Strong synergy between physical and chemical properties:Insight into optimization of atomically dispersed oxygen reduction catalysts

Atomically dispersed catalysts exhibit significant influence on facilitating the sluggish oxygen reduction reaction(ORR)kinetics with high atom economy,owing to remarkable attributes including nearly 100%atomic utilization and exceptional catalytic functionality.Furthermore,accurately controlling atomic physical properties including spin,charge,orbital,and lattice degrees of atomically dispersed catalysts can realize the optimized chemical properties including maximum atom utilization efficiency,homogenous active centers,and satisfactory catalytic performance,but remains elusive.Here,through physical and chemical insight,we review and systematically summarize the strategies to optimize atomically dispersed ORR catalysts including adjusting the atomic coordination environment,adjacent electronic orbital and site density,and the choice of dual-atom sites.Then the emphasis is on the fundamental understanding of the correlation between the physical property and the catalytic behavior for atomically dispersed catalysts.Finally,an overview of the existing challenges and prospects to illustrate the current obstacles and potential opportunities for the advancement of atomically dispersed catalysts in the realm of electrocatalytic reactions is offered.

Defect and Doping Co‑Engineered Non‑Metal Nanocarbon ORR Electrocatalyst

Exploring low-cost and earth-abundant oxygen reduction reaction(ORR)electrocatalyst is essential for fuel cells and metal–air batteries.Among them,non-metal nanocarbon with multiple advantages of low cost,abundance,high conductivity,good durability,and competitive activity has attracted intense interest in recent years.The enhanced ORR activities of the nanocarbons are normally thought to originate from heteroatom(e.g.,N,B,P,or S)doping or various induced defects.However,in practice,carbon-based materials usually contain both dopants and defects.In this regard,in terms of the co-engineering of heteroatom doping and defect inducing,we present an overview of recent advances in developing non-metal carbon-based electrocatalysts for the ORR.The characteristics,ORR performance,and the related mechanism of these functionalized nanocarbons by heteroatom doping,defect inducing,and in particular their synergistic promotion effect are emphatically analyzed and discussed.Finally,the current issues and perspectives in developing carbon-based electrocatalysts from both of heteroatom doping and defect engineering are proposed.This review will be beneficial for the rational design and manufacturing of highly efficient carbon-based materials for electrocatalysis.

电子自旋效应在电催化剂中的作用

高效电催化剂的开发对于能源转换及储存技术的发展至关重要。自旋作为粒子的内禀性质,能够对化学反应的过程产生独特的影响。因此,调控电催化剂内部自旋状态能够有效提升催化剂整体性能。本综述首先介绍了电子自旋以及自旋调控的影响因素,随后从热力学和动力学两方面阐述了自旋效应在电催化中的作用机理。进一步,我们综述了自旋效应在氧还原反应(ORR)、析氧反应(OER)、氮还原反应(NRR)、二氧化碳还原反应(CO_(2)RR)中的最新研究进展,详细介绍了自旋调控在上述四种反应中的催化机理。同时本文总结了电子自旋的先进表征方法和自旋催化的第一性原理计算方法。最后,我们展望了自旋效应在电催化领域的发展趋势。因此,认识并了解电子自旋效应有助于加深对电催化反应过程的机制理解,指导设计高效催化剂,具有巨大的研究价值。

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.

Single-Atom Catalysts for Electrochemical Hydrogen Evolution Reaction: Recent Advances and Future Perspectives

Hydrogen,a renewable and outstanding energy carrier with zero carbon dioxide emission,is regarded as the best alternative to fossil fuels.The most preferred route to large-scale production of hydrogen is by water electrolysis from the intermittent sources(e.g.,wind,solar,hydro,and tidal energy).However,the efficiency of water electrolysis is very much dependent on the activity of electrocatalysts.Thus,designing high-effective,stable,and cheap materials for hydrogen evolution reaction(HER)could have a substantial impact on renewable energy technologies.Recently,single-atom catalysts(SACs)have emerged as a new frontier in catalysis science,because SACs have maximum atom-utilization efficiency and excellent catalytic reaction activity.Various synthesis methods and analytical techniques have been adopted to prepare and characterize these SACs.In this review,we discuss recent progress on SACs synthesis,characterization methods,and their catalytic applications.Particularly,we highlight their unique electrochemical characteristics toward HER.Finally,the current key challenges in SACs for HER are pointed out and some potential directions are proposed as well.

