Engineering Sub-Nanometer Hafnia-Based Ferroelectrics to Break the Scaling Relation for High-Efficiency Piezocatalytic Water Splitting

Polarization Rearrangement Induced High-Efficiency Piezocatalytic Overall Pure Water Splitting in Ultrathin (001)-Confined PbTiO3

Facing the emergencies of global warming and energy shortages, nano ferroelectrics, which exhibit superior charge separation capabilities and polarization tunability, are extensively utilized in piezocatalytic H2 production. However, acquiring polarized structures that behave with robust ferroelectricity and strong piezoelectricity in ultralow dimension nanomaterials for efficient piezocatalysis remains a huge challenge. This research achieved exceptional piezocatalytic overall pure water splitting performance in 3.5 nm-thick (001)-confined PbTiO3 nanosheets, reaching a H2 evolution rate of 1068 μmol g-1 h-1, exceeding those of similar ferroelectric oxides. The highly confined crystallographic polarization orientation in nanosheets induced polarization rearrangement from the c-axis to other nonpolarized crystallographic orientations, as evidenced by piezoelectric force microscopy and phase field simulations, which improve piezoelectricity and boost piezocatalytic behavior significantly. Local structure investigations jointly by neutron pair distribution function, X-ray absorption spectrum, and atomic-scale scanning transmission electron microscopy methods show that the rearranged structure arises from the lattice inhomogeneous tensile strain. TiO6 octahedrons were distorted, with the Ti atom moving diagonally toward the symmetry center. Such ferroelectric reconstruction of a practical nanopolarized structure with remarkable performance in this work will promote the development of high-performance nano ferroelectrics.

Dynamic regulation of ferroelectric polarization using external stimuli for efficient water splitting and beyond

Establishing and regulating the ferroelectric polarization in ferroelectric nano-scale catalysts has been recognized as an emerging strategy to advance water splitting reactions, with the merits of improved surface charge density, high charge transfer rate, increased electronic conductivity, the creation of real active sites, and optimizing the chemisorption energy. As a result, engineering and tailoring the ferroelectric polarization induced internal electric field provides significant opportunities to improve the surface and electronic characteristics of catalysts, thereby enhancing the water splitting reaction kinetics. In this review, an interdisciplinary and comprehensive summary of recent advancements in the construction, characterization, engineering and regulation of the polarization in ferroelectric-based catalysts for water splitting is provided, by exploiting a variety of external stimuli. This review begins with a detailed overview of the classification, benefits, and identification methodologies of the ferroelectric polarization induced internal electric field; this offers significant insights for an in-depth analysis of ferroelectric-based catalysts. Subsequently, we explore the underlying structure-activity relationships for regulating the ferroelectric polarization using a range of external stimuli which include mechanical, magnetic, and thermal fields to achieve efficient water splitting, along with a combination of two or more fields. The review then highlights emerging strategies for multi-scale design and theoretical prediction of the relevant factors to develop highly promising ferroelectric catalysts for efficient water splitting. Finally, we present the challenges and perspectives on the potential research avenues in this fascinating and new field. This review therefore delivers an in-depth examination of the strategies to engineer the ferroelectric polarization for the next-generation of water electrolysis devices, systems and beyond.

Covalent Organic Frameworks for Boosting H2O2 Photosynthesis via the Synergy of Multiple Charge Transfer Channels and Polarized Field

Covalent organic frameworks (COFs) serve as one of the most promising candidates for hydrogen peroxide (H2O2) photosynthesis, while attaining high-performance COFs remains a formidable challenge due to the insufficient separation of photogenerated charges. Here, through the rational design of bicarbazole-based COFs (Cz-COFs), we showcase the first achievement in piezo-photocatalytic synthesis of H2O2 using COFs. Noteworthily, the ethenyl group-modified Cz-COFs (COF-DH-Eth) demonstrates a record-high yield of H2O2 (9212 μmol g-1 h-1) from air and pure water through piezo-photocatalysis, which is ca. 2.5 times higher than that of pristine Cz-COFs without ethenyl groups (COF-DH-H) under identical condition and COF-DH-Eth without ultrasonic treatment. The H2O2 production rate originates from the synergistic effect between an ultrasonication-induced polarized electric field and the spatially separated multiple charge transfer channels, which significantly promote the utilization of photogenerated electrons by directional transfer from bicarbazole groups to the ethenyl group-modified benzene rings. Several Cz-COFs and bifluorenylidene-based COFs (COF-BFTB-H) with similar twisted monomers exhibit obvious piezoelectric performance for promoting H2O2 generation, signifying that organic ligands with a twistable structure play a crucial role in creating broken symmetry structures, thereby establishing piezoelectric properties in COFs.

