Surface Coordination Modulated Morphological Anisotropic Engineering of Iron-Benzoquinone Frameworks for Lithium-Ion Batteries.

Morphological anisotropic engineering is powerful to synthesize metal-organic frameworks (MOF) with versatile physicochemical properties for diverse applications ranging from gas storage/separation to electrocatalysis and batteries, etc. Herein, we developed a carbon substrate guided strategy for facet-anisotropic growth of Fe-THBQ (tetrahydroxy-1,4-benzoquinone) frameworks, which is built with cubic Fe octamer bridged by two parallel THBQ ligands along three orthogonal axes, extending to a three-dimensional (3D) framework with pcu-e network topology. The electronegative O-containing functional groups on carbon surfaces compete with THBQ linkers to interact with the unsaturated coordinated Fe cations on the {111} facets and selectively inhibit crystal growth along the <111> direction. The morphology of Fe-THBQ evolves from thermodynamically favored truncated cube to cuboctahedron depending on the O-containing functional groups on carbon substrate. The Fe-THBQ with varied morphologies exhibits facet-dependent performances for lithium storage. This work will shed lights on morphology modulation of MOFs for promising applications.

Regulating Ion-Dipole Interactions in Weakly Solvating Electrolyte towards Ultra-Low Temperature Sodium-Ion Batteries.

Sodium-ion batteries (SIBs) are recognized as promising energy storage devices. However, they suffer from rapid capacity decay at ultra-low temperatures due to high Na+ desolvation energy barrier and unstable solid electrolyte interphase (SEI). Herein, a weakly solvating electrolyte (WSE) with decreased ion-dipole interactions is designed for stable sodium storage in hard carbon (HC) anode at ultra-low temperatures. 2-methyltetrahydrofuran with low solvating power is incorporated into tetrahydrofuran to regulate the interactions between Na+ and solvents. The reduced Na+-dipole interactions facilitate more anionic coordination in the first solvation sheath, which consistently maintains anion-enhanced solvation structures from room to low temperatures to promote inorganic-rich SEI formation. These enable WSE with a low freezing point of -83.3 °C and faster Na+ desolvation kinetics. The HC anode thus affords reversible capacities of 243.2 and 205.4 mAh g-1 at 50 mA g-1 at -40 and -60 °C, respectively, and the full cell of HC||Na3V2(PO4)3 yields an extended lifespan over 250 cycles with high capacity retention of ~100 % at -40 °C. This work sheds new lights on the ion-dipole regulation for ultra-low temperature SIBs.

Solvation Structure with Enhanced Anionic Coordination for Stable Anodes in Lithium-Oxygen Batteries.

Li-O2 batteries have garnered much attention due to their high theoretical energy density. However, the irreversible lithium plating/stripping on the anode limits their performance, which has been paid little attention. Herein, a solvation-regulated strategy for stable lithium anodes in tetraethylene glycol dimethyl ether (G4) based electrolyte is attempted in Li-O2 batteries. Trifluoroacetate anions (TFA- ) with strong Li+ affinity are incorporated into the lithium bis(fluorosulfonyl)imide (LiTFSI)/G4 electrolyte to attenuate the Li+ -G4 interaction and form anion-dominant solvates. The bisalt electrolyte with 0.5 M LiTFA and 0.5 M LiTFSI mitigates G4 decomposition and induces an inorganic-rich solid electrolyte interphase (SEI). This contributes to decreased desolvation energy barrier from 58.20 to 46.31 kJ mol-1 , compared with 1.0 M LiTFSI/G4, for facile interfacial Li+ diffusion and high efficiency. It yields extended lifespan of 120 cycles in Li-O2 battery with a limited Li anode (7 mAh cm-2 ). This work gains comprehensive insights into rational electrolyte design for Li-O2 batteries.

Reversible Metal and Ligand Redox Chemistry in Two-Dimensional Iron-Organic Framework for Sustainable Lithium-Ion Batteries.

Metal-organic frameworks (MOFs) are emerging as attractive electrode materials for lithium-ion batteries, owing to their fascinating features of sustainable resources, tunable chemical components, flexible molecular skeletons, and renewability. However, they are faced with a limited number of redox-active sites and unstable molecular frameworks during electrochemical processes. Herein, we design a novel two-dimensional (2D) iron(III)-tetraamino-benzoquinone (Fe-TABQ) with dual redox centers of Fe cations and TABQ ligands for high-capacity and stable lithium storage. It is constructed of square-planar Fe-N2O2 linkages and phenylenediamine building blocks, between which the Fe-TABQ chains are connected by multiple hydrogen bonds, and then featured as an extended π-d-conjugated 2D structure. The redox chemistry of both Fe3+ cations and TABQ anions is revealed to render its remarkable specific capacity of 251.1 mAh g-1. Benefiting from the intrinsic robust Fe-N(O) bonds and reinforced Li-N(O) bonds during cycling, Fe-TABQ delivers high capacity retentions over 95% after 200 cycles at various current densities. This work will enlighten more investigations for the molecular designs of advanced MOF-based electrode materials.

Internal Electric Field and Interfacial Bonding Engineered Step-Scheme Junction for a Visible-Light-Involved Lithium-Oxygen Battery.

