Tunable metal hydroxide-organic frameworks for catalysing oxygen evolution

Determining Structures of Layer-by-Layer Spin-Coated Zinc Dicarboxylate-Based Metal-Organic Thin Films

Thin films of crystalline solids with substantial free volume built from organic chromophores and metal secondary building units (SBUs) are promising for engineering new optoelectronic properties through control of interchromophore coupling. Zn-based SBUs are especially relevant in this case because they avoid quenching the chromophore's luminescence. We find that layer-by-layer spin-coating using Zn acetate dihydrate and benzene-1,4-dicarboxylic acid (H2BDC) and biphenyl-4,4'-dicarboxylic acid (H2BPDC) linkers readily produces crystalline thin films. However, analysis of the grazing-incidence wide-angle X-ray scattering (GIWAXS) data reveals the structures of these films vary significantly with the linker, and with the metal-to-linker molar ratio used for fabrication. Under equimolar conditions, H2BPDC creates a type of structure like that proposed for SURMOF-2, whereas H2BDC generates a different metal-hydroxide-organic framework. Large excess of Zn2+ ions causes the growth of layered zinc hydroxides, irrespective of the linker used. Density functional theory (DFT) calculations provide structural models with minimum total energy that are consistent with the experimentally observed diffractograms. In the broader sense, this work illustrates the importance in this field of careful structure determination, e. g., by utilizing GIWAXS and DFT simulations to determine the structure of the obtained crystalline metal-organic thin films, such that properties can be rationally engineered and explained.

Bimetal Oxides Anchored on Carbon Nanotubes/Nanosheets as High-Efficiency and Durable Bifunctional Oxygen Catalyst for Advanced Zn-Air Battery: Experiments and DFT Calculations

To meet increasing requirement for innovative energy storage and conversion technology, it is urgent to prepare effective, affordable, and long-term stable oxygen electrocatalysts to replace precious metal-based counterparts. Herein, a two-step pyrolysis strategy is developed for controlled synthesis of Fe2O3 and Mn3O4 anchored on carbon nanotubes/nanosheets (Fe2O3-Mn3O4-CNTs/NSs). The typical catalyst has a high half-wave potential (E1/2 = 0.87 V) for oxygen reduction reaction (ORR), accompanied with a smaller overpotential (η10 = 290 mV) for oxygen evolution reaction (OER), showing substantial improvement in the ORR and OER performances. As well, density functional theory calculations are performed to illustrate the catalytic mechanism, where the in situ generated Fe2O3 directly correlates to the reduced energy barrier, rather than Mn3O4. The Fe2O3-Mn3O4-CNTs/NSs-based Zn-air battery exhibits a high-power density (153 mW cm-2) and satisfyingly long durability (1650 charge/discharge cycles/550 h). This work provides a new reference for preparation of highly reversible oxygen conversion catalysts.

The mechanism of water oxidation using transition metal-based heterogeneous electrocatalysts

The water oxidation reaction, a crucial process for solar energy conversion, has garnered significant research attention. Achieving efficient energy conversion requires the development of cost-effective and durable water oxidation catalysts. To design effective catalysts, it is essential to have a fundamental understanding of the reaction mechanisms. This review presents a comprehensive overview of recent advancements in the understanding of the mechanisms of water oxidation using transition metal-based heterogeneous electrocatalysts, including Mn, Fe, Co, Ni, and Cu-based catalysts. It highlights the catalytic mechanisms of different transition metals and emphasizes the importance of monitoring of key intermediates to explore the reaction pathway. In addition, advanced techniques for physical characterization of water oxidation intermediates are also introduced, for the purpose of providing information for establishing reliable methodologies in water oxidation research. The study of transition metal-based water oxidation electrocatalysts is instrumental in providing novel insights into understanding both natural and artificial energy conversion processes.

Unleashing the Power of Osmotic Energy: Metal Hydroxide-Organic Framework Membranes for Efficient Conversion

Osmotic energy, as a renewable clean energy with huge energy density and stable yield, has received widespread attention over the past decades. Reverse electrodialysis (RED) based on ion-exchange membranes is an important method of obtaining osmotic energy from salinity gradients. The preparation of ion-exchange membranes with both high ion selectivity and ion permeability is in constant exploration. In this work, metal hydroxide-organic framework (MHOF) membranes are successfully prepared onto porous anodic aluminum oxide (AAO) membranes by a facile hydrothermal method to form Ni2(OH)2@AAO composite membranes, used for osmotic energy conversion. The surface is negatively charged with cation selectivity, and the asymmetric structure and extreme hydrophilicity enhance the ionic flux for effective capture of osmotic energy. The maximum output power density of 5.65 W m-2 at a 50-fold KCl concentration gradient is achieved, which exceeds the commercial benchmark of 5 W m-2. Meanwhile, the composite membrane can also show good performance in different electrolyte solutions and acid-base environments. This work provides a new avenue for the construction and application of MHOF membranes in efficient osmotic energy conversion.

Ce-4f as an electron-modulation reservoir weakening Fe-O bond to induce iron vacancies in CeFevNi hydroxide for enhancing oxygen evolution reaction

Designing novel rare-earth-transition metal composites is at the forefront of electrocatalyst research. However, the modulation of transition metal electronic structures by rare earths to induce vacancy defects and enhance electrochemical performance has rarely been reported. In this study, we systematically investigate the mechanism by which Ce-4f electron modulation weakens the Fe-O bond, thereby altering the electronic structure in CeFevNi hydroxide to improve oxygen evolution reaction (OER) performance. Theoretical calculations and experimental characterizations reveal that Ce-4f orbitals function as electron-modulation reservoirs, capable not only of retaining or donating electrons but also of influencing the material's electronic structure. Moreover, Ce-4f bands optimize the Fe lower Hubbard bands (LHB) and O-2p bands, leading to weakened Fe-O bonds and the formation of cationic vacancies. This change results in the upshift of the d-band center at the active sites, favoring the reaction energy barrier for oxygen intermediates in the OER process. The synthesized catalyst demonstrated an overpotential of 201 mV at 10 mA cm-2 and a lifetime exceeding 200 h at 100 mA cm-2 under alkaline conditions. This work offers a proof-of-concept for the application of the mechanism of rare earth-induced transition metal vacancy defects, providing a general guideline for the design and development of novel highly efficient catalysts.

