2D MOF Nanoflake-Assembled Spherical Microstructures for Enhanced Supercapacitor and Electrocatalysis Performances

Metal–organic frameworks(MOFs) are of great interest as potential electrochemically active materials.However, few studies have been conducted into understanding whether control of the shape and components of MOFs can optimize their electrochemical performances due to the rational realization of their shapes. Component control of MOFs remains a significant challenge. Herein, we demonstrate a solvothermal method to realize nanostructure engineering of 2D nanoflake MOFs. The hollow structures withNi/Co-and Ni-MOF(denoted as Ni/Co-MOF nanoflakes and Ni-MOF nanoflakes) were assembled for their electrochemical performance optimizations in supercapacitors and in the oxygen reduction reaction(ORR). As a result, the Ni/CoMOF nanoflakes exhibited remarkably enhanced performance with a specific capacitance of 530.4 F g^(-1)at 0.5 A g^(-1)in1 M LiO H aqueous solution, much higher than that of NiMOF(306.8 F g^(-1)) and ZIF-67(168.3 F g^(-1)), a good rate capability, and a robust cycling performance with no capacity fading after 2000 cycles. Ni/Co-MOF nanoflakes also showed improved electrocatalytic performance for the ORR compared to Ni-MOF and ZIF-67. The present work highlights the significant role of tuning 2D nanoflake ensembles of Ni/Co-MOF in accelerating electron and charge transportation for optimizing energy storage and conversion devices.

Defect Engineering on Carbon‑Based Catalysts for Electrocatalytic CO2 Reduction

Electrocatalytic carbon dioxide(CO2)reduction(ECR)has become one of the main methods to close the broken carbon cycle and temporarily store renewable energy,but there are still some problems such as poor stability,low activity,and selectivity.While the most promising strategy to improve ECR activity is to develop electrocatalysts with low cost,high activity,and long-term stability.Recently,defective carbon-based nanomaterials have attracted extensive attention due to the unbalanced electron distribution and electronic structural distortion caused by the defects on the carbon materials.Here,the present review mainly summarizes the latest research progress of the construction of the diverse types of defects(intrinsic carbon defects,heteroatom doping defects,metal atomic sites,and edges detects)for carbon materials in ECR,and unveil the structure-activity relationship and its catalytic mechanism.The current challenges and opportunities faced by high-performance carbon materials in ECR are discussed,as well as possible future solutions.It can be believed that this review can provide some inspiration for the future of development of high-performance ECR catalysts.

Recent Progress on Two-Dimensional Nanoflake Ensembles for Energy Storage Applications

The rational design and synthesis of two-dimensional(2D) nanoflake ensemble-based materials have garnered great attention owing to the properties of the components of these materials, such as high mechanical flexibility, high specific surface area, numerous active sites,chemical stability, and superior electrical and thermal conductivity. These properties render the 2D ensembles great choices as alternative electrode materials for electrochemical energy storage systems. More recently,recognition of the numerous advantages of these 2D ensemble structures has led to the realization that the performance of certain devices could be significantly enhanced by utilizing three-dimensional(3D) architectures that can furnish an increased number of active sites. The present review summarizes the recent progress in 2D ensemble-based materials for energy storage applications,including supercapacitors, lithium-ion batteries, and sodium-ion batteries. Further, perspectives relating to the challenges and opportunities in this promising research area are discussed.

Atomic Level Dispersed Metal–Nitrogen–Carbon Catalyst toward Oxygen Reduction Reaction: Synthesis Strategies and Chemical Environmental Regulation

For development and application of proton exchange membrane fuel cell(PEMFC) energy transformation technology, the cost performance must be elevated for the catalyst. At present, compared with noble metal-based catalysts, such as Pt-based catalysts, atomically dispersed metal–nitrogen–carbon(M–N–C) catalysts are popularity and show great potential in maximizing active site density, high atom utilization and high activity,making them the first choice to replace Pt-based catalysts. In the preparation of atomically dispersed metal–nitrogen–carbon catalyst, it is difficult to ensure that all active sites are uniformly dispersed, and the structure system of the active sites is not optimal. Based on this, we focus on various approaches for preparing M–N–C catalysts that are conducive to atomic dispersion, and the influence of the chemical environmental regulation of atoms on the catalytic sites in different catalysts. Therefore, we discuss the chemical environmental regulation of the catalytic sites by bimetals, atom clusters, and heteroatoms(B, S, and P). The active sites of M–N–C catalysts are explored in depth from the synthesis and characterization, reaction mechanisms, and density functional theory(DFT)calculations. Finally, the existing problems and development prospects of the current atomic dispersion M–N–C catalyst are proposed in detail.

