Versatile single atom-perovskite materials: synthesis, characterization, applications, and perspectives

Perovskite materials are highly promising candidates for a wide array of optoelectronic devices because of their unique physical and chemical properties¹. This is because of their exceptional light absorption across a broad spectrum, high photoluminescence efficiency, and extended charge-carrier lifetimes². Furthermore, the tunable bandgaps of perovskites allow for optimized device-specific applications³. Their fabrication via cost-effective methods such as solution processing and thermal decomposition facilitates scalable production and commercialization⁴. The versatility of their compositional and structural attributes further augments their potential for bespoke device engineering. Owing to their exceptional properties, perovskites are extensively employed in diverse fields, including solar cells^5,6, light-emitting diodes⁷, lasers⁸, photodetectors⁹, photocatalysts^10,11, electrocatalysts¹², memory devices¹³, and sensors¹⁴. Despite their exceptional properties, perovskites exhibit instabilities in response to humidity, oxygen, heat, and light. Such environmental influences can lead to degradation or performance decline in perovskites over time, severely affecting the long-term stability and reliability of the devices. Furthermore, their application in various catalytic fields is limited by the scarcity of active catalytic sites, structural collapse owing to their low stability even in mild environments, and low selectivity for targeted reactions. Methods to improve stability and mitigate electronic defects involve applying protective coatings such as polymers, metal oxides, and organic-inorganic hybrids to block oxygen penetration, optimizing crystal structures to minimize defect density, and passivating surface and bulk defects to reduce charge recombination and enhance charge-carrier mobility^15,16,17. Recent studies have also investigated the fabrication of tandem or composite structures (perovskite-nanoparticles, perovskite-nanoclusters, perovskite-organic-inorganic hybrids, etc.) to provide more active catalytic sites, thereby boosting catalytic activity and improving selectivity for targeted reactions^18,19.

Single-atom catalysts (SACs) represent a frontier in catalysis research, offering the potential to manipulate catalytic activity at the atomic scale. These catalysts are characterized by the dispersion of metal atoms as isolated single atoms on support, leading to distinctive catalytic properties²⁰. SACs are promising materials because of their superior activity, remarkable selectivity, and optimal atom efficiency. The selection of ideal support is crucial for SAC design as it impacts (1) stabilization against aggregation, (2) uniform dispersion, (3) modulation of the electronic structure, and (4) formation of active sites. Graphene^21,22, graphitic carbon nitride (C₃N₄)²³, metal-organic frameworks (MOFs)^24,25, and carbon-based materials are the predominant supports for SACs^26,27,28.

This review will delve into the synthesis of perovskite-based catalysts with anchored single atoms, elucidate synthetic techniques such as photoreduction and reduction under an H₂ atmosphere, and provide a comprehensive characterization of the interactions between single atoms and perovskite matrices (Fig. 1). Furthermore, this review explores a variety of applications facilitated by engineered single-atom-perovskite catalysts (SA-PCs), emphasizing their distinct advantages in photocatalytic processes, carbon monoxide (CO) oxidation, oxidative desulfurization (ODS), lithium-oxygen batteries, nitrogen fixation, semi-hydrogenation, and methane activation.

On the synthesis, characterization, and applications of single-atom catalysts supported on perovskites.

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SA-PCs exhibit the most advantageous characteristics when employed as photocatalytic electrodes. Although perovskites have been extensively utilized as photocatalysts, they generally demonstrate inferior performance in terms of generation efficiency compared to electrochemical catalysts^29,30. However, by integrating single atoms, these catalysts benefit from a unique coordination structure and robust metal-support interaction, which significantly facilitate charge separation and transfer, thus boosting the formation efficiency of the target substance production^31,32. Single-atom doping can significantly increase the quality of the electronic environment by augmenting the local charge density and refining the capture of photogenerated electrons, single-atom doping significantly elevates the quality of the electronic environment³³. Despite their superior efficiency achieved through minimal loading, SA-PCs face several inherent limitations: (1) Challenges in synthesis owing to the inherent fragility of perovskites. (2) Inherent weaknesses of perovskites include their susceptibility to humidity and moisture. (3) Precise loading of single atoms and their potential aggregation into nanoclusters or nanoparticles can reduce the overall catalytic activity. (4) Distortions in the crystal structure. These aspects are discussed in detail in the final section. We believe this review serves as an insightful guide that explores efficient synthetic strategies to inhibit atom aggregation in SA-PCs, describes characterization techniques to address structural and chemical degradation of perovskites under high-energy conditions, and offers perspectives on existing challenges and emerging applications.

Improving the efficiency and properties of photocatalysts can be effectively achieved by incorporating metal cocatalysts³⁴. Metal cocatalysts play several key roles in photocatalytic processes. Their primary function is to minimize the recombination of electrons and holes. Metal cocatalysts enhance charge separation by providing trapping sites, which significantly increase the efficiency and stability of the photocatalysts. In addition, the presence of metal cocatalysts can increase the selectivity of photocatalytic reactions and promote specific reaction pathways. Consequently, integrating cocatalysts into photocatalysts has become a major research focus in several scientific fields. Multiple techniques are available for the deposition of metal cocatalysts onto photocatalytic semiconductor materials.

Electrospinning is an efficient technique for producing nanofibers from polymer solutions using a high-voltage electric field³⁵. When voltage is applied to the solutions, an electric field is generated, which pulls the solution into a fine jet from the tip of the needle³⁶. Nanofibers embedded with the metal cocatalyst and photocatalyst are deposited as the jet moves toward the collector and the solvent evaporates. The fibers, collected on a ground surface, form a nonwoven mat that enhances the efficiency and properties of the photocatalyst through improved charge separation and stability.

Kim et al. developed Pt-loaded TiO₂ nanofibers using an electrospinning method with polyethylene oxide solutions containing Ti(OH)n nanoparticles to enhance the catalytic activity for water-gas shift reactions³⁷. A Ti(OH)n slurry was prepared through the hydrolysis and precipitation of TiCl₄, and the electrospinning process produced stable solutions that were advantageous over traditional sol-gel methods. Adding 0.25 wt% Pt to the Ti(OH)_n slurry resulted in Pt-loaded TiO₂ nanofibers with a morphology similar to that of pure TiO₂ nanofibers owing to the small amount of Pt. The photocatalytic activity of the Pt-loaded nanofibers was five to seven times higher than that of the bulk catalyst, which is attributed to the effective dispersion of Pt.

