Rationally designed hollow carbon nanospheres decorated with S,P co-doped NiSe_(2) nanoparticles for high-performance potassium-ion and lithium-ion batteries

Hollow nanostructures with external shells and inner voids have been proved to greatly shorten the transport distance of ions/electrons and buffer volume change,especially for the large-sized potassium-ions in secondary batteries.In this work,hollow carbon(HC) nanospheres embedded with S,P co-doped NiSe_(2)nanoparticles are fabricated by "drop and dry" and "dissolving and precipitation" processes to form Ni(OH)2nanocrystals followed by annealing with S and P dopants to form nanoparticles.The resultant S,P-NiSe_(2)/HC composite exhibits excellent cyclic performance with 131.6 mA h g^(-1)at1000 mA g^(-1)after 3000 cycles for K^(+)storage and a capacity of 417.1 mA h g^(-1)at 1000 mA g^(-1)after1000 cycles for Li^(+)storage.K-ion full cells are assembled and deliver superior cycling stability with a ca pacity of 72.5 mA h g^(-1)at 200 mA g^(-1)after 500 cycles.The hollow carbon shell with excellent electrical conductivity effectively promotes the transporta tion and tolerates large volume variation for both K^(+)and Li^(+).Density functional theory calculations confirm that the S and P co-doping NiSe_(2) enables stronger adsorption of K^(+)ions and higher electrical conductivity that contributes to the improved electrochemical performance.

Sulfur/nitrogen/oxygen tri-doped carbon nanospheres as an anode for potassium ion storage

Carbonaceous materials are considered as ideal anode for potassium ion batteries(PIBs)due to their abundant resources and stable physical and chemical properties.However,improvements of reversible capacity and cycle performance are still needed,aiming to the practical application.Herein,S/N/O tridoped carbon(SNOC)nanospheres are prepared by in-situ vulcanized polybenzoxazine.The S/N/O tridoped carbon matrix provides abundant active sites for potassium ion adsorption and effectively improves potassium storage capacity.Moreover,the SNOC nanospheres possess large carbon interlayer spacing and high specific surface area,which broaden the diffusion pathway of potassium ions and accelerate the electron transfer speed,resulting in excellent rate performance.As an anode for PIBs,SNOC shows attractive rate performance(438.5 mA h g^(-1) at 50 mA g^(-1) and 174.5 mA h g^(-1) at2000 mA g^(-1)),ultra-high reversible capacity(397.4 mA h g^(-1) at 100 mA g^(-1) after 700 cycles)and ultra-long cycling life(218.9 mA h g^(-1) at 2000 mA g^(-1) after 7300 cycles,123.1 mA h g^(-1) at3000 mA g^(-1) after 16500 cycles and full cell runs for 4000 cycles).Density functional theory calculation confirms that S/N/O tri-doping enhances the adsorption and diffusion of potassium ions,and in-situ Fourier-transform infrared explores explored the potassium storage mechanism of SNOC.

Hollow Gradient-Structured Iron-Anchored Carbon Nanospheres for Enhanced Electromagnetic Wave Absorption

In the present paper,a microwave absorber with nanoscale gradient structure was proposed for enhancing the electromagnetic absorption performance.The inorganic-organic competitive coating strategy was employed,which can effectively adjust the thermodynamic and kinetic reactions of iron ions during the solvothermal process.As a result,Fe nanoparticles can be gradually decreased from the inner side to the surface across the hollow carbon shell.The results reveal that it offers an outstanding reflection loss value in combination with broadband wave absorption and flexible adjustment ability,which is superior to other relative graded distribution structures and satisfied with the requirements of lightweight equipment.In addition,this work elucidates the intrinsic microwave regulation mechanism of the multiscale hybrid electromagnetic wave absorber.The excellent impedance matching and moderate dielectric parameters are exhibited to be the dominative factors for the promotion of microwave absorption performance of the optimized materials.This strategy to prepare gradient-distributed microwave absorbing materials initiates a new way for designing and fabricating wave absorber with excellent impedance matching property in practical applications.

