Facets and Defects in Perovskite Nanocrystals for Photocatalytic CO2 Reduction

Recent Advances in Metal Halide Perovskites for CO2 Photocatalytic Reduction: An Overview and Future Prospects

The photocatalytic reduction of CO2 into valuable chemicals and fuels has become a significant research focus in recent years due to its environmental sustainability and energy efficiency. Metal halide perovskites (MHPs), renowned for their remarkable optoelectronic properties and tunable structures, are regarded as promising photocatalysts. Yet, their practical uses are constrained by inherent instability, severe electron-hole recombination, and a scarcity of active sites, prompting substantial research efforts to optimize MHP-based photocatalysts. This review summarizes the latest advancements in MHP-based photocatalysis. First the fundamental principles of photocatalysis are outlined and the structural and optical characteristics of MHPs are evaluated. Then key strategies for enhancing MHP photocatalysts, including morphology and surface modification, encapsulation, metal cation doping, heterojunction engineering, and molecular immobilization are highlighted. Finally, considering recent research progress and the needs for industrial application, challenges and future prospects are explored. This review aims to support researchers in the development of more efficient and stable MHP-based photocatalysts.

Defects of Metal Halide Perovskites in Photocatalytic Energy Conversion: Friend or Foe?

Photocatalytic solar-to-fuel conversion over metal halide perovskites (MHPs) has recently attracted much attention, while the roles of defects in MHPs are still under debate. Specifically, the mainstream viewpoint is that the defects are detrimental to photocatalytic performance, while some recent studies show that certain types of defects contribute to photoactivity enhancement. However, a systematic summary of why it is contradictory and how the defects in MHPs affect photocatalytic performance is still lacking. In this review, the innovative roles of defects in MHP photocatalysts are highlighted. First, the origins of defects in MHPs are elaborated, followed by clarifying certain benefits of defects in photocatalysts including optical absorption, charge dynamics, and surface reaction. Afterward, the recent progress on defect-related MHP photocatalysis, i.e., CO2 reduction, H2 generation, pollutant degradation, and organic synthesis is systematically discussed and critically appraised, putting emphasis on their beneficial effects. With defects offering peculiar sets of merits and demerits, the personal opinion on the ongoing challenges is concluded and outlining potentially promising opportunities for engineering defects on MHP photocatalysts. This critical review is anticipated to offer a better understanding of the MHP defects and spur some inspiration for designing efficient MHP photocatalysts.

Highly efficient and 100 % selectivity of CO generation via CO2 Photoreduction over a novel CsBr@CuBr2 Heterojunction

To address the global challenge posed by excessive carbon dioxide emissions, our research pioneers the transformation of CO2 into valuable hydrocarbon fuels. Central to this approach is the innovation of photocatalysts, engineered to exhibit exceptional photoresponse characteristics. In this research, the CsBr@CuBr2 photocatalyst was innovatively synthesized through a straightforward and effective one-pot method. The catalyst displayed remarkable efficacy, achieving a CO2 photoreduction rate of 201.47 μmol g-1 within just 4 h. The incorporation of CsBr into CuBr2 effectively captures excited-state electrons, thereby significantly enhancing charge separation efficiency. Utilizing in situ DRIFTS and DFT theoretical analysis, the experiment reveals the complex process of CO2 photoreduction to CO. The results of this experiment provide breakthrough insights for the systematic design of metal bromide heterostructures, which possess robust CO2 adsorption/activation potential and notable stability.

g-C3N4 as ballistic electron transport "Tunnel" in CsPbBr3-based ternary photocatalyst for gas phase CO2 reduction