Electrospinning can also be used to fabricate perovskite-based nanofibers, as illustrated in Fig. 2a³⁸. However, drying and calcination processes at high temperatures are required to effectively disperse metal cocatalysts, such as Pt, in perovskite nanofibers. Unlike metal oxides, such as TiO₂, perovskite materials exhibit poor thermal stability. Organic-inorganic perovskites degrade at temperatures around 150 °C or higher, while all-inorganic perovskites, such as CsPbBr₃, degrade from 300 to 400 °C³⁹. Therefore, uniformly dispersing metal cocatalysts on perovskite materials using the electrospinning method can be challenging owing to the thermal sensitivity of perovskite materials. Adaptations, such as implementing low-temperature annealing methods or applying protective polymer coatings, could offer substantial benefits in maintaining the structural integrity of thermally sensitive materials. Low-temperature annealing, for instance, can minimize the risk of thermal degradation to the perovskite support. Meanwhile, polymer coatings around perovskite particles may provide an additional buffer against thermal stress, protecting the support structure during the electrospinning and post-processing stages and enabling stable, uniform SAC deposition.

Strong electrostatic adsorption (SEA) involves the deposition of metal ions onto a support material via electrostatic forces⁴⁰. The procedure begins with modifying the pH of the solution to create a charged support surface. Next, a metal precursor with an opposite charge is added, causing the metal ions to be adsorbed onto the support via electrostatic attraction. Following the adhesion of metal ions to the support, the material is dried and typically undergoes hydrogen reduction to convert the metal ions into metallic atoms. This conversion resulted in metal atoms being uniformly distributed across the support. Such uniform dispersion is crucial because it enhances the catalytic properties of the material. SEA is particularly effective at ensuring a high level of dispersion. In addition, it provides a strong anchoring of the metal atoms to the support. This anchoring is vital for achieving optimal catalytic efficiency.

Sun et al. deposited Pd on CeO₂ using SEA and compared it with impregnation methods, as depicted in Fig. 2b⁴¹. The characteristics of the Pd nanoparticles were significantly influenced by the chosen preparation technique. The sample prepared using impregnation exhibited poor Pd dispersion, whereas the sample prepared using SEA exhibited better Pd dispersion. This was supported by the turnover frequency (TOF) values, indicating that SEA can enhance catalytic activity. Zang et al.⁴² used SEA to load Pt single-atoms (Pt-SAs) onto shape-controlled anatase TiO₂ supports. The essential calcination step determines the final distribution of Pt atoms on the TiO₂ surface, with Pt atoms remaining on the (101) surface and migrating beneath the (001) surface. This difference creates varied coordination environments, affecting the performance of the Pt/TiO₂ catalysts. This process is initiated by adjusting the pH to charge the TiO₂ surface, allowing the adsorption of oppositely charged Pt precursors through strong electrostatic attraction. Subsequently, hydrogen reduction converts the Pt ions into uniformly dispersed Pt single atoms on the TiO₂ surface. Because of their unique coordination environments, SACs offer the advantages of providing more active sites and optimizing the use of metal atoms, resulting in enhanced efficiency⁴³.

Despite the promise of single-atom metal deposition on perovskite materials, the process presents considerable challenges. These obstacles stem from the inherent instability of perovskite materials, the high temperatures required for metal precursor reduction, and the fragile nature of the metal-halide bonds. Consequently, achieving the stable anchoring of single metal atoms on perovskite materials could lead to significant improvements in their catalytic performance and stability. Overcoming these difficulties requires addressing the instability of the material, optimizing the reduction temperatures, and strengthening the metal-halide interactions. Successful tackling of these issues holds the potential for groundbreaking advancements in this area. By resolving these challenges, substantial progress in catalytic technology can be realized, considerably driving the field. Implementing buffering agents or localized pH control could help adapt the SEA method for the pH-sensitive materials.

Zhou et al. deposited Pt-SAs onto Cs₂SnI₆ using complementary impregnation techniques⁴⁴. They synthesized Cs₂SnI₆ via a hydrothermal treatment and impregnated it with a Pt complex. Pt-SAs/ Cs₂SnI₆ were obtained after activation at 160 °C for 1 h under an H₂/Ar atmosphere, as depicted in Fig. 2c. By integrating charge-carrier dynamics studies and density functional theory (DFT) calculations, they compared Pt-SAs with Pt nanoparticles (Pt-NPs) and discovered that the Pt-SAs exhibited higher photocatalytic activity because they have a much lower energy barrier and significantly higher electron density than Pt-NPs. The TOF of the Pt-SA/Cs₂SnI₆ catalyst was 176.5 times higher than that of the Pt-NP/Cs₂SnI₆ catalyst. This significant improvement underscores the importance of SACs for achieving higher catalytic activity. While the synthesis methods described above are promising, they require high temperatures, pressures, and voltages. Implementing low-temperature annealing methods or applying protective polymer coatings, as in the electrospinning method, could potentially mitigate thermal stress on temperature-sensitive supports. However, if the annealing temperature does not reach a sufficient level, the anchoring reaction required for stable single-atom placement may be incomplete, potentially compromising the uniformity and stability of the deposited atoms. To overcome these challenges, the photodeposition method offers an effective alternative, as it can achieve single-atom anchoring without the need for high temperatures, pressures, or complex processing conditions. This method involves illumination of the photocatalyst in a metal precursor solution. There are two methods of photodeposition: reductive and oxidative, as described in Fig. 2d⁴⁵. When light excites the photocatalyst, it generates electron-hole pairs. The electrons in the conduction band reduce metal ions to form metallic deposits, while the holes in the valence band oxidize metal ions to produce metal oxides, respectively. This process typically occurs under UV or visible light, depending on the properties of the photocatalyst. As a result, a uniform distribution of metal cocatalysts forms on the photocatalyst, enhancing its catalytic efficiency by improving charge separation and reactivity. Qin et al. introduced a novel catalyst consisting of Pt-SAs uniformly dispersed on CsPbBr₃ nanocrystals (NCs) using this method⁴⁶. The process was initiated by dispersing the CsPbBr₃ NCs in a solution containing the Pt precursor. Under illumination with UV or visible light, the photocatalyst (CsPbBr₃) generated electron-hole pairs. The photogenerated electrons reduced the Pt ions from the precursor, causing them to be deposited onto the surface of the CsPbBr₃ NCs. This resulted in a uniform distribution of Pt-single-atoms on the NCs, enhancing their electrocatalytic properties for ascorbic acid sensing. An important consideration in this method is the adsorption energy of the cocatalyst for the photocatalysts. Hu et al. also demonstrated that Pt-SAs could be deposited on CsPbBr₃ NCs using photodeposition⁴³. They compared the effects of depositing Pt-SAs and Pt-NPs on CsPbBr₃ NCs. The Pt-SA anchored on the oxidized CsPbBr₃ surface formed strong Pt-O and Pt-Br bonds with high adsorption energies, preventing aggregation. This oxidation occurred under ambient conditions, stabilizing the single atoms. In contrast, Pt-NP formed on the unoxidized CsPbBr₃ surface under inert conditions, where Pt atoms were more likely to aggregate because of the lower adsorption energy and the use of capping ligands such as oleic acid and oleylamine as reducing agents. It is noteworthy that both Pt-SA and Pt-NP deposition methods utilize photodeposition. Despite using the same synthesis method, the deposition of Pt varied significantly depending on the synthesis conditions. In this study, to investigate the impact of oxidation, a comparison was made between CsPbBr₃ NCs synthesized inside a glove box to prevent oxidation and those synthesized outside the glove box to induce oxidation. Although it was expected that synthesis inside the glove box would yield more stable NCs, the results showed that oxidized CsPbBr₃ synthesized under normal conditions was more suitable for anchoring Pt-SAs. These results demonstrate that the synthesis method and necessary conditions vary depending on the type of perovskite material and the specific single metal atom used. This underscores the importance of optimizing synthesis conditions (Table 1).

