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Pyroelectric materials are important functional materials that can generate an electrical response upon a temperature change. Among the many different types of pyroelectric materials, lead-based materials are the most widely-used traditional pyroelectric material and they will soon be banned due to their high toxicity. Therefore, in the past decade, extensive studies have been conducted to search for high performance lead-free pyroelectric materials. Recent experimental efforts have led to significant advances in lead-free pyroelectrics in different forms. This has further motivated their application from a traditional sensing function to a future energy-related prospect. This article provides a comprehensive review on the up-to-date advances in lead-free pyroelectrics, including single crystals, ceramics, inorganic films, polymers and composites. Moreover, the recent rise in energy harvesting and the electrocaloric effect as well as the potential future development of pyroelectric applications will be presented. [ABSTRACT FROM AUTHOR]

Pyroelectric materials have been attracting significant attention due to their intrinsic and permanent polarization, where the induced polarization is not associated with specific conditions, such as ferroelectric phase transition, strain gradient, dopants, and electric field. Thus, these materials have great potential for wide applications in energy conversion. Here, we propose a new 3D porous borocarbonitride termed PH-BCN, which is composed of pentagonal motifs with intrinsic polarization along the [0001] direction. Based on first-principles calculations, we show that PH-BCN possesses a record high longitudinal electromechanical coupling coefficient with the value of k33 = 97.99%, a remarkably strong SHG response (χ (2)xzx (0) = χ (2)yzy (0) = χ (2)zxx (0) = χ (2)zyy (0) = −6.23 pm V−1 and χ (2)zzz (0) = 21.21 pm V−1), and a record high shift current value of 908.58 μA V−2 due to the intrinsic vertical polarization. This study expands the family of pentagon-based materials, and may open a new frontier in the design of high-performance pyroelectric materials as well. [ABSTRACT FROM AUTHOR]

The development of photocatalysis is hindered, in part, by the quick recombination of photogenerated carriers and the instability of light sources. In this study, the problem of too-fast electron–hole pair compounding in photocatalysis is effectively regulated by the polarization field of pyroelectric materials using the pyroelectric method. Self-polarized pyroelectric materials that depend on temperature variations can generate usable electrical energy and polarized charge carriers to degrade organic pollutants. Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN–PT) is a relaxor ferroelectric material with spontaneous polarization characteristics. The PMN–0.30PT:1 mol%Sm3+ catalyst was prepared by applying the high-temperature solid-state reaction method. Under the dark condition and nine cold–hot cycles of 23 °C–68 °C, using H2O2-assisted PMN–0.30PT:1 mol%Sm3+ as a catalyst, the degradation rate of rhodamine 6G (10 mg L−1) was 94.3 ± 2.5%. In addition, the degradation rates of 88.52% and 64.32% were obtained for rhodamine B (10 mg L−1) and methylene blue (10 mg L−1), respectively. This study provides a new approach to the pyroelectric catalytic degradation of organic pollutants. [ABSTRACT FROM AUTHOR]

AgNbO3 is considered as one of the most promising alternatives for lead-containing antiferroelectric (AFE) ceramics, and has been drawing progressively more attention. The AFE/ferroelectric (FE) phase-boundary design based on AgNbO3 is very attractive and is a promising means to develop lead-free high-performance pyroelectric materials. In the present study, compounds with a high tolerance factor and high average electronegativity difference and LiNbO3-type composition were proposed as being able to stabilize the FE phase of AgNbO3. Ceramics with the composition (1 −x)AgNbO3–xLiTaO3 (ANLT) (x = 0–0.10) were designed and fabricated using the conventional solid-state method for pyroelectric applications. The effects of the LiTaO3 content, temperature, and electric field on the phase-transition behavior of the ANLT system were investigated systematically. Based on our results, a composition–temperature phase diagram of the ANLT system was proposed, confirming the existence of the AFE/FE phase boundary. The depolarization and pyroelectric properties of the ANLT system were also studied. It was found that the x = 0.05 composition at the AFE/FE phase boundary had a large room-temperature pyroelectric coefficient (3.68 10−8 C cm−2 K−1) and exhibited excellent figures of merit for infrared detectors due to its low relative permittivity (252 at 1 kHz). Moreover, an ultrahigh pyroelectric energy density (1.4 J cm−3) was harvested using an Olsen cycle for the x = 0.5 composition, which was several times larger than that of other ceramic systems reported recently. These results suggest the ANLT ceramic would be an attractive multifunctional material for applications in infrared detectors and energy harvesting. [ABSTRACT FROM AUTHOR]