Design Engineering,Synthesis Protocols,and Energy Applications of MOF-Derived Electrocatalysts

The core reactions for fuel cells,rechargeable metal-air batteries,and hydrogen fuel production are the oxygen reduction reaction(ORR),oxygen evolution reaction(OER),and hydrogen evolution reaction(HER),which are heavily dependent on the efficiency of electrocatalysts.Enormous attempts have previously been devoted in non-noble electrocatalysts born out of metal-organic frameworks(MOFs)for ORR,OER,and HER applications,due to the following advantageous reasons:(i)The significant porosity eases the electrolyte diffusion;(ii)the supreme catalyst-electrolyte contact area enhances the diffusion efficiency;and(iii)the electronic conductivity can be extensively increased owing to the unique construction block subunits for MOFs-derived electrocatalysis.Herein,the recent progress of MOFs-derived electrocatalysts including synthesis protocols,design engineering,DFT calculations roles,and energy applications is discussed and reviewed.It can be concluded that the elevated ORR,OER,and HER performances are attributed to an advantageously well-designed high-porosity structure,significant surface area,and plentiful active centers.Furthermore,the perspectives of MOF-derived electrocatalysts for the ORR,OER,and HER are presented.

Tuning Active Metal Atomic Spacing by Filling of Light Atoms and Resulting Reversed Hydrogen Adsorption-Distance Relationship for Efficient Catalysis

Precisely tuning the spacing of the active centers on the atomic scale is of great significance to improve the catalytic activity and deepen the understanding of the catalytic mechanism,but still remains a challenge.Here,we develop a strategy to dilute catalytically active metal interatomic spacing(d_(M-M))with light atoms and discover the unusual adsorption patterns.For example,by elevating the content of boron as interstitial atoms,the atomic spacing of osmium(d_(Os-Os))gradually increases from 2.73 to 2.96?.More importantly,we find that,with the increase in dOs-Os,the hydrogen adsorption-distance relationship is reversed via downshifting d-band states,which breaks the traditional cognition,thereby optimizing the H adsorption and H_2O dissociation on the electrode surface during the catalytic process;this finally leads to a nearly linear increase in hydrogen evolution reaction activity.Namely,the maximum dOs-Os of 2.96?presents the optimal HER activity(8 mV@10 mA cm^(-2))in alkaline media as well as suppressed O adsorption and thus promoted stability.It is believed that this novel atomic-level distance modulation strategy of catalytic sites and the reversed hydrogen adsorption-distance relationship can shew new insights for optimal design of highly efficient catalysts.

Epitaxially Grown Ru Clusters-Nickel Nitride Heterostructure Advances Water Electrolysis Kinetics in Alkaline and Seawater Media

The epitaxial heterostructure can be rationally designed based on the in situ growth of two compatible phases with lattice similarity,in which the modulated electronic states and tuned adsorption behaviors are conducive to the enhancement of electrocatalytic activity.Herein,theoretical simulations first disclose the charge transfer trend and reinforced inherent electron conduction around the epitaxial heterointerface between Ru clusters and Ni_(3)N substrate(cRu-Ni_(3)N),thus leading to the optimized adsorption behaviors and reduced activation energy barriers.Subsequently,the defectrich nanosheets with the epitaxially grown cRu-Ni_(3)N heterointerface are successfully constructed.Impressively,by virtue of the superiority of intrinsic activity and reaction kinetics,such unique epitaxial heterostructure exhibits remarkable bifunctional catalytic activity toward electrocatalytic OER(226 mV@20 mA cm^(−2))and HER(32 mV@10 mA cm^(−2))in alkaline media.Furthermore,it also shows great application prospect in alkaline freshwater and seawater splitting,as well as solar-to-hydrogen integrated system.This work could provide beneficial enlightenment for the establishment of advanced electrocatalysts with epitaxial heterointerfaces.

Ultra-small platinum nanoparticles segregated by nickle sites for efficient ORR and HER processes

In the electrochemical process,Pt nanoparticles(NPs)in Pt-based catalysts usually agglomerate due to Oswald ripening or lack of restraint,ultimately resulting in reduction of the active sites and catalytic efficiency.How to uniformly disperse and firmly fix Pt NPs on carbon matrix with suitable particle size for catalysis is still a big challenge.Herein,to prevent the agglomeration and shedding of Pt NPs,Ni species is introduced and are evenly dispersed in the surface of carbon matrix in the form of Ni-N-C active sites(Ni ZIF-NC).The Ni sites can be used to anchor Pt NPs,and then effectively limit the further growth and agglomeration of Pt NPs during the reaction process.Compared with commercial Pt/C catalyst,Pt@Ni ZIF-NC,with ultralow Pt loading(7 wt%)and ideal particle size(2.3 nm),not only increases the active center,but also promotes the catalysis kinetics,greatly improving the ORR and HER catalytic activity.Under acidic conditions,its half-wave potential(0.902 V)is superior to commercial Pt/C(0.861 V),and the mass activity(0.38 A per mg Pt)at 0.9 V is 4.7 times that of Pt/C(0.08 A per mg Pt).Besides,it also shows outstanding HER performance.At 20 and 30 mV,its mass activity is even 2 and 6 times that of Pt/C,respectively.Whether it is under ORR or HER conditions,it still shows excellent durability.These undoubtedly indicate the realization of dual-functional catalysts with low-Pt and high-efficiency properties.