Spontaneous-Spin-Polarized 2D π-d Conjugated Frameworks Towards Enhanced Oxygen Evolution Kinetics

Alternative strategies to design sustainable-element-based electrocatalysts enhancing oxygen evolution reaction (OER) kinetics are demanded to develop affordable yet high-performance water-electrolyzers for green hydrogen production. Here, it is demonstrated that the spontaneous-spin-polarized 2D π-d conjugated framework comprising abundant elements of nickel and iron with a ratio of Ni:Fe = 1:4 with benzenehexathiol linker (BHT) can improve OER kinetics by its unique electronic property. Among the bimetallic NiFex:y-BHTs with various ratios with Ni:Fe = x:y, the NiFe1:4-BHT exhibits the highest OER activity. The NiFe1:4-BHT shows a specific current density of 140 A g-1 at the overpotential of 350 mV. This performance is one of the best activities among state-of-the-art non-precious OER electrocatalysts and even comparable to that of the platinum-group-metals of RuO2 and IrO2. The density functional theory calculations uncover that introducing Ni into the homometallic Fe-BHT (e.g., Ni:Fe = 0:1) can emerge a spontaneous-spin-polarized state. Thus, this material can achieve improved OER kinetics with spin-polarization which previously required external magnetic fields. This work shows that a rational design of 2D π-d conjugated frameworks can be a powerful strategy to synthesize promising electrocatalysts with abundant elements for a wide spectrum of next-generation energy devices.

Tailoring atomic chemistry to refine reaction pathway for the most enhancement by magnetization in water oxidation

Water oxidation on magnetic catalysts has generated significant interest due to the spin-polarization effect. Recent studies have revealed that the disappearance of magnetic domain wall upon magnetization is responsible for the observed oxygen evolution reaction (OER) enhancement. However, an atomic picture of the reaction pathway remains unclear, i.e., which reaction pathway benefits most from spin-polarization, the adsorbent evolution mechanism, the intermolecular mechanism (I2M), the lattice oxygen-mediated one, or more? Here, using three model catalysts with distinguished atomic chemistries of active sites, we are able to reveal the atomic-level mechanism. We found that spin-polarized OER mainly occurs at interconnected active sites, which favors direct coupling of neighboring ligand oxygens (I2M). Furthermore, our study reveals the crucial role of lattice oxygen participation in spin-polarized OER, significantly facilitating the coupling kinetics of neighboring oxygen radicals at active sites.

Nanozyme as a rising star for metabolic disease management

Nanozyme, characterized by outstanding and inherent enzyme-mimicking properties, have emerged as highly promising alternatives to natural enzymes owning to their exceptional attributes such as regulation of oxidative stress, convenient storage, adjustable catalytic activities, remarkable stability, and effortless scalability for large-scale production. Given the potent regulatory function of nanozymes on oxidative stress and coupled with the fact that reactive oxygen species (ROS) play a vital role in the occurrence and exacerbation of metabolic diseases, nanozyme offer a unique perspective for therapy through multifunctional activities, achieving essential results in the treatment of metabolic diseases by directly scavenging excess ROS or regulating pathologically related molecules. The rational design strategies, nanozyme-enabled therapeutic mechanisms at the cellular level, and the therapies of nanozyme for several typical metabolic diseases and underlying mechanisms are discussed, mainly including obesity, diabetes, cardiovascular disease, diabetic wound healing, and others. Finally, the pharmacokinetics, safety analysis, challenges, and outlooks for the application of nanozyme are also presented. This review will provide some instructive perspectives on nanozyme and promote the development of enzyme-mimicking strategies in metabolic disease therapy.

Fe,Ni-Based Metal-Organic Frameworks Embedded in Nanoporous Nitrogen-Doped Graphene as a Highly Efficient Electrocatalyst for the Oxygen Evolution Reaction

The quest for economically sustainable electrocatalysts to replace critical materials in anodes for the oxygen evolution reaction (OER) is a key goal in electrochemical conversion technologies, and, in this context, metal-organic frameworks (MOFs) offer great promise as alternative electroactive materials. In this study, a series of nanostructured electrocatalysts was successfully synthesized by growing tailored Ni-Fe-based MOFs on nitrogen-doped graphene, creating composite systems named MIL-NG-n. Their growth was tuned using a molecular modulator, revealing a non-trivial trend of the properties as a function of the modulator quantity. The most active material displayed an excellent OER performance characterized by a potential of 1.47 V (vs. RHE) to reach 10 mA cm-2, a low Tafel slope (42 mV dec-1), and a stability exceeding 18 h in 0.1 M KOH. This outstanding performance was attributed to the synergistic effect between the unique MOF architecture and N-doped graphene, enhancing the amount of active sites and the electron transfer. Compared to a simple mixture of MOFs and N-doped graphene or the deposition of Fe and Ni atoms on the N-doped graphene, these hybrid materials demonstrated a clearly superior OER performance.

Core-Shell CoS2@MoS2 with Hollow Heterostructure as an Efficient Electrocatalyst for Boosting Oxygen Evolution Reaction

It is imperative to develop an efficient catalyst to reduce the energy barrier of electrochemical water decomposition. In this study, a well-designed electrocatalyst featuring a core-shell structure was synthesized with cobalt sulfides as the core and molybdenum disulfide nanosheets as the shell. The core-shell structure can prevent the agglomeration of MoS2, expose more active sites, and facilitate electrolyte ion diffusion. A CoS2/MoS2 heterostructure is formed between CoS2 and MoS2 through the chemical interaction, and the surface chemistry is adjusted. Due to the morphological merits and the formation of the CoS2/MoS2 heterostructure, CoS2@MoS2 exhibits excellent electrocatalytic performance during the oxygen evolution reaction (OER) process in an alkaline electrolyte. To reach the current density of 10 mA cm-2, only 254 mV of overpotential is required for CoS2@MoS2, which is smaller than that of pristine CoS2 and MoS2. Meanwhile, the small Tafel slope (86.9 mV dec-1) and low charge transfer resistance (47 Ω) imply the fast dynamic mechanism of CoS2@MoS2. As further confirmed by cyclic voltammetry curves for 1000 cycles and the CA test for 10 h, CoS2@MoS2 shows exceptional catalytic stability. This work gives a guideline for constructing the core-shell heterostructure as an efficient catalyst for oxygen evolution reaction.

A linker selective retention strategy to construct hierarchical porous metal-organic frameworks with high catalytic activity for oxidative desulfurization

In order to improve the oxidative desulfurization (ODS) performance of MOF materials, an effective way is to convert a microporous MOF into a hierarchical porous MOF (HP-MOF) by utilizing the linker selective retention strategy. Herein, UiO-66 with the introduction of an unstable linker ligand (dihydro-1,2,4,5-tetrazine-3,6-dicarboxylate, dhtz) can selectively remove dhtz ligands to form HP-MOF (HP-UiO-66-dhtz) through heat treatment at high temperature. While maintaining the original structure of UiO-66, HP-UiO-66-dhtz features mesopores and abundant Lewis acid sites, showing excellent ODS performance for diphenylthiophene (DBT).

