Electrochemical water splitting represents a cornerstone technology for sustainable hydrogen production, yet its practical application remains constrained by the sluggish kinetics of the oxygen evolution reaction (OER) and reliance on noble‐metal‐based electrocatalysts. Developing bifunctional catalysts capable of simultaneously promoting the hydrogen evolution reaction (HER) and OER within a unified platform offers a streamlined approach to reducing system complexity and material cost. Metal–organic frameworks (MOFs), renowned for their high surface area, tunable porosity, and structural versatility, have emerged as transformative precursors for advanced electrocatalyst design. Upon thermal or chemical conversion, MOFs give rise to nanostructured, conductive materials featuring hierarchical architectures, multi‐metallic active sites, and engineered defect domains. This review systematically presents recent progress in MOF‐derived bifunctional electrocatalysts for overall water splitting, beginning with synthetic strategies and structural engineering principles. The discussion then addresses electronic structure modulation and structure–activity correlations, emphasizing synergistic charge transport and morphological control. Key challenges, including durability under operational conditions, scalability of synthesis, and mechanistic elucidation, are critically assessed. The review concludes by outlining future research directions toward rationally designing MOF‐based electrocatalysts that enable efficient, stable, and scalable hydrogen production for next‐generation renewable energy systems.

ABSTRACT As a leading candidate for next‐generation electronics, high‐performance 2D Bi 2 O 2 Se has garnered significant interest in the scientific community. However, the understanding of its defect mechanisms remains elusive, hindering the development of further functionalities. In this study, we utilized Raman spectroscopy and ultrafast pump–probe experiments to investigate Bi 2 O 2 Se thin films prepared via a solution‐based technique. By comparing carrier decay times under low and high fluences in 25 nm‐ and 115 nm‐thick films, we proposed the defect mechanisms associated with two common defects in the thicker film: Se vacancies and Se–Bi antisites, which exhibit shallow donor and deep donor behaviors, respectively. Additionally, Se–Bi antisites became prominent under higher fluences. Our insights into these defect mechanisms offer valuable guidance for defect engineering in high‐power electronics.

Transition metal sulfides are regarded as the underlying substitutes to noble metal electrocatalysts exhibiting semiconductor-like conductivity and rapid charge transfer kinetics. Herein, an unprecedented Y2S3@Ni-S-Co heterostructure has been synthesized on Ni-Co foam (NCF). This heterostructure comprises three phases: Y2S3, Co9S8, and Ni3S2, which serve as the active centers for alkaline overall water splitting. In this Y2S3-modified Ni-SCo heterointerface, electronic transfer occurs from Y2S3 to Ni-S-Co, increasing the electronic density of states on the interface. The intense electronic migration induced by the rare-earth element causes the Ni-S-Co interface and Y2S3 to function as the active centers for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), resulting in excellent activity in 1 M KOH, with overpotentials of 75 mV (10 mA center dot cm-2) and 290 mV (100 mA center dot cm-2), respectively. With Y2S3@Ni-S-Co/NCF serving as both the anode and cathode for overall water splitting, it demonstrated a comparable cell voltage to commercial Pt/C || RuO2 at 50 mA cm-2 (1.64 V vs. 1.63 V). In addition, the current density of the catalyst decreases by only 4 % after 50 h of continuous HER, demonstrating superior stability. This work presents a catalyst design strategy that utilizes Y2S3 to modify the conventional Ni-S-Co heterointerface, enhancing its catalytic activity for overall water splitting to levels comparable to noble metals.

