The Role of Polarization in Photocatalysis Chen, Fang; Huang, Hongwei; Guo, Lin ...
Angewandte Chemie International Edition,
July 22, 2019, Volume:
58, Issue:
30
Journal Article
Peer reviewed
Semiconductor photocatalysis as a desirable technology shows great potential in environmental remediation and renewable energy generation, but its efficiency is severely restricted by the rapid ...recombination of charge carriers in the bulk phase and on the surface of photocatalysts. Polarization has emerged as one of the most effective strategies for addressing the above‐mentioned issues, thus effectively promoting photocatalysis. This review summarizes the recent advances on improvements of photocatalytic activity by polarization‐promoted bulk and surface charge separation. Highlighted is the recent progress in charge separation advanced by different types of polarization, such as macroscopic polarization, piezoelectric polarization, ferroelectric polarization, and surface polarization, and the related mechanisms. Finally, the strategies and challenges for polarization enhancement to further enhance charge separation and photocatalysis are discussed.
Polar opposites: Macroscopic polarization, piezoelectric polarization, ferroelectric polarization, and surface polarization have emerged as promising strategies for accelerating the separation of photogenerated charge carriers either in the bulk phase or on the surface of semiconductor photocatalysts. Recent progress as well as future challenges are discussed.
Semiconductor photocatalysis acts as a sustainable green technology to convert solar energy for environmental purification and production of renewable energy. However, the current photocatalysts ...suffer from inefficient photoabsorption, rapid recombination of photogenerated electrons and holes, and inadequate surface reactive sites. Introduction of oxygen vacancies (OVs) in photocatalysts has been demonstrated to be an efficacious strategy to solve these issues and improve photocatalytic efficiency. This review systematically summarizes the recent progress in the oxygen vacant semiconductor photocatalysts. Firstly, the formation and characterizations of OVs in semiconductor photocatalysts are briefly introduced. Then, highlighted are the roles of OVs in the photocatalytic reactions of three types of typical oxygen‐containing semiconductors, including metal oxides (TiO2, ZnO, WO3, W18O49, MoO3, BiO2‐x, SnO2, etc), hydroxides (In(OH)3, Ln(OH)3 (Ln=La, Pr, and Nd), Layered double hydroxides) and oxysalts (bismuth‐based oxysalts and others) photocatalysts. Moreover, the advanced photocatalytic applications of oxygen vacant semiconductor photocatalysts, such as pollutant removal, H2 production, CO2 reduction, N2 fixation and organic synthesis are systematically summarized. Finally, an overview on the current challenges and a prospective on the future of oxygen vacant materials is proposed.
Oxygen vacancies serve as the most effective defect engineering tactic to improve the photoabsorption, charge separation, and surface catalytic capability of photocatalysts. Here, three types of oxygen vacant semiconductors, including metal oxides (TiO2, ZnO, WO3, MoO3, etc), hydroxides (In(OH)3, Ln(OH)3 (Ln=La, Pr, and Nd), layered double hydroxides) and oxysalts (bismuth‐based oxysalts and others) photocatalysts, with diverse photocatalytic applications are summarized.
Semiconductor‐based photocatalysis as a productive technology furnishes a prospective solution to environmental and renewable energy issues, but its efficiency greatly relies on the effective bulk ...and surface separation of photoexcited charge carriers. Exploitation of atomic‐level strategies allows in‐depth understanding on the related mechanisms and enables bottom‐up precise design of photocatalysts, significantly enhancing photocatalytic activity. Herein, the advances on atomic‐level charge separation strategies toward developing robust photocatalysts are highlighted, elucidating the fundamentals of charge separation and transfer processes and advanced probing techniques. The atomic‐level bulk charge separation strategies, embodied by regulation of charge movement pathway and migration dynamic, boil down to shortening the charge diffusion distance to the atomic‐scale, establishing atomic‐level charge transfer channels, and enhancing the charge separation driving force. Meanwhile, regulating the in‐plane surface structure and spatial surface structure are summarized as atomic‐level surface charge separation strategies. Moreover, collaborative strategies for simultaneous manipulation of bulk and surface photocharges are also introduced. Finally, the existing challenges and future prospects for fabrication of state‐of‐the‐art photocatalysts are discussed on the basis of a thorough comprehension of atomic‐level charge separation strategies.