Piezoelectric-Enhanced Nanocatalysts Trigger Neutrophil N1 Polarization against Bacterial Biofilm by Disrupting Redox Homeostasis

Strategies of manipulating redox signaling molecules to inhibit or activate immune signals have revolutionized therapeutics involving reactive oxygen species (ROS). However, certain diseases with dual resistance barriers to the attacks by both ROS and immune cells, such as bacterial biofilm infections of medical implants, are difficult to eradicate by a single exogenous oxidative stimulus due to the diversity and complexity of the redox species involved. Here, this work demonstrates that metal-organic framework (MOF) nanoparticles capable of disrupting the bacterial ROS-defense system can dismantle bacterial redox resistance and induce potent antimicrobial immune responses in a mouse model of surgical implant infection by simultaneously modulating redox homeostasis and initiating neutrophil N1 polarization in the infection microenvironment. Mechanistically, the piezoelectrically enhanced MOF triggers ROS production by tilting the band structure and acts synergistically with the aurintricarboxylic acid loaded within the MOF, which inhibits the activity of the cystathionine γ-cleaving enzyme. This leads to biofilm structure disruption and antigen exposure through homeostatic imbalance and synergistic activation of neutrophil N1 polarization signals. Thus, this study provides an alternative but promising strategy for the treatment of antibiotic-resistant biofilm infections.

Enhanced Generation of Reactive Oxygen Species via Piezoelectrics based on p-n Heterojunctions with Built-In Electric Field

Tuning the charge transfer processes through a built-in electric field is an effective way to accelerate the dynamics of electro- and photocatalytic reactions. However, the coupling of the built-in electric field of p-n heterojunctions and the microstrain-induced polarization on the impact of piezocatalysis has not been fully explored. Herein, we demonstrate the role of the built-in electric field of p-type BiOI/n-type BiVO4 heterojunctions in enhancing their piezocatalytic behaviors. The highly crystalline p-n heterojunction is synthesized by using a coprecipitation method under ambient aqueous conditions. Under ultrasonic irradiation in water exposed to air, the p-n heterojunctions exhibit significantly higher production rates of reactive species (·OH, ·O2-, and 1O2) as compared to isolated BiVO4 and BiOI. Also, the piezocatalytic rate of H2O2 production with the BiOI/BiVO4 heterojunction reaches 480 μmol g-1 h-1, which is 1.6- and 12-fold higher than those of BiVO4 and BiOI, respectively. Furthermore, the p-n heterojunction maintains a highly stable H2O2 production rate under ultrasonic irradiation for up to 5 h. The results from the experiments and equation-driven simulations of the strain and piezoelectric potential distributions indicate that the piezocatalytic reactivity of the p-n heterojunction resulted from the polarization intensity induced by periodic ultrasound, which is enhanced by the built-in electric field of the p-n heterojunctions. This study provides new insights into the design of piezocatalysts and opens up new prospects for applications in medicine, environmental remediation, and sonochemical sensors.

Strong Interfacial Chemical Bonding in Regulating Electron Transfer and Stabilizing Catalytic Sites in a Metal-Semiconductor Schottky Junction for Enhanced Photocatalysis

The weak electronic interaction at metal-photocatalyst heterointerfaces often compromises solar-to-fuel performance. Here, a trifunctional Schottky junction, involving chemically stabilized ultrafine platinum nanoparticles (Pt NPs, ≈3 nm in diameter) on graphitic carbon nitride nanosheets (CNs) is proposed. The Pt-CN electronic interaction induces a 1.5% lattice compressive strain in Pt NPs and maintains their ultrafine size, effectively preventing their aggregation during photocatalytic reactions. Density functional theory calculations further demonstrate a significant reduction in the Schottky barrier at the chemically bonded CN-Pt heterointerface, facilitating efficient interfacial electron transfer, as supported by femtosecond transient absorption spectra (fs-TAS) measurements. The combined effects of lattice strain, stabilized Pt NPs, and efficient interfacial charge transport collaboratively enhance the photocatalytic performance, leading to over an 11-fold enhancement in visible light H2 production (8.52 mmol g-1 h-1) compared to the CN nanosheets with the in situ photo-deposited Pt NPs (0.76 mmol g-1 h-1). This study highlights the effectiveness of strong metal-semiconductor electronic interactions and underscores the potential for developing high-efficiency photocatalysts.