a Electrospinning method. Reproduced with permission³⁸. Copyright 2018 John Wiley and Sons. b Strong electrostatic adsorption and impregnation method. Reproduced with permission⁴¹. Copyright 2018 Elsevier. c Impregnation and activation method. Reproduced with permission⁴⁴. Copyright 2021 Springer Nature. d Reductive photodeposition (left) and oxidative photodeposition (right) method. Reproduced with permission⁴⁵. Copyright 2022 Elsevier.

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After successfully depositing single metal atoms onto the support under the optimized synthesis conditions, it is essential to verify the quality of the deposition. The positioning of metal atoms at specific anchoring sites can influence their stability and reactivity, thereby dictating overall catalytic efficiency. For optimal catalytic performance, the single atoms should be properly anchored and not form clusters. Furthermore, the electronic properties of the metal centers are essential for shaping the interactions between the catalyst and reactants⁴⁷. Variations in the electronic properties can lead to different activation energies and reaction intermediates, thus altering the reaction mechanisms. Advanced characterization techniques are essential for probing these atomic details. Understanding these intricate relationships will allow for the rational design of SACs with enhanced catalytic properties. Consequently, tailoring the atomic and electronic structures of SACs can significantly improve their catalytic performance and selectivity.

XPS is a powerful method for examining the surface chemistry of materials by detecting the kinetic energy of photoelectrons released from a sample⁴⁸. When a sample is exposed to X-ray radiation, photons interact with atoms and emit core-level electrons. The kinetic energies of these ejected electrons were recorded, and their binding energies were determined using the principles of the photoelectric effect. This binding energy reveals the elemental makeup and chemical states of the atoms in the sample. Each peak in the XPS spectrum signified a particular element and its chemical environment, facilitating qualitative and quantitative analyses. By studying the variations in binding energy, information regarding the oxidation states and electronic surroundings of the atoms can be deduced. Furthermore, XPS can be used to assess the surface composition and thickness of thin films by varying the X-ray incidence angle. This technique is essential for investigating the surface chemistry and other properties of nanomaterials. Therefore, XPS can detect subtle shifts in the binding energies, indicating changes in the electronic structure resulting from single-atom deposition. By analyzing these shifts, XPS enables precise identification of the coordination environment of single atoms and their interaction with specific atomic anchor sites. This capability sets XPS apart from other chemical composition analysis techniques, such as energy-dispersive X-ray spectroscopy, demonstrating its unique advantage in detecting detailed electronic structure changes induced by single-atom deposition.

Qin et al. conducted XPS analysis to compare the electronic states of CsPbBr₃ NCs with those of Pt-SAs deposited on CsPbBr₃ NCs⁴⁶. A comparison of the two samples showed that the loading of the Pt-SAs caused a noticeable positive shift in the spectra (Fig. 3a–f). This shift indicated that the Pt-SAs were successfully deposited onto the CsPbBr₃ NCs.

XPS spectra of a Cs 3 d c Br 3 d e Pb 4 f in Pt SAs/CsPbBr₃, and b Cs 3 d d Br 3 d f Pb 4 f in CsPbBr₃ NCs, respectively. Reproduced with permission⁴⁶. Copyright 2024 Elsevier. XPS spectra of g Pt/TiO₂-truncataed bipyramid h TiO₂-truncataed bipyramid i Pt/TiO₂-nanosheet j TiO₂-nanosheet. Reproduced with permission⁴². Copyright 2024 Springer Nature.

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Zang et al. also conducted an XPS analysis to compare the spectra of TiO₂ samples with and without Pt-SAs⁴². They compared the presence and absence of Pt-SAs and TiO₂-nanosheet and TiO₂-truncated bipyramid samples (Fig. 3g–j). Pt was mostly found beneath the surface of the TiO₂-nanosheets, whereas on TiO₂-truncated bipyramids, Pt was predominantly located on the surface. However, although XPS is effective in confirming the deposition of metals on a sample surface, it has limitations in distinguishing whether the metals are present as single atoms, nanoparticles, or clusters. Therefore, high-resolution imaging techniques such as high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and extended X-ray absorption fine structure (EXAFS) analysis are required to determine whether the metal is in the form of single atoms.

HAADF-STEM is an advanced imaging technique that employs a high-angle annular detector to capture scattered electrons, producing Z-contrast images in which the intensity is proportional to the atomic number⁴⁹. This technology enables the direct visualization of individual metal atoms on a supporting material owing to its high sensitivity to variations in atomic number and its capability to generate high-resolution images. HAADF-STEM allows the spatial distribution and coordination environments of single atoms to be precisely mapped. This level of detail is crucial for understanding the behavior and effectiveness of single-atom cocatalysts. High-resolution imaging makes it possible to observe how the atoms are dispersed on the support material and how they interact with their surroundings. Furthermore, HAADF-STEM can reveal information about the atomic arrangement and bonding characteristics, providing insights into the structural properties that influence catalytic performance.