Three-dimensional flower-like Ni-S/Co-MOF grown on Ni foam as a bifunctional electrocatalyst for efficient overall water splitting

Poor conductivity of the metal-organic frameworks (MOFs) limits their applications in overall water splitting. Surface sulfur (S) doping transition metal hydroxides would effectively improve the conductivity and adjust the electronic structure to generate additional electroactive sites. Herein, we fabricated a Ni-S/Co-MOF/NF catalyst by electroplating a Ni-S film on the 3D flower-like Co-MOF. Because the 3D flower-like structures are covered in Ni foam, the high exposure of active sites and good conductivity are obtained. Moreover, the synergistic effect between Ni-S and Co-MOF contributes to the redistribution of electrons in the catalyst, which can then optimize the catalytic performance of the material. The obtained 3D flower-like Ni-S/Co-MOF/NF demonstrates excellent activity toward both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) in 1 M KOH, which only requires a low overpotential of 248 mV@10 mA cm-2 for the OER and 127 mV@10 mA cm-2 for the HER, respectively. At a current density of 10 mA cm-2, the Ni-S/Co-MOF/NF‖Ni-S/Co-MOF/NF requires a low cell voltage of 1.59 V to split overall water splitting.

Heterometallic Electrocatalysts Derived from High-Nuclearity Metal Clusters for Efficient Overall Water Splitting

The development of cost-effective electrocatalysts with an optimal surface affinity for intermediates is essential for sustainable hydrogen fuel production, but this remains insufficient. Here we synthesize Ni2P/MoS2-CoMo2S4@C heterometallic electrocatalysts based on the high-nuclearity cluster {Co24(TC4A)6(MoO4)8Cl6}, in which Ni2P nanoparticles were anchored to the surface of the MoS2-CoMo2S4@C nanosheets via strong interfacial interactions. Theoretical calculations revealed that the introduction of Ni2P phases induces significant disturbances in the surface electronic configuration of Ni2P/MoS2-CoMo2S4@C, resulting in more relaxed d-d orbital electron transfers between the metal atoms. Moreover, continuous electron transport was established by the formation of multiple heterojunction interfaces. The optimized Ni2P/MoS2-CoMo2S4@C electrocatalyst exhibited ultralow overpotentials of 198 and 73 mV for oxygen and hydrogen evolution reactions, respectively, in alkaline media, at 10 mA cm-2. The alkali electrolyzer constructed using Ni2P/MoS2-CoMo2S4@C required a cell voltage of only 1.45 V (10 mA cm-2) to drive overall water splitting with excellent long-term stability.

Achieving High-Performance Electrocatalytic Water Oxidation on Ni(OH)2 with Optimized Intermediate Binding Energy Enabled by S-Doping and CeO2 -Interfacing

The adsorption energy of the reaction intermediates has a crucial influence on the electrocatalytic activity. Ni-based materials possess high oxygen evolution reaction (OER) performance in alkaline, however too strong binding of *OH and high energy barrier of the rate-determining step (RDS) severely limit their OER activity. Herein, a facile strategy is shown to fabricate novel vertical nanorod-like arrays hybrid structure with the interface contact of S-doped Ni(OH)2 and CeO2 in situ grown on Ni foam (S-Ni(OH)2 /CeO2 /NF) through a one-pot route. The alcohol molecules oxidation reaction experiments and theoretical calculations demonstrate that S-doping and CeO2 -interfacing significantly modulate the binding energies of OER intermediates toward optimal value and reduce the energy barrier of the RDS, contributing to remarkable OER activity for S-Ni(OH)2 /CeO2 /NF with an ultralow overpotential of 196 mV at 10 mA cm-2 and long-term durability over 150 h for the OER. This work offers an efficient doping and interfacing strategy to tune the binding energy of the OER intermediates for obtaining high-performance electrocatalysts.

Amorphous Engineering of Scalable Metal-Organic Framework-Derived Electrocatalyst for Highly Efficient Oxygen Evolution Reaction

The engineering of amorphous metal-organic frameworks (MOFs) offers potential opportunities for the construction of electrocatalysts for efficient oxygen evolution reaction (OER). Herein, highly efficient OER performance and durability in alkaline electrolyte are discovered for MOF-derived amorphous and porous electrocatalysts, which are synthesized in a brief procedure and can be facilely produced in scalable quantities. The structural inheritance of MOF amorphous catalysts is significant for the retention of catalytic sites and the diffusion of electrolytes, and the presence of Fe sites can change the electronic structure and effectively control the adsorption behavior of important intermediates, accelerating reaction kinetics. The obtained amorphous A-FeNi can be transformed from FeNi-MOF effortlessly and instantly, and it only needs low overpotentials of 152 and 232 mV at 10 and 100 mA cm-2 with a Tafel slope of 17 mV dec-1 in 1 m KOH for OER. Moreover, A-FeNi possesses high corrosion resistance and durability, therefore A-FeNi can work continually for at least 400 h at 100 mA cm-2 . This work may pave a new avenue for the design of MOFs-related amorphous electrocatalyst.

Insights on MOF-derived metal-carbon nanostructures for oxygen evolution

Electrochemical water splitting has been regarded a promising method for the production of green hydrogen, addressing the need for efficient energy conversion and storage. However, it is severely hindered by the oxygen evolution reaction (OER) because of its multi-step four-electron transfer pathway with sluggish reaction kinetics. Microporous metal-organic-frameworks (MOFs), by virtue of large specific surface area, high porosity, tunable composition and morphology, find widespread use as precursors of metal-carbon nanostructures. The resulting carbon nanomaterials can well inherit the characteristics and advantages of the crystalline MOF precursors, and exhibit versatile application prospects in the fields of environment and energy, particularly in OER. Herein, a meticulous overview of the synthesis strategy for MOF-derived metal-carbon nanostructures and the origins of their enhanced OER properties has been demonstrated. We comprehensively illustrate these aspects across three dimensions: MOF selection, metal introduction, and carbon structures. Finally, the challenges and future prospects for this emerging field will be presented.

NiFe MOF modified BiVO4 photoanode with strong π-π conjugation enhances built-in electric field for boasting photoelectrochemical water oxidation

The photoelectrochemical (PEC) performance ofBiVO4 is limited by sluggish kinetics and poor stability. In this work, a novel high-performance BiVO4/NiFe MOF(BPDC) photoanode is constructed by loading NiFe MOF with biphenyl-4,4'-dicarboxylic acid (BPDC) as an organic ligand on BiVO4 by a simple one-step hydrothermal method. The XPS, OCP, UPS, and KPFM show that the enhanced π-π conjugation effect causes more electrons transfer from the BiVO4 to the MOFs and affects the magnitude of the work function, leading to a strong built-in electric field to drive carrier separation and migration. Therefore, the BiVO4/NiFe MOF(BPDC) has a strong hole extraction and carrier separation capability to enhance photoelectrochemical water oxidation and improve photostability. The BiVO4/NiFe MOF(BPDC) photoanode has an enhanced photocurrent density of 4.16 mA cm-2 at 1.23 VRHE, which is 4.33 times higher than that of the pure BiVO4 (0.96 mA cm-2) photoanode with a negative shift of 376 mV in the onset potential plot, exhibiting excellent photostability of 7 h at 1.23 VRHE. This work demonstrates that the composite photoanodes constructed by BiVO4 and the MOFs with strong π-π conjugation are promising, which provides an effective strategy for the preparation of efficient and stable photoanodes.