MOF‑Derived CoSe2@N‑Doped Carbon Matrix Confined in Hollow Mesoporous Carbon Nanospheres as High‑Performance Anodes for Potassium‑Ion Batteries

In this work,a novel vacuum-assisted strategy is proposed to homogenously form Metal-organic frameworks within hollow mesoporous carbon nanospheres(HMCSs)via a solid-state reaction.The method is applied to synthesize an ultrafine CoSe2 nanocrystal@N-doped carbon matrix confined within HMCSs(denoted as CoSe2@NC/HMCS)for use as advanced anodes in highperformance potassium-ion batteries(KIBs).The approach involves a solvent-free thermal treatment to form a Co-based zeolitic imidazolate framework(ZIF-67)within the HMCS templates under vacuum conditions and the subsequent selenization.Thermal treatment under vacuum facilitates the infiltration of the cobalt precursor and organic linker into the HMCS and simultaneously transforms them into stable ZIF-67 particles without any solvents.During the subsequent selenization process,the“dual confinement system”,composed of both the N-doped carbon matrix derived from the organic linker and the small-sized pores of HMCS,can effectively suppress the overgrowth of CoSe2 nanocrystals.Thus,the resulting uniquely structured composite exhibits a stable cycling performance(442 mAh g^−1 at 0.1 A g^−1 after 120 cycles)and excellent rate capability(263 mAh g^−1 at 2.0 A g^−1)as the anode material for KIBs.

Integrated carbon nanospheres arrays as anode materials for boosted sodium ion storage

Developing cost-effective advanced carbon anode is critical for innovation of sodium ion batteries. Herein, we develop a powerful combined method for rational synthesis of free-standing binder-free carbon nanospheres arrays via chemical bath plus hydrothermal process. Impressively,carbon spheres with diameters of 150-250 nm are randomly interconnected with each other forming highly porous arrays. Positive advantages including large porosity, high surface and strong mechanical stability are combined in the carbon nanospheres arrays. The obtained carbon nanospheres arrays are tested as anode material for sodium ion batteries(SIBs) and deliver a high reversible capacity of 102 mAh g^(-1) and keep a capacity retention of 95% after 100 cycles at a current density of 0.25 A g^(-1) and good rate performance(65 mAh g^(-1) at a high current density of 2 A g^(-1)). The good electrochemical performance is attributed to the stable porous nanosphere structure with fast ion/electron transfer characteristics.

High-loading, ultrafine Ni nanoparticles dispersed on porous hollow carbon nanospheres for fast (de)hydrogenation kinetics of MgH_(2)

Magnesium hydride(MgH2) is one of the most promising hydrogen storage materials for practical application due to its favorable reversibility, low cost and environmental benign;however, it suffers from high dehydrogenation temperature and slow sorption kinetics.Exploring proper catalysts with high and sustainable activity is extremely desired for substantially improving the hydrogen storage properties of MgH2. In this work, a composite catalyst with high-loading of ultrafine Ni nanoparticles(NPs) uniformly dispersed on porous hollow carbon nanospheres is developed, which shows superior catalytic activity towards the de-/hydrogenation of MgH2. With an addition of 5wt% of the composite, which contains 90 wt% Ni NPs, the onset and peak dehydrogenation temperatures of MgH2are lowered to 190 and 242 ℃, respectively. 6.2 wt% H2is rapidly released within 30 min at 250 ℃. The amount of H2that the dehydrogenation product can absorb at a low temperature of 150 ℃ in only 250 s is very close to the initial dehydrogenation value. A dehydrogenation capacity of 6.4wt% remains after 50 cycles at a moderate cyclic regime, corresponding to a capacity retention of 94.1%. The Ni NPs are highly active,reacting with MgH2and forming nanosized Mg2Ni/Mg2NiH4. They act as catalysts during hydrogen sorption cycling, and maintain a high dispersibility with the help of the dispersive role of the carbon substrate, leading to sustainably catalytic activity. The present work provides new insight into designing stable and highly active catalysts for promoting the(de)hydrogenation kinetics of MgH2.

In-situ formation of nitrogen doped microporous carbon nanospheres derived from polystyrene as lubricant additives for anti-wear and friction reduction