Figure 4a, c shows the schematic illustration of Pt-SAs dispersed on TiO₂-nanosheet and TiO₂-truncated bipyramid, respectively⁴². The related atomic models for the (001) surface and (101) surface are depicted in Fig. 4b, d, respectively. From these figures, Zang et al. revealed that, as previously mentioned, Pt is primarily located beneath the surface on TiO₂-nanosheets, whereas on TiO₂-truncated bipyramids, Pt is predominantly found on the surface. In the HAADF-STEM images shown in Fig. 4e, f, Pt-SA is highlighted within the dotted yellow circle. Pt-SAs are dispersed along the [001] projection of the TiO₂-nanosheet (Fig. 4e) and on the (101) surfaces of the TiO₂-truncated bipyramid (Fig. 4f). Therefore, it can be concluded that HAADF-STEM images effectively reveal the distribution of single-atoms on the support surface when analyzing SACs.

a Schematic of Pt SAs on TiO₂-nanosheet, b atomic model for the (001) surface, c schematic of Pt SAs on TiO₂-truncated bipyramid, d atomic model for the (101) surface, e HAADF-STEM images of Pt SAs/TiO₂-nanosheet, f HAADF-STEM images of Pt SAs/TiO₂-truncated bipyramid. Reproduced with permission⁴². Copyright 2024 Springer Nature. g HAADF-STEM images of Au SAs/LaFeO₃/Mesoporous cellular foam (MCF). Reproduced with permission⁵¹. Copyright 2020 Elsevier.

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They also confirmed that a low Pt loading (0.05 wt%) allows for the deposition of primarily Pt-SAs on TiO₂ supports, whereas higher loading can cause increased atom interactions and clustering, degrading the catalytic performance specific to single atoms. Wu et al. also showed that Pt-SAs tended to aggregate into small clusters as the Pt loading amount increased⁵⁰. Therefore, when anchoring a single atom, it is important to optimize the loading amount and synthesis method. The reason there are many cases of Pt-SA deposition among various metal single-atoms is that Pt has the highest work function, resulting in superior photocatalytic activity⁵¹. However, because of the high cost of Pt, other noble metals can be used as alternatives. Tian et al. developed single-atom Au catalysts supported on perovskite oxides⁵². They confirmed atomically dispersed Au atoms without any Au clusters or nanoparticles in the HAADF-STEM images, as illustrated in Fig. 4g.

However, due to the inherent instability of halide perovskites under electron beam exposure, confirming the presence of single atoms on these supports with HAADF-STEM can be challenging, as structural damage may occur. To mitigate this, electron beam intensity can be carefully managed by reducing exposure time and lowering screen current, which helps to minimize damage while maintaining high-resolution imaging capabilities. Such adjustments are crucial for capturing the atomic arrangement on perovskites, enabling detailed visualization of single atoms while reducing the risk of decomposition.

X-ray absorption fine spectroscopy (XAFS) involves irradiating samples with X-rays and measuring the resulting changes in absorbed X-ray energy, thereby providing insights into the atomic and electronic structures, chemical states, and physical properties of the material. XAFS analysis can be divided into two main components: X-ray absorption near-edge structure (XANES) and EXAFS⁵³. XANES focuses on the region near the absorption edge of an X-ray spectrum. This region provided detailed information on the oxidation states of the elements in the sample. Additionally, XANES helps understand the electronic structure around the absorption edge, providing insights into the local chemical environment and symmetry of the atoms. In contrast, EXAFS deals with the region beyond the absorption edge, known as the post-edge region. EXAFS analysis is crucial for determining the distances between neighboring atoms, which helps to elucidate the coordination number and type of neighboring atoms around a specific element. By analyzing fine oscillations in the absorption spectrum in the post-edge region, EXAFS provides precise structural information at the atomic level. Together, XANES and EXAFS offer a comprehensive understanding of the electronic and atomic structures of the materials. XAFS is particularly useful for analyzing the dispersion of single atoms in a material due to its sensitivity to local atomic environments⁵⁴. XANES profiles help identify whether the atoms are single or form clusters, and EXAFS profiles reveal how these single atoms are coordinated with the surrounding atoms, mitigating the limitations of XPS. Qin et al. analyzed the electronic structure and coordination of Pt-SAs in CsPbBr₃ NCs using XANES and EXAFS profiles⁴⁶. The XANES profile indicated that the Pt in the Pt-SA/CsPbBr₃ NCs was oxidized, similar to PtO₂, as shown in Fig. 5a, b. The EXAFS spectra revealed prominent peaks for the Pt–O and Pt–Br bonds, confirming the presence of isolated Pt atoms without Pt–Pt contributions, as illustrated in Fig. 5c. The spectra indicated that the Pt atoms were well dispersed on the CsPbBr₃ NCs. The wavelet transform (WT)-EXAFS spectra further supported the isolated nature of the Pt atoms, showing maxima consistent with those of Pt–Br₂ and PtO₂ and no Pt–Pt scattering signals (Fig. 5d).

a XANES spectra of Pt SA/CsPbBr₃ and Pt SA/Cs₂SnI₆, b zoomed-in view of the Pt K-edge for Pt SA/CsPbBr₃, c Fourier transform of the EXAFS spectra, and d wavelet transform of the EXAFS signals for Pt foil, PtO₂, and Pt SAs/CsPbBr₃. Reproduced with permission⁴⁶. Copyright 2024 Elsevier. e XANES spectra of Pt SA/Cs₂SnI₆, f Fourier transform spectra at k-space, g Fourier transform spectra at R space, h XANES k-space fitting curves of Pt SAs/Cs₂SnI₆, i XANES R space fitting curves of Pt SAs/Cs₂SnI₆, and j XPS spectra of Pt 4 f in Pt SAs/Cs₂SnI₆. Reproduced with permission⁴⁴. Copyright 2021 Springer Nature.

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Zhou et al. investigated the oxidation state and coordination environment of the Pt species in Pt-SA/Cs₂SnI₆ using XAFS spectroscopy⁴⁴. The Pt L₃-edge XANES spectra revealed that the Pt in Pt-SA/Cs₂SnI₆ had an oxidation state higher than +2, as illustrated in Fig. 5e. The EXAFS spectra (Fig. 5f, g) showed a prominent peak at ~2.49 Å, indicating that Pt atoms are anchored on the surface by Pt–I bonds, with each Pt atom coordinated with approximately three I atoms. WT-EXAFS further confirmed the atomic dispersion of Pt, showing a maximum similar to the Pt–I bond in Pt–I₂ rather than the Pt–Pt bond in the Pt foil, indicating isolated Pt atoms on the surface of Pt-SA/Cs₂SnI_6, as shown in Fig. 5h, i. Figure 5j further supported these findings, as the XPS spectrum of Pt 4 f in Pt-SA/Cs₂SnI₆ reveals a mixed oxidation state of Pt²⁺ and Pt⁴⁺ (2 < δ < 4), aligning well with the Pt L₃-edge XANES results.