Metal-Organic-Framework-Based Nanoarrays for Oxygen Evolution Electrocatalysis

The development of highly active and stable electrode materials for the oxygen evolution reaction (OER) is essential for the widespread application of electrochemical energy conversion systems. In recent years, various metal-organic frameworks (MOFs) with self-supporting array structures have been extensively studied because of their high porosity, abundant metal sites, and flexible and adjustable structures. This review provides an overview of the recent progress in the design, preparation, and applications of MOF-based nanoarrays for the OER, beginning with the introduction of the architectural advantages of the nanoarrays and the characteristics of MOFs. Subsequently, the design principles of robust and efficient MOF-based nanoarrays as OER electrodes are highlighted. Furthermore, detailed discussions focus on the composition, structure, and performance of pristine MOF nanoarrays (MOFNAs) and MOF-based composite nanoarrays. On the one hand, the effects of the two components of MOFs and several modification methods are discussed in detail for MOFNAs. On the other hand, the review emphasizes the use of MOF-based composite nanoarrays composed of MOFs and other nanomaterials, such as oxides, hydroxides, oxyhydroxides, chalcogenides, MOFs, and metal nanoparticles, to guide the rational design of efficient OER electrodes. Finally, perspectives on current challenges, opportunities, and future directions in this research field are provided.

Complete Glucose Electrooxidation Enabled by Coordinatively Unsaturated Copper Sites in Metal-Organic Frameworks

The electrocatalytic oxidation of glucose plays a vital role in biomass conversion, renewable energy, and biosensors, but significant challenges remain to achieve high selectivity and high activity simultaneously. In this study, we present a novel approach for achieving complete glucose electrooxidation utilizing Cu-based metal-hydroxide-organic framework (Cu-MHOF) featuring coordinatively unsaturated Cu active sites. In contrast to traditional Cu(OH)2 catalysts, the Cu-MHOF exhibits a remarkable 40-fold increase in electrocatalytic activity for glucose oxidation, enabling exclusive oxidation of glucose into formate and carbonate as the final products. The critical role of open metal sites in enhancing the adsorption affinity of glucose and key intermediates was confirmed by control experiments and density functional theory simulations. Subsequently, a miniaturized nonenzymatic glucose sensor was developed showing superior performance with a high sensitivity of 214.7 μA mM-1  cm-2 , a wide detection range from 0.1 μM to 22 mM, and a low detection limit of 0.086 μM. Our work provides a novel molecule-level strategy for designing catalytically active sites and could inspire the development of novel metal-organic framework for next-generation electrochemical devices.

Molecular Engineering of a Metal-Organic Polymer for Enhanced Electrochemical Nitrate-to-Ammonia Conversion and Zinc Nitrate Batteries

Metal-organic framework-based materials are promising single-site catalysts for electrocatalytic nitrate (NO3 - ) reduction to value-added ammonia (NH3 ) on account of well-defined structures and functional tunability but still lack a molecular-level understanding for designing the high-efficient catalysts. Here, we proposed a molecular engineering strategy to enhance electrochemical NO3 - -to-NH3 conversion by introducing the carbonyl groups into 1,2,4,5-tetraaminobenzene (BTA) based metal-organic polymer to precisely modulate the electronic state of metal centers. Due to the electron-withdrawing properties of the carbonyl group, metal centers can be converted to an electron-deficient state, fascinating the NO3 - adsorption and promoting continuous hydrogenation reactions to produce NH3 . Compared to CuBTA with a low NO3 - -to-NH3 conversion efficiency of 85.1 %, quinone group functionalization endows the resulting copper tetraminobenzoquinone (CuTABQ) distinguished performance with a much higher NH3 FE of 97.7 %. This molecular engineering strategy is also universal, as verified by the improved NO3 - -to-NH3 conversion performance on different metal centers, including Co and Ni. Furthermore, the assembled rechargeable Zn-NO3 - battery based on CuTABQ cathode can deliver a high power density of 12.3 mW cm-2 . This work provides advanced insights into the rational design of metal complex catalysts through the molecular-level regulation for NO3 - electroreduction to value-added NH3 .

Lattice tensile strain cobalt phosphate with modulated hydroxide adsorption and structure transformation towards improved oxygen evolution reaction

The adsorption energy of oxygen-containing intermediates for the oxygen evolution reaction (OER) electrocatalysts plays a key role on their electrocatalytic performances. Rational optimization and regulation of the binding energy of intermediates can effectively improve the catalytic activities. Herein, the binding strength of Co phosphate to *OH was weakened by generating lattice tensile strain via Mn replacement, which modulated the electronic structure and optimized the reactive intermediates adsorption with active sites. The tensile-strained lattice structure and stretched interatomic distance were confirmed by X-ray diffraction and extended X-ray absorption fine structure (EXAFS) spectra measurements. The as-obtained Mn-doped Co phosphate exhibits excellent OER activity with an overpotential of 335 mV at 10 mA cm-2, which is much higher than pristine Co phosphate. In-situ Raman spectra and methanol oxidation reaction experiments demonstrated that Mn-doped Co phosphate with lattice tensile strain shows optimized *OH adsorption strength, and is favorable to structure reconstruction and form highly active Co oxyhydroxide intermediate during OER process. Our work provides insight into the effects of the lattice strain on the OER activity from the standpoint of intermediate adsorption and structure transformation.

Two Dimensional Ir-Based Catalysts for Acidic OER

Electrochemical water splitting in acidic media is one of the most promising hydrogen production technologies, yet its practical applications in proton exchange membrane (PEM) water electrolyzers are limited by the anodic oxygen evolution reaction (OER). Iridium (Ir)-based materials are considered as the state-of-the-art catalysts for acidic OER due to their good stability under harsh acidic conditions. However, their activities still have much room for improvement. Two-dimensional (2D) materials are full of the advantages of high-surface area, unique electrical properties, facile surface modification, and good stability, making the development of 2D Ir-based catalysts more attractive for achieving high catalytic performance. In this review, first, the unique advantages of 2D catalysts for electrocatalysis are reviewed. Thereafter, the classification, synthesis methods, and recent OER achievements of 2D Ir-based materials, including pure metals, alloys, oxides, and perovskites are introduced. Finally, the prospects and challenges of developing 2D Ir-based catalysts for future acidic OER are discussed.

Bioinspired trimesic acid anchored electrocatalysts with unique static and dynamic compatibility for enhanced water oxidation

Layered double hydroxides are promising candidates for the electrocatalytic oxygen evolution reaction. Unfortunately, their catalytic kinetics and long-term stabilities are far from satisfactory compared to those of rare metals. Here, we investigate the durability of nickel-iron layered double hydroxides and show that ablation of the lamellar structure due to metal dissolution is the cause of the decreased stability. Inspired by the amino acid residues in photosystem II, we report a strategy using trimesic acid anchors to prepare the subsize nickel-iron layered double hydroxides with kinetics, activity and stability superior to those of commercial catalysts. Fundamental investigations through operando spectroscopy and theoretical calculations reveal that the superaerophobic surface facilitates prompt release of the generated O2 bubbles, and protects the structure of the catalyst. Coupling between the metals and coordinated carboxylates via C‒O‒Fe bonding prevents dissolution of the metal species, which stabilizes the electronic structure by static coordination. In addition, the uncoordinated carboxylates formed by dynamic evolution during oxygen evolution reaction serve as proton ferries to accelerate the oxygen evolution reaction kinetics. This work offers a promising way to achieve breakthroughs in oxygen evolution reaction stability and dynamic performance by introducing functional ligands with static and dynamic compatibilities.

