability of these non-oxide photoelectrodes are emphasized. As screening, evaluation and optimization have led to substantial improvement in both PEC performance and operational durability, non-oxide semiconductors will provide new opportunities, in addition to classical metal oxide semiconductors, to realize efficient and cost-effective PEC solar fuel production. [ABSTRACT FROM AUTHOR]

Large-scale single crystals have potential applications in many fields, such as in ferroelectric and photoelectric energy conversion devices. Perovskite oxynitrides have also attracted attention in photoelectrochemical water splitting systems because of their high theoretical solar-to-hydrogen efficiencies. Nevertheless, the synthesis of perovskite oxynitride single crystals requires the coupling of cation exchange and ammonization processes, which is exceptionally challenging. The present study demonstrates an inorganic vapor method that provides, for the first time ever, high-quality epitaxial perovskite SrTaO 2 N single crystals on the centimeter scale. Assessments using Raman spectroscopy, crystal structure analysis and density functional theory determined that the conversion mechanism followed a topotactic transition mode. Compared with conventional SrTaO 2 N particle-assembled films, the SrTaO 2 N single crystals made in this work were free of interparticle interfaces and grain boundaries, which exhibited extremely high performance during photoelectrochemical water oxidation. In particular, these SrTaO 2 N single crystals showed the highest photocurrent density at 0.6 V vs. RHE (1.20 mA cm−2) and the highest photocurrent filling factor (47.6%) reported to date, together with a low onset potential (0.35 V vs. RHE). This onset potential was 200 mV less than that of the reported in situ SrTaO 2 N film, and the photocurrent fill factor was improved by 2 to 3 times. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Charge compensation doping lowers the onset potential of Ta 3 N 5. • Charge compensation doping improves the water reduction ability of Ta 3 N 5. • The Ti, Zr and Hf doping elements are more effective in the selected elements. Abstract Ta 3 N 5 was potentially a high efficient semiconductor in photocatalytic and photoelectrochemical water splitting but its practical performances were unsatisfactory. The oxygen impurity, which substituted N and acted as an electron donor, was one possible source of the poor photocatalytic and photoelectrochemical activities of Ta 3 N 5. In this study, 24 elements, which substituted Ta and acted as the electron acceptor, were codoped with the oxygen impurity to achieve charge compensation in Ta 3 N 5. Based on the density functional theory calculations, the defect formation energies, electronic structures and carrier mobility were investigated. The results showed that the charge compensation doping method was able to improve the conduction band position of Ta 3 N 5 , suggesting that this method was effective to enhance water reduction ability and lower onset potential of Ta 3 N 5. The Ti, Zr and Hf elements were found to be more effective than other elements because they were able to keep the carrier mobility of Ta 3 N 5. Our calculation results agreed well with experiments and provided useful guidance for future investigations of Ta 3 N 5. [ABSTRACT FROM AUTHOR]

Abstract: Lanthanum tantalum oxynitride (LaTaON2) powders were prepared by one-step flux method. LaTaON2 photoanodes, which are fabricated by using LaTaON2 powders, are found to exhibit photoelectrochemical activity for overall water splitting. The photocurrent for LaTaON2 photoelectrodes was ca. 120 μA cm−2 at 1.5 V vs. reversible hydrogen electrode (RHE) in 1 M NaOH aqueous solutions (pH = 13.6) under AM 1.5 G simulated sunlight irradiation (100 mW cm−2). The photocurrent of LaTaON2 photoelectrode from back-side illumination is much larger than that from front-side illumination, suggesting that the photoelectrochemical property is mainly limited by poor continuous electron transport in the bulk. Further efforts to ameliorate the electron transport in the bulk of LaTaON2 photoelectrodes are expected to significantly improve their photoelectrochemical performance. [Copyright &y& Elsevier]

Abstract: Cuprous oxides with different dendrite morphologies were formed on F-doped tin oxide (FTO) covered glass substrates by potentiostatic deposition of cupric acetate. The effects of pH value (varied from 5.00 to 5.80) of electrolytes on the crystal morphologies of cuprous oxide were studied. Different crystal morphologies of cuprous oxides were obtained by the change of velocity of vertical growth and lateral growth through varying the pH value of electrolyte. The processes of Cu2O dendrite crystal growth were analyzed through SEM images at different deposition times. Photoelectrochemical properties of the Cu2O thin films prepared in the system are also studied. [ABSTRACT FROM AUTHOR]