Perovskite CsPbBr3 quantum dot shows great potential in artificial photosynthesis, attributed to its outstanding optoelectronic properties. Nevertheless, its photocatalytic activity is hindered by insufficient catalytic active sites and severe charge recombination. In this work, a CsPbBr3@Ag-C3N4 ternary heterojunction photocatalyst is designed and synthesized for high-efficiency CO2 reduction. The CsPbBr3 quantum dots and Ag nanoparticles are chemically anchored on the surface of g-C3N4 sheets, forming an electron transfer tunnel from CsPbBr3 quantum dots to Ag nanoparticles via g-C3N4 sheets. The resulting CsPbBr3@Ag-C3N4 ternary photocatalyst, with spatial separation of photogenerated carriers, achieves a remarkable conversion rate of 19.49 μmol·g-1·h-1 with almost 100 % CO selectivity, a 3.13-fold enhancement in photocatalytic activity as compared to CsPbBr3 quantum dots. Density functional theory calculations reveal the rapid CO2 adsorption/activation and the decreased free energy (0.66 eV) of *COOH formation at the interface of Ag nanoparticles and g-C3N4 in contrast to the g-C3N4, leading to the excellent photocatalytic activity, while the thermodynamically favored CO desorption contributes to the high CO selectivity. This work presents an innovative strategy of constructing perovskite-based photocatalyst by modulating catalyst structure and offers profound insights for efficient CO2 conversion.

Design of highly selective and stable CsPbI3 perovskite catalyst for photocatalytic reduction of CO2 to C1 products

Finding efficient photocatalytic carbon dioxide reduction catalysts is one of the core issues in addressing global climate change. Herein, the pristine CsPbI3 perovskite and doped CsPbI3 perovskite were evaluated in carbon dioxide reduction reaction (CO2RR) to C1 products by using density functional theory. Free energy testing and electronic structure analysis methods have shown that doped CsPbI3 exhibits more effective catalytic performance, higher selectivity, and stability than undoped CsPbI3. Additionally, it is discovered that CsPbI3 (100) and (110) crystal surfaces have varied product selectivity. The photo-catalytic effectiveness is increased by the narrower band gap of Bi and Sn doped CsPbI3, which broadens the absorption spectrum of visible light and makes electron transport easier. The calculation results indicate that Bi doped CsPbI3 (100) and CsPbI3 (110) crystal faces exhibit good selectivity towards CH4, with free energy barriers as low as 0.55 eV and 0.58 eV, respectively. Sn doped CsPbI3 (100) and CsPbI3 (110) crystal planes exhibit good selectivity for HCOOH and CH3OH, respectively. The results indicate that the Bi and Sn doped CsPbI3 perovskite catalyst can further improve the CO2 photocatalytic activity and high selectivity for C1 products, making it a suitable substrate material for high-performance CO2RR.

Enhanced CO2 Sensing by Oxygen Plasma-Treated Perovskite-Graphene Nanocomposites

Carbon dioxide (CO2) is a major greenhouse gas responsible for global warming and climate change. The development of sensitive CO2 sensors is crucial for environmental and industrial applications. This paper presents a novel CO2 sensor based on perovskite nanocrystals immobilized on graphene and functionalized with oxygen plasma treatment. The impact of this post-treatment method was thoroughly investigated using various characterization techniques, including Raman spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The detection of CO2 at parts per million (ppm) levels demonstrated that the hybrids subjected to 5 min of oxygen plasma treatment exhibited a 3-fold improvement in sensing performance compared to untreated layers. Consequently, the CO2 sensing capability of the oxygen-treated samples showed a limit of detection and limit of quantification of 6.9 and 22.9 ppm, respectively. Furthermore, the influence of ambient moisture on the CO2 sensing performance was also evaluated, revealing a significant effect of oxygen plasma treatment.