Effective solutions to the two primary dilemmas of inadequate energy supply and environmental contamination have become a significant focus of researchers for the sustainable development of society and the ecological system. Transforming ubiquitous mechanical force and temperature variation energies into chemical energy by means of the intrinsic characteristics of piezoelectric and pyroelectric nanomaterials is widely considered to be a powerful strategy to counteract the environmental and energy crisis owing to prominent advantages such as the efficient utilization of directional electric charges and enormous source of stress and temperature fluctuation. This review summarizes the advances in energy and environmental catalysis driven by stress and temperature variation based on piezoelectric and pyroelectric effects. Firstly, the internal characteristics of charge carrier separation and transportation of piezoelectric/pyroelectric catalysts in response to external stress and temperature oscillations and the rational mechanisms of piezoelectric/pyroelectric catalysis are elucidated. Then, the catalytic production of renewable fuels (H2 evolution from water splitting and CO2 reduction) and environment remediation (decomposition of organic dyes, mineralization of antibiotics, bacterial inactivation, and removal of heavy metal ions) based on a large number of piezocatalytic and pyrocatalytic catalysts with diverse modification strategies are thoroughly summarized. Finally, the existing challenges and future prospects in this emerging territory are proposed. This comprehensive review is anticipated to offer a powerful reference for the profound research and applications of piezoelectric and pyroelectric materials in the fields of the environment and energy by utilizing ubiquitous mechanical and temperature fluctuation energies. [ABSTRACT FROM AUTHOR]

Pyroelectric materials have a huge market in daily life applications and high pyroelectric performances near room temperature are highly desired. Here we report high pyroelectric performance with adjustable peak performance temperature of 29–46.2 °C in the (1 − x)Pb0.99Nb0.02[(Zr0.57Sn0.43)0.937Ti0.063]0.98O3–xZnO ((1 − x)PNZST–xZnO) composite. The x = 0.1 composite has a peak pyroelectric coefficient of 1053.9 × 10−4 C m−2 K−1 and figures of merit of Fv = 1249.4 × 10−2 m2 C−1, Fd = 876.3 × 10−5 Pa−1/2, and Fi = 832.7 × 10−10 m V−1 at around 39 °C. It is found that a robust room temperature ferroelectric state is realized in antiferroelectric PNZST due to ZnO-induced internal strain. The thermal-driven ferroelectric to antiferroelectric transition leads to high pyroelectric performance. This work provides a promising material candidate for high performance pyroelectric devices. [ABSTRACT FROM AUTHOR]

In this report, a recently invented novel pyro-phototronic effect is explored in an optoelectronic device containing a fully organic thin film. A unique plasma-based process is implemented for the synthesis of rubrene crystal directly grown in the form of thin film using a single-step approach. Applicability of the as-prepared crystalline rubrene thin film is demonstrated as a light-responsive device working under a photovoltaic (self-powered) mode. In particular, the detailed transient photoresponse of the device highlights the coupling of pyro-phototronic and photovoltaic effects. Thus the two important aspects of this study are: report of a novel one-step process for synthesis of crystalline rubrene containing thin film and demonstration of an optoelectronic device with crystalline rubrene, where the key governing mechanism is a coupled effect of pyro-phototronic and photovoltaic processes. This work also delivers a new experimental approach for realizing the pyro-phototronic effect based on a fully organic crystalline medium with rubrene, which has not been explored yet. Moreover, a symmetry-imposed limitation on pyroelectric materials, which states that the crystal has to be non-centrosymmetric in order to show pyroelectric behavior, is circumvented in this particular study. The present study shows that the occurrence of pyro-phototronic effect in a film containing a centrosymmetric rubrene crystal is solely due to the presence of a thin amorphous oxide layer formed over the crystalline film thereby inducing the surface polarization effect. Hence the existence of pyro-phototronic effect coupled with photovoltaic effect in a crystalline rubrene film indicates the huge potential of the two effects in improving the performance of optoelectronic devices. Moreover, generation of pyroelectricity due to surface polarization in rubrene crystals can be used as a possible analytical tool for probing the organization and dynamics of different biological systems. [ABSTRACT FROM AUTHOR]

