Engineering the Active Sites of MOF-derived Catalysts:From Oxygen Activation to Activate Metal-Air Batteries

The electrochemical processes of oxygen reduction reaction(ORR)and oxygen evolution reaction(OER)play a crucial role in various energy storage and conversion systems.However,the inherently slow kinetics of reversible oxygen reactions present an urgent demand for the development of efficient oxygen electrocatalysts.Recently,metal-organic framework(MOF)derivatives have attracted extensive attention in electrocatalysis research due to their unique porous structure,abundant active sites,and tunable structural properties.Especially,the optimization of the electronic structure of active sites in MOF derivatives has been proven as an effective strategy to enhance the catalytic activity.In this review,we provide an overview of the electronic structure optimization strategies for active sites in MOF derivatives as advanced catalysts in various O—O bond activation reactions,including the construction of synergistic effects between multiple sites,the development of heterogeneous interfaces,the utilization of metal support interactions,and the precise modulation of organic ligands surrounding catalytic active sites at the atomic level.Furthermore,this review offers theoretical insights into the oxygen activation and catalytic mechanisms of MOF derivatives,as well as the identification of active sites.Finally,the potential challenges and prospects of MOF derivatives in electrocatalysis are discussed.This review contributes to the understanding and advancement of efficient oxygen electrocatalysis in energy systems.

Metal-organic framework derived NiFe_(2)O_(4)/FeNi_(3)@C composite for efficient electrocatalytic oxygen evolution reaction

Reducing the cost and improving the electrocatalytic activity are the key to developing high efficiency electrocatalysts for oxygen evolution reaction(OER).Here,bimetallic NiFe-based metal-organic framework(MOF)was prepared by solvothermal method,and then used as precursor to prepare NiFe-based MOF-derived materials by pyrolysis.The effects of different metal ratios and pyrolysis temperatures on the sample structure and OER electrocatalytic performance were investigated and compared.The experimental results showed that when the metal molar ratio was Fe:Ni=1:5 and the pyrolysis temperature was 450℃,the sample(FeNi_(5)-MOF-450)exhibits a composite structure of Ni Fe_(2)O_(4)/FeNi_(3)/C and owns the superior electrocatalytic activity in OER.When the current density is 100 mA·cm^(-2),the overpotential of the sample was 377 mV with Tafel slope of 56.2 mV·dec^(-1),which indicates that FeNi_(5)-MOF-450 exhibits superior electrocatalytic performance than the commercial RuO_(2).Moreover,the long-term stability of FeNi_(5)-MOF-450 further promotes its development in OER.This work demonstrated that the regulatory methods such as component optimization can effectively improve the OER catalytic performance of NiFe-based MOF-derived materials.

Porous carbon matrix-encapsulated MnO in situ derived from metalorganic frameworks as advanced anode materials for Li-ion capacitors

Conversion-type anode materials hold great potential for Li+storage applications owing to their high specific capacity,while large volume expansion and poor electrical conductivity limit their rate and cycling performances.Herein,a bimetal ZnMn-based metal-organic framework(ZnMn-MOF)is engineered for in situ conversion of MnO-encapsulated porous carbon(MnO/PC)composite.The templating and activation effects of coordinated Zn endow the converted PC matrix with a highly porous structure.This enhances the compatibility of PC matrix with MnO particles,resulting in the full encapsulation of MnO particles in the PC matrix.More significantly,the PC matrix provides enough void space to buffer the volume change,which fully wraps the MnO without crack or fracture during repeated cycling.As a result,MnO/PC shows high charge storage capability,extraordinary rate performance,and long-term cycling stability at the same time.Thus MnO/PC exhibits high delithiation capacities of 768mA h g^(-1)at 0.1Ag^(-1)and 487mA h g^(-1)at a high rate of 0.7Ag^(-1),combined with an unattenuated cycling performance after 500 cycles at 0.3Ag^(-1).More significantly,MnO/PC demonstrates a well-matched performance with the capacitive activated carbon electrode in a Li-ion capacitor(LIC)full cell.LIC demonstrates a high specific energy of 153.6W h kg^(-1)at 210W kg^(-1),combined with a specific energy of 71.8W h kg^(-1)at a high specific power of 63.0kW kg^(-1).