The Structure, Preparation, Characterization, and Intercalation Mechanism of Layered Hydroxides Intercalated with Guest Anions

Since the intercalation of anions into layered hydroxides (LHs) has a great impact not only on their nucleation and growth but also on their structure, composition, and size, the intercalation chemistry of LHs has aroused the strong interest of researchers. However, the progress in the fundamental understanding of LHs intercalated with guest anions have not been paralleled by a concomitant development of the preparation and performance improvement of such materials. Considering the guidance of a timely in-depth review for scientists in this area, a systematic introduction about the development that is made on the above-mentioned issues is highly needed but yet missing so far. Herein, recent advances in understanding the chemical composition and structure of LHs intercalated with guest anions are systematically summarized. Meanwhile, typical and emerging bottom-up synthesis methods of LHs intercalated with anions are reviewed, and the potential impact of external reaction parameters on the intercalation of anions into LHs are discussed . Besides, different analytical characterization techniques employed in the examination of guest anion-intercalated LHs are deliberated upon. Finally, although progress is slow in exploring the intercalation mechanism, as many examples as possible are included in this review and inferred the possible intercalation mechanism.

Self-Reconstructed Two-Dimensional Cluster-Based Co-Organic Layer Heterojunctions for Enhanced Oxygen Evolution Reactions

When it comes to an efficient catalytic oxygen evolution reaction (OER) in the production of renewable energy and chemicals, the construction of heterogeneous structures is crucial to break the linear scalar relationship of a single catalyst. This heterogeneous structure construction helps creatively achieve high activity and stability. However, the synthesis process of heterogeneous crystalline materials is often complex and challenging to capture and reproduce, which limits their application. Here, the dynamic process of structural changes in Co-MOFs in alkali was captured by in situ powder X-ray diffraction, FT-IR spectroscopy, and Raman spectroscopy, and several self-reconfigured MOF heterogeneous materials with different structures were stably isolated. The created β-Co(OH)2/Co-MOF heterojunction structure facilitates rapid mass-charge transfer and exposure of active sites, which significantly enhanced OER activity. Experimental results show that this heterogeneous structure achieves a low overpotential of 333 mV at 10 mA cm-2. The findings provide new insights and directions for the search for highly reactive cobalt-based MOFs for sustainable energy technologies.

Length-tunable Pd2Sn@Pt core-shell nanorods for enhanced ethanol electrooxidation with concurrent hydrogen production

The electrooxidation of ethanol as an alternative to the oxygen evolution reaction presents a promising approach for low-cost hydrogen production. However, the design and synthesis of efficient ethanol oxidation electrocatalysts remain key challenges. Here, a colloidal procedure is developed to prepare Pd2Sn@Pt core-shell nanorods with an expanded Pt lattice and tunable length. The obtained Pd2Sn@Pt catalysts exhibit superior activity and stability for ethanol electrooxidation compared to Pd2Sn and commercial Pt/C catalysts. By tuning the length of the Pd2Sn@Pt nanorods, remarkable mass activity of up to 4.75 A mgPd+Pt-1 and specific activity of 20.14 mA cm-2 are achieved for the short nanorods owing to their large specific surface area. A hybrid electrolysis system for ethanol oxidation and hydrogen evolution is constructed using Pd2Sn@Pt as the anodic catalyst and Pt mesh as the cathode. The system requires a low cell voltage of 0.59 V for the simultaneous production of acetic acid and hydrogen at a current density of 10 mA cm-2. Density functional theory calculations further reveal that the strained Pt shell reduces energy barriers in the ethanol electrooxidation pathway, facilitating the conversion of ethanol to acetic acid. This work provides valuable guidance for developing highly efficient ethanol electrooxidation catalysts for integrated hydrogen production systems.

Lattice-Strain Engineering for Heterogenous Electrocatalytic Oxygen Evolution Reaction

The energy efficiency of metal-air batteries and water-splitting techniques is severely constrained by multiple electronic transfers in the heterogenous oxygen evolution reaction (OER), and the high overpotential induced by the sluggish kinetics has become an uppermost scientific challenge. Numerous attempts are devoted to enabling high activity, selectivity, and stability via tailoring the surface physicochemical properties of nanocatalysts. Lattice-strain engineering as a cutting-edge method for tuning the electronic and geometric configuration of metal sites plays a pivotal role in regulating the interaction of catalytic surfaces with adsorbate molecules. By defining the d-band center as a descriptor of the structure-activity relationship, the individual contribution of strain effects within state-of-the-art electrocatalysts can be systematically elucidated in the OER optimization mechanism. In this review, the fundamentals of the OER and the advancements of strain-catalysts are showcased and the innovative trigger strategies are enumerated, with particular emphasis on the feedback mechanism between the precise regulation of lattice-strain and optimal activity. Subsequently, the modulation of electrocatalysts with various attributes is categorized and the impediments encountered in the practicalization of strained effect are discussed, ending with an outlook on future research directions for this burgeoning field.

Metal-organic frameworks (MOFs) based luminescent and electrochemical sensors for food contaminant detection

With the increasing population, food toxicity has become a prevalent concern due to the growing contaminants of food products. Therefore, the need for new materials for toxicant detection and food quality monitoring will always be in demand. Metal-organic frameworks (MOFs) based on luminescence and electrochemical sensors with tunable porosity and active surface area are promising materials for food contaminants monitoring. This review summarizes and studies the most recent progress on MOF sensors for detecting food contaminants such as pesticides, antibiotics, toxins, biomolecules, and ionic species. First, with the introduction of MOFs, food contaminants and materials for toxicants detection are discussed. Then the insights into the MOFs as emerging materials for sensing applications with luminescent and electrochemical properties, signal changes, and sensing mechanisms are discussed. Next, recent advances in luminescent and electrochemical MOFs food sensors and their sensitivity, selectivity, and capacities for common food toxicants are summarized. Further, the challenges and outlooks are discussed for providing a new pathway for MOF food contaminant detection tools. Overall, a timely source of information on advanced MOF materials provides materials for next-generation food sensors.

