Autogenous Production and Stabilization of Highly Loaded Sub-Nanometric Particles within Multishell Hollow Metal-Organic Frameworks and Their Utilization for High Performance in Li-O2 Batteries

Orbital Coupling of PbO7 Node in Single-Crystal Metal-Organic Framework Enhances Li-O2 Battery Electrocatalysis

Optimizing the local coordination environment of metal centers in metal-organic frameworks (MOFs) is crucial yet challenging for regulating the overpotential of lithium-oxygen (Li-O2) batteries. Herein, we report the synthesis of a class of PbO7 nodes in a single crystal MOF (naphthalene-lead-MOF, known as Na-Pb-MOF) to significantly enhance the kinetics of both discharge and charge processes. Compared to the PbO6 node in the single-crystal tetramethoxy-lead-MOF (4OMe-Pb-MOF), the bond length between Pb and O in the PbO7 node of Na-Pb-MOF increases, resulting in weaker Pb 5d-O 2p orbital coupling, which optimizes the adsorption interaction toward intermediates, and thereby promotes the rate-determining steps of both the reduction of LiO2 to Li2O2 and the oxidation of LiO2 to O2 for reducing the activation energy of the overall reaction. Consequently, Li-O2 batteries based on Na-Pb-MOF electrocatalysts exhibit a low total charge-discharge overpotential of 0.52 V and an excellent cycle life of 140 cycles.

Advances of Electroactive Metal-Organic Frameworks

The preparation of electroactive metal-organic frameworks (MOFs) for applications of supercapacitors and batteries has received much attention and remarkable progress during the past few years. MOF-based materials including pristine MOFs, hybrid MOFs or MOF composites, and MOF derivatives are well designed by a combination of organic linkers (e.g., carboxylic acids, conjugated aromatic phenols/thiols, conjugated aromatic amines, and N-heterocyclic donors) and metal salts to construct predictable structures with appropriate properties. This review will focus on construction strategies of pristine MOFs and hybrid MOFs as anodes, cathodes, separators, and electrolytes in supercapacitors and batteries. Descriptions and discussions follow categories of electrochemical double-layer capacitors (EDLCs), pseudocapacitors (PSCs), and hybrid supercapacitors (HSCs) for supercapacitors. In contrast, Li-ion batteries (LIBs), Lithium-sulfur batteries (LSBs), Lithium-oxygen batteries (LOBs), Sodium-ion batteries (SIBs), Sodium-sulfur batteries (SSBs), Zinc-ion batteries (ZIBs), Zinc-air batteries (ZABs), Aluminum-sulfur batteries (ASBs), and others (e.g., LiSe, NiZn, H⁺ , alkaline, organic, and redox flow batteries) are categorized for batteries.

Covalent organic frameworks with Ni-Bis(dithiolene) and Co-porphyrin units as bifunctional catalysts for Li-O2 batteries

The rational design of efficient and stable catalysts for the oxygen reduction reaction and oxygen evolution reaction (ORR/OER) is the key to improving Li-O₂ battery performance. Here, we report the construction of ORR/OER bifunctional cathode catalysts in a covalent organic framework (COF) platform by simultaneously incorporating Ni-bis(dithiolene) and Co-porphyrin units. The resulting bimetallic Ni/Co-COF exhibits high surface area, fairly good electrical conductivity, and excellent chemical stability. Li-O₂ batteries with the Ni/Co-COF-based cathode show a low discharge/charge potential gap (1.0 V) and stable cycling (200 cycles) at a current density of 500 mA g^-1, rivaling that of PtAu nanocrystals. Density functional theory computations and control experiments using nonmetal or single metal-based isostructural COFs reveal the critical role of Ni and Co sites in reducing the discharge/charge overpotentials and regulating the Li₂O₂ deposition. This work highlights the advantage of bimetallic COFs in the rational design of efficient and stable Li-O₂ batteries.

