Recent Functionalized Strategies of Metal-Organic Frameworks for Anode Protection of Aqueous Zinc-Ion Battery.

The inherent benefits of aqueous Zn-ion batteries (ZIBs), such as environmental friendliness, affordability, and high theoretical capacity, render them promising candidates for energy storage systems. Nevertheless, the Zn anodes of ZIBs encounter severe challenges, including dendrite formation, hydrogen evolution reaction, corrosion, and surface passivation. These would result in the infeasibility of ZIBs in practical situations. To this end, artificial interfaces with functionalized materials are crafted to protect the Zn anode. They have the capability to modulate the zinc ion flux in proximity to the electrode surface and shield it from aqueous electrolytes by leveraging either size effects or charge effects. Considering metal-organic frameworks (MOFs) with tunable pore size, chemical composition, and stable framework structures, they have emerged as effective materials for building artificial interfaces, prolonging the lifespan, and improving the unitization of Zn anode. In this review, the contributions of MOFs for protecting Zn anode, which mainly involves facilitating homogeneous nucleation, manipulating selective deposition, regulating ion and charge flux, accelerating Zn desolvation, and shielding against free water and anions are comprehensively summarized. Importantly, the future research trajectories of MOFs for the protection of the Zn anode are underscored, which may propose new perspectives on the practical Zn anode and endow the MOFs with high-value applications.

Micro Area Interface Wetting Structure with Tailored Li+-Solvation and Fast Transport Properties in Composite Polymer Electrolytes for Enhanced Performance in Solid-State Lithium Batteries.

To satisfy the demand for high safety and energy density in energy storage devices, all-solid-state lithium metal batteries with solid polymer electrolytes (SPE) replacing traditional liquid electrolytes and separators have been proposed and are increasingly regarded as one of the most promising candidates as next-generation energy storage systems. In this study, poly(vinylidene fluoride)-hexafluoropropylene/lignosulfonic acid (PVDF-HFP/LSA) composite polymer electrolyte (CPE) membranes with a micro area interface wetting structure were successfully prepared by incorporating LSA into the PVDF-HFP polymer matrix. The enhanced interaction between the polar functional group in LSA and the C═O in N-methylpyrrolidone (NMP) hinders the evaporation of solvent NMP, thus creating a micro area wetting structure, which offers a flexible region for the chain segment movement and enlarging the area of the amorphous zone in PVDF-HFP. From the results of IR and Raman spectroscopy, it was found that the presence of LSA induced unique ion transport channels created by the massive aggregated ion pair (AGG) and contact ion pair (CIP) of ion cluster structures composed of Li+ and multiple TFSI- and, at the same time, effectively reduced the crystallinity of the polymer electrolyte, hence further contributing to the Li+ diffusion. As a result, at a rate of 2 C, the Li|CPE-15|LiFePO4 solid-state battery delivers an initial discharge-specific capacity of 134.9 mAh g-1 and maintains stability with a retention of 84% during 400 charge-discharge cycles while the Li|CPE-0|LiFePO4 battery fails after only a few cycles at the same rate.

The Recent Progress of Oxygen Reduction Electrocatalysts Used at Fuel Cell Level.

Proton exchange membrane fuel cells (PEMFCs) are gaining significant interest as an attractive substitute for traditional fuel cells, with higher energy density, lower environmental pollution, and better operation efficiency. However, the cathode reaction, i.e., the oxygen reduction reaction (ORR), is widely proved to be inefficient, and therefore an obstacle to the widespread development of PEMFCs. The requirement for affordable highly-efficient ORR catalysts is extremely urgent to be met, especially at fuel cell level. Unfortunately, most previous reports focus on the ORR performance at rotating disk electrodes (RDE) level instead of membrane electrode assembly (MEA) level, making it harder to evaluate ORR catalysts operating under real vehicle conditions. Obviously, it is extremely necessary to develop an in-depth understanding of the structure-activity relationship of highly-efficient ORR catalysts applied at MEA level. In this work, an overview of the latest advances in ORR catalysts is provided with an emphasis on their performance at MEA level, hoping to cover the novel and systemic insights for innovative and efficient ORR catalyst design and applications in PEMFCs.

Electrocatalytic reforming of waste plastics into high value-added chemicals and hydrogen fuel.