Efficient O-O Coupling at Catalytic Interface to Assist Kinetics Optimization on Concerted and Sequential Proton-Electron Transfer for Water Oxidation

A catalyst kinetics optimization strategy based on tuning active site intermediates adsorption is proposed. Construction of the M-OOH on the catalytic site before the rate-determining step (RDS) is considered a central issue in the strategy, which can optimize the overall catalytic kinetics by avoiding competition from other reaction intermediates on the active site. Herein, the kinetic energy barrier of the O-O coupling for as-prepared sulfated Co-NiFe-LDH nanosheets is significantly reduced, resulting in the formation of M-OOH on the active site at low overpotential, which is directly confirmed by in situ Raman and charge transfer fitting results. Moreover, catalysts constructed from active sites of highly efficient intermediates make a reliable model for studying the mechanism of the OER in proton transfer restriction. In weakly alkaline environments, a sequential proton-electron transfer (SPET) mechanism replaces the concerted proton-electron transfer (CPET) mechanism, and the proton transfer step becomes the RDS; high-speed consumption of reaction intermediates (M-OOH) induces sulfated Co-NiFe-LDH to exhibit excellent kinetics.

Molecular Engineering of Metal-Organic Frameworks as Efficient Electrochemical Catalysts for Water Oxidation

Metal-organic framework (MOF) solids with their variable functionalities are relevant for energy conversion technologies. However, the development of electroactive and stable MOFs for electrocatalysis still faces challenges. Here, a molecularly engineered MOF system featuring a 2D coordination network based on mercaptan-metal links (e.g., nickel, as for Ni(DMBD)-MOF) is designed. The crystal structure is solved from microcrystals by a continuous-rotation electron diffraction (cRED) technique. Computational results indicate a metallic electronic structure of Ni(DMBD)-MOF due to the Ni-S coordination, highlighting the effective design of the thiol ligand for enhancing electroconductivity. Additionally, both experimental and theoretical studies indicate that (DMBD)-MOF offers advantages in the electrocatalytic oxygen evolution reaction (OER) over non-thiol (e.g., 1,4-benzene dicarboxylic acid) analog (BDC)-MOF, because it poses fewer energy barriers during the rate-limiting *O intermediate formation step. Iron-substituted NiFe(DMBD)-MOF achieves a current density of 100 mA cm^-2 at a small overpotential of 280 mV, indicating a new MOF platform for efficient OER catalysis.

Assembly of Supramolecular Nanoplatelets with Tailorable Geometrical Shapes and Dimensions

The craving for controllable assembly of geometrical nanostructures from artificial building motifs, which is routinely achieved in naturally occurring systems, has been a perpetual and outstanding challenge in the field of chemistry and materials science. In particular, the assembly of nanostructures with different geometries and controllable dimensions is crucial for their functionalities and is usually achieved with distinct assembling subunits via convoluted assembly strategies. Herein, we report that with the same building subunits of α-cyclodextrin (α-CD)/block copolymer inclusion complex (IC), geometrical nanoplatelets with hexagonal, square, and circular shapes could be produced by simply controlling the solvent conditions via one-step assembly procedure, driven by the crystallization of IC. Interestingly, these nanoplatelets with different shapes shared the same crystalline lattice and could therefore be interconverted to each other by merely tuning the solvent compositions. Moreover, the dimensions of these platelets could be decently controlled by tuning the overall concentrations.

Cascade reaction triggering and photothermal AuNPs@MIL MOFs doped intraocular lens for enhanced posterior capsular opacification prevention

Posterior capsular opacification (PCO) is the most common complication after cataract surgery. Present strategies can't meet the clinical needs of long-term prevention. This research reports a novel intraocular lens (IOL) bulk material with high biocompatibility and synergistic therapy. Gold nanoparticles (AuNPs) doped MIL-101-NH₂ metal-organic frameworks (MOFs) (AuNPs@MIL) was firstly fabricated via in situ reductions. Then the functionalized MOFs were uniformly mixed with glycidyl methacrylate (GMA) and 2-(2-ethoxyethoxy) ethyl acrylate (EA) to form the nanoparticle doped polymer (AuNPs@MIL-PGE), and which was used to fabricate IOL bulk materials. The materials' optical and mechanical properties with different mass contents of nanoparticles are investigated. Such bulk functionalized IOL material could efficiently remove residual human lens epithelial cells (HLECs) in the capsular bag in the short term, and can prevent PCO on demand in the long run by near-infrared illumination (NIR) action. In vivo and in vitro experiments demonstrate the biosafety of the material. The AuNPs@MIL-PGE exhibits excellent photothermal effects, which could inhibit cell proliferation under NIR and doesn't cause pathological effects on the surrounding tissues. Such functionalized IOL can not only avoid the side effects of the antiproliferative drugs but also realize the enhanced PCO prevention in clinical practice.

Deeper mechanistic insights into epitaxial nickelate electrocatalysts for the oxygen evolution reaction

Mass production of green hydrogen via water electrolysis requires advancements in the performance of electrocatalysts, especially for the oxygen evolution reaction. In this feature article, we highlight how epitaxial nickelates act as model systems to identify atomic-level composition-structure-property-activity relationships, capture dynamic changes under operating conditions, and reveal reaction and failure mechanisms. These insights guide advanced electrocatalyst design with tailored functionality and superior performance. We conclude with an outlook for future developments via operando characterization and multilayer electrocatalyst design.

Introducing non-bridging ligand in metal-organic framework-based electrocatalyst enabling reinforced oxygen evolution in seawater

Using seawater as the replacement of freshwater for electrolysis, with the integration of renewable energy, is deemed as an attractive manner to harvest green hydrogen. However, the complexity of seawater puts forward stricter requirement to the electrocatalyst to alleviate the chlorine electrochemistry and corrosion. Herein, a nanosheet array of NiFe-MOF@Ni₂P/Ni(OH)₂ is devised by partially substituting terephthalic acid (H₂BDC) ligand by ferrocenecarboxylic acid (FcCA). Tailoring the active site into an under-coordinated fashion affords NiFe-MOF@Ni₂P/Ni(OH)₂ excellent performance towards oxygen evolution reaction (OER), only requiring the overpotentials of 302 mV and 394 mV in alkaline seawater to drive the current densities of 100 and 1000 mA cm^-2, respectively. Moreover, the as-obtained electrocatalyst showed robust durability for operating more than 120 h at 500 mA cm^-2 under harsh condition (6 M KOH + 1.5 M NaCl, 60 ℃). Density functional theory (DFT) calculations confirmed that tuning the coordination environment of Ni in NiFe-MOF by incorporating the non-bridging FcCA ligands could boost the formation of more active catalytic sites, which can simultaneously enhance the electronic conductivity and accelerate OER kinetics. This work provides beneficial enlightenment of combining MOF-based electrocatalyst with direct electrolysis of seawater.