Synergistic catalytic enhancement of metal-organic framework derived nanoarchitectures decorated on graphene as a high-efficiency bifunctional electrocatalyst for methanol oxidation and oxygen reduction

Designing highly efficient, long-lasting, and cost-effective cathodic and anodic functional materials as a bifunctional electrocatalyst is essential for overcoming the bottleneck in fuel cell development. Herein, a novel two-step synthesis strategy is developed to synthesize metal-organic framework (MOF) derived nitrogen-doped carbon (NC) with improved spatial isolation and a higher loading amount of cobalt (Co) and nickel carbide (Ni₃C) nanocrystal decorated on graphene (denoted as Co@NC-Ni₃C/G). Benefiting from multiple active sites of high N-doping level, uniform dispersion of Co and Ni₃C nanocrystals, and a large active area of graphene, the Co@NC-Ni₃C/G hybrids exhibit excellent methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR) efficiency in an alkaline environment. For MOR, the optimized Co@NC-Ni₃C/G-350 catalyst achieved a current density of 44.8 mA cm^-2 at an applied potential of 1.47 V (V vs. RHE), which is significantly higher than Co@NC-Ni₃C (42.07 mA cm^-2) and Co@NC (24.1 mA cm^-2) in 0.5 M methanol + 1.0 M KOH solutions. In addition, during the CO retention test, the Co@NC-Ni₃C/G-350 catalyst exhibits excellent CO tolerance capacity. Excitingly, the as-prepared Co@NC-Ni₃C/G-350 hybrid exhibits significantly improved ORR catalytic efficiency in terms of positive onset and half-wave potential (E_onset = 0.90 V, E_1/2 = 0.830 V vs. RHE), small Tafel slope (34 mV dec^-1) and excellent durability (only reduced 0.016 V after 5000 s test). This work provides new insights into MOF-derived functional nanomaterials for anode and cathode co-catalysts for methanol fuel cells.

Rational Design of MOF-Based Materials for Next-Generation Rechargeable Batteries

This review summarizes recent progresses in pristine metal–organic frameworks (MOFs), MOF composites, and their derivatives for next-generation rechargeable batteries including lithium–sulfur batteries, lithium–oxygen batteries, sodium-ion batteries, potassium-ion batteries, Zn-ion batteries, and Zn–air batteries.

The design strategies for MOF-based materials as the electrode, separator, and electrolyte are outlined and discussed.

The challenges and development strategies and of MOF-related materials for battery applications are highlighted.

Metal–organic framework (MOF)-based materials with high porosity, tunable compositions, diverse structures, and versatile functionalities provide great scope for next-generation rechargeable battery applications. Herein, this review summarizes recent advances in pristine MOFs, MOF composites, MOF derivatives, and MOF composite derivatives for high-performance sodium-ion batteries, potassium-ion batteries, Zn-ion batteries, lithium–sulfur batteries, lithium–oxygen batteries, and Zn–air batteries in which the unique roles of MOFs as electrodes, separators, and even electrolyte are highlighted. Furthermore, through the discussion of MOF-based materials in each battery system, the key principles for controllable synthesis of diverse MOF-based materials and electrochemical performance improvement mechanisms are discussed in detail. Finally, the major challenges and perspectives of MOFs are also proposed for next-generation battery applications.

Ru-Embedded Highly Porous Carbon Nanocubes Derived from Metal-Organic Frameworks for Catalyzing Reversible Li2O2 Formation

Rechargeable lithium-oxygen batteries (LOBs) have attracted increasing attention due to their high energy density but highly rely on the development of efficient oxygen catalysts for reversible Li₂O₂ deposition/decomposition. Herein, highly porous carbon nanocubes with a specific surface area up to 1600 m² g^-1 are synthesized and utilized to tightly anchor Ru nanoparticles for using as the oxygen-cathode catalyst in LOBs, achieving a low charge/discharge potential gap of only 0.75 V, a high total discharge capacity of 17,632 mA h g^-1, and a superb cycling performance of 550 cycles at 1000 mA g^-1. Comprehensive ex situ and operando characterizations unravel that the outstanding LOB performance is ascribed to the highly porous catalyst structure embedding rich active sites that synergistically function in reducing overpotentials, suppressing parasitic reactions, accommodating reaction products, and promoting mass and charge transportation.