Struvite (MgNH4PO4·6H2O) is a mineral first identified in 1845. It is being tested for several reasons: (1) it is a problem in liquid wastewater treatment plants; (2) on the other hand, it is recovered from these wastewaters for its phosphorus, magnesium and nitrogen; (3) is the main component of microbial-induced urinary stones. We have recently shown that struvite is ferroelectric and piezoelectric. In this paper, we present the first experimental evidence of the pyroelectric nature of struvite. Using a single-diffusion gel growth technique, we grew struvite crystals as flat, parallel plates. We performed measurements of pyroelectric currents on struvite of this shape, using it as a dielectric of a plate capacitor. The occurrence of pyroelectric effects in struvite was investigated by measuring depolarization currents as a function of temperature. This technique allows the disclosure of ferroelectric/pyroelectric transitions as well as the reconstruction of the ferroelectric loop. We found that the value of the pyroelectric coefficient p attains a maximum of 22 × 10−6 C m−2 K−1 slightly below room temperature, going down to p ≅ 10 × 10−6 C m−2 K−1 at room temperature. This value is comparable to values for other minerals. For example, the pyroelectric polarization coefficient of tourmaline, the mineral for which the pyroelectric effect was first discovered, is 4 × 10−6 C m−2 K−1. This value is 2.5 times lower than that measured for struvite, illustrating struvite's fairly strong pyroelectricity. [ABSTRACT FROM AUTHOR]

Organic and metal-free molecules with piezoelectric and ferroelectric properties have gained wide interest for their applications in the domain of mechanical energy harvesting due to their desirable properties such as light weight, thermal stability, mechanical flexibility, feasibility to achieve high Curie temperatures, and ease of synthesis. However, the understanding and design of these materials for piezoelectric energy harvesting applications is still in its early stages. This review paper presents a comprehensive overview of the fundamental characterization of piezoelectricity for a range of organic ferro- and piezoelectric materials and their composites. It also discusses the limitations of traditional piezoelectric materials and highlights the advantages of organic materials in this area in the introduction part. In addition, the paper provides a detailed description of peptide-based and other biomolecular piezoelectric materials as a bio-friendly alternative to current materials. This perspective aims to guide researchers in designing functional organic materials and composites for practical mechanical energy harvesting applications and to highlight current limitations and future perspectives in this emerging area of research. [ABSTRACT FROM AUTHOR]

The increasing desire for aesthetically pleasing teeth has resulted in the widespread use of tooth whitening treatments. Clinical tooth whitening products currently rely on hydrogen peroxide formulations to degrade dental pigments through oxidative processes. However, they usually cause side effects such as tooth sensitivity and gingival irritation due to the use of high concentrations of hydrogen peroxide or long-time contact. In recent years, various novel materials and reaction patterns have been developed to tackle the issues related to H2O2-based tooth whitening. These can be broadly classified as advanced oxidation processes (AOPs). AOPs generate free radicals that have potent oxidizing properties, which can thereby increase the oxidation power and/or reduce the exposure time and can probably minimize the side effects of tooth bleaching. While there have been several reviews on clinical tooth whitening and the application of novel nanomaterials, a review based on the concept of AOPs in tooth bleaching application has not yet been conducted. This review describes the common types and mechanisms of AOPs, summarizes the latest research progress of new tooth bleaching materials based on AOPs, and proposes a model for tooth bleaching and a rate control step at the molecular level. The paper also reviews the shortcomings and suggests future development directions. [ABSTRACT FROM AUTHOR]

The pyro-electro-catalytic induced generation of hydrogen gas is an environmentally friendly and sustainable way to convert excess thermal energy into a storable form. The main idea is to make use of spontaneous polarization of pyroelectric materials that can be altered by temperature changes. Thus, surface potential changes and subsequent electron exchange with surrounding molecules can be induced. In this work, a fundamental model to describe the behavior of a thermally excited pyroelectric material in pure water is developed. The model combines the fields of pyroelectricity, electrochemistry, diffusion and semiconductor theory. After derivation, it was used to explore some basic questions on pyro-electro-catalytic hydrogen production and the accuracy was tested with experimental data. The results show that p/εr has to be balanced depending on the temperature gradient to maximize the hydrogen production. The validation of the experimental data revealed good agreement. [ABSTRACT FROM AUTHOR]