Self-swelling derived frameworks with rigidity and flexibility enabling high-reversible silicon anodes

Silicon is recognized as the most advantageous next-generation anode material for LIBs in terms of its extremely high theoretical capacity and appropriate operating voltage.However,the application of Si anode is limited by huge volume expansion emerging with cycling,which in turn induces the collapse of the electrode structure,resulting in rapid capacity decay.Here,we report a strategy using self-swelling artificial laponite to prepare a laponite/MXene/CNT composite framework with both rigidity and flexibility,which can excellently address these challenges of Si anode.The self-swelling artificial laponite participates in the construction of hierarchical and porous structures,providing sufficient buffer space to mitigate the volume expansion of the LixSi alloying reaction.Meanwhile,tough and tightly cross-linked silicate nanosheets can improve the mechanical strength of the framework for strong structural stability.More importantly,the negative charge between the layers of artificial laponite can effectively promote fast Li-ion transport in the electrode.This free-standing silicon anode enables the preparation of high areal capacity electrodes to further enhance the energy density of LIBs and a higher reversible capacity of 2381.8 mAh/g at 0.1 C after 50 cycles with an initial coulombic of 85.6%.This work provides a simple and practical fabrication strategy for developing high-performance Si-based batteries,which can speed up their commercialization.

The synthesis of MOF derived carbon and its application in water treatment

In recent years,since water pollution has aroused great public concern,various carbon materials have already been widely applied for water treatment.In this respect,tremendous effort has been made to provide different synthesis methods of carbon materials.Among all carbon materials,metal-organic framework(MOF)derived carbon has always been favored as it possesses several appealing merits such as high specific surface area,large pore volume,and outstanding chemical stability.This review presents the latest development of MOFs as templates and precursors for the fabrication of various carbon materials,including porous carbon,nanocarbon,and graphene,which are pyrolyzed at different temperatures.The article also emphasizes on their future trends and perspectives on the application of water treatment.

Confined Pyrolysis Synthesis of Well-dispersed Cobalt Copper Bimetallic Three-dimensional N-Doped Carbon Framework as Efficient Water Splitting Electrocatalyst

Hydrogen is one of the most desirable alternatives to fossil fuels due to its renewability and large energy density.Electrochemical water splitting,as an environmental-friendly way to produce H_(2) of high-purity,is drawing more and more attention.Conductive nitrogen-doped carbon frameworks derived from metal-organic frameworks(MOFs)have been applied as promising electrocatalysts thanks to their superior conductivity,numerous active sites and hierarchical porous structures.However,traditional uncontrolled pyrolysis will lead to aggregation or fusion of the metal sites in MOFs or even cause collapse of the three-dimensional structures.Herein,we provide a confinement pyrolysis strategy to fabricate a CoCu bimetallic N-doped carbon framework derived from MOFs,which exhibits satisfactory catalytic performance with overpotentials of 199 mV towards hydrogen evolution reaction and 301 mV towards oxygen evolution reaction to reach 10 mA/cm^(2) in an alkaline solution.This work presents further inspirations for preserving the original skeleton of MOFs during high temperature pyrolysis in order to obtain more stable and efficient electrocatalyst.

Hetero-phase zirconia encapsulated with Au nanoparticles for boosting electrocatalytic nitrogen reduction

Electrocatalytic nitrogen reduction reaction(NRR)is considered as an attractive approach for ammonia synthesis under mild conditions.A bottleneck of NRR is the exploration of efficient catalysts for accelerating reaction kinetics,among which heterogeneous structures possessing distinct atomic arrangement could modify electronic structure,and therefore altering their NRR activity.Here,we report a facile strategy for fabricating hetero-phase metal oxides derived from metal organic framework that are further integrated with Au nanoparticles as NRR catalysts.The phase composition of zirconia can be easily adjusted by simply changing the reaction temperature,where the monoclinic and tetragonal phases with the roughly close proportions have a distinct interface,leading to a strong interaction between Au and ZrO_(2).The enhanced interaction renders Au to be more electropositive and facilitates stronger binding to N_(2).As a result,a remarkable ammonia yield of 22.32μg h^(-1)mg_(cat.)^(-1) and a Faradaic efficiency of 31.92%can be achieved at low overpotential.This work is expected to pave the way for the design of heterogeneous structures and the exploration of hetero-phase nanostructures in boosting the electrocatalytic NRR.