Photocatalytic CO2 Reduction Coupled with Oxidation of Benzyl Alcohol over CsPbBr3@PANI Nanocomposites

Herein, we successfully prepare conductive polyaniline (PANI)-encapsulated CsPbBr3 perovskite nanocrystals (PNCs) that demonstrate much improved photocatalytic performance and stability toward the CO2 reduction reaction (CRR) coupled with oxidation of benzyl alcohol (BA) to benzaldehyde. Due to the acid-base interaction between CO2 and PANI, CO2 molecules are selectively adsorbed on PANI in the form of carbamate. As a result, the rate of production of CO (rCO) reaches 26.1 μmol g-1 h-1 with a selectivity of 98.1%, which is in good agreement with the rate of oxidation (∼27.0 μmol g-1 h-1) of BA. Such a high reduction/oxidation rate is enabled by the fast electron transfer (∼2.2 ps) from PNCs to PANI, as revealed by femtosecond transient absorption spectroscopy. Moreover, because of the benefit of the encapsulation of PANI, no significant decrease in rCO is observed in a 10 h CRR test. This work offers insight into how to simultaneously achieve improved photocatalytic performance and stability of CsPbX3 PNCs.

Stabilizing Metal Halide Perovskites for Solar Fuel Production: Challenges, Solutions, and Future Prospects

Metal halide perovskites (MHPs) are emerging photocatalyst materials that can enable sustainable solar-to-chemical energy conversion by virtue of their broad absorption spectra, effective separation/transport of photogenerated carriers, and solution processability. Although preliminary studies show the excellent photocatalytic activities of MHPs, their intrinsic structural instability due to the low formation energy and soft ionic nature is an open challenge for their practical applications. This review discusses the latest understanding of the stability issue and strategies to overcome this issue for MHP-based photocatalysis. First, the origin of the instability issue at atomic levels and the design rules for robust structures are analyzed and elucidated. This is then followed by presenting several different material design strategies for stability enhancement, including reaction medium modification, material surface protection, structural dimensionality engineering, and chemical composition engineering. Emphases are placed on understanding the effects of these strategies on photocatalytic stability as well as the possible structure-performance correlation. Finally, the possible future research directions for pursuing stable and efficient MHP photocatalysts in order to accelerate their technological maturity on a practical scale are outlined. With that, it is hoped to provide readers a valuable snapshot of this rapidly developing and exciting field.

In Situ Constructed Perovskite-Chalcogenide Heterojunction for Photocatalytic CO2 Reduction

Perovskite nanocrystals (PNCs) are promising candidates for solar-to-fuel conversions yet exhibit low photocatalytic activities mainly due to serious recombination of photogenerated charge carriers. Constructing heterojunction is regarded as an effective method to promote the separation of charge carriers in PNCs. However, the low interfacial quality and non-directional charge transfer in heterojunction lead to low charge transfer efficiency. Herein, a CsPbBr3 -CdZnS heterojunction is designed and prepared via an in situ hot-injection method for photocatalytic CO2 reduction. It is found that the high-quality interface in heterojunction and anisotropic charge transfer of CdZnS nanorods (NRs) enable efficient spatial separation of charge carriers in CsPbBr3 -CdZnS heterojunction. The CsPbBr3 -CdZnS heterojunction achieves a higher CO yield (55.8 µmol g-1  h-1 ) than that of the pristine CsPbBr3 NCs (13.9 µmol g-1  h-1 ). Furthermore, spectroscopic experiments and density functional theory (DFT) simulations further confirm that the suppressed recombination of charge carriers and lowered energy barrier for CO2 reduction contribute to the improved photocatalytic activity of the CsPbBr3 -CdZnS heterojunction. This work demonstrates a valid method to construct high-quality heterojunction with directional charge transfer for photocatalytic CO2 reduction. This study is expected to pave a new avenue to design perovskite-chalcogenide heterojunction.