Li-O2 batteries have aroused considerable interest in recent years, however they are hindered by high kinetic barriers and large overvoltages at cathodes. Herein, a step-scheme (S-scheme) junction with hematite on carbon nitride (Fe2 O3 /C3 N4 ) is designed as a bifunctional catalyst to facilitate oxygen redox for a visible-light-involved Li-O2 battery. The internal electric field and interfacial Fe-N bonding in the heterojunction boost the separation and directional migration of photo-carriers to establish spatially isolated redox centers, at which the photoelectrons on C3 N4 and holes on Fe2 O3 remarkably accelerate the discharge and charge kinetics. These enable the Li-O2 battery with Fe2 O3 /C3 N4 to present an elevated discharge voltage of 3.13 V under illumination, higher than the equilibrium potential 2.96 V in the dark, and a charge voltage of 3.19 V, as well as superior rate capability and cycling stability. This work will shed light on rational cathode design for metal-O2 batteries.

Spin-State Manipulation of Two-Dimensional Metal-Organic Framework with Enhanced Metal-Oxygen Covalency for Lithium-Oxygen Batteries.

Aprotic Li-O2 batteries have attracted extensive attention in the past decade owing to their high theoretical energy density; however, they are obstructed by the sluggish reaction kinetics at the cathode and large voltage hysteresis. We regulate the spin state of partial Ni2+ metal centers (t2g 6 eg 2 ) of conductive nickel catecholate framework (NiII -NCF) nanowire arrays to high-valence Ni3+ (t2g 6 eg 1 ) for NiIII -NCF. The spin-state modulation enables enhanced nickel-oxygen covalency in NiIII -NCF, which facilitates electron exchange between the Ni sites and oxygen adsorbates and accelerates the oxygen redox kinetics. Upon discharging, the high affinity of Ni3+ sites with the intermediate LiO2 promotes formation of nanosheet-like Li2 O2 in the void space among NiIII -NCF nanowires. The Li-O2 battery based on NiIII -NCF offers remarkably reduced discharge/charge voltage gaps, superior rate capability, and a long cycling stability of over 200 cycles. This work highlights the importance of electron spin state on the redox kinetics and will provide insight into electronic structure regulation of electrocatalysts for Li-O2 batteries and beyond.

Surface plasmon mediates the visible light-responsive lithium-oxygen battery with Au nanoparticles on defective carbon nitride.

Aprotic lithium-oxygen (Li-O2) batteries have gained extensive interest in the past decade, but are plagued by slow reaction kinetics and induced large-voltage hysteresis. Herein, we use a plasmonic heterojunction of Au nanoparticle (NP)-decorated C3N4 with nitrogen vacancies (Au/NV-C3N4) as a bifunctional catalyst to promote oxygen cathode reactions of the visible light-responsive Li-O2 battery. The nitrogen vacancies on NV-C3N4 can adsorb and activate O2 molecules, which are subsequently converted to Li2O2 as the discharge product by photogenerated hot electrons from plasmonic Au NPs. While charging, the holes on Au NPs drive the reverse decomposition of Li2O2 with a reduced applied voltage. The discharge voltage of the Li-O2 battery with Au/NV-C3N4 is significantly raised to 3.16 V under illumination, exceeding its equilibrium voltage, and the decreased charge voltage of 3.26 V has good rate capability and cycle stability. This is ascribed to the plasmonic hot electrons on Au NPs pumped from the conduction bands of NV-C3N4 and the prolonged carrier life span of Au/NV-C3N4 This work highlights the vital role of plasmonic enhancement and sheds light on the design of semiconductors for visible light-mediated Li-O2 batteries and beyond.

Tunable Hollow Pt@Ru Dodecahedra via Galvanic Replacement for Efficient Methanol Oxidation.

Pt-Ru nanocrystals are promising electrocatalysts for methanol oxidation in fuel cells. However, owing to the lattice mismatch and high reduction potential of Ru, the shape-controlled synthesis of Pt-Ru nanocrystals faces great challenges. Herein, we employ a galvanic replacement method to synthesize tunable hollow Pt@Ru dodecahedra via controlling the precursor concentration. Two typical structures, hollow Pt@Ru dodecahedra (h-Pt@Ru) and deformed hollow Pt@Ru dodecahedra (d-Pt@Ru), are obtained to exhibit superior electrocatalytic activities for methanol oxidation. The optimal d-Pt@Ru dodecahedra present a mass activity of 0.80 A mgPt-1 and a specific activity of 1.61 mA cmPt-2, which are 5.25 and 7.78 times higher than those of the commercial Pt/C, respectively. Remarkably, both h-Pt@Ru and d-Pt@Ru show lower oxidation potentials and higher CO-poisoning resistance for methanol oxidation than PtRu nanoparticles (NPs) and commercial Pt/C. This is attributed to the hollow dodecahedron structures with optimal spatial elemental distributions, leading to high utilization of Pt at edges and corners and the exposure of abundant Pt-Ru interfaces. Our strategy offers a facile method to engineer bimetallic metal catalysts regardless of lattice mismatch.