This study presents a nitrogen-doped microporous carbon nanospheres(N@MCNs)prepared by a facile polymerization–carbonization process using low-cost styrene.The N element in situ introduces polystyrene(PS)nanospheres via emulsion polymerization of styrene with cyanuric chloride as crosslinking agent,and then carbonization obtains N@MCNs.The as-prepared carbon nanospheres possess the complete spherical structure and adjustable nitrogen amount by controlling the relative proportion of tetrachloromethane and cyanuric chloride.The friction performance of N@MCNs as lubricating oil additives was surveyed utilizing the friction experiment of ball-disc structure.The results showed that N@MCNs exhibit superb reduction performance of friction and wear.When the addition of N@MCNs was 0.06 wt%,the friction coefficient of PAO-10 decreased from 0.188 to 0.105,and the wear volume reduced by 94.4%.The width and depth of wear marks of N@MCNs decreased by 49.2% and 94.5%,respectively.The carrying capacity of load was rocketed from 100 to 400 N concurrently.Through the analysis of the lubrication mechanism,the result manifested that the prepared N@MCNs enter clearance of the friction pair,transform the sliding friction into the mixed friction of sliding and rolling,and repair the contact surface through the repair effect.Furthermore,the tribochemical reaction between nanoparticles and friction pairs forms a protective film containing nitride and metal oxides,which can avert direct contact with the matrix and improve the tribological properties.This experiment showed that nitrogen-doped polystyrene-based carbon nanospheres prepared by in-situ doping are the promising materials for wear resistance and reducing friction.This preparing method can be ulteriorly expanded to multi-element co-permeable materials.Nitrogen and boron co-doped carbon nanospheres(B,N@MCNs)were prepared by mixed carbonization of N-enriched PS and boric acid,and exhibited high load carrying capacity and good tribological properties.

Synthesis and applications of carbon nanospheres:A review

The synthesis of carbon nanospheres(CNS)has developed rapidly in recent years,and they are widely used owing to the tunability of their porous structures and surface properties and the unique hydrodynamic advantages conferred by their spherical structures.This review summarizes the methods used to synthesize CNS and their applications in various fields.The review first describes the four main methods of CNS synthesis,i.e.the template,spray-drying,hydrothermal carbonization,Stöber and chemical vapor depo-sition method.Next,applications in the fields of energy storage,adsorption,biological medicine,and catalysis are expounded.Finally,some insights on the development and design of CNS are presented.

Size-controllable synthesis of monodispersed nitrogen-doped carbon nanospheres from polydopamine for high-rate supercapacitors

Monodispersed nitrogen-doped carbon nanospheres with tunable particle size(100-230 nm)were synthesized via self-polymerization of biochemical dopamine in the presence of hexamethylenetetramine as a buffer and F127 as a size controlling agent.Hexamethylenetetramine can mildly release NH3,which in turn initiates the polymerization reaction of dopamine.The carbon nanospheres obtained exhibited a significant energy storage capability of 265 F·g^(-1)at 0.5 A·g^(-1)and high-rate performance of 82%in 6 mol·L^(-1)KOH(20 A·g^(-1)),which could be attributed to the presence of abundant micromesoporous structure,doped nitrogen functional groups and the small particle size.Moreover,the fabricated symmetric supercapacitor device displayed a high stability of 94%after 5000 cycles,revealing the considerable potential of carbon nanospheres as electrode materials for energy storage.

Nitrogen doped hollow carbon nanospheres as efficient polysulfide restricted layer on commercial separators for high-performance lithium-sulfur batteries

The polysulfide shuttle limits the development of lithium-sulfur(Li-S) batteries with high energy density and long lifespan. Herein, nitrogen doped hollow carbon nanospheres(NHCS) derived from polymerization of dopamine on SiO_(2)nanospheres are employed to modify the commercial polypropylene/polyethylene/polypropylene tri-layer separators(PP/PE/PP@NHCS). The abundant nitrogen heteroatoms in NHCS exhibit strong chemical adsorption toward polysulfides, which can effectively suppress the lithium polysulfides shuttle and further enhance the utilization of active sulfur. Lithium-sulfur batteries employing the PP/PE/PP@NHCS deliver an initial discharge capacity of 1355 mAh/g and retain high capacity of 921 mAh/g after 100 cycles at 0.2 C. At a high rate of 2 C, the lithium-sulfur batteries exhibit capacity of 461 mAh/g after 1000 cycles with a capacity fading rate of 0.049% per cycle. This work demonstrates that the NHCS coated PP/PE/PP separator is promising for future commercial applications of lithium-sulfur batteries with improved electrochemical performances.