Pyroelectric materials are promising for thermal energy scavenging from waste-heat sources and new materials with exotic properties are constantly being discovered. Antiferroelectrics (AFE) are of particular interest since such materials have been observed to possess both conventional, negative pyroelectricity and inverse, positive pyroelectricity. In this study, we compare direct and indirect measurements of the pyroelectric coefficient and use the temperature dependence on the dielectric constant to show the inverse pyroelectric regime arises primarily from field-induced pyroelectricity. Energy conversion cycles are performed in both pyroelectric regimes using a 1 kHz pulsed laser heat source, realizing a maximum power density of 2.25 W cm−3 in the conventional regime and 0.68 W cm−3 in the inverse regime. A new pyroelectric energy conversion model, using parameters taken from direct measurements of the pyroelectric coefficient, capacitance, loss tangent, and leakage current agrees with the energy conversion experiments, showing both the validity of the model and the origin of pyroelectricity in the inverse regime. Finally, a resonant circuit for pyroelectric energy harvesting is proposed that takes full advantage of the bi-directional functionality of AFE materials. This work clarifies the debate on the origin of pyroelectric features in AFE materials and demonstrates the potential for future energy conversion applications. [ABSTRACT FROM AUTHOR]

The harvesting of waste heat is attracting increasing attention, due to its abundance and potential benefits to the environment. However, the need for high heat transfer rates in thermal harvesting systems is a longstanding obstacle for their practical application. In this work, we construct thermally conductive networks in Pb[(MnxNb1−x)1/2(MnxSb1−x)1/2]y(Zr95Ti5)1−yO3 (lead magnesium niobate–lead antimony–manganese–lead zirconate titanate: PMN–PMS–PZT) ceramics to improve heat transfer and enhance their ferroelectric properties by use of a thermally conductive AlN additive dispersed in the ceramic matrix. The ferroelectric properties, pyroelectric coefficient and thermal conductivity of the PMN–PMS–PZT: AlN composite materials are influenced by the AlN content as a result of the formation of random bridges or thermally conductive networks for phonon transfer in the ceramic matrix, thereby leading to high heat transfer. For a PMN–PMS–PZT composite with a 0.2 wt% AlN content, the ferroelectric properties, pyroelectric coefficient and thermal conductivity are shown to be enhanced owing to the improved crystallinity and density, and the relative permittivity is also reduced, which results in optimized pyroelectric figure of merits. This combination of materials property enhancements is shown to be beneficial for high performance pyroelectric materials in devices for energy harvesting applications. [ABSTRACT FROM AUTHOR]

Metal sulfide photoelectrodes are considered as common catalysts for PEC water splitting, but their instability and carrier density limitations still restrict their applications. Phase modification plays a vital role in improving photocatalytic efficiency. Here, we successfully constructed In2S3 heterophase junctions in CdS/In2S3 heterojunctions by phase modulation engineering for efficient pyro-photoelectrochemical catalytic (Pyro-PEC) water splitting. The experimental results show that the CdS/In2S3 generated by phase engineering displays a high current density of 3.52 mA cm−2 at 1.23 V vs. RHE under the Pyro-PEC conditions, which is a 14.67-fold enhancement of bare CdS under the photoelectrocatalytic conditions, and exhibits a 63.98% bulk transport capacity, which is a 49.51% enhancement of bare CdS under photoelectrocatalytic conditions, and the stability also improved very well. This is due to the fact that photoelectrodes with heterojunctions and heterophase junctions formed abundant phase boundaries and active surfaces to promote catalytic reactions, and enhanced the polarization force to optimize the pyroelectric performance, which ultimately achieved excellent pyro-photoelectrochemical performance. This work provides evidence for the effect of phase engineering on photoelectric and pyroelectric properties, and provides a simple and effective method for modulating the phase structure for photoanodes using hydrothermal methods. [ABSTRACT FROM AUTHOR]

Pyroelectricity in a recently developed all-organic composite electret with a polar polynorbornene-based filler and polydimethylsiloxane (PDMS) matrix has been studied with the help of thermal and dielectric techniques. Measurement of the pyroelectric p coefficient using a quasi-static periodic temperature variation at RT shows a non-linear dependence with the applied poling field, which is uncharacteristic of amorphous materials. Dielectric relaxation spectroscopy (DRS) and the thermally stimulated depolarization current (TSDC) technique reveal that this behaviour can be attributed to Maxwell–Wagner interface (MWI) polarization that occurs at the filler–matrix interface. These charges released during the onset of dipolar α and β relaxations of the filler particles contribute majorly to the observed pyroelectricity at RT. The saturation of both MWI TSDC shoulders and spontaneous polarization at higher electric fields correlates with the p coefficient value reaching a plateau at these applied fields. A maximum p coefficient of 0.54 μC m−2 K−1 is calculated for a poling field of 30 V μm−1. [ABSTRACT FROM AUTHOR]