Semiconductor photocatalytic efficiency greatly relies on effective charge separation. The recent progress of atomic‐level strategies for promoting charge separation and migration in the bulk, on the surface, and both bulk and surface of a photocatalyst are highlighted and a guideline for the bottom‐up design of high‐performance photocatalysts suggested.
Prompt recombination of photogenerated electrons and holes in bulk and on the surface of photocatalysts harshly impedes the photocatalytic efficiency. However, the simultaneous manipulation of ...photocharges in the two locations is challenging. Herein, the synchronous promotion of bulk and surface separation of photoinduced charges for prominent CO2 photoreduction by coupling macroscopic spontaneous polarization and surface oxygen vacancies (OVs) of BiOIO3 single crystals is reported. The oriented growth of BiOIO3 single‐crystal nanostrips along the 001 direction, ensuing substantial well‐aligned IO3 polar units, renders a large enhancement for the macroscopic polarization electric field, which is capable of driving the rapid separation and migration of charges from bulk to surface. Meanwhile the introduction of surface OVs establishes a local electric field for charge migration to catalytic sites on the surface of BiOIO3 nanostrips. Highly polarized BiOIO3 nanostrips with ample OVs demonstrate outstanding CO2 reduction activity for CO production with a rate of 17.33 µmol g−1 h−1 (approximately ten times enhancement) without any sacrificial agents or cocatalysts, being one of the best CO2 reduction photocatalysts in the gas–solid system reported so far. This work provides an integrated solution to governing charge movement behavior on the basis of collaborative polarization from bulk and surface.
Collaborative polarization by macroscopic spontaneous polarization and surface oxygen vacancies induces efficient bulk and surface charge separation of BiOIO3 nanostrips, which gives rise to extraordinary CO2 photoreduction activity with a CO evolution rate of 17.33 µmol g−1 h−1, over ten times that of BiOIO3 nanoparticles, also outperforming most previously reported high‐performance photocatalysts.
Solar‐driven conversion of CO2 into high value‐added fuels is expected to be an environmental‐friendly and sustainable approach for relieving the greenhouse gas effect and countering energy crisis. ...Metal sulfide semiconductors with wide photoresponsive range and favorable band structures are suitable photocatalysts for CO2 photoreduction. This review summarizes the recent progress on metal sulfide semiconductors for photocatalytic CO2 reduction. First, the fundamentals, mechanisms and some principles, like product selectivity, of photocatalytic CO2 reduction are introduced. Then, according to the elemental composition, the metal sulfide photocatalysts applied for CO2 reduction are classified into binary (CdS, ZnS, MoS2, SnS2, Bi2S3, In2S3,Cu2S, NiS/NiS2, and CoS2), ternary (ZnIn2S4, CdIn2S4, CuInS2, Cu3SnS4, and CuGaS2), and quaternary (Cu2ZnSnS4) systems, in which their crystal structures, photochemical characteristics, and photocatalytic CO2 reduction applications are systematically demonstrated. Especially, the diverse modification strategies for improving the activity and product selectivity of photocatalytic CO2 reduction on these metal sulfides are summarized. Finally, the current challenges and future directions for the development of metal sulfide photocatalysts for CO2 reduction are proposed. This review is expected to serve as a powerful reference for exploiting high‐efficiency metal sulfide photocatalysts for CO2 conversion and furthering related mechanism understanding.
Metal sulfide semiconductors present unique optical/electronic characteristics, which are advantageous for CO2 photoreduction. The advancements in binary, ternary, and quaternary metal sulfide photocatalysts in CO2 photoreduction are elaborately summarized, and the effects of various modification strategies on the reduction activity and product selectivity are highlighted, providing a reference for development of efficient metal sulfides for photocatalytic CO2 reduction to carbonaceous fuels.