Photocatalytic nitrogen fixation is a promising strategy for sustainable energy production, with efficient and cost-effective photocatalysts being crucial for its success. In this study, oxygen vacancy-rich photocatalysts (100-U, 200-U, and 300-U) were successfully synthesized via low-temperature calcination of NH2-UiO-66. Electron paramagnetic resonance analysis confirmed a significant increase in oxygen vacancies during calcination, enhancing active sites for photogenerated charge carrier capture. The bond length, thermogravimetric analysis, and X-ray diffraction revealed that calcination at 200 degrees C, compared to other temperatures, led to the cleavage of C1-C2 bonds and the breakage of Zr-OH-Zr bonds, promoting oxygen vacancy formation while preserving structural integrity. Photocatalytic results showed that the 200-U sample exhibited the highest nitrogen fixation performance, with an NH3 yield of 17.2 mu mol g-1 h-1, approximately twice that of the original NH2-UiO-66. This work provides valuable insights into the partial decomposition process and oxygen vacancy formation mechanism, contributing to the design of photocatalysts with abundant oxygen vacancies.

Schematic of the HBNG nanogenerator with a micro-pyramidal structure, illustrating layers of Kapton tape, Al foil, and PDMS-BaTiO 3 composite. The micropyramidal design enhances contact sensitivity, boosting output voltages under mechanical stress.

Advancing green hydrogen production via electrochemical water splitting remains a global challenge, with innovations in electrocatalysts being essential for improving efficiency, scalability, and sustainability. Metallenes, atomically thin materials composed of coordination-deficient metal atoms, represent a new class of two-dimensional (2D) materials characterized by a high aspect ratio, large surface area, abundant unsaturated surface atoms, and enhanced electron mobility, making them highly promising for electrocatalysis. Recent advances in 2D metallenes highlight their potential in energy conversion reactions, emphasizing the need for a comprehensive review of these emerging materials. This review examines the critical role of electrocatalysts, focusing on the evolution, classification, and synthesis of metallenes, including main group, transition metal-based, and alloy-based types. It details the synthesis of metallenes using top-down, bottom-up, and topotactic metallization methods and highlights optimization strategies such as strain modulation, phase control, defect incorporation, interface engineering, doping, and alloying. It analyzes metallenes applications in oxygen reduction (ORR), hydrogen evolution (HER), oxygen evolution (OER), overall water splitting, and seawater electrolysis, with comparative insights into other 2D materials. The review concludes by discussing the future of metallenes in electrocatalytic applications, addressing key challenges, and highlighting innovative strategies to enhance their integration into sustainable energy systems.

A mononuclear single source zinc precursor [Zn (OAc)2 (dmae)2] (dmae = N, N dimethylaminoethanol, OAc = acetate) (I), was synthesized using vacuum line and glove box technique and used for the fabrication of zinc oxide (ZnO) thin films via aerosol assisted chemical vapour deposition technique (AACVD). The precursor (I) was characterized structurally, morphologically, and optically using XRD, FESEM and UV-visible spectroscopy. [Zn (OAc)2 (dmae)2] (I) having low decomposition temperature besides excellent solubility in organic solvents makes it a perfect precursor for producing ZnO thin films. The structural analysis confirmed the growth of crystalline and single-phase ZnO thin film. The morphological analysis confirmed the presence of uniformly distributed grains of ZnO on the surface of the substrate. The optical properties were examined using an optical spectrometer in a range between 200 and 700 nm. The XRD analysis of the synthesized ZnO film on fluorine-doped tin oxide (FTO) reveals its crystalline nature, with a distinct hexagonal wurtzite structure. Moreover, EDX confirmed the presence of oxygen and Zn peaks and FESEM analysis revealed the presence of a uniform, homogeneous, and consistent ZnO thin layer on the FTO substrate. Additionally, Tauc's calculation was engaged to estimate the energy band gap of the deposited film of ZnO, revealing a value of approximately 3.45 eV. Likewise, the water splitting was carried out for green hydrogen production via photoelectrochemical (PEC) measurements, revealing a notable enhancement in photocurrent when exposed to 150 W halogen light with active potential windows of 0 - 1.5 Vin contrast to the dark condition.

