Trimetallic MOF-74 Films Grown on Ni Foam as Bifunctional Electrocatalysts for Overall Water Splitting

Multi-metallic MOF based composites for environmental applications: synergizing metal centers and interactions

The escalating threat of environmental issues to both nature and humanity over the past two decades underscores the urgency of addressing environmental pollutants. Metal-organic frameworks (MOFs) have emerged as highly promising materials for tackling these challenges. Since their rise in popularity, extensive research has been conducted on MOFs, spanning from design and synthesis to a wide array of applications, such as environmental remediation, gas storage and separation, catalysis, sensors, biomedical and drug delivery systems, energy storage and conversion, and optoelectronic devices, etc. MOFs possess a multitude of advantageous properties such as large specific surface area, tunable porosity, diverse pore structures, multi-channel design, and molecular sieve capabilities, etc., making them particularly attractive for environmental applications. MOF-based composites inherit the excellent properties of MOFs and also exhibit unique physicochemical properties and structures. The tailoring of central coordinated metal ions in MOFs is critical for their adaptability in environmental applications. Although many reviews on monometallic, bimetallic, and polymetallic MOFs have been published, few reviews focusing on MOF-based composites with monometallic, bimetallic, and multi-metallic centers in the context of environmental pollutant treatment have been reported. This review addresses this gap by providing an in-depth overview of the recent progress in MOF-based composites, emphasizing their applications in hazardous gas sensing, electromagnetic wave absorption (EMWA), and pollutant degradation in both aqueous and atmospheric environments and highlighting the importance of the number and type of metal centers present. Additionally, the various categories of MOFs are summarized. MOF-based composites demonstrate significant promise in addressing environmental challenges, and this review provides a clear and valuable perspective on their potential in environmental applications.

Rational Design of Organic Electrocatalysts for Hydrogen and Oxygen Electrocatalytic Applications

Efficient electrocatalysts are pivotal for advancing green energy conversion technologies. Organic electrocatalysts, as cost-effective alternatives to noble-metal benchmarks, have garnered attention. However, the understanding of the relationships between their properties and electrocatalytic activities remains ambiguous. Plenty of research articles regarding low-cost organic electrocatalysts started to gain momentum in 2010 and have been flourishing recently though, a review article for both entry-level and experienced researchers in this field is still lacking. This review underscores the urgent need to elucidate the structure-activity relationship and design suitable electrode structures, leveraging the unique features of organic electrocatalysts like controllability and compatibility for real-world applications. Organic electrocatalysts are classified into four groups: small molecules, oligomers, polymers, and frameworks, with specific structural and physicochemical properties serving as activity indicators. To unlock the full potential of organic electrocatalysts, five strategies are discussed: integrated structures, surface property modulation, membrane technologies, electrolyte affinity regulation, and addition of anticorrosion species, all aimed at enhancing charge efficiency, mass transfer, and long-term stability during electrocatalytic reactions. The review offers a comprehensive overview of the current state of organic electrocatalysts and their practical applications, bridging the understanding gap and paving the way for future developments of more efficient green energy conversion technologies.

MOF-based/derived catalysts for electrochemical overall water splitting

Water-splitting electrocatalysis has gained increasing attention as a promising strategy for developing renewable energy in recent years, but its high overpotential caused by the unfavorable thermodynamics has limited its widespread implementation. Therefore, there is an urgent need to design catalytic materials with outstanding activity and stability that can overcome the high overpotential and thus improve the electrocatalytic efficiency. Metal-organic frameworks (MOFs) based and/or derived materials are widely used as water-splitting catalysts because of their easily controlled structures, abundant heterointerfaces and increased specific surface area. Herein, some recent research findings on MOFs-based/derived materials are summarized and presented. First, the mechanism and evaluation parameters of electrochemical water splitting are described. Subsequently, advanced modulation strategies for designing MOFs-based/derived catalysts and their catalytic performance toward water splitting are summarized. In particular, the correlation between chemical composition/structural functionalization and catalytic performance is highlighted. Finally, the future outlook and challenges for MOFs materials are also addressed.