However, XAFS can only provide the average distance to surrounding atoms, meaning it cannot pinpoint each atom’s exact location. Although it can detect bond length variations, its precision falls short of the sub-nanometer level needed to determine the precise anchoring sites of single atoms within the perovskite lattice. These limitations can be addressed by atom probe tomography (APT), which offers precise 3D mapping at the sub-nanometer scale.

APT is a technique that reveals 3D images and chemical composition at the atomic level⁵⁵. As the atoms are ionized and ejected, they travel to a position-sensitive detector that records their time-of-flight and impact positions. Time-of-flight data were used to determine the mass-to-charge ratio of the ions and identify their elemental composition. At the same time, the impact positions enable the reconstruction of the three-dimensional atomic structure at near-atomic resolution. Its high spatial resolution enables the detection and visualization of the distribution of single atoms. Owing to its capability of providing atomic scale 3D coordinates, it allows for detailed observation of how anchored single atoms are distributed within the perovskite structure. For example, unlike XAFS, which only provides average interatomic distances, APT can precisely determine the exact position of a single atom within the perovskite lattice and the specific distances to surrounding atoms. Additionally, APT enables the detection of trace elements at the ppb level. This precise combination of compositional and spatial information renders APT particularly useful for studying anchored single atoms. Thus, APT is highly valuable for studying the detailed atomic structure, chemical composition, and elemental distribution of a material. Its ability to analyze single atoms makes it an indispensable tool.

Jiang et al. confirmed the existence of single Fe atoms dispersed in a carbon nanotube (CNT) through APT analysis (Fig. 6a–c)⁵⁶. They revealed that isolated Fe atoms were dispersed in the carbon support. The 3D tomography image collected from nine million atoms and the 2D projection show that single Fe atoms may bind to neighboring C and O atoms, indicating possible Fe–C–O coordination. Although APT cannot provide the exact atomic structure due to signal loss, it effectively identifies the distribution and coordination environments of single atoms on the support⁵⁵. The green dots in Fig. 6a represent uniformly dispersed Fe atoms. Figure 6b shows a 2D contour map of the C atom distribution around a CNT, and, as depicted in Fig. 6c, single Fe atoms are well distributed along the CNT.

a APT data of Fe-CNT catalyst, b 2D contour map of carbon atom distribution in Fe-CNT, and c reconstructed APT data surrounding a CNT. Reproduced with permission⁵⁶. Copyright 2019 Springer Nature. d 2D projection of NiN-GS, e 2D projection of Ni atoms in NiN-GS, f 2D contour map of Ni concentration, g close-up side view (top) and top view (bottom) of graphene layers with Ni single atoms located in vacancies, h atomic map of the area highlighted by the yellow circle in Fig. 6d, and i the statistical analysis of the area highlighted in Fig. 6h. Reproduced with permission⁵⁷. Copyright 2019 Elsevier.

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Jiang et al. studied the coordination of Ni SACs to a graphene shell for CO₂ reduction before their work on Fe single atoms⁵⁷. They reported Ni single atoms as active centers for CO₂ reduction and introduced APT to confirm the presence of Ni single atoms in the graphene shells. The Ni nanoparticle–graphene shell (NiN-GS) catalyst is shown as a 2D projection in Fig. 6d, where each pixel represents a single atom and highlights areas with dispersed Ni atoms. The detailed view in Fig. 6e indicates numerous Ni atoms distributed in carbon away from the concentrated Ni regions, which is consistent with the EDX mapping results. As depicted in Fig. 6f, a contour map with 2 at% intervals provides detailed distribution information, showing decreased Ni concentrations further away from the Ni sources. The local coordination environment within the graphene layers is illustrated in Fig. 6g, revealing some Ni single atoms in the graphene vacancies. The area marked by the yellow circle in Fig. 6h is enlarged in Fig. 6d, demonstrating that 83% of the Ni atoms were single atoms without neighboring Ni atoms closer than 2.2 Å. Finally, a statistical and quantitative analysis of the Ni atomic sites is presented in Fig. 6i, indicating that only 0.2% of the Ni single atoms are coordinated with N atoms, with most being coordinated with C atoms.

Photocatalytic hydrogen generation

The photocatalytic hydrogen evolution reaction is a groundbreaking approach to hydrogen generation that harnesses the absorption of visible light by semiconductor materials to facilitate the water-splitting process⁵⁸. Despite the superior efficiency of noble metal catalysts such as Pt, Pd, and Au, their prohibitive cost and scarcity necessitate the exploration of non-precious metal alternatives. The efficacy of the HER hinges on overcoming challenges related to energy band tuning, photogenerated carrier recombination, and surface reaction kinetics. Therefore, researchers have focused on optimizing cocatalysts and constructing heterojunctions to enhance photocatalytic performance and ensure sustainable, large-scale green hydrogen production. Heterojunction perovskite photocatalysts employing various architectures, such as the S-scheme, direct Z-scheme, and indirect Z-scheme, are advanced materials recognized for their improved charge transfer efficiency (Fig. 7)⁵⁹. In these systems, photoexcited electrons in the conduction band of semiconductor I are transferred to the valence band of semiconductor II, spatially separating the electrons and holes to minimize charge recombination and enhance the redox potential. The Z-scheme and S-scheme mechanisms utilize the Fermi level differences between semiconductors I and II to facilitate efficient charge separation and transfer, thereby improving photocatalytic efficiency. This capability generates high-energy electrons and holes that are essential for catalyzing redox reactions and hydrogen production. Noteworthy substances for constructing heterojunctions with perovskites and establishing Z/S schemes include MOFs⁶⁰, TiO₂⁶¹, molybdenum disulfide (MoS₂)⁶², and g-C₃N₄⁶³. In addition, anchoring single atoms onto perovskites offers significant advantages, such as enhancing catalytic activity, suppressing electron-hole recombination, ensuring structural stability, maximizing atom efficiency, and promoting environmental sustainability in energy production technologies.

a Z-scheme and b S-scheme. Reproduced with permission⁵⁹. Copyright 2021 John Wiley and Sons.