Ferroelectricity, which has diverse important applications such as memory elements, capacitors, and sensors, was first discovered in a molecular compound, Rochelle salt, in 1920 by Valasek. Owing to their superiorities of lightweight, biocompatibility, structural tunability, mechanical flexibility, etc., the past decade has witnessed the renaissance of molecular ferroelectrics as promising complementary materials to commercial inorganic ferroelectrics. Thus, on the 100th anniversary of ferroelectricity, it is an opportune time to look into the future, specifically into how to push the boundaries of material design in molecular ferroelectric systems and finally overcome the hurdles to their commercialization. Herein, we present a comprehensive and accessible review of the appealing development of molecular ferroelectrics over the past 10 years, with an emphasis on their structural diversity, chemical design, exceptional properties, and potential applications. We believe that it will inspire intense, combined research efforts to enrich the family of high-performance molecular ferroelectrics and attract widespread interest from physicists and chemists to better understand the structure–function relationships governing improved applied functional device engineering. [ABSTRACT FROM AUTHOR]

This paper demonstrates the significant benefits of exploiting highly aligned porosity in piezoelectric and pyroelectric materials for improved energy harvesting performance. Porous lead zirconate (PZT) ceramics with aligned pore channels and varying fractions of porosity were manufactured in a water-based suspension using freeze-casting. The aligned porous PZT ceramics were characterized in detail for both piezoelectric and pyroelectric properties and their energy harvesting performance figures of merit were assessed parallel and perpendicular to the freezing direction. As a result of the introduction of porosity into the ceramic microstructure, high piezoelectric and pyroelectric harvesting figures of merits were achieved for porous freeze-cast PZT compared to dense PZT due to the reduced permittivity and volume specific heat capacity. Experimental results were compared to parallel and series analytical models with good agreement and the PZT with porosity aligned parallel to the freezing direction exhibited the highest piezoelectric and pyroelectric harvesting response; this was a result of the enhanced interconnectivity of the ferroelectric material along the poling direction and reduced fraction of unpoled material that leads to a higher polarization. A complete thermal energy harvesting system, composed of a parallel-aligned PZT harvester element and an AC/DC converter, was successfully demonstrated by charging a storage capacitor. The maximum energy density generated by the 60 vol% porous parallel-connected PZT when subjected to thermal oscillations was 1653 μJ cm−3, which was 374% higher than that of the dense PZT with an energy density of 446 μJ cm−3. The results are beneficial for the design and manufacture of high performance porous pyroelectric and piezoelectric materials in devices for energy harvesting and sensor applications. [ABSTRACT FROM AUTHOR]

The increasing expense and complexity of conventional physical exams may lead to delayed disease diagnoses, creating substantial difficulties for many patients. In response, smartphone-based sensing technologies have emerged, offering a promising solution to make health diagnostics more accessible. Perovskite-based nanomaterials stand out with their adaptable structure, making them an important player in sensor enhancement due to their wide-ranging sensing capabilities and excellent physicochemical characteristics. While perovskites demonstrate advantageous optoelectronic properties, fortifying their stability is a crucial aspect that continues to be a central theme in current research and development endeavors. This article examines the advancement of smartphone-based sensors via the incorporation of Perovskite-based nanomaterials and suggests strategies for further optimizing their characteristics. It provides a detailed overview of their applications in different smartphone sensing areas, including but not limited to optical and photothermal-pyroelectric methods. Our in-depth analysis highlights the crucial role of Perovskite-based nanomaterials in the development of devices and the complexity of sensor manufacturing. We also explore their potential in seamlessly integrating with wearable devices connected to smartphones, thus streamlining the diagnosis process. Moreover, we anticipate their revolutionary impact in advancing smartphone sensors. This combination is poised to establish a more accessible and unified method for health monitoring. [ABSTRACT FROM AUTHOR]

Immunotherapy harnesses the inherent immune system in the body to generate systemic antitumor immunity, offering a promising modality for defending against cancer. However, tumor immunosuppression and evasion seriously restrict the immune response rates in clinical settings. Catalytic nanomedicines can transform tumoral substances/metabolites into therapeutic products in situ, offering unique advantages in antitumor immunotherapy. Through catalytic reactions, both tumor eradication and immune regulation can be simultaneously achieved, favoring the development of systemic antitumor immunity. In recent years, with advancements in catalytic chemistry and nanotechnology, catalytic nanomedicines based on nanozymes, photocatalysts, sonocatalysts, Fenton catalysts, electrocatalysts, piezocatalysts, thermocatalysts and radiocatalysts have been rapidly developed with vast applications in cancer immunotherapy. This review provides an introduction to the fabrication of catalytic nanomedicines with an emphasis on their structures and engineering strategies. Furthermore, the catalytic substrates and state-of-the-art applications of nanocatalysts in cancer immunotherapy have also been outlined and discussed. The relationships between nanostructures and immune regulating performance of catalytic nanomedicines are highlighted to provide a deep understanding of their working mechanisms in the tumor microenvironment. Finally, the challenges and development trends are revealed, aiming to provide new insights for the future development of nanocatalysts in catalytic immunotherapy. [ABSTRACT FROM AUTHOR]

