Hierarchically porous Co@N-doped carbon fiber assembled by MOF-derived hollow polyhedrons enables effective electronic/mass transport:An advanced 1D oxygen reduction catalyst for Zn-air battery

Developing advanced oxygen reduction reaction(ORR)electrocatalysts with rapid mass/electron transport as well as conducting relevant kinetics investigations is essential for energy technologies,but both still face ongoing challenges.Herein,a facile approach was reported for achieving the highly dispersed Co nanoparticles anchored hierarchically porous N-doped carbon fibers(Co@N-HPCFs),which were assembled by core-shell MOFs-derived hollow polyhedrons.Notably,the unique one-dimensional(1D)carbon fibers with hierarchical porosity can effectively improve the exposure of active sites and facilitate the electron transfer and mass transfer,resulting in the enhanced reaction kinetics.As a result,the ORR performance of the optimal Co@N-HPCF catalysts remarkably outperforms that of commercial Pt/C in alkaline solution,reaching a limited diffusion current density(J)of 5.85 m A cm^(-2)and a half-wave potential(E_(1/2))of 0.831 V.Particularly,the prepared Co@N-HPCF catalysts can be used as an excellent air-cathode for liquid/solid-state Zn-air batteries,exhibiting great potentiality in portable/wearable energy devices.Furthermore,the reaction kinetic during ORR process is deeply explored by finite element simulation,so as to intuitively grasp the kinetic control region,diffusion control region,and mixing control region of the ORR process,and accurately obtain the relevant kinetic parameters.This work offers an effective strategy and a reliable theoretical basis for the engineering of first-class ORR electrocatalysts with fast electronic/mass transport.

Hierarchically porous Fe/N/S/C nanospheres with high-content of Fe-Nx for enhanced ORR and Zn-air battery performance

Heteroatom-doped carbon-based transition-metal single-atom catalysts(SACs) are promising electrocatalysts for oxygen reduction reaction(ORR). Herein, with the aid of hierarchically porous silica as hard template, a facile and general melting perfusion and mesopore-confined pyrolysis method was reported to prepare single-atomic Fe/N–S-doped carbon catalyst(FeNx/NC-S) with hierarchically porous structure and well-defined morphology. The FeNx/NC-S exhibited excellent ORR activity with a half-wave potential(E_(1/2)) of 0.92 V, and a lower overpotential of 320 mV at a current density of 10 mA cm^(-2)for OER under alkaline condition. The remarkable electrocatalysis performance can be attributed to the hierarchically porous carbon nanospheres with S doping and high content of Fe-Nx sites(up to 3.7 wt% of Fe), resulting from the nano-confinement effect of the hierarchically porous silica spheres(NKM-5) during the pyrolysis process. The rechargeable Zn-air battery with FeNx/NC-S as a cathode catalyst demonstrated a superior power density of 194.5 mW cm-2charge–discharge stability. This work highlights a new avenue to design advanced SACs for efficient sustainable energy storage and conversion.

Preparation and performance of hierarchically porous carbons as oxygen electrodes for lithium oxygen batteries

The hierarchically porous carbons （HPCs） were prepared by sol-gel selassembly technology in different surfactant concentrations and were used as the potential electrode for lithium oxygen batteries. The physical and electrochemical properties of the as-prepared HPCs were investigated by filed emission scanning electron microscopy （FE-SEM）, transmission electron microscopy （TEM）, nitrogen adsorption-desorption isotherm and galvanostatic charge/discharge. The results indicate that all of the HPCs mainly possess mesoporous structure with nearly similar pore size distribution. Using the HPCs as the electrode, a high discharge capacity for lithium oxygen battery can be achieved, and the discharge capacity increases with the specific surface area. Especially, the HPCs-3 oxygen electrode with CTAB concentration of 0.27 mol/L exhibits good capacity retention through controlling discharge depth to 800 mA·h/g and the highest discharge capacity of 2050 mA·h/g at a rate of 0.1 mA/cm2.