Reactive oxygen species (ROS) as green oxidants are of great importance for environmental and biological applications. Photocatalysis is one of the major routes for ROS evolution, which is seriously ...restricted by rapid charge recombination. Herein, piezocatalysis and photocatalysis (i.e., piezo–photocatalysis) are coupled to efficiently produce superoxide radicals (•O2−), hydrogen peroxide (H2O2), and hydroxyl radicals (•OH) via oxygen reduction reaction (ORR), by using Bi4NbO8X (X = Cl, Br) single crystalline nanoplates. Significantly, the piezo‐photocatalytic process leads to the highest ORR performance of the Bi4NbO8Br nanoplates, exhibiting •O2−, H2O2, and •OH evolution rates of 98.7, 792, and 33.2 µmol g−1 h−1, respectively. The formation of a polarized electric field and band bending allows directional separation of charge carriers, promoting the catalytic activity. Furthermore, the reductive active sites are found enriched on all the facets in the piezo–photocatalytic process, also contributing to the ORR. By piezo–photodeposition of Pt to artificially plant reductive reactive sites, the Bi4NbO8Br plates demonstrate largely enhanced photocatalytic H2 production activity with a rate of 203.7 µmol g−1 h−1. The present work advances piezo–photocatalysis as a new route for ROS generation, but also discloses the potential of piezo–photocatalytic active sites enriching for H2 evolution.
Efficient charge separation and enriched reductive reactive sites are synchronously achieved by coupling piezocatalysis and photocatalysis of layered piezoelectric semiconductor Bi4NbO8X (X = Cl, Br) single crystalline nanoplates, which results in the efficient production of reactive oxygen species (•O2−, H2O2, and •OH) and hydrogen.
Thin layer fabrication and crystal facet engineering favor the prompt charge transfer from bulk to the surface of a material and spatial charge separation among different facets, tremendously ...benefitting photocatalytic activity. However, the thickness and surface facet composition are considered as two entwined characteristics of layered materials with well‐defined and tunable shapes, which possess great promise to achieve the simultaneous manipulation of charge transfer and spatial separation. Herein, it is demonstrated that one solution for the aforementioned issue by controllably regulating the surface {010}/{100} facet junctions of a layered thickness‐tunable bismuth‐based material, BiOIO3. The attenuation in thickness of BiOIO3 nanoplates shortens the diffusion pathway of charge carriers, and more importantly the tuning of nanolayer thickness renders the ratio variation of the top {010} facet to the lateral {100} facet, which dominates the spatial separation of photogenerated electrons and holes. As a result, the highest CO evolution rate from CO2 reduction over BiOIO3 nanoplates with the optimal thickness and ratio of exposed facets reaches 5.42 µmol g−1 h−1, over 300% that of the bulk counterpart (1.77 µmol g−1 h−1). This work paves a new way for governing charge movement behaviors on the basis of the synergistic engineering of layer structure and exposing facets.
The interlayer charge migration and surface spatial charge separation are synchronously optimized through controllable regulation of the {010}/{100} facet junctions of a layered bismuth‐based material—BiOIO3, which results in efficient photocatalytic CO2 reduction for CO evolution.
Piezoelectric‐based catalysis that relies on the charge energy or separation efficiency of charge carriers has attracted significant attention. The piezo‐potential induced by strain or stress can ...induce a giant electric field, which has been demonstrated to be an effective means for charge energy shifting or transferring electrons and holes. In recent years, intense efforts have been made in this subject, and the research has mainly focussed on two aspects: i) Alteration of surface charge energy by piezo‐potential in piezocatalysis; ii) the separation of photo‐generated charge carriers and the catalytic activity enhancement of an integrated piezoelectric semiconductor or coupled system composed of piezoelectrics and semiconductors. Systematically summarizing the advances of the above two aspects is helpful in the context of deepening understanding of the relevant issues and developing new ideas for piezoelectric‐based catalysis. In this review, a comprehensive summary on piezocatalysis and piezo‐photocatalysis is provided. The charge transfer behaviors and catalytic mechanisms over a large variety of piezocatalysts and piezo‐photocatalysts are systematically analyzed. In addition, the types of mechanical energy, strategies for enhancing piezocatalysis, and the advanced applications of piezocatalysis and piezo‐photocatalysis are discussed. Finally, the promising development directions of piezocatalysis and piezo‐photocatalysis, such as materials, assembly forms, and applications in the future are proposed.