The upcycling of waste plastic offers an attractive way to protect the environment and turn waste into value-added chemicals and H2 fuel. Herein, we report a novel electroreforming strategy to upcycle waste polyethylene terephthalate into high value-added chemicals, such as terephthalate and carbonate, over a Pd modified Ni foam catalyst. This system exhibits excellent electrocatalytic activity (400 mA cm-2 at 0.7 V vs. RHE) and high selectivity (95%)/faradaic efficiency (93%) for the product carbonate. Our work demonstrates a technology that can not only transform waste polyethylene terephthalate into value-added chemicals but also generate H2 fuel via an all-in-one electro-driven process.

A Gas-Steamed MOF Route to P-Doped Open Carbon Cages with Enhanced Zn-Ion Energy Storage Capability and Ultrastability.

Carbon micro/nanocages have received great attention, especially in electrochemical energy-storage systems. Herein, as a proof-of-concept, a solid-state gas-steamed metal-organic-framework approach is designed to fabricate carbon cages with controlled openings on walls, and N, P dopants. Taking advantage of the fabricated carbon cages with large openings on their walls for enhanced kinetics of mass transport and N, P dopants within the carbon matrix for favoring chemical adsorption of Zn ions, when used as carbon cathodes for advanced aqueous Zn-ion hybrid supercapacitors (ZHSCs), such open carbon cages (OCCs) display a wide operation voltage of 2.0 V and an enhanced capacity of 225 mAh g-1 at 0.1 A g-1 . Also, they exhibit an ultralong cycling lifespan of up to 300 000 cycles with 96.5% capacity retention. Particularly, such OCCs as electrode materials lead to a soft-pack ZHSC device, delivering a high energy density of 97 Wh kg-1 and a superb power density of 6.5 kW kg-1 . Further, the device can operate in a wide temperature range from -25 to + 40 °C, covering the temperatures for practical applications in daily life.

Single-Atom Catalysts Derived from Metal-Organic Frameworks for Electrochemical Applications.

Single-atom catalysts (SACs) have received tremendous attention due to their extraordinary catalytic performances. The synthesis of this kind of catalysts is highly desired and challenging. In the last few years, metal-organic frameworks (MOFs) have been demonstrated as a promising precursor for fabricating SACs. In this review, the progress and recent advances in the synthesis of MOF-derived SACs and their electrochemical applications are summarized. First, the synthetic approaches based on MOFs and accessible characterization techniques for SACs as well as their advantages/disadvantages are discussed. Then, the electrochemical applications of these MOF-derived SACs including the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER), CO2 reduction reaction (CO2 RR), nitrogen reduction reaction (NRR), and other energy-related reactions are reviewed. Finally, insights into the current challenges and future prospects of this field are briefly presented.

Uniformly bimetal-decorated holey carbon nanorods derived from metal-organic framework for efficient hydrogen evolution.

The hydrogen evolution reaction (HER) as a fundamental process in electrocatalysis plays a significant role in clean energy technologies. For an energy-efficient HER, it demands an effective, durable, and low-cost catalyst to trigger proton reduction with minimal overpotential and fast kinetics. Here, we successfully fabricate a highly efficient HER catalyst of N-C/Co/Mo2C holey nanorods with Co/ß-Mo2C nanoparticles uniformly embedded in nitrogen-doped carbon (N-C/Co/Mo2C) by pyrolyzing the molybdate-coordinated zeolitic imidazolate framework (ZIF-67/MoO42-) holey nanorods, which result from the reaction between CoMoO4 and MeIM in a methanol/water/triethylamine mixed solution. The uniform distribution of MoO42- in the ZIF-67/MoO42- enables Co/ß-Mo2C nanoparticles to be well-distributed within nitrogen-doped carbon holey nanorods. This synthetic strategy endows the N-C/Co/Mo2C catalyst with uniformly decorated bimetal, thus attaining excellent HER electrocatalytic activities with a small overpotential of 142.0 mV at 10 mA cm-2 and superior stability in 1.0 mol L-1 KOH aqueous solution.

Multiple catalytic sites in MOF-based hybrid catalysts for organic reactions.