Rapid Data-Efficient Optimization of Perovskite Nanocrystal Syntheses through Machine Learning Algorithm Fusion

With the demand for renewable energy and efficient devices rapidly increasing, a need arises to find and optimize novel (nano)materials. With sheer limitless possibilities for material combinations and synthetic procedures, obtaining novel, highly functional materials has been a tedious trial and error process. Recently, machine learning has emerged as a powerful tool to help optimize syntheses; however, most approaches require a substantial amount of input data, limiting their pertinence. Here, three well-known machine-learning models are merged with Bayesian optimization into one to optimize the synthesis of CsPbBr₃ nanoplatelets with limited data demand. The algorithm can accurately predict the photoluminescence emission maxima of nanoplatelet dispersions using only the three precursor ratios as input parameters. This allows us to fabricate previously unobtainable seven and eight monolayer-thick nanoplatelets. Moreover, the algorithm dramatically improves the homogeneity of 2-6-monolayer-thick nanoplatelet dispersions, as evidenced by narrower and more symmetric photoluminescence spectra. Decisively, only 200 total syntheses are required to achieve this vast improvement, highlighting how rapidly material properties can be optimized. The algorithm is highly versatile and can incorporate additional synthetic parameters. Accordingly, it is readily applicable to other less-explored nanocrystal syntheses and can help rapidly identify and improve exciting compositions' quality.

Charge Carrier Dynamics of CsPbBr3/g-C3N4 Nanoheterostructures in Visible-Light-Driven CO2-to-CO Conversion

The photon energy-dependent selectivity of photocatalytic CO₂-to-CO conversion by CsPbBr₃ nanocrystals (NCs) and CsPbBr₃/g-C₃N₄ nanoheterostructures (NHSs) was demonstrated for the first time. The surficial capping ligands of CsPbBr₃ NCs would adsorb CO₂, resulting in the carboxyl intermediate to process the CO₂-to-CO conversion via carbene pathways. The type-II energy band structure at the heterojunction of CsPbBr₃/g-C₃N₄ NHSs would separate the charge carriers, promoting the efficiency in photocatalytic CO₂-to-CO conversion. The electron consumption rate of CO₂-to-CO conversion for CsPbBr₃/g-C₃N₄ NHSs was found to intensively depend on the rate constant of interfacial hole transfer from CsPbBr₃ to g-C₃N₄. An in situ transient absorption spectroscopy investigation revealed that the half-life time of photoexcited electrons in optimized CsPbBr₃/g-C₃N₄ NHS was extended two times more than that in the CsPbBr₃ NCs, resulting in the higher probability of charge carriers to carry out the CO₂-to-CO conversion. The current work presents important and novel insights of semiconductor NHSs for solar energy-driven CO₂ conversion.

Effect of Sr-Doping on the Photocatalytic Performance of LaNiO3−σ

In this study, to investigate how oxygen vacancy impacts the photocatalytic performance of LaNiO3, undoped and Sr-doped LaNiO3−σ nanoparticles are successfully prepared by the sol-gel method. The X-ray diffractometer (XRD) results show both two samples belong to the R-3c space group of the rhombohedral system. According to the conservation of valence and the X-ray photoelectron spectroscopy (XPS) results, it is demonstrated that Sr-doping can introduce more oxygen vacancy into LaNiO3−σ. According to photocatalytic experiments of the degradation of methyl orange (MO) solution, La0.875Sr0.125NiO3−σ shows higher photocatalytic performance than undoped LaNiO3−σ. First-principle calculation results show that the introduction of oxygen vacancy and Sr-doping can lead to the narrowing of the band gap width of LaNiO3.

Lattice distortion inducing exciton splitting and coherent quantum beating in CsPbI3 perovskite quantum dots

Anisotropic exchange splitting in semiconductor quantum dots results in bright-exciton fine-structure splitting important for quantum information processing. Direct measurement of fine-structure splitting usually requires single/few quantum dots at liquid-helium temperature because of its sensitivity to quantum dot size and shape, whereas measuring and controlling fine-structure splitting at an ensemble level seem to be impossible unless all the dots are made to be nearly identical. Here we report strong bright-exciton fine-structure splitting up to 1.6 meV in solution-processed CsPbI₃ perovskite quantum dots, manifested as quantum beats in ensemble-level transient absorption at liquid-nitrogen to room temperature. The splitting is robust to quantum dot size and shape heterogeneity, and increases with decreasing temperature, pointing towards a mechanism associated with orthorhombic distortion of the perovskite lattice. Effective-mass-approximation calculations reveal an intrinsic 'fine-structure gap' that agrees well with the observed fine-structure splitting. This gap stems from an avoided crossing of bright excitons confined in orthorhombically distorted quantum dots that are bounded by the pseudocubic {100} family of planes.