Metal-Organic Framework (MOF)-Based Clean Energy Conversion: Recent Advances in Unlocking its Underlying Mechanisms

Carbon neutrality is an important goal for humanity . As an eco-friendly technology, electrocatalytic clean energy conversion technology has emerged in the 21st century. Currently, metal-organic framework (MOF)-based electrocatalysis, including oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER), hydrogen oxidation reaction (HOR), carbon dioxide reduction reaction (CO2RR), nitrogen reduction reaction (NRR), are the mainstream energy catalytic reactions, which are driven by electrocatalysis. In this paper, the current advanced characterizations for the analyses of MOF-based electrocatalytic energy reactions have been described in details, such as density function theory (DFT), machine learning, operando/in situ characterization, which provide in-depth analyses of the reaction mechanisms related to the above reactions reported in the past years. The practical applications that have been developed for some of the responses that are of application values, such as fuel cells, metal-air batteries, and water splitting have also been demonstrated. This paper aims to maximize the potential of MOF-based electrocatalysts in the field of energy catalysis, and to shed light on the development of current intense energy situations.

3D Magnetic Metal-Organic Frameworks Current Collectors Accelerate the Lithium-Ion Diffusion Rate for Superlong Cyclic Lithium Metal Anode

Lithium, is the most ideal anode material for lithium-based batteries. However, the overgrowth of lithium dendrites and the low lithium-ion diffusion rate at low temperatures limit the further application of lithium metal anodes. Here, the applied magnetic field is introduced inside the lithium metal anode by using a novel magnetic metal-organic framework as a current collector. The magnetic field can improve the conductivity of this novel current collector, thus accelerating the diffusion of lithium ions in the battery, an advantage that is particularly prominent at low temperatures. In addition, the current collector can stabilize the solid electrolyte interface and inhibit the growth of lithium dendrites, resulting in excellent electrochemical performance. The symmetrical cell at room temperature can exceed 4600 h with a hysteresis voltage of only 9 mV. After 300 cycles at room temperature, the capacity of full cell is still 142 mA h g-1 , and it remains stable for 380 cycles at 5 °C (capacity above 120 mA h g-1 ). The strategy of constructing novel current collector with magnetic field can promote the further application of lithium batteries in extreme conditions such as low temperatures.

Unleashing the room temperature boronization: Blooming of Ni-ZIF nanobuds for efficient photo/electro catalysis of water

Water splitting provides an environmental-friendly and sustainable approach for generating hydrogen fuel. The inherent energetic barrier in two-core half reactions such as the Hydrogen Evolution Reaction (HER) and Oxygen Evolution Reaction (OER) leads to undesired increased overpotential and constrained reaction kinetics. These challenges pose significant challenges that demand innovative solutions to overcome. One of the efficient ways to address this issue is tailoring the morphology and crystal structure of metal-organic frameworks (MOF). Nickel Zeolite Imidazolate Framework (Ni-ZIF) is a popular MOF and it can be tailored using facile chemical methods to unleash a remarkable bifunctional electro/photo catalyst. This innovative solution holds the capability to address prevailing obstacles such as inadequate electrical conductivity and limited access to active metal centers due to the influence of organic ligands. Thereby, applying boronization to the Ni-ZIF under different duration, one can induce blooming of nanobuds under room temperature and modify oxygen vacancies in order to achieve higher reaction kinetics in electro/photo catalysis. It can be evidenced by the 24-h boronized Ni-ZIF (BNZ), exhibiting lower overpotentials as electrocatalyst (OER-396 mV & HER-174 mV @ 20 mA/cm2) in 1 M KOH electrolyte and augmented gas evolution rates when employed as a photocatalyst (Hydrogen-14.37 μmol g-1min-1 & Oxygen-7.40 μmol g-1min-1). The 24-h boronization is identified as the optimum stage of crystalline to amorphous transformation which provided crystalline/amorphous boundaries as portrayed by X-Ray diffraction (XRD) and High Resolution-Transmission Electron Microscopy (HR-TEM) analysis. The flower-like transformation of 24-BNZ, characterized by crystalline-amorphous boundaries initiates with partial disruption of Ni-N bonds and formation of Ni-B bonds as evident from X-ray Photoelectron Spectroscopy (XPS). Further, the 24-h BNZ exhibit bifunctional catalytic activities with pre-longed stability. Overall, this work presents a comprehensive study of the electrocatalytic and photocatalytic water splitting properties of the tailored Ni-ZIF material.

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.

(FeMnCe)-co-doped MOF-74 with significantly improved performance for overall water splitting

Developing inexpensive electrocatalysts with high activity and stability is of great value for overall water splitting. In this work, we designed a series of 3d-4f (FeMnCe)-trimetallic MOF-74 with different ratios of 3d- and 4f-metal centers. Among them, FeMn6Ce0.5-MOF-74/NF exhibited the best electrocatalytic performance for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in an alkaline solution. It only requires a low overpotential of 281 mV@100 mA cm-2 for OER and 186 mV@-10 mA cm-2 for HER in 1 M KOH. With FeMn6Ce0.5-MOF-74/NF as the anode and cathode in the overall water splitting system, only 1.65 V is needed to deliver a current density of 10 mA cm-2. In particular, for the as-fabricated FeMn6Ce0.5-MOF-74/NF||Pt/C cell unit, only 1.40 V is needed to achieve 10 mA cm-2. Therefore, the successful design of 3d-4f mixed-metallic MOF-74 provides a new viewpoint to develop highly efficient non-precious metal electrocatalysts.