Metal-organic frameworks (MOFs) are promising materials for energy-related applications, but their poor electrical conductivity limits their potential in electrocatalysis. In this study, p-NixCo1-x-MOF cathode catalysts were synthesized via a hydrothermal method followed by low-temperature annealing. This approach preserves the organic ligands within the MOF structure while exposing metal particles, thereby improving conductivity. The resulting catalyst demonstrates remarkable hydrogen evolution reaction (HER) performance, achieving an overpotential of only 35 mV and 142 mV at a geometric current density of 10 mA cm-2 and 300 mA cm-2, respectively, with a small Tafel slope of 34.78 mV dec-1, along with excellent long-term stability that pNi0.8Co0.2-MOF enabled sustained electrolysis at current densities of 10 mA cm-2 and 100 mA cm-2 for one week, compared with the MOF-based catalysts used for hydrogen evolution in recent years, the performance is excellent. The low-temperature annealing maintains the integrity of the organic framework and induces beneficial surface modifications, increasing the number of active sites and enhancing reaction kinetics and electron transfer efficiency for the superior electrocatalytic performance of the catalysts.

Platinum (Pt) is renowned for its remarkable catalytic activity in the hydrogen evolution reaction (HER); however, its significant cost constrains its widespread use. Integrating Pt with transition metals optimizes its electronic structure, enhancing catalytic efficiency while reducing Pt reliance. This study reports the synthesis of PtIrCoNixFe1-x high-entropy alloy nanoparticles (HEA NPs) via a moderate-temperature solvothermal method, offering a cost-efficient solution for achieving high HER activity with reduced Pt content. Structural analyses (PXRD, XPS, TEM, EDX mapping) confirm the formation of single-phase HEAs with evenly distributed elements. By adjusting Ni and Fe ratios, PtIrCoNi2 & sdot;9Fe3.9 HEA NPs sample show superior HER activity, outperforming commercial Pt/C with a low overpotential of 27 mV at-10 mA cm-2 and a Tafel slope of 37.8 mV dec-1 in alkaline media. DFT simulations reveal that the enhanced HER activity of the HEAs is due to d-d electron interactions and multiple active sites that lower energy barriers. Ir-5d orbitals facilitate electron transfer, while Pt-5d orbitals act as an electron reservoir. Ni-3d, Fe-3d, and Co-3d orbitals near the Fermi level create an electron depletion center, further improving HER activity. These findings highlight the potential of PtIrCoNixFe1-x HEA NPs as tunable HER electrocatalysts.

Efficient hydrogen production via electrochemical water splitting is vital for sustainable energy applications, with the HER in acidic media requiring highly effective catalysts. In this study, we report the synthesis of Bi2O2Se nanosheets through a scalable hydrothermal method, achieving exceptional catalytic performance in acidic conditions. The Bi2O2Se nanosheets exhibit a low overpotential of 104 mV at 10 mA cm-2, significantly outperforming other bismuth-based HER catalysts. The superior activity is attributed to the unique structural and electronic properties of Bi2O2Se, which provide abundant active sites and enhance charge transfer efficiency. Electrochemical studies, including Tafel slope analysis and impedance spectroscopy, confirm rapid HER kinetics and reduced charge-transfer resistance. Additionally, the catalysts demonstrate excellent long-term stability under acidic conditions, maintaining their performance during extended electrolysis. This work highlights the potential of Bi2O2Se as a highly efficient and cost-effective catalyst tailored for acidic HER applications. The dual-electrode system comprising Bi2O2Se@CP as the cathode and RuO2@CP as the anode demonstrated outstanding performance in overall water splitting. This system required a battery voltage of only 1.49 V to achieve a current density of 10 mA cm-2, highlighting the superior electrocatalytic efficiency of Bi2O2Se in conjunction with RuO2. By offering valuable insights into the design and optimization of bismuth-based materials, these findings pave the way for advancing sustainable hydrogen production technologies through scalable and efficient catalytic solutions.

Formation of a well-controlled Ni nanothorn geometry nanoarray-based electrode for thermally active hydrogen evolution reaction at high current density.