Realizing Highly Efficient Sonodynamic Bactericidal Capability through the Phonon-Electron Coupling Effect Using Two-Dimensional Catalytic Planar Defects

Conferring catalytic defects in sonosensitizers is of paramount importance in reinforcing sonodynamic therapy. However, the formation of such 0D defects is governed by the Schottky defect principle. Herein, 2D catalytic planar defects are designed within Ti₃ C₂  sheets to address this challenge. These specific planar slip dislocations with abundant Ti³⁺ species (Ti₃ C₂ -SD(Ti³⁺ )) can yield surface-bound O due to the effective activation of O₂ , thus resulting in a substantial amount of ¹ O₂  generation and the 99.72% ± 0.03% bactericidal capability subject to ultrasound (US) stimulation. It is discovered that the 2D catalytic planar defects can intervene in electron transfer through the phonon drag effect-a coupling effect between surface electrons and US-triggered phonons-that simultaneously contributes to a dramatic decrease in O₂  activation energy from 1.65 to 0.06 eV. This design has achieved a qualitative leap in which the US catalytic site has transformed from 0D to 2D. Moreover, it is revealed that the electron origin, electron transfer, and visible O₂  activation pathway triggered by US can be attributed to the phonon-electron coupling effect. After coating with neutrophil membrane (NM) proteins, the NM-Ti₃ C₂ -SD(Ti³⁺ ) sheets further demonstrate a 6-log₁₀  reduction in methicillin-resistant Staphylococcus aureus burden in the infected bony tissue.

Altering Oxygen Binding by Redox-Inactive Metal Substitution to Control Catalytic Activity: Oxygen Reduction on Manganese Oxide Nanoparticles as a Model System

Establishing generic catalyst design principles by identifying structural features of materials that influence their performance will advance the rational engineering of new catalytic materials. In this study, by investigating metal-substituted manganese oxide (spinel) nanoparticles, Mn₃ O₄ :M (M=Sr, Ca, Mg, Zn, Cu), we rationalize the dependence of the activity of Mn₃ O₄ :M for the electrocatalytic oxygen reduction reaction (ORR) on the enthalpy of formation of the binary MO oxide, Δ_f H°(MO), and the Lewis acidity of the M²⁺ substituent. Incorporation of elements M with low Δ_f H°(MO) enhances the oxygen binding strength in Mn₃ O₄ :M, which affects its activity in ORR due to the established correlation between ORR activity and the binding energy of *O/*OH/*OOH species. Our work provides a perspective on the design of new compositions for oxygen electrocatalysis relying on the rational substitution/doping by redox-inactive elements.

Amorphous Metal-Organic Framework-Derived Electrocatalyst to Boost Water Oxidation

Amorphous metal-organic framework (MOF) materials have drawn extensive interest in the design of high-performance electrocatalysts for use in the electrochemical oxygen evolution reaction. However, there are limitations to the utilization of amorphous MOFs due to their low electrical conductivity and unsatisfactory stability. Herein, a novel amorphous-crystalline (AC) heterostructure is successfully constructed by synthesizing a crystalline metal sulfide (MS)-embedded amorphous Ni_0.67Fe_0.33-MOF, namely an MS/Ni_0.67Fe_0.33-MOF. It exhibits excellent catalytic performance (a low overpotential of 248 mV at 10 mA cm^-2 with a small Tafel slope of 50 mV decade^-1), durability, and stability (only 8% degradation of the current density at a constant voltage after 24 h). This work thus sheds light on the engineering of highly efficient catalysts with AC heterointerfaces for optimizing water-splitting systems.

Covalent Organic Framework Thin-Film Photodetectors from Solution-Processable Porous Nanospheres

The synthesis of homogeneous covalent organic framework (COF) thin films on a desired substrate with decent crystallinity, porosity, and uniform thickness has great potential for optoelectronic applications. We have used a solution-processable sphere transmutation process to synthesize 300 ± 20 nm uniform COF thin films on a 2 × 2 cm² TiO₂-coated fluorine-doped tin oxide (FTO) surface. This process controls the nucleation of COF crystallites and molecular morphology that helps the nanospheres to arrange periodically to form homogeneous COF thin films. We have synthesized four COF thin films (TpDPP, TpEtBt, TpTab, and TpTta) with different functional backbones. In a close agreement between the experiment and density functional theory, the TpEtBr COF film showed the lowest optical band gap (2.26 eV) and highest excited-state lifetime (8.52 ns) among all four COF films. Hence, the TpEtBr COF film can participate in efficient charge generation and separation. We constructed optoelectronic devices having a glass/FTO/TiO₂/COF-film/Au architecture, which serves as a model system to study the optoelectronic charge transport properties of COF thin films under dark and illuminated conditions. Visible light with a calibrated intensity of 100 mW cm^-2 was used for the excitation of COF thin films. All of the COF thin films exhibit significant photocurrent after illumination with visible light in comparison to the dark. Hence, all of the COF films behave as good photoactive substrates with minimal pinhole defects. The fabricated out-of-plane photodetector device based on the TpEtBr COF thin film exhibits high photocurrent density (2.65 ± 0.24 mA cm^-2 at 0.5 V) and hole mobility (8.15 ± 0.64 ×10^-3 cm² V^-1 S^-1) compared to other as-synthesized films, indicating the best photoactive characteristics.

Molecule-Enhanced Electrocatalysis of Sustainable Oxygen Evolution Using Organoselenium Functionalized Metal-Organic Nanosheets

Remolding the reactivity of metal active sites is critical to facilitate renewable electricity-powered water electrolysis. Doping heteroatoms, such as Se, into a metal crystal lattice has been considered an effective approach, yet usually suffers from loss of functional heteroatoms during harsh electrocatalytic conditions, thus leading to the gradual inactivation of the catalysts. Here, we report a new heteroatom-containing molecule-enhanced strategy toward sustainable oxygen evolution improvement. An organoselenium ligand, bis(3,5-dimethyl-1H-pyrazol-4-yl)selenide containing robust C-Se-C covalent bonds equipped in the precatalyst of ultrathin metal-organic nanosheets Co-SeMON, is revealed to significantly enhance the catalytic mass activity of the cobalt site by 25 times, as well as extend the catalyst operation time in alkaline conditions by 1 or 2 orders of magnitude compared with these reported metal selenides. A combination of various in situ/ex situ spectroscopic techniques, ab initio molecular dynamics, and density functional theory calculations unveiled the organoselenium intensified mechanism, in which the nonclassical bonding of Se to O-containing intermediates endows adsorption-energy regulation beyond the conventional scaling relationship. Our results showcase the great potential of molecule-enhanced catalysts for highly efficient and economical water oxidation.

Ensemble effects of high entropy alloy for boosting alkaline water splitting coupled with urea oxidation

FeCoNiMoRu/CNFs exhibits a small potential of 1.43 V vs. RHE (100 mA cm^-2) and superior stability for 90 h toward urea electro-oxidation (UOR). In situ electrochemical Raman results strongly demonstrate the ensemble effects of the various metal sites on improving the UOR activity by co-stabilizing the important intermediates. This work will open new directions in the application of high-entropy alloys for small molecule oxidation reactions.

Heterogenization of Molecular Electrocatalytic Active Sites through Reticular Chemistry

The electrochemical conversion of small molecules, such as CO₂ , O₂ , and H₂ O, has received significant attention as a potential engine for sustainable life. Metal-organic frameworks (MOFs) are a promising class of electrocatalytic materials for such processes. An attractive aspect of utilizing this class of materials as electrocatalysts is that well-known molecular active sites can be introduced to well-defined crystalline heterogeneous catalytic systems with high tunability. This review offers strategic insights into recent studies on MOF-based electrocatalysts by discussing the notable active sites that have been utilized in both homogeneous and heterogeneous catalysts, while highlighting instances where such active sites have been introduced into MOFs. In addition, material design principles enabling the integration of electrochemically active components with the MOF platform are outlined. Viewpoints on the viability of MOFs as an alternative to currently used electrocatalysts are also discussed. Finally, the future direction of MOF-based electrocatalysis research is established.