3D MoS_(2) foam integrated with carbon paper as binder-free anode for high performance sodium-ion batteries

Molybdenum sulfide(MoS_(2))with well-designed porous structure has the potential to be great electrode materials in sodium-ion batteries due to its high theoretical capacity and abundant resource,however,hindered by its intrinsic low conductivity and stability.Herein,MoS_(2) with 3 D macroporous foam structure and high conductivity was obtained through SiO_(2) templates and integrated with carbon paper(3 D FMoS_(2)/CP).It has showed superior specific capacity(225 m A h g^(-1),0.4–3 V)and cycling stability(1000 cycles)at high rate(2000 m A g^(-1)),with a low decay rate(0.033%per cycle)in sodium-ion batteries.The excellent electrochemical performance may originate from its unique integrated structure:3 D MoS_(2) macropores providing high surface area and abundant transfer channels while carbon paper enhancing the conductivity of MoS_(2) and avoiding unnecessary side reactions brought by binder addition.

Work-function effect of Ti_(3)C_(2)/Fe-N-C inducing solid electrolyte interphase evolution for ultra-stable sodium storage

In the quest to enhance the efficiency of sodium-ion batteries,the dynamics of solid electrolyte interphase(SEI)formation are of paramount importance.The SEI layer’s integrity is integral to the charge–discharge efficiency and the overall longevity of the battery.Herein,a novel two-dimensional Ti_(3)C_(2) fragments enmeshed on iron-nitrogen-carbon(Fe-N-C)nanosheets(Ti_(3)C_(2)/Fe-NC)has been synthesized.This electrode features a matrix which has been shown to expedite SEI layer formation through the facilitation of selective anion adsorption,thus augmenting battery performance.Density functional theory calculation reveals that the SEI evolution energy of NaPF6 at the Ti_(3)C_(2)/Fe-N-C interface is 0.81 eV,significantly lower than the Ti_(3)C_(2)(1.23 eV).This process is driven by the electron transportation from Ti_(3)C_(2) to Fe-N-C substrate,facilitated by their work-function difference,leading to the formation of ferromagnetic Fe species,which possesses Fe 3d d_(xz)d_(z)2 orbitals and undergoes hybridization with theπandσorbitals of NaF,creating a key intermediate during charging.This process diminishes the antibonding energy and attenuates the orbital interaction with NaF,thus reducing the activation energy and improving the SEI formation reaction kinetics.Consequently,it leads to the creation of multi-interface SEI characterized by high-throughput ion transport and an efficient reaction network.

Mechanism of interfacial effects in sodium-ion storage devices

Rechargeable sodium-ion batteries(SIBs)are considered as the next-generation secondary batteries.The performance of SIB is determined by the behavior of its electrode surface and the electrode–electrolyte interface during charging and discharging.Thus,the characteristics of these surfaces and interfaces should be analyzed to realize large-scale energy storage systems with high energy density and long-cycle stability.Although various studies have investigated the properties of electrode materials,few studies have focused on the construction of stable and efficient SIB interfaces,and even fewer have explored the mechanisms of interfacial effects;however,the strategies of regulating interfacial effects are yet to be completely developed.Moreover,the results obtained thus far are insufficient to draw systematic conclusions.The present study reviews the literature on the mechanism of interfacial effects in Na+storage devices.The interfaces in a sodium-ion storage device include a heterogeneous interface between electrode materials,a solid electrolyte interphase,and a cathode electrolyte interphase.The interfacial effects during the intercalation,transformation,and alloy reactions and the resulting overall battery performance were theoretically analyzed.In this review,we aim to provide a theoretical basis for optimizing the structures of electrode surface and electrode–electrolyte interface to optimize the performance of SIBs.In addition,the challenges of investigating interfacial effects and several possible helpful methods and opportunities for studying the mechanisms of interfacial effects in SIBs will be presented.

Fabrication of Fe-doped Co-MOF with mesoporous structure for the optimization of supercapacitor performances

The synergy effect between different components has attracted widespread attentions because of improved activity, selectivity and stability than single component. In this paper, we fabricated mesoporous hybrid dual-metal Co and Fe containing metallic organic framework（Co/Fe-MOF）, Fe-MOF,and Co-MOF in the ionic liquid（IL）/supercritical CO2（SC）/surfactant emulsion system, and then studied the electrochemical properties of the three MOFs systematically. Experiment results indicate that, by taking advantages of coexistence of double metal, hybrid bi-metal Co/Fe-MOF exhibits the highest specific capacitance and the best cycling stability, with specific capacitance to 319.5 F/g at 1 A/g, 1.4 and 4 times for single Co-MOF and Fe-MOF, respectively.