In the present study, the effect of heterovalent Fe3+ ions on the dielectric, pyroelectric, and ferroelectric properties of the (1 − x)AgNbO3–xFeNbO4 (x = 0.005, 0.01, 0.025, 0.05, and 0.1) system was investigated. The substitution of smaller ionic radius Fe3+ in B-sites and the formation of FeNbO4 as a secondary phase contributed to improved dielectric performance, especially the pyroelectric effect, of (1 − x)AgNbO3–xFeNbO4 ceramics by generating electron-rich ceramics. The (1 − x)AgNbO3–xFeNbO4 ceramics were prepared by conventional solid-state sintering. Pure AgNbO3 had a perovskite crystal structure with an orthorhombic crystal system, but the FeNbO4 in (1 − x)AgNbO3–xFeNbO4 ceramics was formed as a secondary phase with a monoclinic structure. In addition, the XRD and Raman spectroscopy data showed that some Fe3+ was substituted into B-sites of AgNbO3. The introduction of FeNbO4 effectively reduced the average grain size from 1.85 ± 0.09 μm to 1.22 ± 0.03 μm for pure AgNbO3 and 0.9AgNbO3–0.1FeNbO4, respectively. In addition, the relative density of the (1 − x)AgNbO3–xFeNbO4 ceramics decreased from 97.96% ± 0.01 for x = 0 to 96.75% ± 0.03 for x = 0.1. The real part of the permittivity ε′, at room temperature, increased from 186.6 for x = 0 to a value of 738.7 for x = 0.1. Additionally, the maximum pyroelectric coefficient increased fivefold, reaching values of 2270 nC cm−2 K−1 for x = 0.1. Furthermore, a harvested pyroelectric energy density (W) of 1140 μJ cm−3 for x = 0.025 was achieved, which is appreciably higher than the 840 μJ cm−3 value for x = 0. [ABSTRACT FROM AUTHOR]

Catalytically reducing CO2 offers an effective way to produce energy-rich fuels and high-value chemicals while simultaneously sequestrating CO2 from the environment. However, driving the CO2 reduction reaction (CO2RR) is challenging, because the linear molecular structure of CO2 is chemically inert with a low electron affinity. Thermal, light, and electrochemical energy are typically utilized to drive the CO2RR. One alternative route to reduce CO2 is via piezocatalysis. Piezocatalysis exploits the polarization of a material upon applying mechanical stress which enables spatial separation of the mechanically produced charge carriers to inhibit recombination. A piezocatalyst is uniquely suited to drive the CO2RR even in the dark without external heating and a sacrificial compound. Although the piezocatalytic CO2RR is just beginning to be explored, it is foreseen to become one of the most important scenarios for CO2 utilization. In this perspective, we discuss prospects and challenges of the piezocatalytic CO2RR. The received hypotheses on the piezocatalysis mechanism are critically discussed. Guidelines to obtain a potentially efficient piezocatalyst are outlined. We expect our contribution to inspire readers to get involved in this promising new area of research and bring it in the right direction. [ABSTRACT FROM AUTHOR]

Beyond three-dimensional (3D) architectures, polar semiconductor heterostructures are developing in the direction of two-dimensional (2D) scale with mix-dimensional integration for novel properties and multifunctional applications. Herein, we stacked 2D Janus MoSSe and 3D wurtzite GaN polar semiconductors to construct MoSSe/GaN polar heterostructures by polarity configurations. The structural stability was enhanced as binding energy changed from −0.08 eV/−0.17 eV in the N polarity to −0.24 eV/−0.42 eV in the Ga polarity. In particular, the polarity reversal of GaN in contact with Janus MoSSe not only determined the charge transfer direction but also significantly increased the electrostatic potential difference from 0.71 eV/0.78 eV in the N polarity to 3.13 eV/2.24 eV in the Ga polarity. In addition, strain modulation was further utilized to enhance interfacial polarization and tune the electronic energy band profiles of Janus MoSSe/GaN polar heterostructures. By applying in-plane biaxial strains, the AA and AA′ polarity configurations induced band alignment transition from type I (tensile) to type II (compressive). As a result, both the polarity reversal and strain modulation provide effective ways for the multifunctional manipulation and facile design of Janus MoSSe/III-nitrides polar heterostructures, which broaden the Janus 2D/3D polar semiconducting devices in advanced electronics, optoelectronics, and energy harvesting applications. [ABSTRACT FROM AUTHOR]