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.

In situ constructing of ultrastable ceramic@graphene core-shell architectures as advanced metal catalyst supports toward oxygen reduction

The changeable structure of 2 D graphene nanosheets makes the Pt-based nanoparticles（NPs） possess a low efficiency toward oxygen reduction reaction（ORR） and a short lifetime for proton exchange membrane fuel cells. Thus, a unique Ti C@graphene core-shell structure material with low surface energy is designed and prepared by an in situ forming strategy, and firstly applied as a stable support of Pt NPs.The as-prepared Pt/GNS@Ti C catalyst presents a high activity. Especially, its ORR stability is remarkably improved. Even after 15000 potential cycles, the half-wave potential and mass activity toward ORR have almost no change. This can be attributed to that the graphene nanosheet existing in a sphere shape effectively avoids the restacking or folding caused by the giant surface tension in 2 D graphene nanosheets,impeding the decrease of the triple-phase boundary on Pt NPs. Significantly, the power density of fuel cells with our novel catalyst reaches 853 m V cmunder a low Pt loading(0.25 mg Pt cm) and H/Air conditions. These indicate the new ceramic@graphene core-shell nanocomposite is a promising application in fuel cells and other fields.

Robust MOF-253-derived N-doped carbon confinement of Pt single nanocrystal electrocatalysts for oxygen evolution reaction

Although carbon-supported platinum(Pt/C) is still considered the most active electrocatalyst for hydrogen evolution reaction(HER) and oxygen reduction reaction(ORR), its applications in metal–air batteries as a cathode catalyst, or for oxygen generation via water splitting electrolysis as an anode catalyst is mainly constrained by the insufficient kinetic activity and stability in the oxygen evolution reaction(OER). Here, MOF-253-derived nitrogen-doped carbon(N/C)-confined Pt single nanocrystals(Pt@N/C) have been synthesized and shown to be efficient catalysts for the OER. Even with low Pt mass loading of 6.1 wt%(Pt@N/C-10), the catalyst exhibits greatly improved activity and long-time stability as an efficient OER catalyst. Such high catalytic performance is attributed to the core-shell structure relationship, in which the active N-doped-C shell not only provides a protective shield to avoid rapid Pt nanocrystal oxidation at high potentials and inhibits the Pt migration and agglomeration, but also improves the conductivity and charge transfer kinetics.

Awakening the oxygen evolution activity of MoS_(2) by oxophilic-metal induced surface reorganization engineering

Although molybdenum disulfide (MoS_(2))-based materials are generally known as active electrocatalysts for the hydrogen evolution reaction (HER), the inert performance for the oxygen evolution reaction (OER) seriously limits their wide applications in alkaline electrolyzers due to there exists too strong metal-sulfur (M−S) bond in MoS_(2). Herein, by means of surface reorganization engineering of bimetal Al, Co-doped MoS_(2) (devoted as AlCo_(3)-MoS_(2)) through in situ substituting partial oxidation, we successfully significantly activate the OER activity of MoS_(2), which affords a considerably low overpotential of 323 mV at −30 mA cm^(−2), far lower than those of MoS_(2), Al-MoS_(2) and Co-MoS_(2) catalysts. Essentially, the AlCo_(3)-MoS_(2) substrate produces lots of M−O (M=Al, Co and Mo) species with oxygen vacancies, which trigger the surface self-reconstruction of pre-catalysts and simultaneously boost the electrocatalytic OER activity. Moreover, benefiting from the moderate M−O species formed on the surface, the redistribution of surface electron states is induced, thus optimizing the adsorption of OH* and OOH* intermediates on metal oxyhydroxides and awakening the OER activity of MoS_(2).

Highly sensitive wearable sensor based on a flexible multi-layer graphene film antenna

The use of advanced carbon nanomaterials for flexible antenna sensors has attracted great attention due to their outstanding electromechanical properties. However, carbon nanomaterial based composites have yet to overcome drawbacks, such as low conductivity and toughness. In this work, a flexible multi-layer graphene film(FGF) with a high conductivity of 10~6 S/m for antenna based wearable sensors is investigated. A 1.63 GHz FGF antenna sensor exhibits significantly high strain sensitivity of 9.8 for compressive bending and 9.36 for tensile bending, which is super than the copper antenna sensor(5.39 for compressive bending and 4.05 for tensile bending). Moreover, the FGF antenna sensor shows very good mechanical flexibility, reversible deformability and structure stability, and thus is well suited for applications like wearable devices and wireless strain sensing.