Rational confinement engineering of MOF-derived carbonbased electrocatalysts toward CO_(2)reduction and O_(2)reduction reactions

The goal of global carbon peak and neutrality gives an impetus to the utilization of clean energy(e.g.,fuel cell)and carbon dioxide(CO_(2))at a large scale,where the oxygen reduction reaction(ORR)and CO_(2)reduction reaction(CO_(2)RR)are the key reactions via the sustainable system,respectively.As a main precursor for fabricating affordable carbon-based electrocatalysts with uniformly dispersed active centers and tailorable performances for ORR and CO_(2)RR,metal organic frameworks(MOFs)have captured a surge of interest in recent years.Despite the facilitated development of MOF-derived carbon-based electrocatalysts by many investigations,it is still plagued by high overpotential and unsatisfied life span,which are greatly determined by the efficient and alterable confinement effect on synthesis and performance.In this review,firstly,the confined synthetic strategies(doping engineering,defect engineering,geometric engineering,etc.)of MOF-derived carbon-based electrocatalysts with multi-sized active centers(atom,atomic clusters and nanoparticles(NPs))are systematically summarized;secondly,the confinement effect on the interaction of ORR and CO_(2)RR intermediates,as well as the catalytic durability and activity,was discussed from chemical and physical aspects.In the end,the review discusses the remaining challenges and emerging research topics in the future,including support upgradation and catalyst innovation,high selectivity and effective confinement synthesis,in situ and operando characterization techniques,theoretical investigation,and artificial intelligence(AI)assistant.The new understanding and insights into these aspects will guide the rational confinement concept of MOF-derived carbon-based electrocatalysts for ORR and CO_(2)RR with optimized performances in terms of confinement engineering and are believed to be helpful for filling the existing gaps between scientific communities and practical use.

Probing the active sites of 2D nanosheets with Fe-N-C carbon shell encapsulated Fe_(x)C/Fe species for boosting sodium-ion storage performances

Developing stable but high active metal-nitrogen-carbon(M-N-C)-based hard carbon anode is a promising way to be the alternatives to graphene and blank hard carbon for sodium-ion batteries(SIBs),requiring the precise tailoring of the electronic structure for optimizing the Na+intercalation behavior,yet is greatly challenging.Herein,Fe-N-C graphitic layer-encapsulating Fe3C species within hard carbon nanosheets(Fe-N-C/Fe3C@HCNs)are rationally engineered by pyrolysis of self-assembled polymer.Impressively,the Fe-N-C/Fe3C@HCNs exhibit outstanding rate capacity(242 mAh·g^(−1)at 2,000 mA·g^(−1)),which is 2.1 and 4.2 times higher than that of Fe-N-C and N-doped carbon(N-C),respectively,and prolonged cycling stability(176 mAh·g^(−1)at 2,000 mA·g^(−1)after 2,000 cycles).Theoretical calculations unveil that the Fe3C species enhance the electronic transfer from Na to Fe-N-C,resulting in the charge redistribution between the interfaces of Fe3C and Fe-N-C.Thus,the optimized adsorption behavior towards Na+reduces the thermodynamic energy barriers.The synergistic effect of Fe3C and Fe-N-C species maintains the structural integrity of electrode materials during the sodiation/desodiation process.The in-depth insight into the advanced Na+storage mechanisms of Fe3C@Fe-N-C offers precise guidance for the rational establishment of confinement heterostructures in SIBs.

Catalytic effect of carbon-based electrode materials in energy storage devices

The catalytic effect of electrode materials is one of the most crucial factors for achieving efficient electrochemical energy conversion and storage.Carbon-based metal composites were widely synthesized and employed as electrode materials because of their inherited outstanding properties.Usually,electrode materials can provide a higher capacity than the anticipated values,even beyond the theoretical limit.The origin of the extra capacity has not yet been explained accurately,and its formation mechanism is still ambiguous.Herein,we first summarized the current research progress and drawbacks in energy storage devices(ESDs),and elaborated the role of catalytic effect in enhancing the performance of ESDs as follows:promoting the evolution of the solid electrolyte interphase(SEI),accelerating the reversible conversion of discharge/charge products,and improving the conversion speed of the intermediate and the utilization rate of the active materials,thereby avoiding the shuttling effect.Additionally,a particular focus was placed on the interaction between the catalytic effect and energy storage performance in order to highlight the efficacy and role of the catalytic effect.We hope that this review could provide innovative ideas for designing the electrode materials with an efficient catalytic effect for ESDs to promote the development of this research field.

Inactivating SARS-CoV-2 by electrochemical oxidation

Fully inactivating SARS-Co V-2, the virus causing coronavirus disease 2019, is of key importance for interrupting virus transmission but is currently performed by using biologically or environmentally hazardous disinfectants. Herein, we report an eco-friendly and efficient electrochemical strategy for inactivating the SARS-Co V-2 using in-situ formed nickel oxide hydroxide as anode catalyst and sodium carbonate as electrolyte. At a voltage of 5 V, the SARS-Co V-2 viruses can be rapidly inactivated with disinfection efficiency reaching 95% in only 30 s and 99.99% in 5 min. Mass spectrometry analysis and theoretical calculations indicate that the reactive oxygen species generated on the anode can oxidize the peptide chains and induce cleavage of the peptide backbone of the receptor binding domain of the SARS-Co V-2 spike glycoprotein, and thereby disables the virus. This strategy provides a sustainable and highly efficient approach for the disinfection of the SARS-CoV-2 viruliferous aerosols and wastewater.