Engineering Directional Charge Carrier Transport Using Ferroelectric Polarization for Enhanced Photoelectrochemical Water Oxidation

Introducing ferroelectric polarization has shown great potential to facilitate interfacial charge separation in photoelectrochemical (PEC) water splitting. However, unambiguous evidence of the actual influence of spontaneous ferroelectric polarization, as compared to heterojunction formation, on electron extraction and PEC water splitting is still lacking to date. Herein, core-shell BaTiO3/TiO2 nanostructures are designed as photoanodes based on paraelectric cubic and ferroelectric tetragonal phases BaTiO3 (BTO) perovskite. The cubic and tetragonal crystalline phases are stabilized using selected elaboration methods. Compared to the paraelectric cubic (c-BTO), the ferroelectric tetragonal (t-BTO) leads to a favorable ferroelectric polarization, enhancing directional charge separation and as a consequence to increased photocurrent up to a factor of 1.95. More interestingly, the charge separation efficiency can be tuned by applying positive or negative polarization, with the highest charge separation obtained for the positive one. When loading Ni(OH)2 as a cocatalyst on the t-BTO@TiO2 photoanode, the Ni(OH)2/TiO2/t-BTO exhibits a high performance and superior stability toward PEC water oxidation with a photocurrent almost 6.7 times that of the reference SiO2@TiO2. The proposed facilitation may open an avenue to engineer charge separation and transport for high-performance PEC water oxidation.

Developing sustainable, high-performance perovskites in photocatalysis: design strategies and applications

Solar energy is attractive because it is free, renewable, abundant and sustainable. Photocatalysis is one of the feasible routes to utilize solar energy for the degradation of pollutants and the production of fuel. Perovskites and their derivatives have received substantial attention in both photocatalytic wastewater treatment and energy production because of their highly tailorable structural and physicochemical properties. This review illustrates the basic principles of photocatalytic reactions and the application of these principles to the design of robust and sustainable perovskite photocatalysts. It details the structures of the perovskites and the physics and chemistry behind photocatalytic reactions and describes the advantages and limitations of popular strategies for the design of photoactive perovskites. This is followed by examples of how these strategies are applied to enhance the photocatalytic efficiency of oxide, halide and oxyhalide perovskites, with a focus on materials with potential for practical application, that is, not containing scarce or toxic elements. It is expected that this overview of the development of photocatalysts and deeper understanding of photocatalytic principles will accelerate the exploitation of efficient perovskite photocatalysts and bring about effective solutions to the energy and environmental crisis.

Crystallization time in ZnO: the role of surface OH groups in its photoactivity

The crystallization time and surface modifications concerning the hydroxyl groups on the ZnO catalyst were studied and the results suggest that there is a balance between the surface groups and morphology playing a critical role in its photoactivity.

Oriented arrays of Co3O4 nanoneedles for highly efficient electrocatalytic water oxidation

We described an effective way to generate a Co₃O₄ mesocrystal array with well-developed porosity, simply by uniting a coupled interface with hydrazine treatment. Due to the fast electron transfer and sufficient active sites, the Ti mesh-supported Co₃O₄ nanoneedles electrode could provide a current density of 49.9 mA cm^-2 at 570 mV OER overpotential and has exceptionally high stability.

Mesocrystals for photocatalysis: a comprehensive review on synthesis engineering and functional modifications

Mesocrystals are a new class of superstructures that are generally made of crystallographically highly ordered nanoparticles and could function as intermediates in a non-classical particle-mediated aggregation process. In the past decades, extensive research interest has been focused on the structural and morphogenetic aspects, as well as the growth mechanisms, of mesocrystals. Unique physicochemical properties including high surface area and ordered porosity provide new opportunities for potential applications. In particular, the oriented interfaces in mesocrystals are considered to be beneficial for effective photogenerated charge transfer, which is a promising photocatalytic candidate for promoting charge carrier separation. Only recently, remarkable advances have been reported with a special focus on TiO2 mesocrystal photocatalysts. However, there is still no comprehensive overview on various mesocrystal photocatalysts and their functional modifications. In this review, different kinds of mesocrystal photocatalysts, such as TiO2 (anatase), TiO2 (rutile), ZnO, CuO, Ta2O5, BiVO4, BaZrO3, SrTiO3, NaTaO3, Nb3O7(OH), In2O3-x (OH) y , and AgIn(WO4)2, are highlighted based on the synthesis engineering, functional modifications (including hybridization and doping), and typical structure-related photocatalytic mechanisms. Several current challenges and crucial issues of mesocrystal-based photocatalysts that need to be addressed in future studies are also given.

Towards Sustainable H2 Production: Rational Design of Hydrophobic Triphenylamine-based Dyes for Sensitized Ethanol Photoreforming

Donor-acceptor dyes are a well-established class of photosensitizers, used to enhance visible-light harvesting in solar cells and in direct photocatalytic reactions, such as H₂ production by photoreforming of sacrificial electron donors (SEDs). Amines-typically triethanolamine (TEOA)-are commonly employed as SEDs in such reactions. Dye-sensitized photoreforming of more sustainable, biomass-derived alcohols, on the other hand, was only recently reported by using methanol as the electron donor. In this work, several rationally designed donor-acceptor dyes were used as sensitizers in H₂ photocatalytic production, comparing the efficiency of TEOA and EtOH as SEDs. In particular, the effect of hydrophobic chains in the spacer and/or the donor unit of the dyes was systematically studied. The H₂ production rates were higher when TEOA was used as SED, whereas the activity trends depended on the SED used. The best performance was obtained with TEOA by using a sensitizer with just one bulky hydrophobic moiety, propylenedioxythiophene, placed on the spacer unit. In the case of EtOH, the best-performing sensitizers were the ones featuring a thiazolo[5,4-d]thiazole internal unit, needed for enhancing light harvesting, and carrying alkyl chains on both the donor part and the spacer unit. The results are discussed in terms of reaction mechanism, interaction with the SED, and structural/electrochemical properties of the sensitizers.

Construction of vesicle CdSe nano-semiconductors photocatalysts with improved photocatalytic activity: Enhanced photo induced carriers separation efficiency and mechanism insight

Visible-light-driven photocatalysis as a green technology has attracted a lot of attention due to its potential applications in environmental remediation. Vesicle CdSe nano-semiconductor photocatalyst are successfully prepared by a gas template method and characterized by a variety of methods. The vesicle CdSe nano-semiconductors display enhanced photocatalytic performance for the degradation of tetracycline hydrochloride, the photodegradation rate of 78.824% was achieved by vesicle CdSe, which exhibited an increase of 31.779% compared to granular CdSe. Such an exceptional photocatalytic capability can be attributed to the unique structure of the vesicle CdSe nano-semiconductor with enhanced light absorption ability and excellent carrier transport capability. Meanwhile, the large surface area of the vesicle CdSe nano-semiconductor can increase the contact probability between catalyst and target and provide more surface-active centers. The photocatalytic mechanisms are analyzed by active species quenching. It indicates that h⁺ and O₂^- are the main active species which play a major role in catalyzing environmental toxic pollutants. Simultaneously, the vesicle CdSe nano-semiconductor had high efficiency and stability.

Chloride capping of CdTiO3 for higher crystallinity and enhanced photocatalytic activity

The crystallinity of cadmium titanate (CdTiO₃) was greatly improved when synthesized under mild reaction conditions, in the presence of chloride.

Inorganic perovskite photocatalysts for solar energy utilization

This review specifically summarizes the recent development of perovskite photocatalysts and their applications in water splitting and environmental remediation.