Highly efficient and stable electrocatalyst for hydrogen evolution by molybdenum doped Ni-Co phosphide nanoneedles at high current density

There is an increasingly urgent need to develop cost-effective electrocatalysts with high catalytic activity and stability as alternatives to the traditional Pt/C in catalysts in water electrolysis.In this study,microspheres composed of Mo-doped NiCoP nanoneedles supported on nickel foam were prepared to address this challenge.The results show that the nanoneedles provide sufficient active sites for efficient electron transfer;the small-sized effect and the micro-scale roughness enhance the entry of reactants and the release of hydrogen bubbles;the Mo doping effectively improves the electrocatalytic performance of NiCoP in alkaline media.The catalyst exhibits low hydrogen evolution overpotentials of 38.5 and 217.5 mV at a current density of 10 mA·cm^(-2) and high current density of 500 mA·cm^(-2),respectively,and only 1.978 V is required to achieve a current density of 1000 mA·cm^(-2) for overall water splitting.Density functional theory(DFT)calculations show that the improved hydrogen evolution performance can be explained as a result of the Mo doping,which serves to reduce the interaction between NiCoP and intermediates,optimize the Gibbs free energy of hydrogen adsorption(△G_(*H)),and accelerate the desorption rate of *OH.This study provides a promising solution to the ongoing challenge of designing efficient electrocatalysts for high-current-density hydrogen production.

Defects enriched hollow porous Co-N-doped carbons embedded with ultrafine CoFe/Co nanoparticles as bifunctional oxygen electrocatalyst for rechargeable flexible solid zinc-air batteries

The construction and design of highly efficient and inexpensive bifunctional oxygen electrocatalysts substitute for noble-metal-based catalysts is highly desirable for the development of rechargeable Zn-air battery(ZAB).In this work,a bifunctional oxygen electrocatalysts of based on ultrafine CoFe alloy(4-5 nm)dispersed in defects enriched hollow porous Co-N-doped carbons,made by annealing SiO2 coated zeolitic imidazolate framework-67(ZIF-67)encapsulated Fe ions.The hollow porous structure not only exposed the active sites inside ZIF-67,but also provided efficient charge and mass transfer.The strong synergetic coupling among high-density CoFe alloys and Co-N_(x) sites in Co,N-doped carbon species ensures high oxygen reduction reaction(ORR)and oxygen evolution reaction(OER)activity.First-principles simulations reveal that the synergistic promotion effect between CoFe alloy and Co-N site effectively reduced the formation energy of from O^(*)to OH^(*).The optimized CoFe-Co@PNC exhibits outstanding electrocatalytic stability and activity with the overpotential of only 320 mV for OER at 10 mA·cm^(−2) and the half-wave potential of 0.887 V for ORR,outperforming that of most recent reported bifunctional electrocatalysts.A rechargeable ZAB constructed with CoFe-Co@PNC as the air cathode displays long-term cyclability for over 200 h and high power density(152.8 mW·cm^(−2)).Flexible solid-state ZAB with our CoFe-Co@PNC as the air cathode possesses a high open circuit potential(OCP)up to 1.46 V as well as good bending flexibility.This universal structure design provides an attractive and instructive model for the application of nanomaterials derived from MOF in the field of sustainable flexible energy applications device.

ZIF-8/LiFePO4 derived Fe-N-P Co-doped carbon nanotube encapsulated Fe2P nanoparticles for efficient oxygen reduction and Zn-air batteries

Iron-based oxygen reduction reaction(ORR)catalysts have been the focus of research,and iron sources play an important role for the preparation of efficient ORR catalysts.Here,we successfully use LiFePO4 as ideal sources of Fe and P to construct the heteroatom doped Fe-based carbon materials.The obtained Fe-N-P co-doped coral-like carbon nanotube arrays encapsulated Fe2P catalyst(C-ZIF/LFP)shows very high half-wave potential of 0.88 V in alkaline electrolytes toward ORR,superior to Pt/C(0.85 V),and also presents a high half-wave potential of 0.74 V in acidic electrolytes,comparable to Pt/C(0.8 V).When further applied into a home-made Zn-air battery as cathode,a peak power density of 140 mW·cm^-2 is reached,exceeds commercial Pt/C(110 mW·cm^-2).Besides,it also presents exceptional durability and methanol resistance compared with Pt/C.Noticeably,the preparation method of such a high-performance catalyst is simple and easy to optimize,suitable for the large-scale production.What’s more,it opens up a more sustainable development scenario to reduce the hazardous wastes such as LiFePO4 by directly using them for preparing high-performance ORR catalysts.