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Zhou et al. introduced a novel class of Single-atom Pt-I₃ sites anchored onto all-inorganic Cs₂SnI₆ perovskites (Pt-SA/Cs₂SnI₆) using an environmentally friendly approach to enhance H₂ evolution through HI splitting⁴⁴. Pt-SA/Cs₂SnI₆ achieved a TOF 176.5 times higher than Pt nanoparticles anchored on Cs₂SnI₆, demonstrating superior catalytic stability that surpasses all previously reported Pt-loaded halide perovskite photocatalysts. Analysis of charge-carrier dynamics and theoretical calculations attribute this enhanced performance to the unique coordination structure and electronic properties of the Pt-I₃ sites, as well as the strong metal-support interaction effect. This interaction facilitated the efficient transfer of photogenerated electrons from Cs₂SnI₆ to Pt-SAs, thereby reducing the Gibbs free energy and accelerating the kinetics of hydrogen production. As depicted in Fig. 8a–d, the incorporation of Pt into Cs₂SnI₆ resulted in superior photocatalytic performance in an aqueous HI solution under visible light irradiation compared to pristine Cs₂SnI₆. Specifically, with an optimal Pt loading of 0.12 wt%, Pt-SA/Cs₂SnI₆ demonstrated significantly improved H₂ generation (403 μmol h⁻¹ g⁻¹), surpassing Pt-NP/Cs₂SnI₆ by 5.8 times, and achieved a TOF of 70.6 h⁻¹ per Pt, exceeding Pt-NP/Cs₂SnI₆ by 176.5 times (Fig. 8a, b). The degradation in performance due to higher Pt loading on the perovskite resulted from a reduction in the available light-absorbing active sites. Furthermore, Pt-SA/Cs₂SnI₆ maintained its photocatalytic stability over repeated cycles and a continuous 180-hour assessment, with Pt species remaining atomically dispersed on the surface of the perovskite (Fig. 8c, d). They employed DFT calculations to explore the electronic and catalytic distinctions between PtSA and PtNP on Cs₂SnI₆ HER. The findings reveal that PtSA demonstrates a more favorable electronic structure and catalytic efficiency. Specifically, projected density of states analysis indicated that the electron density localized around PtSA is significantly higher, with an integrated area of uncaptured Pt 5 d states above the Fermi level calculated at 0.71 for PtSA, compared to 1.19 for PtNP, indicating a greater electron-saturated state in PtSA. Additionally, the free energy barrier for hydrogen evolution on PtSA was determined to be 0.11 eV, substantially lower than the 0.92 eV barrier observed for PtNP. This distinct advantage underscores PtSA’s enhanced catalytic activity and its strong potential to improve photocatalytic hydrogen production efficiency. In conclusion, due to their soft chemical bonds, flexible crystal structure, and inherent defect sites that serve as anchoring traps, halide perovskites stand out as promising supports for single-atom stabilization, comparable to oxide perovskite materials.

a Photocatalytic H₂ evolution rate assessed for Pt-SA/Cs₂SnI₆, Pt-NP/Cs₂SnI₆, and Cs₂SnI₆ catalysts using a 300 W Xe lamp as the light source, with the reaction temperature held at 25 °C by a circulating water-cooling system; b TOF activity of Pt-SA/Cs₂SnI₆ and Pt-NP/Cs₂SnI₆ catalysts as a function of Pt loading; c comparison of the TOF and H₂ evolution rate of Pt-SA/Cs₂SnI₆ with previously reported perovskite-based catalysts; and d extended photocatalytic activity of Pt-SA/Cs₂SnI₆ for 24 h. Reproduced with permission⁴⁴. Copyright 2021 Springer Nature. e Photocatalytic H₂ production rates under solar light for pristine FAPbBr₃ and w-Pt/FAPbBr₃-_XI_X (where w indicates the Pt loading amount confirmed through Inductively Coupled Plasma Spectrometry (ICP)), f durability assessment of hydrogen generation for 1.8-Pt/FAPbBr₃-_XI_X, and analysis of catalytic properties before and after cycling tests using g XRD and h Cs-STEM. Reproduced with permission⁵⁰. Copyright 2022 RSC Publishing.

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Wu et al. examined Pt-SAs anchored on a perovskite substrate (Pt/FAPbBr_3-xI_x) for their efficacy in photocatalytic H₂ evolution under simulated sunlight⁵⁰. As illustrated in Fig. 8e, f, while pristine FAPbBr_3-xI_x exhibited a modest photocatalytic activity of 39.8 μmol h⁻¹, the introduction of 1.8% Pt loading on FAPbBr₃-_xI_x (1.8-Pt/FAPbBr_3-xI_x) significantly enhanced its performance to 682.6 μmol h⁻¹. Additionally, extended stability tests over 30 h demonstrated minimal performance degradation, as unveiled by various characterization techniques, including XRD and STEM-HAADF, which verified sustained structural integrity and Pt atom dispersion (Fig. 8g, h). SACs supported on perovskites exhibit excellent performances as photocatalysts for hydrogen evolution. However, the loading amount significantly affects efficiency, necessitating the optimization of single-atom quantities while preserving the active sites.

CO oxidation

CO, a colorless but highly toxic gas, arises from the incomplete combustion and partial oxidation of hydrocarbon fuels. Its conversion to CO₂ aims to alleviate the detrimental effects of catalysts, particularly in fuel cell applications. The process of CO oxidation typically adheres to the Langmuir-Hinshelwood (L-H) mechanism, which involves the adsorption of O₂ and CO, starting with O₂ dissociation and culminating in the reaction between adsorbed O and CO^64,65. Currently, the dominant approach for CO oxidation employs noble metal catalysts, notably palladium; however, their widespread use is limited by their high costs. Consequently, there is ongoing research on alternative materials that can serve as cost-effective substitutes for these catalysts. One particularly promising catalyst among these is the cost-competitive SA-PCs. Kothari et al. introduced fully Pt-doped perovskite materials (Pt@LCT and Pt@LST perovskites), each containing 0.5 wt% Pt in their crystal structures (La_0.4Ca_0.3925Ba_0.0075Pt_0.005Ti_0.995O₃ and La_0.4Sr_0.3925Ba_0.0075Pt_0.005Ti_0.995O₃, respectively), engineered to enhance catalytic efficacy⁶⁶. They employed high-temperature solid-state synthesis to improve phase purity and stability. Pt@LCT exhibited superior activity and sintering resistance compared to traditional Pt/γ-Al₂O₃ catalysts, underscoring the effectiveness of dispersed Pt nanoparticles on the perovskite surface in promoting efficient oxidation reactions and suggesting potential practical applications in emission control. Specifically, Pt@LCT was developed to enhance CO oxidation efficiency, achieving 100% CO conversion at 190 °C and retaining high activity under low oxygen conditions (Fig. 9a). Experimental findings demonstrated that non-doped perovskite had minimal catalytic activity, but the incorporation of Pt significantly boosted the performance, especially with the emergence of Pt nanoparticles. Additionally, as shown in Fig. 9b, Pt@LCT outperformed commercial Pt/γ-Al₂O₃ and maintained stability during aging tests at 800 °C for over two weeks, whereas impregnated Pt/LCT and Pt/γ-Al₂O₃ displayed significant Pt agglomeration and reduced activity.