Metal-Organic Fragments with Adhesive Excipient and Their Utilization to Stabilize Multimetallic Electrocatalysts for High Activity and Robust Durability in Oxygen Evolution Reaction

Multimetallic electrocatalysts have shown great potential to improve electrocatalytic performance, but their deteriorations in activity and durability are yet to be overcome. Here, metal-organic fragments with adhesive excipient to realize high activity with good durability in oxygen evolution reaction (OER) are developed. First, a leaf-like zeolitic-imidazolate framework (ZIF-L) is synthesized. Then, ionized species in hydrogen plasma attack preferentially the organic linkers of ZIF-L to derive cobalt-imidazole fragments (CIFs) as adhesive excipient, while they are designed to retain the coordinated cobalt nodes. Moreover, the vacant coordination sites at cobalt nodes and the unbound nitrogen at organic linkers induce high porosity and conductivity. The CIFs serve to stably impregnate trimetallic FeNiMo electrocatalysts (CIF:FeNiMo), and CIF:FeNiMo containing Fe contents of 22% and hexavalent Mo contents show to enable high activity with low overpotentials (203 mV at 10 mA cm-2 and 238 mV at 100 mA cm-2 ) in OER. The near O K-edge extended X-ray absorption fine structure proves further that high activity for OER originates from the partially filled eg orbitals. Additionally, CIF:FeNiMo exhibit good durability, as demonstrated by high activity retention during at least 45 days in OER.

Sub-nanometric Manganous Oxide Clusters in Nitrogen Doped Mesoporous Carbon Nanosheets for High-Performance Lithium-Sulfur Batteries

The greatest challenge for lithium-sulfur (Li-S) batteries application is the development of cathode hosts to address the low conductivity, huge volume change, and shuttling effect of sulfur or lithium polysulfides (LiPs). Herein, we demonstrate a composite host to circumvent these problems by confining sub-nanometric manganous oxide clusters (MOCs) in nitrogen doped mesoporous carbon nanosheets. The atomic structure of MOCs is well-characterized and optimized via the extended X-ray absorption fine structure analysis and density functional theory (DFT) calculations. Benefiting from the unique design, the assembled Li-S battery displays remarkable electrochemical performances including a high reversible capacity (990 mAh g^-1 after 100 cycles at 0.2 A g^-1) and a superior cycle life (60% retention over 250 cycles at 2 A g^-1). Both the experimental results and DFT calculations demonstrate that the well-dispersed MOCs could significantly promote the chemisorption of LiPs, thus greatly improving the capacity and rate performance.

Quantitative Delineation of the Low Energy Decomposition Pathway for Lithium Peroxide in Lithium-Oxygen Battery

Identification of a low-potential decomposition pathway for lithium peroxide (Li2O2) in nonaqueous lithium-oxygen (Li-O2) battery is urgently needed to ameliorate its poor energy efficiency. In this study, experimental data and theoretical calculations demonstrate that the recharge overpotential (η RC) of Li-O2 battery is fundamentally dependent on the Li2O2 crystallization pathway which is intrinsically related to the microscopic structural properties of the growing crystals during discharge. The Li2O2 grown by concurrent surface reduction and chemical disproportionation seems to form two discrete phases that have been deconvoluted and the amount of Li2O2 deposited by these two routes is quantitatively estimated. Systematic analyses have demonstrated that, regardless of the bulk morphology, solution-grown Li2O2 shows higher η RC (>1 V) which can be attributed to higher structural order in the crystal compared to the surface-grown Li2O2. Presumably due to a cohesive interaction between the electrode surface and growing crystals, the surface-grown Li2O2 seems to possess microscopic structural disorder that facilitates a delithiation induced partial solution-phase oxidation at lower η RC (<0.5 V). This difference in η RC for differently grown Li2O2 provides crucial insights into necessary control over Li2O2 crystallization pathways to improve the energy efficiency of a Li-O2 battery.