Mechanical energy and solar energy can enable charge energy alteration or effective separation of electron–hole pairs, which trigger various catalytic reactions. The recent research progress on piezocatalysis and piezo‐photocatalysis is summarized, concentrating especially on the typical piezocatalysts, mechanical energy forms, piezocatalysis modulation strategies, piezo‐photocatalyst types, and catalytic applications to offer a guideline for the development of piezoelectric‐based catalysts.
Nitrogen‐coordinated metal single atoms in carbon have aroused extensive interest recently and have been growing as an active research frontier in a wide range of key renewable energy reactions and ...devices. Herein, a step‐by‐step self‐assembly strategy is developed to allocate nickel (Ni) and iron (Fe) single atoms respectively on the inner and outer walls of graphene hollow nanospheres (GHSs), realizing separate‐sided different single‐atom functionalization of hollow graphene. The Ni or Fe single atom is demonstrated to be coordinated with four N atoms via the formation of a Ni‐N4 or Fe‐N4 planar configuration. The developed Ni‐N4/GHSs/Fe‐N4 Janus material exhibits excellent bifunctional electrocatalytic performance, in which the outer Fe‐N4 clusters dominantly contribute to high activity toward the oxygen reduction reaction (ORR), while the inner Ni‐N4 clusters are responsible for excellent activity toward the oxygen evolution reaction (OER). Density functional theory calculations demonstrate the structures and reactivities of Fe‐N4 and Ni‐N4 for the ORR and OER. The Ni‐N4/GHSs/Fe‐N4 endows a rechargeable Zn–air battery with excellent energy efficiency and cycling stability as an air‐cathode, outperforming that of the benchmark Pt/C+RuO2 air‐cathode. The current work paves a new avenue for precise control of single‐atom sites on carbon surface for the high‐performance and selective electrocatalysts.
Separate‐sided Ni‐N4 and Fe‐N4 single‐atomic functionalization of hollow graphene spheres (Ni‐N4/GHSs/Fe‐N4) is realized. The outer Fe‐N4 clusters dominantly contribute to high activity toward the oxygen reduction reaction (ORR), while the inner Ni‐N4 clusters are responsible for excellent activity toward the oxygen evolution reaction (OER). The Ni‐N4/GHSs/Fe‐N4 air‐cathode delivers excellent energy efficiency and cycling stability in rechargeable Zn–air batteries.
A facile and controllable in situ reduction strategy is used to create surface oxygen vacancies (OVs) on Aurivillius‐phase Sr2Bi2Nb2TiO12 nanosheets, which were prepared by a mineralizer‐assisted ...soft‐chemical method. Introduction of OVs on the surface of Sr2Bi2Nb2TiO12 extends photoresponse to cover the whole visible region and also tremendously promotes separation of photoinduced charge carriers. Adsorption and activation of CO2 molecules on the surface of the catalyst are greatly enhanced. In the gas‐solid reaction system without co‐catalysts or sacrificial agents, OVs‐abundant Sr2Bi2Nb2TiO12 nanosheets show outstanding CO2 photoreduction activity, producing CO with a rate of 17.11 μmol g−1 h−1, about 58 times higher than that of the bulk counterpart, surpassing most previously reported state‐of‐the‐art photocatalysts. Our study provides a three‐in‐one integrated solution to advance the performance of photocatalysts for solar‐energy conversion and generation of renewable energy.
Surface oxygen vacancies introduced on Sr2Bi2Nb2TiO12 nanosheets provide a three‐in‐one integrated solution to simultaneously promote photoabsorption, separation of photoinduced carrier carriers, and the adsorption and activation of CO2 molecules. This results in a prominent CO2 photoreduction activity.
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