a CO conversion rate for a Pt-perovskite and Pt/γ-Al₂O₃ photocatalysts at various temperatures (50–300 °C) with a gas flow rate of 200 ml/min and b CO conversion rate of Pt-perovskite and Pt/γ-Al₂O₃ photocatalysts after an aging test at 800 °C for 2 weeks with a 50 ml/min gas flow. Reproduced with permission⁶⁶. Copyright 2021 Springer Nature. c CO light-off plots for LaFeO₃/MCF and Au₁/LaFeO₃/MCF and d Comparative analysis of catalytic activity vs. time-on-stream for LaFeO₃/MCF and Au₁/LaFeO₃/MCF photocatalysts⁵². Copyright 2020 Elsevier.

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Tian et al. engineered a novel class of supported Au SACs using a heterostructured perovskite support (Au₁/LaFeO₃/mesoporous cellular foam; MCF)⁵². They achieved remarkable thermal stability up to 700 °C and demonstrated heightened catalytic efficiency for CO oxidation, along with distinctive self-activation under operational conditions. This work represents a pioneering advancement in this field and opens avenues for further exploration of catalyst design and applications. By validating their findings through theoretical calculations and experimental evidence, they definitively identified that the surface Au active sites predominantly display a positively charged state, emphasizing their potential as durable and effective catalysts. As depicted in Fig. 9c, Au₁/LaFeO₃/MCF catalysts were engineered for efficient CO oxidation, achieving 100% CO conversion at 170 °C, attributed to the catalytic activity of single Au atoms that facilitate oxygen dissociation and surface oxide generation. The Au₁/LaFeO₃ catalyst maintained consistent performance over 90 h at elevated temperatures, highlighting its robust stability (Fig. 9d). Leveraging insights from previous studies, it has been established that integrating single atoms with perovskite substrates profoundly augments the efficacy of the L-H mechanism during CO oxidation. While this investigation focuses on perovskite-supported catalysts, ceria (CeO₂) and MCFs are also employed as substrates for deploying single-atoms in CO oxidation at low temperatures^67,68.

Further applications

The application of perovskite as a single-atom support is impeded by its inherent structural and chemical instability, defect states, reduced charge-carrier mobility, and mechanical susceptibility. Consequently, there is a notable scarcity of studies addressing the various synthesis routes, characterization techniques, and applications. In this section, we briefly report the various applications of perovskite catalysts embedded with single atoms and examine the specific characteristics of these SA-PCs for each application.

Wan et al. examined Pt₁ single atoms supported on Sr-based perovskites (SrBO₃) for methane adsorption and activation⁶⁹. Employing DFT, they scrutinized the effect of varying B ions on the interaction between Pt₁ and SrBO₃, revealing that Pt₁ on the A terminations of SrTiO₃(100) and SrVO₃(100) exhibited the most advantageous characteristics for methane chemisorption and activation, despite showing lower stability than bulk Pt (Fig. 10a). They found that Pt₁ on A terminations, being negatively charged, facilitated strong, chemical, and occasionally dissociative methane adsorption, whereas Pt₁ on B (or BO₂) terminations, being positively charged, leads to weaker physical adsorption. These insights suggest that Pt₁ single-atoms on the A terminations of SrBO₃(100) are well suited for methane C–H bond activation, highlighting their potential for effective methane conversion (Fig. 10b).

a Adsorption energy of Pt-SAs on the SrBO₃ (100) perovskite surface, with B being Ti, V, Cr, Mn, Fe, Co, Ni, or Cu and b CH₄ absorption energy of Pt₁ single-atoms on the A and B terminations of the SrBO₃(100) surface. Reproduced with permission⁶⁹. Copyright 2020 RSC Publishing. c TOFs and propylene selectivity values for Pt/CsPbBr₃ with 0.22, 0.35, 0.71, and 1.04 wt% Pt and d long-term durability testing of the optimal 0.71 wt% Pt/CsPbBr₃ sample. Reproduced with permission⁴³. Copyright 2021 American Chemical Society.

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Another notable application of propyne semi-hydrogenation (PSH) is in which propyne (C₃H₄) undergoes selective partial hydrogenation to yield propene (C₃H₆) while circumventing excessive hydrogenation to propane (C₃H₈). This reaction is pivotal in the petrochemical industry for the refinement and enhancement of olefin streams, where propene serves as a critical precursor for the synthesis of various chemicals and polymers, including polypropylene. Precise control of the extent of hydrogenation is essential for maximizing the yield and maintaining high product purity. Hu et al. advanced the field by employing CsPbBr₃ NCs as a matrix to stabilize Pt-SA/CsPbBr₃, thereby enhancing their catalytic performance for photocatalytic PSH⁴³. They discovered that partial oxidation of the CsPbBr₃ surface induces Pb–O bond formation, which effectively anchors Pt single atoms and stabilizes them through interactions with Br atoms, thereby eliminating the need for high-temperature treatment. As shown in Fig. 10c, d, increasing the Pt loading increased the TOF of PSH, with Pt-SA/CsPbBr₃ demonstrating exceptional stability and selectivity over extended cycles, whereas Pt nanoparticles on CsPbBr₃ exhibited inferior stability and reduced catalytic performance.

Yang et al. synthesized a Pd-SrTiO₃ photocatalyst, wherein Pd is anchored as single atoms on the SrTiO₃ perovskite support, facilitating the semi-hydrogenation of phenylacetylene to styrene. The interaction between Pd and the SrTiO₃ matrix leads to an optimized electronic structure that overcomes the low stability of Pd metal, achieving an outstanding selectivity of 99.9%⁷⁰.