Self-Supporting Co/CeO2 Heterostructures for Ampere-Level Current Density Alkaline Water Electrolysis

Remodeling the active surface through fabricating heterostructures can substantially enhance alkaline water electrolysis driven by renewable electrical energy. However, there are still great challenges in the synthesis of highly reactive and robust heterostructures to achieve both ampere-level current density hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Herein, we report a new Co/CeO₂ heterojunction self-supported electrode for sustainable overall water splitting. The self-supporting Co/CeO₂ heterostructures required only low overpotentials of 31.9 ± 2.2, 253.3 ± 2.7, and 316.7 ± 3 mV for HER and 214.1 ± 1.4, 362.3 ± 1.9, and 400.3 ± 3.7 mV for OER at 0.01, 0.5, and 1.0 A·cm^-2, respectively, being one of the best Co-based bifunctional electrodes. Electrolyzer constructed from this electrode acting as an anode and cathode merely required cell voltages of 1.92 ± 0.02 V at 1.0 A·cm^-2 for overall water splitting. Multiple characterization techniques combined with density functional theory calculations disclosed the different active sites on the anode and cathode, and the charge redistributions on the heterointerfaces that can optimize the adsorption of H and oxygen-containing intermediates, respectively. This study presents the tremendous prospective of self-supporting heterostructures for effective and economical overall water splitting.

Rationally Reconstructed Metal-Organic Frameworks as Robust Oxygen Evolution Electrocatalysts

Reconstructing metal-organic framework (MOFs) toward a designed framework structure provides breakthrough opportunities to achieve unprecedented oxygen evolution reaction (OER) electrocatalytic performance, but has rarely, if ever, been proposed and investigated yet. Here, the first successful fabrication of a robust OER electrocatalyst by precision reconstruction of an MOF structure is reported, viz., from MOF-74-Fe to MIL-53(Fe)-2OH with different coordination environments at the active sites. Due to the radically reduced e_g -t_2g crystal-field splitting in Fe-3d and the much suppressed electron-hopping barriers through the synergistic effects of the O species the efficient OER of in MIL-53(Fe)-2OH is guaranteed. Benefiting from this desired electronic structure, the designed MIL-53(Fe)-2OH catalyst exhibits high intrinsic OER activity, including a low overpotential of 215 mV at 10 mA cm^-2 , low Tafel slope of 45.4 mV dec^-1 and high turnover frequency (TOF) of 1.44 s^-1 at 300 mV overpotential, over 80 times that of the commercial IrO₂ catalyst (0.0177 s^-1 ).Consistent with the density functional theory (DFT) calculations, the real-time kinetic simulation reveals that the conversion from O* to OOH* is the rate-determining step on the active sites of MIL-53(Fe)-2OH.

Sequential galvanic replacement mediated Pd-doped hollow Ru-Te nanorods for enhanced hydrogen evolution reaction mass activity in alkaline media

High catalytic activity, long-term stability, and economical Pt-free catalysts for the hydrogen evolution reaction (HER) are required for the conversion of renewable energy systems. Noble nanomaterial Pt is a superior electrolysis catalyst for water splitting under typical experimental conditions with a relatively low overpotential. However, the use of Pt is limited by its high cost and activity degradation over time. Among several prospective alternatives, Ru has emerged as a promising alkaline electrolysis catalyst because of its significant catalytic activity and reduced cost compared to Pt. We designed and suggested Pd-doped hollow Ru-Te nanorods (PdRuTeNRs) via successive galvanic replacement reactions of sacrificial Te nanotemplates to further boost efficiency. The Pd/partially oxidized RuO₂/Ru/Te hetero-interfaced composition exhibited an HER mass activity of 11.3 A g^-1 Ru, twice that of Pt. In addition, the present PdRuTeNRs sufficiently maintained the activity from the 2000-cycle continuous test, greatly reducing the required cost by a quarter.