The amelioration of brilliantly effective electrocatalysts working at high current density for the oxygen evolution reaction (OER) is imperative for cost-efficient electrochemical hydrogen production. Yet, the kinetically sluggish and unstable catalysts remain elusive to large-scale hydrogen (H2) generation for industrial applications. Herein, a new strategy is demonstrated to significantly enhance the intrinsic activity of Ni1-xFex nanochain arrays through a trace proportion of heteroatom phosphorus doping that permits robust water splitting at an extremely large current density of 1000 and 2000 mA cm-2 for 760 h. The in situ formation of Ni2P and Ni5P4 on Ni1-xFex nanochain arrays surface and hierarchical geometry of the electrode significantly promote the reaction kinetics and OER activity. The OER electrode provides exceptionally low overpotentials of 222 and 327 mV at current densities of 10 and 2000 mA cm-2 in alkaline media, dramatically lower than benchmark IrO2 and is among the most active catalysts yet reported. Remarkably, the alkaline electrolyzer renders a low voltage of 1.75 V at a large current density of 1000 mA cm-2, indicating outperformed overall water splitting. The electrochemical fingerprints demonstrate vital progress toward large-scale H2 production for industrial water electrolysis.

Electrocatalytic water splitting is crucial for H2 2 production, which faces challenges with expensive and scarce noble metal catalysts. There is a persistent need for affordable, efficient electrodes facilitating both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). This study introduces a facile microwave synthesis method for nickel phosphide nanosheets (Ni5P4 5 P 4 NSs). These NSs demonstrate low overpotentials 110 mV for HER, 235 mV for OER at 10 mA cm-- 2 in 1 M KOH. Additionally, they show excellent overpotential 1.44 V at 10 mA cm-2 and remarkable durability for overall water splitting in the same conditions. This research highlights Ni5P4 5 P 4 NSs as promising bifunctional catalysts for electrochemical water splitting, offering a costeffective and efficient alternative to noble metal catalysts in energy storage and conversion applications.

The global pursuit of sustainable energy is focused on producing hydrogen through electrocatalysis driven by renewable energy. Recently, High entropy alloys (HEAs) have taken the spotlight in electrolysis due to their intriguing cocktail effect, broad design space, customizable electronic structure, and entropy stabilization effect. The tunability and complexity of HEAs allow a diverse range of active sites, optimizing adsorption strength and activity for electrochemical water splitting. This review comprehensively covers contemporary advancements in synthesis technique, design framework, and physio-chemical evaluation approaches for HEA-based electrocatalysts. Additionally, it explores design principles and strategies aimed at optimizing the catalytic activity, stability, and effectiveness of HEAs in hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and overall water splitting. Through an in-depth investigation of these aspects, the complexity inherent in constituent element interactions, reaction processes, and active sites associated with HEAs is aimed to unravel. Eventually, an outlook regarding challenges and impending difficulties and an outline of the future direction of HEA in electrocatalysis is provided. The thorough knowledge offered in this review will assist in formulating and designing catalysts based on HEAs for the next generation of electrochemistry-related applications.

Although 2D Bi2O2Se plays an important role in the electronics and optoelectronics based on its in-plane property, its out-of-plane electrical transport behavior remains unclear, especially in fabricating vertical devices with high integration density for novel functionality. Here, a solution-processed method is developed to prepare 2D Bi2O2Se with mass production (e.g., hundreds of milliliter scale). The out-of-plane ferroelectric property of 2D Bi2O2Se is observed by piezoresponse force microscopy and the ferroelectric dipole map atom-by-atom at the Bi2O2Se surface, which shows an atomically resolved dipolar displacement of Se ions. The out-of-plane resistant switching property of 2D Bi2O2Se is revealed by conductive atomic force microscopy. Moreover, the electric field on the local polarization of Bi2O2Se is addressed by using ab initio simulations, which shows a broken inversion symmetry along the z-axis of Bi2O2Se. The working mechanism of resistant switching behavior in Bi2O2Se is attributed to the diffusion and shuttle of Se ions. Besides, a controllable wet-assembled method is developed to prepare Bi2O2Se thin film with centimeter scale and explores its application on photodetectors under 808 nm laser light. This work reveals the unique out-of-plane transport behavior of 2D Bi2O2Se, providing the basis for fabricating multifunctional devices with high integration based on this 2D material.