Significant hydrogen generation via photo-mechanical coupling in flexible methylammonium lead iodide nanowires

The flexoelectric effect, which refers to the mechanical-electric coupling between strain gradient and charge polarization, should be considered for use in charge production for catalytically driving chemical reactions. We have previously revealed that halide perovskites can generate orders of higher magnitude flexoelectricity under the illumination of light than in the dark. In this study, we report the catalytic hydrogen production by photo-mechanical coupling involving the photoflexoelectric effect of flexible methylammonium lead iodide (MAPbI3) nanowires (NWs) in hydrogen iodide solution. Upon concurrent light illumination and mechanical vibration, large strain gradients were introduced in flexible MAPbI3 NWs, which subsequently induced significant hydrogen generation (at a rate of 756.5 μmol g-1 h-1, surpassing those values from either photo- or piezocatalysis of MAPbI3 nanoparticles). This photo-mechanical coupling strategy of mechanocatalysis, which enables the simultaneous utilization of multiple energy sources, provides a potentially new mechanism in mechanochemistry for highly efficient hydrogen production.

Constructing Symmetry-Mismatched RuxFe3-xO4 Heterointerface-Supported Ru Clusters for Efficient Hydrogen Evolution and Oxidation Reactions

Ru-related catalysts have shown excellent performance for the hydrogen evolution reaction (HER) and hydrogen oxidation reaction (HOR); however, a deep understanding of Ru-active sites on a nanoscale heterogeneous support for hydrogen catalysis is still lacking. Herein, a click chemistry strategy is proposed to design Ru cluster-decorated nanometer RuxFe3-xO4 heterointerfaces (Ru/RuxFe3-xO4) as highly effective bifunctional hydrogen catalysts. It is found that introducing Ru into nanometric Fe3O4 species breaks the symmetry configuration and optimizes the active site in Ru/RuxFe3-xO4 for HER and HOR. As expected, the catalyst displays prominent alkaline HER and HOR performance with mass activity much higher than that of commercial Pt/C as well as robust stability during catalysis because of the strong interaction between the Ru cluster and the RuxFe3-xO4 support, and the optimized adsorption intermediate (Had and OHad). This work sheds light on a promsing approach to improving the electrocatalysis performance of catalysts by the breaking of atomic dimension symmetry.

Defect Engineered Microcrystalline Cellulose for Enhanced Cocatalyst-Free Piezo-Catalytic H2 Production

Mechanical energy driven piezocatalytic hydrogen (H2 ) production is a promising way to solve the energy crisis . But limited by the slow separation and transfer efficiency of piezoelectric charges generated on the surface of piezocatalysts , the piezocatalytic performance is still not satisfactory. Here, defect engineering is first used to optimize the piezocatalytic performance of microcrystalline cellulose (MCC). The piezocatalytic H2 production rate of MCC with the optimal defect concentration can reach up to 84.47 µmol g-1 h-1 under ultrasonic vibration without any co-catalyst, which is ≈3.74 times higher than that of the pure MCC (22.65 µmol g-1 h-1 ). The enhanced H2 production rate by piezoelectric catalysis is mainly due to the introduction of defect engineering on MCC, which disorders the symmetry of MCC crystal structure, improves the electrical conductivity of the material, and accelerates the separation and transfer efficiency of piezoelectric charges. Moreover, the piezocatalytic H2 production rate of MCC with the optimal defect concentration can still reach up to 93.61 µmol g-1 h-1 in natural seawater, showingits commendable practicability. This study presents a novel view for designing marvelous-performance biomass piezocatalysts through defect engineering, which can efficiently convert mechanical energy into chemical energy .