In Situ Grown Mn(II) MOF upon Nickel Foam Acts as a Robust Self-Supporting Bifunctional Electrode for Overall Water Splitting: A Bimetallic Synergistic Collaboration Strategy

The design of highly efficient, cost-effective non-noble metal-based electrocatalysts with superior stability for overall water splitting (OWS) reactions is of great importance as well as of immense challenge for the upcoming sustainable and green energy conversion technologies. Herein, a convenient and simple in situ solvothermal method has been adopted to fabricate a self-supported, binder-free 3D electrode (Mn-MOF/NF) by the direct growth of a newly synthesized carboxylate-based pristine Mn(II)-metal-organic framework (Mn-MOF) upon the conducting substrate nickel foam (NF). The binder-free Mn-MOF/NF electrode exhibits excellent performances toward OWS with ultralow overpotentials of 280 mV@20 mA cm^-2 for the oxygen evolution reaction (OER) and 125 mV@10 mA cm^-2 for the hydrogen evolution reaction (HER) with remarkable durability. Mn-MOF/NF can also attain a current density of 10 mA cm^-2 with a low cell voltage of 1.68 V in a 0.1 M KOH solution in a two-electrode system for OWS. The direct growth of nonconducting electroactive Mn-MOF materials upon conducting substrate NF provides an excellent mass transport of the electrolyte with a relatively low contact resistance due to the strong catalyst-substrate contact and enhances the efficient electron transport for OWS. The redox chemical etching of the self-sacrificial substrate NF during solvothermal synthesis introduces redox-active Ni²⁺ in Mn-MOF/NF. Thus, the excellent OWS electrocatalytic activity can mainly be attributed to the bimetallic synergistic collaboration of the two redox active metal centers (Mn²⁺ and Ni²⁺) along with the excellent support surface of NF, which provides a high specific surface area and maximum utilization of the electroactive metal ion sites by preventing the self-aggregation of the active sites. The Mn-MOF/NF electrode also exhibits superb stability and durability for a prolonged time throughout the multiple cycles of full water splitting reactions. Therefore, this work elucidates a convenient and smart approach for constructing MOF-based bifunctional electrocatalysts for OWS.

Critical Review, Recent Updates on Zeolitic Imidazolate Framework-67 (ZIF-67) and Its Derivatives for Electrochemical Water Splitting

Design and construction of low-cost electrocatalysts with high catalytic activity and long-term stability is a challenging task in the field of catalysis. Metal-organic frameworks (MOF) are promising candidates as precursor materials in the development of highly efficient electrocatalysts for energy conversion and storage applications. This review starts with a summary of basic concepts and key evaluation parameters involved in the electrochemical water-splitting reaction. Then, different synthesis approaches reported for the cobalt-based Zeolitic imidazolate framework (ZIF-67) and its derivatives are critically reviewed. Additionally, several strategies employed to enhance the electrocatalytic activity and stability of ZIF-67-based electrocatalysts are discussed in detail. The present review provides a succinct insight into the ZIF-67 and its derivatives (oxides, hydroxides, sulfides, selenides, phosphide, nitrides, telluride, heteroatom/metal-doped carbon, noble metal-supported ZIF-67 derivatives) reported for oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and overall water splitting applications. Finally, this review concludes with the associated challenges and the perspectives on developing the best economic, durable electrocatalytic materials.

Two new bis(pyridine)-bis(amide)-based copper(II) coordination compounds for the electrochemical detection of trace Cr(VI) and efficient electrocatalytic oxygen evolution

Two new metal-organic compounds (MOCs) [Cu(L)0.5(3-nba)2] (1) and [Cu(L)(2,5-tdc)] (2) have been hydrothermally synthesized by employing the ligand N,N′-di(3-pyridyl)adipoamide (L) and two carboxylic acids (3-Hnba = 3-nitrobenzoic acid, 2,5-H2tdc = 2,5-thiophenedicarboxylic acid) as ligands. Compound 1 displays a metal-organic chain-like structure formed by the {Cu2(3-nba)4} double-paddle wheel units and the µ 2-bridging L ligands. The adjacent polymeric chains form a supramolecular layered structure through hydrogen bonding. Compound 2 shows a 3D metal-organic polymeric framework derived from Cu-L layers and µ 2-bridging 2,5-tdc ligands, which presents a 3,5-connected {4.62}{4.66.83} topology. The electrochemical and electrocatalytic behavior of the two compounds has been studied in detail. Carbon paste working electrodes modified with compounds 1 and 2 can be used as highly selective sensors for detecting traces Cr(VI). Both electrodes show also electrocatalytic performance in oxygen evolution reactions (OERs).