Spatial confinement of zeolitic imidazolate framework deposits by porous carbon nanospheres for dual-atom catalyst towards high-performance oxygen reduction reaction

Dual atom catalysts(DACs),are promising electrocatalysts for oxygen reduction reaction(ORR)on account of the potential dual-atom active sites for the optimized adsorption of catalytic intermediates and the lower reaction energy barriers.Herein,spatial confinement strategy to fabricate DACs with well-defined Fe,Co dual-atom active site is proposed by implanting zeolitic imidazolate frameworks inside the pores of highly porous carbon nanospheres(Fe/Co-SAs-Nx-PCNSs).The atomically dispersed dual-atom active sites facilitate the adsorption/desorption of intermediates.Furthermore,the spatial confinement effect protects metal atoms aggregating.Benefiting from the rich accessible dual-atom active sites and boosted mass transport,we achieve remarkable ORR performance with half-wave potential up to 0.91 and 0.8 V(vs.reversible hydrogen electrode(RHE)),and long-term stability up to 10 h in both alkaline and acidic electrolytes.The remarkably enhanced ORR catalytic property of our as-developed DACs is in the rank of excellence for 1%.The as-developed rechargeable Zn-air battery(ZAB)with Fe/Co-SAs-Nx-PCNSs air cathode delivers ultrahigh power density of 216 mW·cm^(−2),outstanding specific capacity of 813 mAh·g^(−1),and promising cycling operation durability over 160 h.The flexible Zn-air battery also exhibits excellent specific capacity,cycling stability,and flexibility performance.This work opens up a new pathway for the multiscale design of efficient electrocatalysts with atomically dispersed multiple active sites.

Advanced all-solid-state lithium-selenium batteries enabled by selenium-nitrogen doped hierarchic meso-microporous carbon nanospheres composite cathode

Selenium,an element belonging to the same group in the periodic table as sulfur,has a high electronic conductivity(1×10^(-5)S/cm)and a high volumetric energy density(3253 mA h/cm^(3)),which is a prospective cathode material for high-energy all-solid-state rechargeable batteries.However,its wide use is hindered by large volume expansion and low utilization rate.In this work,Se-infused nitrogen-doped hierarchical meso-microporous carbon composites(Se/NHPC)are prepared by a melt-diffusion process.Amorphous Se is uniformly dispersed in meso-micropores of NHPC with a high mass loading of 81%.All-solid-state Li-Se batteries fabricated by using Se/NHPC as the cathode,a Li-In alloy as the anode,and Li_(6)PS_(5)Cl as the solid-state electrolyte,deliver a highly reversible capacity of 621 m Ah/g(92%of theoretical capacity),a good rate capability and a high capacity retention value of 80.9%after 100 cycles.It is found that the capacity decay of Se cathode is mainly related to the interfacial degradation and the separation of Se from the carbon substrate,as suggested by the continuous increase of interfacial resistance and the structural transformation from amorphous Senchains to Se8rings initial discharge/charge cycle and then to the trigonally crystalline Se chains structure after the long-term cycles.

Interlayer and doping engineering in partially graphitic hollow carbon nanospheres for fast sodium and potassium storage

Constructing anodes with fast ions/electrons transfer paths is an effective strategy to achieve high-performance sodium ion batteries(SIBs)/potassium ion batteries(PIBs). Amorphous carbon is a promising candidate anode for SIBs/PIBs owing to its disordered carbon layers, abundant defects/pores, and lowcost resources. However, the larger radius of Na^(+)/K^(+) leading to depressed kinetics and poor cycling performance, impeding their further applications. Herein, we propose an efficient strategy to construct of nitrogen, sulfur co-doped hollow carbon nanospheres(NS-HCS) involving an in situ growth of polydopamine on nano-Ni(OH)2template with subsequent sulfur doping process. During the formation process, the produced Ni nanospheres play as the hard template and catalyst for the formation of hollow carbon nanosphere with partially graphite microcrystalline structure, while the sulfur doping process can enlarge the interlayer space and create more defects on the surface of carbon nanospheres, thus synchronous improve the Na^(+)/K^(+) insertion and adsorption ability in NS-HCS. With the synergistic control of the enlarged interlayer spacing, high content of pyridinic N/pyrrolic N and graphitization, a hybrid storage mechanism facilitates the transport kinetics and endows the NS-HCS electrode with high capacities and good cycling stability in SIBs and PIB. Benefit from the multiple effects, NS-HCS exhibits the improved capacity of 274.8 m Ah/g at 0.1 A/g and excellent cycling stability of 149.5 m Ah/g after 5000 cycles at2.5A/g in SIBs, as well as good potassium ion storage behavior with a high capacity retention of 76.5%after 700 cycles at 1.0 A/g, demonstrating the potential applications of NS-HCS for high-performance SIBs and PIBs.