Hybrid catalysis provides an effective pathway to improve the catalytic efficiency and simplify the synthesis operation, but multiple catalytic sites are required. Catalysts with multiple functions based on/derived from metal-organic frameworks (MOFs) have received growing attention in organic synthesis due to their wide variety and outstanding designability. This review provides an overview of significant advances in the field of organic reactions by MOF-based hybrid catalysts with emphasis on multiple catalytic sites and their synergies, including inherent sites on host frameworks, sites of MOF composites and metal sites in/on MOF-derived hybrid catalysts.

MOF-Mediated Fabrication of a Porous 3D Superstructure of Carbon Nanosheets Decorated with Ultrafine Cobalt Phosphide Nanoparticles for Efficient Electrocatalysis and Zinc-Air Batteries.

Superstructures have attracted great interest owing to their potential applications. Herein, we report the first scalable preparation of a porous nickel-foam-templated superstructure of carbon nanosheets decorated with ultrafine cobalt phosphide nanoparticles. Uniform two-dimensional (2D) Co-metal organic framework (MOF) nanosheets (Co-MNS) grow on nickel foam, followed by a MOF-mediated tandem (carbonization/phosphidation) pyrolysis. The resulting superstructure has a porous 3D interconnected network with well-arranged 2D carbon nanosheets on it, in which ultrafine cobalt phosphide nanoparticles are tightly immobilized. A single piece of this superstructure can be directly used as a self-supported electrode for electrocatalysis without any binders. This "one-piece" porous superstructure with excellent mass transport and electron transport properties, and catalytically active cobalt phosphide nanoparticles with ultrasmall size (3-4 nm), shows excellent trifunctional electrocatalytic activities for oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and oxygen reduction reaction (ORR), achieving great performances in water splitting and Zn-air batteries.

A Honeycomb-Like Bulk Superstructure of Carbon Nanosheets for Electrocatalysis and Energy Storage.

Superstructures have attracted extensive attention because of their potential applications in materials science and biology. Herein, we fabricate the first centimeter-sized porous superstructure of carbon nanosheets (SCNS) by using metal-organic framework nanoparticles as a template and polyvinylpyrrolidone as an additional carbon source. The SCNS shows a honeycomb-like morphology with wall-sharing carbon cages, in each cavity of which a porous carbon sphere is encapsulated. A single piece of SCNS is directly used as the electrode for a two-electrode symmetrical supercapacitor cell without any binders and supports, benefiting from its advantage in ultra-large geometric size, and the Fe-immobilized SCNS exhibits excellent catalytic performances for oxygen reduction reaction and in a Zn-air battery. This synthetic strategy presents a facile approach for preparing functional SCNS at centimetric scale with controllable morphologies and compositions favoring the fabrication of energy devices.

Single-Atom Iron Catalysts on Overhang-Eave Carbon Cages for High-Performance Oxygen Reduction Reaction.

Single-atom catalysts have drawn great attention, especially in electrocatalysis. However, most of previous works focus on the enhanced catalytic properties via improving metal loading. Engineering morphologies of catalysts to facilitate mass transport through catalyst layers, thus increasing the utilization of each active site, is regarded as an appealing way for enhanced performance. Herein, we design an overhang-eave structure decorated with isolated single-atom iron sites via a silica-mediated MOF-templated approach for oxygen reduction reaction (ORR) catalysis. This catalyst demonstrates superior ORR performance in both alkaline and acidic electrolytes, comparable to the state-of-the-art Pt/C catalyst and superior to most precious-metal-free catalysts reported to date. This activity originates from its edge-rich structure, having more three-phase boundaries with enhanced mass transport of reactants to accessible single-atom iron sites (increasing the utilization of active sites), which verifies the practicability of such a synthetic approach.

A Hydrangea-Like Superstructure of Open Carbon Cages with Hierarchical Porosity and Highly Active Metal Sites.