Research on the development of green and renewable energy sources is becoming more important due to the increasing energy consumption. Various common physical effects can be used to produce generators for gathering energy from the surrounding environment. The uses of these devices for the growing Internet of Things can be significantly improved by adding flexibility. In this study, the improved pyroelectric figures of merit and pyroelectric coefficients of polymer-based flexible multiferroic composite films with two different ferrites are reported. With varying weight percentages of ferrite compositions, PVDF/manganese ferrite and PVDF/nickel ferrite composite films were prepared using the spin coating technique. The enhanced electroactive β-phase was observed, using hysteresis loops and Fourier transform infrared spectroscopy, in the composite films with 5 and 10 weight percentages of manganese ferrite and nickel ferrite, respectively. The dielectric permittivity and magnetization values of the films increased with the increasing weight percentage of ferrite. The pyroelectric current measurements revealed a maximum pyroelectric energy conversion figure of merit values of 8.67% and 12.19% on the PVDF/manganese ferrite and PVDF/nickel ferrite composite films with 5 wt% of MnFe2O4 content and 10 wt% NiFe2O4 content, respectively. [ABSTRACT FROM AUTHOR]

Scientific research is involved in the inception of flexible energy devices, and ferroelectric (FE) materials are making their mark on the process. In particular, devices based on inorganic FE (IFE) materials are finding a remarkable role in flexible energy devices, such as energy harvesters, infrared (IR) sensors, and energy storage capacitors because the latest technologies are particularly concentrating on self-powered flexible sensors and energy harvesters for a sustainable world. Moreover, the combination of IFEs with organic/inorganic polymers in flexible devices seems to satisfy the requirements of high mechanical strength, piezoelectric coefficient, pyroelectric coefficient, and energy storage properties essential for harvesting, sensing, and storage applications, respectively. In this review article, a systematic analysis of flexible IFE-based energy materials is presented. Starting with a brief introduction about energy generation in dielectric materials, the importance of IFEs, and the current state-of-the-art of IFE-based flexible materials in harvesting energy, IR sensing, and storing energy capacity are discussed. Further, the existing challenges and future perspectives in facilitating high-quality flexible IFE devices for real-world applications are envisaged. [ABSTRACT FROM AUTHOR]

Semiconductor photocatalysts have been widely investigated in the field of selective organic transformation. However, the practical application of photocatalysts is greatly limited due to their low charge separation efficiency. Recently, electron–hole separation using intrinsic electric field of polar semiconductors has attracted much attention. Polarity exists widely in polar noncentrosymmetric (NCS) materials, such as piezoelectric, pyroelectric and ferroelectric materials. In the crystal structure of NCS materials, the asymmetric arrangement of ions or ion groups leads to the distribution of positive and negative charges on the surface in opposite directions, which could effectively separate the electron–hole pairs. This perspective summarized recent progress in the synthesis and photocatalytic application of polar semiconductors for selective organic synthesis. This paper also briefly introduces the working mechanism of a light free or vibration catalyst (piezoelectric catalyst). Generally, this perspective mainly focuses on five kinds of polar semiconductors, including CdS, ZnO, ABO3, bismuth layered materials and two-dimensional polar materials. The challenges encountered, as well as the current and future scopes of this field are also discussed in this perspective. [ABSTRACT FROM AUTHOR]

The use of renewable energies to produce hydrogen has been an important issue in recent years. In this paper, a Ba1−xSrxTiO3 photoelectrode is designed on the basis of temperature and light excitation, and the influence of doping on pyro-photo-electric catalysis is explored by changing the doping amount of Sr2+ ions. Under the conditions of 50 °C temperature, illumination and external bias voltage, the current density of Ba0.7Sr0.3TiO3 at 1.23 V vs. RHE is the highest, reaching 0.698 mA·cm−2, which is significantly higher than the sum of photocurrent (0.427 mA·cm−2) and pyroelectric current (0.007 mA·cm−2). The main reason for the improvement of performance is that doping expands the response of semiconductors to visible light and the effect of a polarization built-in electric field. In this work, it is proposed to improve the pyro-photo-electric performance of the Ba1−xSrxTiO3 photoelectrode by changing the Sr2+ doping concentration, improve the separation and transfer efficiency of carriers, and provide a practical method for designing semiconductor photoelectrodes with excellent catalytic performance. [ABSTRACT FROM AUTHOR]