AbstractDeveloping cost‐efficient trifunctional catalysts capable of facilitating hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR) activity is essential for the progression of energy devices. Engineering these catalysts to optimize their active sites and integrate them into a cohesive system presents a significant challenge. This study introduces a nanoflower (NFs)‐like carbon‐encapsulated FeNiPt nanoalloy catalyst (FeNiPt@C NFs), synthesized by substituting Co2+ ions with high‐spin Fe2+ ions in Hofmann‐type metal‐organic framework, followed by carbonization and pickling processes. The FeNiPt@C NFs catalyst, characterized by its nitrogen‐doped carbon‐encapsulated metal alloy structure and phase‐segregated FeNiPt alloy with slight surface oxidization, exhibits excellent trifunctional catalytic performance. This is evidenced by its activities in HER (−25 mV at 10 mA cm−2), ORR (half‐wave potential of 0.93 V), and OER (294 mV at 10 mA cm−2), with the enhanced water oxidation activity attributed to the high‐spin state of the Fe element. Consequently, the Zn‐air battery and anion exchange membrane water electrolyzer assembled by FeNiPt@C NFs catalyst demonstrate remarkable power density (168 mW cm−2) and industrial‐scale current density (698 mA cm−2 at 1.85 V), respectively. This innovative integration of multifunctional catalytic sites paves the way for the advancement of sustainable energy systems.

The amelioration of atomically thin ferroelectric materials is imperative for next-generation outperformed two-dimensional (2D) electronics, which is elusive by their bulk counterparts. These remarkable materials' ferroelectric and piezoelectric features are the fundamental urges in optoelectronics, electronics, and energy harvesting. In this work, 2D ferroelectric Bi2O2Se flakes have been synthesized using a modified chemical vapor deposition technique. The 6 nm thick Bi2O2Se flake provides a robust ferroelectric switching under an applied voltage of +/- 10 V by piezoresponse force microscopy, further confirmed by first principles. Leveraging the successful growth, the high-quality Bi2O2Se flakes permit the fabrication of a field-effect transistor (FET) with state-of-the-art performance. The FET device rewards a high current on-off ratio of 108 and field effect mobility of almost 131 cm(2) V-1 s(-1), owing to the small carrier effective mass of 0.2 m(0). Combined, the electric field-induced local polarization of ferroelectric switching and unprecedented device performance of Bi2O2Se semiconductors are certified for their utilization in advanced nanoelectronics and miniaturization of multifunctional devices with multifunctionalities.

The development of efficient and low-cost catalysts for cathodic oxygen reduction reaction (ORR) in Zn-air battery (ZAB) is a key factor in reducing costs and achieving industrialization. Here, a novel segregated CoNiPt alloy embedded in N-doped porous carbon with a nanoflowers (NFs)-like hierarchy structure is synthesized through pyrolyzing Hofmann-type metal-organic frameworks (MOFs). The unique hierarchical NFs structure exposes more active sites and facilitates the transportation of reaction intermediates, thus accelerating the reaction kinetics. Impressively, the resulting 15% CoNiPt@C NFs catalyst exhibits outstanding alkaline ORR activity with a half-wave potential of 0.93 V, and its mass activity is 7.5 times higher than that of commercial Pt/C catalyst, surpassing state-of-the-art noble metal-based catalysts. Furthermore, the assembled CoNiPt@C+RuO2 ZAB demonstrates a maximum power density of 172 mW cm-2 , which is superior to that of commercial Pt/C+RuO2 ZAB. Experimental results reveal that the intrinsic ORR mass activity is attributed to the synergistic interaction between oxygen defects and pyrrolic/graphitic N species, which optimizes the adsorption energy of the intermediate species in the ORR process and greatly enhances catalytic activity. This work provides a practical and feasible strategy for synthesizing cost-effective alkaline ORR catalysts by optimizing the electronic structure of MOF-derived catalysts.