Retarded Charge Recombination to Enhance Photocatalytic Performance for Water-Free CO2 Reduction Using Perovskite Nanocrystals as Photocatalysts

Femtosecond transient absorption spectral (TAS) investigations were performed to understand the carrier relaxation mechanism for perovskite nanocrystals Cs_1-xFA_xPbBr₃ (CF, x = 0.45) and CsPbBr₃ (CS), which served as efficient photocatalysts for splitting of CO₂ into CO and O₂ in the absence of water. Upon light irradiation for 12 h, formation of deep trap states was found for both CS and CF samples with spectral characteristics of the TAS photobleach (PB) band showing a long spectral tail extending to the long wavelength region. The charge recombination rates at the shallow surface states, bulk states, and deep-trapped surface state were found to be significantly retarded for the CF sample than for the CS sample, in agreement with the photocatalytic performances for CO product yields of the CF catalyst being greater by a factor of 3 compared to those of the CS catalyst.

Facets-Directed Epitaxially Grown Lead Halide Perovskite-Sulfobromide Nanocrystal Heterostructures and Their Improved Photocatalytic Activity

Lead halide perovskite nanocrystal heterostructures have been extensively studied in the recent past for improving their photogenerated charge carriers mobility. However, most of such heterostructures are formed with random connections without having strong evidence of epitaxial relation. Perovskite-chalcohalides are the first in this category, where all-inorganic heterostructures are formed with epitaxial growth. Going beyond one facet, herein, different polyhedral nanocrystals of CsPbBr₃ are explored for facet-selective secondary epitaxial sulfobromide growths. Following a decoupled synthesis process, the heterojunctions are selectively established along {110} as well as {200} facets of 26-faceted rhombicuboctahedrons, the {110} facets of armed hexapods, and the {002} facets of 12-faceted dodecahedron nanocrystals of orthorhombic CsPbBr₃. Lattice matching induced these epitaxial growths, and their heterojunctions have been extensively studied with electron microscopic imaging. Unfortunately, these heterostructures did not retain the intense host emission because of their indirect band structures, but such combinations are found to be ideal for promoting photocatalytic CO₂ reduction. The pseudo-Type-II combination helped here in the successful movement of charge carriers and also improved the rate of catalysis. These results suggest that facet-selective all-inorganic perovskite heterostructures can be epitaxially grown and this could help in improving their catalytic activities.

Crystal Facet Dependent Energy Band Structures of Polyhedral Cu2O Nanocrystals and Their Application in Solar Fuel Production

We demonstrated a facile hydrothermal method to synthesize the (100)-, (110)- and (111)-oriented Cu₂O nanocrystals (NCs) by controlling the concentration of the incorporated anions (CO₃^2- and SO₃^2-). The crystal facet dependent activity of the orientation controlled Cu₂O NCs in the rhodamine B (RhB) photodegradation and photocatalytic hydrogen (H₂) evolution was found to follow the trend: (111) > (110) > (100). The mechanism was investigated by characterizing the optical property, energy band structure, interfacial charge carrier dynamics and reducing ability. The results indicated that the (111)-oriented Cu₂O NCs exhibit the higher conduction band (CB) potential as compared with the (110)-oriented and (100)-oriented Cu₂O NCs, which resulted in the largest driving force of interfacial electron transfer for (111)-oriented Cu₂O NCs to carry out solar fuel generation. The current study offers an easy strategy for crystal facet engineering of semiconductors and provides important physical insights into their electronic properties for the desired solar energy conversions.