A photoresponse can be classified based on the mode of generation of an electrical signal upon interaction with the photons, such as in the photovoltaic effect, the bolometric effect, the photogating effect, the photoconductive effect, the photothermoelectric effect and the pyro-phototronic effect, etc. The photovoltaic effect has been implemented to design self-powered photodetectors (PDs), and further, the pyro-phototronic effect has been used for augmenting the performance of PDs. The pyro-phototronic effect is an amalgamation of the generation of carriers due to photoinduction, transportation of the generated charge carriers and their recombination. The basic principles and properties of the pyro-phototronic effect have been studied thoroughly by analyzing the process of charge transfer and the current response time of PDs upon light illumination. Zinc oxide (ZnO) has been well exploited for numerous applications due to its direct bandgap for photodetection and its piezoelectric properties for sensors and actuators. Thus, it efficiently contributes to both the pyroelectric and pyro-phototronic effects. Numerous approaches have revealed the modulation of pyro-phototronic current using heterointerfaces with ZnO, which include doping, heating, bandgap tuning, etc., for the self-powering capability of PDs. This review article summarizes the efforts toward developing self-powered PDs using ZnO-based heterointerfaces for an improved pyro-phototronic effect. ZnO-based materials with the pyro-phototronic effect, doped ZnO-based materials with the pyro-phototronic effect and ZnO-based materials with the plasmonic effect are discussed in detail. Highlighting various research directions, this article concludes with a discussion on the present challenges in state-of-the-art technology and the possible directions of future research in the field. [ABSTRACT FROM AUTHOR]

The pyroelectric effect converts thermal energy into usable electrical energy. It is an ideal and effective strategy to enhance the surface-enhanced Raman scattering (SERS) detection sensitivity by tuning the electromagnetic fields. In this work, a plasmonic metal/ferroelectric hybrid SERS substrate was fabricated by integrating a pyroelectric functional layer composed of BiFeO3 with an electron/heat conduction layer of carbon nanofibers (CNFs) using the electrospinning technique. The initial layer was followed by a plasmonic layer of Ag nanowires, which were uniformly spin-coated on BiFeO3/CNFs. By introducing periodically switched near-infrared (NIR) light, the BiFeO3/CNFs could effectively convert the thermal energy induced by light into pyroelectric charge, which could adjust the electron densities of Ag, and in turn boost the electromagnetic fields at the "hot spots". The hybrid Ag–BiFeO3/CNFs were used to test the Raman signals of methylene blue (MB), and a 5.6-fold enhancement of the SERS signal was achieved compared with that noted without the pyroelectric effect and the following parameters were obtained: an ultra-low detection of 10−13 M, a high enhancement factor of 8.3 × 109, and excellent reproducibility with an RSD of 4.08%. The theoretical calculations revealed that the excellent sensitivity was mainly ascribed to the synergistic light-induced pyroelectric and plasmon effects. In addition, this substrate was also used for the detection of ciprofloxacin (CIP) in milk with a limit of detection as low as 10−10 M. Furthermore, the Ag–BiFeO3/CNFs were used to successfully in situ monitor the photocatalytic reduction of p-nitrophenol (p-NTP) to 4,4′-dimercaptoazobenzene (DMAB) by SERS in real time. This work provides an efficient strategy to develop highly sensitive SERS substrates through pyroelectric-plasmonic hybrid structures, and opens a new avenue for the development of energy harvesters that can be used for extensive applications. [ABSTRACT FROM AUTHOR]

A proper understanding of structural phase transitions and cation dynamics in hybrid lead halide perovskites is important for further enhancement of the photovoltaic properties of these materials. Here, we propose a model describing the FA cation ordering in FAPbX3 (X = Br, I) hybrid perovskites. Our model is based on the available structural information of these compounds and involves short-range framework-mediated interactions between the FA cations. We solve the model using Monte Carlo simulations, which allows us to reproduce the cubic-tetragonal phase transition and the FA cation arrangement. We show that a spontaneous electric polarization does not appear during this transition, which is supported by the thermally stimulated depolarization current experiments. We also extend our model to describe the FA cation ordering and frustration in the mixed FA1−xCsxPbX3 system, which reveals a frustrated dipole behavior at low temperature. [ABSTRACT FROM AUTHOR]