Highly Conductive Proton Selectivity Membrane Enabled by Hollow Carbon Sieving Nanospheres for Energy Storage Devices

Ion conductive membranes(ICMs)with highly conductive proton selectivity are of significant importance and greatly desired for energy storage devices.However,it is extremely challenging to construct fast proton-selective transport channels in ICMs.Herein,a membrane with highly conductive proton selectivity was fabricated by incorporating porous carbon sieving nanospheres with a hollow structure(HCSNs)in a polymer matrix.Due to the precise ion sieving ability of the microporous carbon shells and the fast proton transport through their accessible internal cavities,this advanced membrane presented a proton conductivity(0.084 S·cm^(-1))superior to those of a commercial Nation 212(N212)membrane(0.033S·cm^(-1))and a pure polymer membrane(0.049 S·cm^(-1)).The corresponding proton selectivity of the membrane(6.68×10^(5) S·min·cm^(-3))was found to be enhanced by about 5.9-fold and 4.3-fold,respectively,compared with those of the N212 membrane(1.13×10^(5) S·min·cm^(-3))and the pure membrane(1.56×10^(5) S·min·cm^(-3)).Low-field nuclear magnetic resonance(LF-NMR)clearly revealed the fast protonselective transport channels enabled by the HCSNs in the polymeric membrane.The proposed membrane exhibited an outstanding energy efficiency(EE)of 84%and long-term stability over 1400 cycles with a0.065%capacity decay per cycle at 120 mA·cm^(-2) in a typical vanadium flow battery(VFB)system.

Scalable synthesis of sub-lO0 nm hollow carbon nanospheres for energy storage applications

Sub-100 nm hollow carbon nanospheres with thin shells are highly desirable anode materials for energy storage applications. However, their synthesis remains a great challenge with conventional strategies. In this work, we demonstrate that hollow carbon nanospheres of unprecedentedly small sizes （down to - 32.5 nm and with thickness of - 3.9 nm） can be produced on a large scale by a templating process in a unique reverse micelle system. Reverse micelles enable a spatially confined Stober process that produces uniform silica nanospheres with significantly reduced sizes compared with those from a conventional Stober process, and a subsequent well-controlled sol-gel coating process with a resorcinol-formaldehyde resin on these silica nanospheres as a precursor of the hollow carbon nanospheres. Owing to the short diffusion length resulting from their hollow structure, as well as their small size and microporosity, these hollow carbon nanospheres show excellent capacity and cycling stability when used as anode materials for lithium/sodium-ion batteries.

Assembly of N-and P-functionalized carbon nanostructures derived from precursor-defined ternary copolymers for high-capacity lithiumion batteries

Synthesis of new carbon nanostructures with tunable properties is vital for precisely regulating electrochemical performance in the wide applications.Herein,we report a novel approach for the oxidative polymerization of N-and P-bearing copolymers from the self-assembly of three different monomers(aniline,pyrrole,and phytic acid),and further prepare the respective carbon nanostructures with relatively consistent N dopant(6.2%–8.0%,atom)and varying P concentrations(0.4%–2.8%,atom)via controllable pyrolysis.The impacts of phytic acid addition on the compositional,structural,and morphological evolution of the copolymers and the resulting nanocarbons are well studied through a spectrum of characterizations including N2 sorption,Fourier transform infrared spectroscopy,gel permeation chromatograph,scanning/transmission electron microscopy,and X-ray photoelectron spectroscopy.Gradual fragmentation of the nanosphere structures is evidenced with increasing addition of phytic acid,leading to different nanostructures from hollow nanospheres to 3D aggregates.Nanocarbons decorated with N and P dopants from pyrolysis are further utilized as anode materials in lithium-ion batteries,demonstrating enhanced electrochemical performance,i.e.,a reversible capacity of 380 mA
h
g^(-1)at 2 A
g^(-1)for NPC-0.5 during 200 cycles.The superior performance originates from the balanced porosity,and appropriate concentrations of P and pyrrolic N,thus pointing the direction for designing high-performance anode materials.