Potential Application of Perovskite Structure for Water Treatment: Effects of Band Gap, Band Edges, and Lifetime of Charge Carrier for Photocatalysis

Perovskite structures have attracted scientific interest as a promising alternative for water treatment due to their unique structural, high oxidation activity, electronic stability, and optical properties. In addition, the photocatalytic activity of perovskite structures is higher than that of many transition metal compounds. A critical property that determines the high-performance photocatalytic and optical properties is the band gap, lifetime of carrier charge, and band edges relative to the redox potential. Thus, the synthesis/processing and study of the effect on the band gap, lifetime of carrier charge, and band edges relative to the redox potential in the development of high-performance photocatalysts for water treatment are critical. This review presents the basic physical principles of optical band gaps, their band gap tunability, potentials, and limitations in the applications for the water treatment. Furthermore, it reports recent advances in the synthesis process and comparatively examines the band gap effect in the photocatalytic response. In addition to the synthesis, the physical mechanisms associated with the change in the band gap have been discussed. Finally, the conclusions of this review, along with the current challenges of perovskites for photocatalysis, are presented.

Direct Conversion of CO2 into Hydrocarbon Solar Fuels by a Synergistic Photothermal Catalysis

Photothermal coupling catalysis technology has been widely studied in recent years and may be a promising method for CO2 reduction. Photothermal coupling catalysis can improve chemical reaction rates and realize the controllability of reaction pathways and products, even in a relatively moderate reaction condition. It has inestimable value in the current energy and global environmental crisis. This review describes the application of photothermal catalysis in CO2 reduction from different aspects. Firstly, the definition and advantages of photothermal catalysis are briefly described. Then, different photothermal catalytic reductions of CO2 products and catalysts are introduced. Finally, several strategies to improve the activity of photothermal catalytic reduction of CO2 are described and we present our views on the future development and challenges of photothermal coupling. Ultimately, the purpose of this review is to bring more researchers’ attention to this promising technology and promote this technology in solar fuels and chemicals production, to realize the value of the technology and provide a better path for its development.

Transformation of Metal Halides to Facet-Modulated Lead Halide Perovskite Platelet Nanostructures on A-Site Cs-Sublattice Platform

The conversion of metal halides to lead halide perovskites with B-site metal ion diffusion has remained a convenient approach for obtaining shape-modulated perovskite nanocrystals. These transformations are typically observed for materials having a common A-site Cs-sublattice platform. However, due to the fast reactions, trapping the interconversion process has been difficult. In an exploration of the tetragonal phase of Cs₇Cd₃Br₁₃ platelets as the parent material, herein, a slower diffusion of Pb(II) leading to facet-modulated CsPbBr₃ platelets is reported. This was expected due to the presence of Cd(II) halide octahedra along with Cd(II) halide tetrahedra in the parent material. This helped in microscopically monitoring their phase transformation via an epitaxially related core/shell intermediate heterostructure. The transformation was also derived and predicted by density functional theory calculations. Further, when the reaction chemistry was tuned, core/shell platelets were transformed to different facet-modulated and hollow CsPbBr₃ platelet nanostructures. These platelets having different facets were also explored for catalytic CO₂ reduction, and their catalytic rates were compared.

ZnSe Nanorods-CsSnCl3 Perovskite Heterojunction Composite for Photocatalytic CO2 Reduction

Utilizing sunlight to convert CO₂ into chemical fuels could simultaneously address the greenhouse effect and fossil fuel crisis. ZnSe nanocrystals are promising candidates for photocatalysis because of their low toxicity and excellent photoelectric properties. However, pristine ZnSe generally has low catalytic activities due to serious charge recombination and the lack of efficient catalytic sites for CO₂ reduction. Herein, a ZnSe nanorods-CsSnCl₃ perovskite (ZnSe-CsSnCl₃) type II heterojunction composite is designed and prepared for photocatalytic CO₂ reduction. The ZnSe-CsSnCl₃ type II heterojunction composite exhibits enhanced photocatalytic activity for CO₂ reduction with respect to pristine ZnSe nanorods. The experimental characterizations and theoretical calculations reveal that the efficient charge separation and lowered free energy of CO₂ reduction facilitate the CO₂ conversion on the ZnSe-CsSnCl₃ heterojunction composite. This work presents a type II heterojunction composite photocatalyst based on ecofriendly metal chalcogenides and metal halide perovskites. Our study has also promoted the understanding of the CO₂ reduction mechanisms on perovskite nanocrystals, which could be valuable for the development of metal halide perovskite photocatalysts.