Carbon micro-/nanocages have attracted great attention owing to their wide potential applications. Herein, a self-templated strategy is presented for the synthesis of a hydrangea-like superstructure of open carbon cages through morphology-controlled thermal transformation of core@shell metal-organic frameworks (MOFs). Direct pyrolysis of core@shell zinc (Zn)@cobalt (Co)-MOFs produces well-defined open-wall nitrogen-doped carbon cages. By introducing guest iron (Fe) ions into the core@shell MOF precursor, the open carbon cages are self-assembled into a hydrangea-like 3D superstructure interconnected by carbon nanotubes, which are grown in situ on the Fe-Co alloy nanoparticles formed during the pyrolysis of Fe-introduced Zn@Co-MOFs. Taking advantage of such hierarchically porous superstructures with excellent accessibility, synergetic effects between the Fe and the Co, and the presence of catalytically active sites of both metal nanoparticles and metal-Nx species, this superstructure of open carbon cages exhibits efficient bifunctional catalysis for both oxygen evolution reaction and oxygen reduction reaction, achieving a great performance in Zn-air batteries.

Chemically Robust, Cu-based Porous Coordination Polymer Nanosheets for Efficient Hydrogen Evolution: Experimental and Theoretical Studies.

Due to the extremely high number of accessible active sites and short diffusion path, porous coordination polymer (PCP) nanosheets have demonstrated a variety of promising applications, especially for energy conversion and mass transfer. However, the development of chemically stable PCP nanosheets with dense active sites and large lateral size is a great challenge in terms of feasible considerations. Herein, we first designed and prepared a kind of chemically stable PCP nanosheets via a bottom-up and a top-down integral strategy. Featuring densely exposed and periodic Cu2+ active sites (2.1 × 106 per µm2), as well as ultrathin nature (5 nm) and significant pores (18 Å), this nanosheet demonstrated remarkable performance of electrocatalytic hydrogen evolution. Furthermore, one plausible process and the effect of Cu2+ active sites were proposed and validated by density functional theory calculations.

Superlong Single-Crystal Metal-Organic Framework Nanotubes.

Nanotubes have attracted great attention. Here, we report the fabrication of the first single-crystal metal-organic framework (MOF) nanotubes. Superlong single-crystal cobalt-organic framework (Co-MOF) nanotubes, which have a diameter of ∼70 nm and length of 20-35 µm with parallel multichannels (window size: 1.1 nm), have been successfully synthesized via an amorphous MOF-mediated recrystallization approach. The synthesized MOF nanotubes can be used as a nanocolumn for separation of large molecules. Carbonization of the Co-MOF nanotubes in an argon atmosphere preserves the 1D morphology, affording long carbon nanofibers. A hierarchical architecture composed of carbon nanofibers wrapped by carbon nanotubes (20-30 nm in diameter and 200-300 nm in length) with cobalt nanoparticles on the top is formed by the carbonization of the Co-MOF nanotubes along with dicyandiamide as a nitrogen and a secondary carbon source. The resulting hierarchical dendrites with carbon nanofiber trunks and carbon nanotube branches exhibit excellent electrocatalytic activity for oxygen reduction reaction and exceptional applications in rechargeable Zn-air batteries. This work demonstrates a new strategy to fabricate MOF nanotubes and relative 1D nanostructures.

Visible-light-driven CO2 photoreduction over ZnxCd1-xS solid solution coupling with tetra(4-carboxyphenyl)porphyrin iron(iii) chloride.

Construction of solid solution semiconductors has attracted much attention in photocatalysis by virtue of their tunable elemental composition and band structure. The integration of semiconductor sensitizers with molecular catalysts provides a promising way to fabricate highly efficient, selective and stable systems for CO2 photoreduction. Here ZnxCd1-xS (ZCS) solid solutions with a well-defined floccule-like morphology composed of nanoribbons are synthesized and used as the photosensitizer to couple with tetra(4-carboxyphenyl)porphyrin iron(iii) chloride (FeTCPP) for CO2 reduction. The effects of changes in surface atoms of the ZCS solid solution on the performance of CO2 photoreduction are investigated. Regardless of the presence of FeTCPP, our results show that the introduction of Zn into CdS can affect the activity and selectivity of CO2 photoreduction, as well as the stability of the obtained photocatalysts. More importantly, the presence of Zn can build efficient electron transfer channels from ZCS to FeTCPP and, thus, greatly facilitate the interfacial charge transfer. Benefitting from the efficient charge separation and electron transfer, ZCS-1/FeTCPP (Zn0.14Cd0.84S/FeTCPP) exhibits the highest activity for CO2 reduction under visible-light irradiation, with a CO yield of 1.28 µmol and a selectivity up to 93% after 4 h.