Low-dimensional cobalt doped carbon composite towards wideband electromagnetic dissipation

Composites composed of a carbon matrix decorated with a metal or metal oxide derived from zeolitic imidazolate frameworks(ZIFs)have been widely applied as suitable electromagnetic wave absorbers due to their high porosity and controllable morphology.However,achieving ideal absorption performance remains a challenge owing to the inadequate conductivity and high density of the metal components.Therefore,a temperature-controlling treatment was employed for the bimetal ZIFs,and the corresponding derivatives exhibited an excellent dissipation ability with a minimum reflection loss value of−54.3 dB and an effective bandwidth of 7.0 GHz at a thickness of 2.4 mm,which resulted from the strong dipole polarization behavior.Furthermore,after successfully controlling the Zn/Co ratio,the attenuation capability was greatly enhanced at a thickness of 1.4 mm,with bandwidths of 13.0–18.0 GHz.Overall,this work provides an ameliorated strategy for microwave absorption performance of carbon-based materials.

Carbon-supported layered double hydroxide nanodots for efficient oxygen evolution: Active site identification and activity enhancement

In this study,we developed a novel confinement-synthesis approach to layered double hydroxide nanodots(LDH-NDs)anchored on carbon nanoparticles,which formed a three-dimensional(3D)interconnected network within a porous carbon support derived from pyrolysis of metal-organic frameworks(C-MOF).The resultant LDH-NDs@C-MOF nonprecious metal catalysts were demonstrated to exhibit super-high catalytic performance for oxygen evolution reaction(OER)with excellent operation stability and low overpotential(-230 mV)at an exchange current density of 10 mA·cm^(-2).The observed overpotential for the LDH-NDs@C-MOF is much lower than that of large-sized LDH nanosheets(321 mV),pure carbonized MOF(411 mV),and even commercial RuO_(2)(281 mV).X-ray absorption measurements and density functional theory(DFT)calculations revealed partial charge transfer from Fe^(3+)through an O bridge to Ni^(2+)at the edge of LDH-NDs supported by C-MOF to produce the optimal binding energies for OER intermediates.This,coupled with a large number of exposed active sides and efficient charge and electrolyte/reactant/product transports associated with the porous 3D C-MOF support,significantly boosted the OER performance of the LDH-ND catalyst with respect to its nanosheet counterpart.Apart from the fact that this is the first active side identification for LDH-ND OER catalysts,this work provides a general strategy to enhance activities of nanosheet catalysts by converting them into edge-rich nanodots to be supported by 3D porous carbon architectures.

Accelerating water dissociation at carbon supported nanoscale Ni/NiO heterojunction electrocatalysts for high-efficiency alkaline hydrogen evolution

The synergistic catalysis of heterojunction electrocatalysts for the multi-step process in hydrogen evolution reaction(HER)is a promising approach to enhance the kinetics of alkaline HER.Herein,we proposed a strategy to form nanoscale Ni/NiO heterojunction porous graphitic carbon composites(Ni/NiO-PGC)by reduction-pyrolysis of the preformed Ni-metal-organic framework(MOF)under H2/N2 atmosphere.Benefiting from low electron transfer resistance,increased number of active sites,and unique hierarchical micro-mesoporous structure,the optimized Ni/NiO-PGC_(10-1-400)exhibited excellent electrocatalytic performance and robust stability for alkaline HER(η10=30 mV,65 h).Density functional theory(DFT)studies revealed that the redistribution of electrons at the Ni/NiO interface enables the NiO phase to easily initiate the dissociation of alkaline H_(2)O,and shifts down the d-band center of Ni and optimizes the H*adsorption-desorption process of Ni,thereby leading to extremely high HER activity.This work contributes to a further understanding of the synergistic promotion of the multi-step HER processes by heterojunction electrocatalysts.