Graphitizing N-doped mesoporous carbon nanospheres via facile single atom iron growth for highly efficient oxygen reduction reaction

Single atom catalyst is of great importance for the oxygen reduction reaction(ORR).However,facile preparation of single atom catalyst without using well-designed precursors or labor-intensive acid leaching remains an urgent challenge.Herein,a simple pyrolysis of Fe3+-loaded mesoporous phenolic resin(mPF)-melamine precursor is used to prepare the single atom iron-anchored N-doped mesoporous graphitic carbon nanospheres(Fe/N-MGN).Investigation of the synthesis reveals the appropriate Fe-assisted catalysis effect and mPF template effect,which not only spurs the highly graphitic porous framework of Fe/N-MGN with plentiful pyridinic N/graphitic N,but also assures the dispersed single atom Fe anchoring without elaborated procedures.As a result,the as-synthesized Fe/N-MGN demonstrates high catalytic activity,good durability and excellent methanol tolerance for ORR.This work promises a facile method to regulate the graphitic carbon growth and single atom Fe loading for the highly efficient electrocatalysis.

Synthesis of MnO2/N-doped ultramicroporous carbon nanospheres for high-performance supercapacitor electrodes

We demonstrate a simple and highly efficient strategy to synthesize MnO2/nitrogen-doped ultramicroporous carbon nanospheres（MnO2/N-UCNs） for supercapacitor application.MnO2/N-UCNs were fabricated via a template-free polymerization of resorcinol/formaldehyde on the surface of phloroglucinol/terephthalaldehyde colloids in the presence of hexamethylenetetramine,followed by carbonization and then a redox reaction between carbons and KMnO4.As-prepared MnO2/N-UCNs exhibits regular ultramicropores,high surface area,nitrogen heteroatom,and high content of MnO2.A typical MnO2/N-UCNs with 57 wt.%MnO2 doping content（denoted as MnO2（57%）/N-UCNs） makes the most use of the synergistic effect between carbons and metal oxides.MnO2（57%）/N-UCNs as a supercapacitor electrode exhibits excellent electrochemical performance such as a high specific capacitance（401 F/g at 1.0 A/g） and excellent charge/discharge stability（86.3%of the initial capacitance after 10,000 cycles at 2.0 A/g） in 1.0 mol/L Na2SO4 electrolyte.The well-designed and high-performance MnO2/N-UCNs highlight the great potential for advanced supercapacitor applications.

Nanohollow Carbon for Rechargeable Batteries:Ongoing Progresses and Challenges

Among the various morphologies of carbon-based materials,hollow carbon nanostructures are of particular interest for energy storage.They have been widely investigated as electrode materials in different types of rechargeable batteries,owing to their high surface areas in association with the high surface-to-volume ratios,controllable pores and pore size distribution,high electrical conductivity,and excellent chemical and mechanical stability,which are beneficial for providing active sites,accelerating electrons/ions transfer,interacting with electrolytes,and giving rise to high specific capacity,rate capability,cycling ability,and overall electrochemical performance.In this overview,we look into the ongoing progresses that are being made with the nanohollow carbon materials,including nanospheres,nanopolyhedrons,and nanofibers,in relation to their applications in the main types of rechargeable batteries.The design and synthesis strategies for them and their electrochemical performance in rechargeable batteries,including lithium-ion batteries,sodium-ion batteries,potassium-ion batteries,and lithium–sulfur batteries are comprehensively reviewed and discussed,together with the challenges being faced and perspectives for them.

“On-off”switch for H_(2)and O_(2)generation from HCOOH resp.H_(2)O_(2)

In spite of the numerous advances in the development of H_(2)and O_(2)evolutions upon water splitting,the separation of H_(2)from O_(2)still remains a severe challenge.Herein,the novel dual-functional nanocatalysts Pd/carbon nanosphere(CNS),obtained via immobilization of ultrafine Pd nanoparticles onto CNS,are developed and employed for both selective H_(2)generation from HCOOH dehydrogenation and O_(2)evolution from H_(2)O_(2)decomposition.In these reactions,the highest activities for Pd/CNS-800(i.e.,calcinated at 800℃)are 2478 h−1 and 993 min^(−1)for H_(2)and O_(2)evolution,respectively.The highly efficient and selective“on-off”switch for selective H_(2)generation from HCOOH is successfully realized by pH adjustment.This novel and highly efficient nanocatalyst Pd/CNS-800 not only provides new approaches for the promising application of HCOOH and H_(2)O_(2)as economic and safe H_(2)and O_(2)carriers,respectively,for fuel cells,but also promotes the development of“on-off”switch for on-demand H_(2)evolution.