Ir4+-Doped NiFe LDH to expedite hydrogen evolution kinetics as a Pt-like electrocatalyst for water splitting.

NiFe-layered double hydroxide (NiFe LDH) is a state-of-the-art oxygen evolution reaction (OER) electrocatalyst, yet it suffers from rather poor catalytic activity for the hydrogen evolution reaction (HER) due to its extremely sluggish water dissociation kinetics, severely restricting its application in overall water splitting. Herein, we report a novel strategy to expedite the HER kinetics of NiFe LDH by an Ir4+-doping strategy to accelerate the water dissociation process (Volmer step), and thus this catalyst exhibits superior and robust catalytic activity for finally oriented overall water splitting in 1 M KOH requiring only a low initial voltage of 1.41 V delivering at 20 mA cm-2 for more than 50 h.

Cu(OH)2 supported on Fe(OH)3 as a synergistic and highly efficient system for the dehydrogenation of ammonia-borane.

Herein, we first describe the physical mixture of Cu(OH)2/Fe(OH)3 as a composite catalyst precursor for the dehydrogenation of ammonia borane (AB) in methanol. During the initial period of catalytic reaction, Cu nanoparticles were formed in-situ. The catalytic activity of Cu nanoparticles can be significantly enhanced with the assistance of Fe species and OH-. A maximum turnover frequency (TOF) of 50.3 molH2 moltotal metal-1 min-1 (135.6 molH2 molCu-1 min-1) was achieved at ambient temperature, which is superior to those of previously reported Fe or Cu based systems.

Rapid synthesis of ultralong Fe(OH)3:Cu(OH)2 core-shell nanowires self-supported on copper foam as a highly efficient 3D electrode for water oxidation.

One-dimensional core-shell nanowire materials have recently received great attention as durable catalysts for water splitting. Herein we report the facile and rapid synthesis of ultralong Fe(OH)3:Cu(OH)2 core-shell nanowires grown in situ on an open 3D electrode to function as a highly efficient electrocatalyst for water oxidation. It only requires an overpotential of ∼365 mV to reach a 10 mA cm-2 current density in 1.0 M KOH. As far as we know, this shows the best result amongst Cu-based heterogeneous OER systems reported to date.

Self-Supported Cedarlike Semimetallic Cu3P Nanoarrays as a 3D High-Performance Janus Electrode for Both Oxygen and Hydrogen Evolution under Basic Conditions.

There has been strong and growing interest in the development of cost-effective and highly active oxygen evolution reaction (OER) electrocatalysts for alternative fuels utilization and conversion devices. We report herein that semimetallic Cu3P nanoarrays directly grown on 3D copper foam (CF) substrate can function as effective electrocatalysts for water oxidation. Specifically, the surface oxidation-activated Cu3P only required a relatively low overpotential of 412 mV to achieve a current density of 50 mA cm(-2) and displayed a small Tafel slope of 63 mV dec(-1) in 0.1 M KOH solution, on account of the collaborative effect of large roughness factor (RF) and semimetallic character. Following that, investigations into the mechanism revealed the formation of a unique active phase during the water oxidation process in which conductive Cu3P was the core covered with a thin copper oxide/hydroxide layer. Moreover, this Cu3P 3D electrode was also applied to the hydrogen evolution reaction (HER) and showed good catalytic performance and stability under the same basic conditions.

Self-Supported Cu-Based Nanowire Arrays as Noble-Metal-Free Electrocatalysts for Oxygen Evolution.

Crystalline Cu-based nanowire arrays (NWAs) including Cu(OH)2 , CuO, Cu2 O, and CuOx are facilely grown on Cu foil and are found to act as highly efficient, low-cost, and robust electrocatalysts for the oxygen evolution reaction (OER). Impressively, this noble-metal-free 3 D Cu(OH)2 -NWAs/Cu foil electrode shows the highest catalytic activity with a Tafel slope of 86 mV dec(-1) , an overpotential (η) of about 530 mV at ∼10 mA cm(-2) (controlled-potential electrolysis method without iR correction) and almost 100 % Faradic efficiency, paralleling the performance of the state-of-the-art RuO2 OER catalyst in 0.1 m NaOH solution (pH 12.8). To the best of our knowledge, this work represents one of the best results ever reported on Cu-based OER systems.