Defect engineering of oxide perovskites for catalysis and energy storage: synthesis of chemistry and materials science

Oxide perovskites have emerged as an important class of materials with important applications in many technological areas, particularly thermocatalysis, electrocatalysis, photocatalysis, and energy storage. However, their implementation faces numerous challenges that are familiar to the chemist and materials scientist. The present work surveys the state-of-the-art by integrating these two viewpoints, focusing on the critical role that defect engineering plays in the design, fabrication, modification, and application of these materials. An extensive review of experimental and simulation studies of the synthesis and performance of oxide perovskites and devices containing these materials is coupled with exposition of the fundamental and applied aspects of defect equilibria. The aim of this approach is to elucidate how these issues can be integrated in order to shed light on the interpretation of the data and what trajectories are suggested by them. This critical examination has revealed a number of areas in which the review can provide a greater understanding. These include considerations of (1) the nature and formation of solid solutions, (2) site filling and stoichiometry, (3) the rationale for the design of defective oxide perovskites, and (4) the complex mechanisms of charge compensation and charge transfer. The review concludes with some proposed strategies to address the challenges in the future development of oxide perovskites and their applications.

Chemically Spiraling CsPbBr3 Perovskite Nanorods

Light emitting lead halide perovskite nanocrystals are currently emerging as the workhorse in quantum dot research. Most of these reported nanocrystals are isotropic cubes or polyhedral; but anisotropic nanostructures with controlled anisotropic directions still remain a major challenge. For orthorhombic CsPbBr₃, the 1D shaped nanostructures reported are linear and along either of the axial directions ⟨100⟩. In contrast, herein, spiral CsPbBr₃ perovskite nanorods in the orthorhombic phase are reported with unusual anisotropy having (101) planes remaining perpendicular to the major axis [201]. While these nanorods are synthesized using the prelattice of orthorhombic Cs₂CdBr₄ with Pb(II) diffusion, the spirality is controlled by manipulation of the compositions of alkylammonium ions in the reaction system which selectively dissolve some spiral facets of the nanorods. Further, as spirality varied with facet creation and elimination, these nanorods were explored as photocatalysts for CO₂ reduction, and the evolution of methane was also found to be dependent on the depth of the spiral nanorods. The entire study demonstrates facet manipulation of complex nanorods, and these results suggest that even if perovskites are ionic in nature, their shape could be constructed by design with proper reaction manipulation.

Metal Halide Perovskites for Solar Fuel Production and Photoreactions

Photocatalysis is an easily configurable and cost-effective technology for the conversion of solar energy into chemical energy. Recently, increasing attention has been given to metal halide perovskite (MHP) photocatalysts because of the development of stabilization strategies for MHPs under reaction conditions. From this perspective, we first describe several substantial breakthroughs in the photocatalytic application of MHPs. Performance trends in the solar fuel production applications of MHPs, including photocatalytic H₂ generation and photocatalytic CO₂ reduction reactions, are then described. Recent developments to extend the use of MHPs to various photocatalytic organic transformations are also highlighted. Finally, we propose several scientific challenges for the practical implications of MHPs for solar fuel production and various photoreactions.

Recent Advances in Ligand Design and Engineering in Lead Halide Perovskite Nanocrystals

Lead halide perovskite (LHP) nanocrystals (NCs) have recently garnered enhanced development efforts from research disciplines owing to their superior optical and optoelectronic properties. These materials, however, are unlike conventional quantum dots, because they possess strong ionic character, labile ligand coverage, and overall stability issues. As a result, the system as a whole is highly dynamic and can be affected by slight changes of particle surface environment. Specifically, the surface ligand shell of LHP NCs has proven to play imperative roles throughout the lifetime of a LHP NC. Recent advances in engineering and understanding the roles of surface ligand shells from initial synthesis, through postsynthetic processing and device integration, finally to application performances of colloidal LHP NCs are covered here.