Expediting hole transfer via surface states in hematite-based composite photoanodes

Regarding the indirect hole transfer route in hematite-based photoelectrodes, the widely accepted viewpoint is that the Fe^IVO states act as a hole transfer medium, while other types of surface states act as recombination centers. Alternatively, it has rarely been reported that the recombining surface states may contribute to the charge transport in modified photoelectrodes. In this study, we employed CoCr layered double hydroxide (LDH)/Fe₂O₃ and CoCr LDH/Zr:Fe₂O₃ as research models to investigate the distinct charge transfer pathways in composite photoanodes. Different from the adverse role of surface states at ∼0.7 V versus the reversible hydrogen electrode (r-SS) in the bare hematite photoelectrodes (Fe₂O₃ or Zr:Fe₂O₃), the r-SS in the composite photoanodes (CoCr LDH/Fe₂O₃ or CoCr LDH/Zr:Fe₂O₃) served as a hole transfer station to induce high-valent Co cations, and the position of r-SS determined the onset potential of the composite photoelectrodes. Moreover, the Fe^IVO states still acted as active intermediates to transport numerous holes to the cocatalyst, which enhanced the charge utilization efficiency at 1.23 V versus the reversible hydrogen electrode (RHE) to a large extent. Besides, a noteworthy fact is that Zr doping increased the number of active Fe^IVO states, which significantly contributed to the enhancement in current density. However, it led to a delayed onset potential because of the positively shifted surface states (r-SS and Fe^IVO). Evidently, the different surface state distributions between Fe₂O₃ and Zr:Fe₂O₃ gave rise to anisotropic charge transfer and recombination behavior in the composite photoanodes. This study gives extensive insight into the hole transfer route in composite photoanodes and reveals the surface state-tuning effects of dopants and cocatalysts, which are significant for a deep understanding of the surface states and optimal design of composite photoanodes via surface state modulation.

Dynamic Electrochemical Interfaces for Energy Conversion and Storage

Electrochemical energy conversion and storage are central to developing future renewable energy systems. For efficient energy utilization, both the performance and stability of electrochemical systems should be optimized in terms of the electrochemical interface. To achieve this goal, it is imperative to understand how a tailored electrode structure and electrolyte speciation can modify the electrochemical interface structure to improve its properties. However, most approaches describe the electrochemical interface in a static or frozen state. Although a simple static model has long been adopted to describe the electrochemical interface, atomic and molecular level pictures of the interface structure should be represented more dynamically to understand the key interactions. From this perspective, we highlight the importance of understanding the dynamics within an electrochemical interface in the process of designing highly functional and robust energy conversion and storage systems. For this purpose, we explore three unique classes of dynamic electrochemical interfaces: self-healing, active-site-hosted, and redox-mediated interfaces. These three cases of dynamic electrochemical interfaces focusing on active site regeneration collectively suggest that our understanding of electrochemical systems should not be limited to static models but instead expanded toward dynamic ones with close interactions between the electrode surface, dissolved active sites, soluble species, and reactants in the electrolyte. Only when we begin to comprehend the fundamentals of these dynamics through operando analyses can electrochemical conversion and storage systems be advanced to their full potential.

Exceptional catalytic activity of oxygen evolution reaction via two-dimensional graphene multilayer confined metal-organic frameworks

Oxygen evolution reaction (OER) plays a key role in many renewable energy technologies such as water splitting and metal-air batteries. Metal-organic frameworks (MOFs) are appealing to design efficient OER electrocatalysts, however, their intrinsic poor conductivity strongly hinders the activity. Here, we show a strategy to boost the OER activity of poor-conductive MOFs by confining them between graphene multilayers. The resultant NiFe-MOF//G gives a record-low overpotential of 106 mV to reach 10 mA cm⁻² and retains the activity over 150 h, which is in significant contrast to 399 mV of the pristine NiFe-MOF. We use X-ray absorption spectroscopy (XAS) and computations to demonstrate that the nanoconfinement from graphene multilayers not only forms highly reactive NiO₆-FeO₅ distorted octahedral species in MOF structure but also lowers limiting potential for water oxidation reaction. We also demonstrate that the strategy is applicable to other MOFs of different structures to largely enhance their electrocatalytic activities.

While metal-organic frameworks offer a diverse array of structural motifs for electrocatalysis, poor conductivity and mass permeability limit performances. Here, authors confine low-conductivity metal-organic frameworks between graphene multilayers to enhance oxygen evolution performances.

Metal-Organic Framework-Based Nanomaterials for Electrocatalytic Oxygen Evolution

Oxygen evolution reaction (OER) is an energy-determined half-reaction for water splitting and many other energy conversion processes, such as rechargeable metal-air batteries and CO₂ reduction, due to its four-electron sluggish process. To reduce the energy consumption and cost of these advanced technologies, various transition metal-based nanomaterials, like metal oxides/hydroxides, nitride, and phosphide are synthesized. Among these, metal-organic framework (MOF)-based materials are considered as the ideal candidate for the fabrication of efficient OER electrocatalysts owing to their unique physicochemical properties. In this review, the fundamental catalytic mechanisms and key evaluation parameters of OER in acidic and alkaline media are presented first. Then, design strategies for MOF-based OER catalysts and research progress in the study of the structure-performance relationship are summarized. Subsequently, the recent research advances of MOF-based OER electrocatalysts in alkaline, acidic, and neutral electrolytes are overviewed. Finally, current challenges and future opportunities are provided under the frame of materials design, theoretical understanding, advanced characterization techniques, and industrial applications.

Facile Synthesis of FeCoNiCuIr High Entropy Alloy Nanoparticles for Efficient Oxygen Evolution Electrocatalysis

The lack of an efficient and stable electrocatalyst for oxygen evolution reaction (OER) greatly hinders the development of various electrochemical energy conversion and storage techniques. In this study, we report a facile synthesis of FeCoNiCuIr high-entropy alloy nanoparticles (HEA NPs) by a one-step heat-up method. The involvement of glucose made the NPs grow uniformly and increased the valence of Ir. The resulting FeCoNiCuIr NPs exhibit excellent OER performance in alkaline solution, with a low overpotential of 360 mV to achieve a current density of 10 mA cm−2 at a Tafel slope of as low as 70.1 mV dec‒1. In addition, high stability has also been observed, which remained at 94.2% of the current density after 10 h constant electrolysis, with a constant current of 10 mA cm‒2. The high electrocatalytic activity and stability are ascribed to the cocktail effect and synergistic effect between the constituent elements. Our work holds the potential to be extended to the design and synthesis of high-performance electrocatalysts.