TriMOF synergized on the surface of activated carbon produced from pineapple leaves for the environmental pollutant reduction and oxygen evolution process

Facile and modest synthesis of significantly effective and less-cost catalysts for environmental pollutant degradation and oxygen evolution holds substantial potential in environmental and energy fields. Hereby, Trimetallic organic frameworks (TriMOF) consisting of Fe, Co, and Zn synergized on the surface of activated carbon (AC) from pineapple leaves tend to show exponential catalytic activity due to the more excellent ionic conductivity, catalytic stability and multiple active sites provided by different metal precursors. Furthermore, the developed nanocomposite was coated on the stainless-steel electrode substrate at room temperature, delivering greater electrocatalytic surface area and numerous active sites. The oxidation reaction kinetics drives the catalytic reduction of 4-nitrophenol to 4-aminophenol with a minimal time of 12 min @ >97 % efficiency. Furthermore, on electrocatalytic oxidation of water splitting process due to the presence of multiple metallic, active sites, the overpotential is at 370 mV having Tafel slope of 40 mV/dec and electrochemically active surface area of is 9.9 mF/cm². This superior catalytic reduction of 4-nitrophenol and electrocatalytic water oxidation process is attributed to the developed composite's active centre and conductivity.

Multiscale structural regulation of Metal-organic framework nanofilm arrays for efficient oxygen evolution reaction

A novel MOF nanofilm arrays (NiCoBDC-Fc) grown on Ni foam via a multiscale structural regulation strategy. The introducing of metal doping and defects regulated the morphology structure of NiBDC for...

Controlling alloy to core-shell structure transformation of Au-Pd icosahedral nanoparticles

The structure transformation between Au-Pd alloy and core-shell icosahedral nanoparticles was achieved by a one-step aqueous-phase strategy. This strategy provided a way to tune the structure and atomic distribution of Au-Pd icosahedral nanoparticles. It could modulate the electronic structure of Pd, achieving promoted electrocatalytic ability toward the hydrogen evolution reaction.

Highly Enhanced OER Performance by Er-Doped Fe-MOF Nanoarray at Large Current Densities

Great expectations have been held for the electrochemical splitting of water for producing hydrogen as a significant carbon-neutral technology aimed at solving the global energy crisis and greenhouse gas issues. However, the oxygen evolution reaction (OER) process must be energetically catalyzed over a long period at high output, leading to challenges for efficient and stable processing of electrodes for practical purposes. Here, we first prepared Fe-MOF nanosheet arrays on nickel foam via rare-earth erbium doping (Er_0.4 Fe-MOF/NF) and applied them as OER electrocatalysts. The Er_0.4 Fe-MOF/NF exhibited wonderful OER performance and could yield a 100 mA cm⁻² current density at an overpotential of 248 mV with outstanding long-term electrochemical durability for at least 100 h. At large current densities of 500 and 1000 mA cm⁻², overpotentials of only 297 mV and 326 mV were achieved, respectively, revealing its potential in industrial applications. The enhancement was attributed to the synergistic effects of the Fe and Er sites, with Er playing a supporting role in the engineering of the electronic states of the Fe sites to endow them with enhanced OER activity. Such a strategy of engineering the OER activity of Fe-MOF via rare-earth ion doping paves a new avenue to design other MOF catalysts for industrial OER applications.

In situ assembly of bimetallic MOF composites on IF as efficient electrocatalysts for the oxygen evolution reaction

Since the complicated multiple electron transfer process and slow kinetics in the OER process seriously hinder the electrochemical decomposition of water, it is urgent to design and develop electrocatalysts with excellent performance and superior stability to reduce overpotential and accelerate the reaction dynamics of the OER. Herein, a unique ultra-thin nanosheet bimetal electrocatalyst NiFe-MOF/IF was synthesized by a one-step hydrothermal method, and characterized by SEM, XRD, TEM, and XPS. NiFe-MOF/IF shows superior OER electrocatalytic activity in 1 M KOH electrolyte solution, and an ultralow overpotential of only 230 and 262 mV was required to achieve a current density of 10 and 100 mA cm^-2, respectively, with a relatively small Tafel slope of 30.46 mV dec^-1 for the OER. No obvious degradation of the current density at 10 mA cm^-2 was observed over about 16 h, which indicates the excellent stability of the catalyst. Favourable activity and benign durability of NiFe-MOF/IF can be attributed to the three-dimensional high porosity conductive substrates, in situ growth of MOF nanosheets, bimetallic synergy, and unique layering. This research provides a promising strategy for the application of MOF materials in the field of electrocatalysis.