Offering a greener alternative to ammonia synthesis, the electrochemical nitrogen reduction reaction (ENRR) contends with the difficult N≡N bond and concurrent hydrogen evolution. Ammonia (NH₃), essential for industries ranging from fertilizers to pharmaceuticals, is predominantly produced through the energy-demanding and environmentally detrimental Haber-Bosch process. Despite promising developments in the use of perovskite oxides for the ENRR, significant advancements are still needed, highlighting the necessity for continued research into more efficient catalysts. By applying plasma-enhanced chemical vapor deposition (PECVD), Han et al. incorporated transition metals (TMs, such as Pt, Ru, Pd, Co, and Ni) into perovskite oxides (LaMO, with M=Cr, Mn, Fe, Co, and Ni), thereby substantially improving their catalytic efficacy for the ENRR⁷¹. The Ru-doped perovskite oxide (LaFeO₃-Ru) stands out with a Faradaic efficiency of 57% at −0.7 V vs RHE, significantly surpassing the performance of current SACs. It also achieves a yield rate of 137.5 µg h^⁻1 mg_cat⁻¹, which is 8.3 times greater than that of pristine LaFeO₃.

With their remarkable energy density, lithium-oxygen (Li-O₂) batteries are emerging as a key technology for future low-carbon energy systems, including electric vehicles and advanced power grids⁷². These batteries consist of a lithium metal anode and porous oxygen cathode connected by a lithium-ion electrolyte. However, the formation of lithium peroxide (Li₂O₂) during discharge causes electrode passivation due to its insolubility and non-conductivity, which significantly hampers performance and underscores the need for advanced catalytic materials, such as high-entropy compounds, to overcome these challenges. The Ru SACs incorporated into lanthanum-based high-entropy perovskite oxide La(Mn_0.2Co_0.2Fe_0.2Ni_0.2Cr_0.2)O₃ (Ru@high-entropy perovskite oxide (HEPO)) for Li-O₂ batteries demonstrates remarkable electrochemical performance, achieving discharge and charge capacities of 12,275/11,882 mAh g⁻¹ and Coulombic efficiency of 96.8%, greatly surpassing the capabilities of conventional HEPO and LaMnO₃ (LMO) electrodes⁷³. This impressive efficiency is due to its exceptionally low overpotential (0.65 V, excellent kinetic properties, and outstanding rate capability, with a proven durability of 345 cycles without voltage degradation. Additionally, aerobic ODS, which employs HEPOs as single-atom supports, is a sophisticated approach for sulfur removal from fuels. This technique, which utilizes oxygen to oxidize sulfur compounds, stands out for its ability to deliver significant energy and cost savings, surpassing traditional methods that require elevated temperatures and pressures. Liu et al. unveiled Mo/HEPO-SAC as an exceptionally effective catalyst for the ODS of dibenzothiophene (DBT), significantly outperforming other materials⁷⁴. Mo/HEPO-SAC achieved complete DBT conversion within one hour, whereas pristine HEPO and LMO were inactive. The high Mo utilization and unique single-atom structure of the catalyst contributed to its superior performance, with kinetic studies indicating an activation energy of 71.6 kJ/mol. However, the ODS efficiency decreases as the DBT concentration increases, which is attributed to the limited number of active sites and slower product desorption.

Despite the limited research on SA-PCs, they have shown exceptional efficiency and distinct properties in various applications, including photocatalytic hydrogen evolution, CO oxidation, methane activation, ODS, nitrogen fixation, and PSH, far exceeding those of conventional perovskites (Table 2).

Summary and outlook

We elucidated innovative SA-PCs, including diverse synthetic approaches, detailed characterizations, and potential applications. SA-PCs exhibit exceptional optical performance, light absorption, and physicochemical characteristics derived from their distinctive properties; however, their applicability in a wide range of fields remains somewhat restricted.

1. 1.

   Inherent instability of perovskite materials (both environmental and mechanical robustness): several advanced strategies can be employed to address these challenges. One approach involves the incorporation of additives, such as chalcogenides, to enhance ionic bonding and improve stability. The formation of composites by combining perovskite materials with other substances is another effective method for improving stability⁷⁵. Furthermore, applying protective coatings or utilizing encapsulation technologies can mitigate mechanical stress, thereby preserving both the longevity and efficiency of perovskite materials.

2. 2.

   Toxicity concerns associated with lead-containing perovskite materials. One of the most widely recognized approaches involves the introduction of perovskites based on alternatives to lead, such as Sn, Bi, and Sb⁷⁶. Sn-based perovskites, particularly methylammonium lead iodide (MAPbI₃), have been frequently cited as promising candidates. However, they exhibit clear disadvantages in terms of stability and performance compared with lead-based perovskites. Mixed-cation perovskites are viable alternatives. These materials minimize Pb content while maintaining performance characteristics and are the subject of extensive research because of their potential to reduce toxicity.

3. 3.

   The complexity of synthesis techniques for perovskite and single-atom anchoring. In this study, we explored various synthesis methods for SA-PCs, including the electrospinning method, sea method, photoreduction, and heat treatment under an H₂ atmosphere. However, these methods are still under-researched. We propose several strategies to address these challenges. Simplifying complex synthesis techniques and adopting low-temperature synthesis processes can alleviate the difficulties associated with the low stability of perovskites. Additionally, by integrating the entire synthesis process, the processing time can be reduced through direct SA-PCs synthesis rather than sequential perovskite synthesis followed by single-atom anchoring.

4. 4.

   The scalability issue of SA-PCs. SACs have demonstrated scalability through synthesis methods that produce kilograms of material, suggesting the potential for large-scale industrial applications. Likewise, ongoing research into large-area and mass production of perovskites is yielding encouraging results, with notable advancements in the scalability and uniformity of these materials. However, adopting SA-PCs for factory applications still faces challenges due to the tendency of single atoms to aggregate, which can occur due to subtle environmental differences, ultimately leading to diminished catalytic activity. To overcome this difficulty, the metal molar ratio during synthesis should be fine-tuned, and different photoreduction conditions should be explored to establish a manual to guide optimal synthesis conditions. Additionally, a theoretical approach incorporating molecular dynamics and DFT calculations to predict the optimal metal loading could potentially streamline the above procedures, reducing experimental trial and error.

SA-PCs exhibit remarkable potential owing to their versatility across various fields, high efficiencies, and unique properties. However, it remains an underexplored material, necessitating continued in-depth research to fully uncover its capabilities and optimize its applications.