High conductive graphene assembled films with porous micro-structure for freestanding and ultra-low power strain sensors

Graphene emerges as an ideal material for constructing high-performance strain sensors,due to its superior mechanical property and high conductivity.However,in the process of assembling graphene into macroscopic materials,its conductivity decreases significantly.Also,tedious fabrication process hinders the application of graphene-based strain sensors.In this work,we report a freestanding graphene assembled film(GAF)with high conductivity((2.32±0.08)×105 S m-1).For the sensitive materials of strain sensors,it is higher than most of reported carbon nanotube and graphene materials.These advantages enable the GAF to be an ultra-low power consumption strain sensor for detecting airflow and vocal vibrations.The resistance of the GAF remains unchanged with increasing temperature(20-100℃),exhibiting a good thermal stability.Also,the GAF can be used as a strain sensor directly without any flexible substrates,which greatly simplifies the fabrication process in comparison with most reported strain sensors.Additionally,the GAF used as a pressure sensor with only^4.7μW power is investigated.This work provides a new direction for the preparation of advanced sensors with ultra-low power consumption,and the development of flexible and energy-saving electronic devices.

In situ generated layered NiFe-LDH/MOF heterostructure nanosheet arrays with abundant defects for efficient alkaline and seawater oxidation

As the main limiting step of overall water splitting,oxygen evolution reaction(OER)is urgent to be enhanced by developing efficient catalysts to promote the process of electrolytic water.Based on theoretical analysis,the Ni-metal-organic framework(Ni-MOF)and NiFe-layered double hydroxide(NiFe-LDH)(NiFe-LDH/MOF)heterostructure can optimize the energy barrier of the OER process and decrease the adsorption energy of oxygen-containing intermediates,effectively accelerating the OER kinetics.Accordingly,layered NiFe-LDH/MOF heterostructures are in situ constructed through a facile two-step reaction process,with substantial oxygen defects and lattice defects that further improve the catalytic performance.As a result,only 208 and 275 mV OER overpotentials are needed for NiFe-LDH/MOF to drive the current densities of 20 and 100 mA·cm^(-2)in 1 M KOH solutions,and even maintain catalytic stability of 100 h at 20 mA·cm^(-2).When applied to seawater oxidation,only 235 and 307 mV OER overpotentials are required to achieve the current densities of 20 and 100 mA·cm^(-2),respectively,with almost no attenuation for 100 h stability test at 20 mA·cm^(-2),all better than commercial RuO_(2).This work provides the theoretical and experimental basis and a new idea for efficiently driving fresh water and seawater cracking by heterostructure and defect coupling design toward catalysts.

Tuning the dual-active sites of ZIF-67 derived porous nanomaterials for boosting oxygen catalysis and rechargeable Zn-air batteries

The rational control of the active site of metal-organic frameworks(MOFs)derived nanomaterials is essential to build efficient bifunctional oxygen reduction/evolution reaction(ORR/OER)catalysts.Accordingly,through designing and constructing a Co_(3)O_(4)-Co heterostructure embedded in Co,N co-doped carbon polyhedra derived(Co_(3)O_(4)-Co@NC)from the in-situ compositions of ZIF-67 and cobalt nanocrystals synthesized by the strategy of in-situ NaBH4 reduction,the dual-active site(Co_(3)O_(4)-Co and Co-N_(x))is synchronously realized in a MOFs derived nanomaterials.The formed Co_(3)O_(4)-Co@NC shows excellent bifunctional electrocatalytic activity with ultra-small potential gap(ΔE=E_(j=10)(OER)–E_(1/2)(ORR))of 0.72 V,which surpasses the commercial Pt/C and RuO_(2) catalysts.The theory calculation results reveal that the excellent bifunctional electrocatalytic activity can be attributed to the charge redistribution of Co of Co-N_(x) induced by the synergistic effects of well-tuned active sites of Co_(3)O_(4)-Co nanoparticle and Co-N_(x),thus optimizing the rate-determining step of the desorption of O_(2)^(*)intermediate in ORR and OH^(*)intermediate in OER.The rechargeable Zn-air batteries with our bifunctional catalysts exhibit superior performance as well as high cycling stability.This simple-effective optimization strategy offers prospects for tuning the active site of MOF derived bifunctional catalyst in electrochemical energy devices.