Glycine-Functionalized CsPbBr3 Nanocrystals for Efficient Visible-Light Photocatalysis of CO2 Reduction

Capping ligands are indispensable for the preparation of metal-halide-perovskite (MHP) nanocrystals (NCs) with good stability; however, the long alkyl-chain capping ligands in conventional MHP NCs will be unfavorable for CO₂ adsorption and hinder the efficient carrier separation on the surface of MHP NCs, leading to inferior catalytic activity in artificial photosynthesis. Herein, CsPbBr₃ nanocrystals with short-chain glycine as ligand are constructed through a facile ligand-exchange strategy. Owing to the reduced hindrance of glycine and the presence of the amine group in glycine, the photogenerated carrier separation and CO₂ uptake capacity are noticeably improved without compromising the stability of the MHP NCs. The CsPbBr₃ nanocrystals with glycine ligands exhibit a significantly increased yield of 27.7 μmol g^-1  h^-1 for photocatalytic CO₂ -to-CO conversion without any organic sacrificial reagents, which is over five times higher than that of control CsPbBr₃ NCs with conventional long alkyl-chain capping ligands.

Metal halide perovskites as an emergent catalyst for CO2 photoreduction: a minireview

The present minireview summarizes recent advances in the application of metal halide perovskite for CO₂ photoreduction.

Photocorrosion at Irradiated Perovskite/Electrolyte Interfaces

Metal-halide perovskites transformed optoelectronics research and development during the past decade. They have also gained a foothold in photocatalytic and photoelectrochemical processes recently, but their sensitivity to the most commonly applied solvents and electrolytes together with their susceptibility to photocorrosion hinders such applications. Understanding the elementary steps of photocorrosion of these materials can aid the endeavor of realizing stable devices. In this Perspective, we discuss both thermodynamic and kinetic aspects of photocorrosion processes occurring at the interface of perovskite photocatalysts and photoelectrodes with different electrolytes. We show how combined in situ and operando electrochemical techniques can reveal the underlying mechanisms. Finally, we also discuss emerging strategies to mitigate photocorrosion (such as surface protection, materials and electrolyte engineering, etc.).

Identification of Halogen-Associated Active Sites on Bismuth-Based Perovskite Quantum Dots for Efficient and Selective CO2-to-CO Photoreduction

All-inorganic Pb-free bismuth (Bi) halogen perovskite quantum dots (PQDs) with distinct structural and photoelectric properties provide plenty of room for selective photoreduction of CO₂. However, the efficient conversion of CO₂-to-CO with high selectivity on Bi-based PQDs driven by solar light remains unachieved, and the precise reaction path/mechanism promoted by the surface halogen-associated active sites is still poorly understood. Herein, we screen a series of nontoxic and stable Cs₃Bi₂X₉ (X = Cl, Br, I) PQDs for selective photocatalytic reduction of CO₂-to-CO at the gas-solid interface. Among all the reported pure-phase PQDs, the as-synthesized Cs₃Bi₂Br₉ PQDs exhibited the highest CO₂-to-CO conversion efficiency generating 134.76 μmol g^-1 of CO yield with 98.7% selectivity under AM 1.5G simulated solar illumination. The surface halogen-associated active sites and reaction intermediates were dynamically monitored and precisely unraveled based on in situ DRIFTS investigation. In combination with the DFT calculation, it was revealed that the surface Br sites allow for optimizing the coordination modes of surface-bound intermediate species and reducing the reaction energy of the rate-limiting step of COOH^- intermediate formation from ^•CO₂^-. This work presents a mechanistic insight into the halogen-involved catalytic reaction mechanism in solar fuel production.