Hierarchically porous nitrogen-doped carbon as cathode for lithium–sulfur batteries

Porous nitrogen-doped carbon is an especially promising material energy storage due to its excellentconductivity, stable physicochemical properties, easy processability, controllable porosity and low price.Herein, we reported a novel well-designed hierarchically porous nitrogen-doped carbon （HPNC） via acombination of salt template （ZnC12） and hard template （SiO2） as sulfur host for lithium-sulfur batter-ies. The low-melting ZnC12 is boiled off and leaves behind micropores and small size mesopores duringpyrolysis process, while the silica spheres are removed by acid leaching to generate interconnected 3Dnetwork of macropores. The HPNC-S electrode exhibits an initial specific capacity of 1355 mAh g^-l at 0.IC （IC= 1675 mAh g^-1 ）, a high-rate capability of 623 mAh g-l at 2 C, and a small decay of 0.13% per cycleover 300 cycles at 0.2 C. This excellent rate capability and remarkable long-term cyclability of the HPNC-Selectrode are attributed to its hierarchical porous structures for confining the soluble lithium polysulfideas well as the nitrogen doping for high absorbability of lithium polysulfide.

Hierarchically porous Cu current collector with lithiophilic CuxO interphase towards high-performance lithium metal batteries

Lithium metal is one of the most promising anode materials for next-generation electrochemical energy storage due to low electrochemical potential and high specific capacity.However,large volume change and uncontrollable formation of lithium dendrite during cycling severely hinder the practical application of rechargeable Li metal batteries.Herein,we report a hierarchically porous Cu covered with lithiophilic CuxO(HPCu-CuxO) via femtosecond laser strategy in about 2 min as current collector for highperformance Li metal batteries.With precisely tunable pore volume and depth as well as lithiophilic CuxO interphase,the HPCu-CuxO not only guides homogeneous Li nucleation,resulting in a smooth and dendrite-free lithium surface,but also provides space to alleviate the volume expansion of Li metal anode,achieving excellent structure stability.Consequently,highly stable Coulombic efficiency and ultralow overpotential of 15 mV even up to 1000 h were achieved at the current density of 1 mA cm^(-2).Moreover,the resultant Li@HPCu-CuxO//LiFePO_(4) full battery delivered outstanding cycle stability and rate capability.These results offer a pathway toward high-energy-density and safe rechargeable Li metal batteries.

Hierarchically porous S-scheme CdS/UiO-66 photocatalyst for efficient 4-nitroaniline reduction

Unveiling the pore-size performance of metal organic frameworks(MOFs)is imperative for controllable design of sophisticated catalysts.Herein,UiO-66 with distinct macropores and mesopores were intentionally created and served as substrates to create advanced CdS/UiO-66 catalysts.The pore size impacted the spatial distribution of CdS nanoparticles(NPs):CdS tended to deposit on the external surface of mesoporous UiO-66,but spontaneously penetrated into the large cavity of macroporous UiO-66 nanocage.Normalized to unit amount of CdS,the photocatalytic reaction constant of macroporous CdS/UiO-66 over 4-nitroaniline reduction was~3 folds of that of mesoporous counterpart,and outperformed many other reported state-of-art CdS-based catalysts.A confinement effect of CdS NPs within UiO-66 cage could respond for its high activity,which could shorten the electron-transport distance of NPs-MOFs-reactant,and protect the active CdS NPs from photocorrosion.The finding here provides a straightforward paradigm and mechanism to rationally fabricate advance NPs/MOFs for diverse applications.

Self-supporting and hierarchically porous Ni_(x)Fe-S/NiFe_(2)O_(4) heterostructure as a bifunctional electrocatalyst for fluctuating overall water splitting

Stable non-noble metal bifunctional electrocatalysts are one of the challenges to the fluctuating overall water splitting driven by re-newable energy.Herein,a novel self-supporting hierarchically porous Ni_(x)Fe-S/NiFe_(2)O_(4) heterostructure as bifunctional electrocatalyst was constructed based on porous Ni-Fe electrodeposition on three-dimensional(3D)carbon fiber cloth,in situ oxidation,and chemical sulfuration.Results showed that the Ni_(x)Fe-S/NiFe_(2)O_(4) heterostructure with a large specific surface area exhibits good bifunctional activity and stability for both hydrogen evolution reaction(HER)and oxygen evolution reaction(OER)because of the abundance of active sites,synergistic effect of the heterostructure,superhydrophilic surface,and stable,self-supporting structure.The results further confirmed that the Ni_(x)Fe-S phase in the heterostructure is transformed into metal oxides/hydroxides and Ni_(3)S_(2) during OER.Compared with the commercial 20wt%Pt/C||IrO_(2)-Ta_(2)O_(5) electrolyzer,the self-supporting Ni1/5Fe-S/NiFe_(2)O_(4)||Ni1/2Fe-S/NiFe_(2)O_(4) electrolyzer exhibits better stability and lower cell voltage in the fluctu-ating current density range of 10-500 mA/cm^(2).Particularly,the cell voltage of Ni1/5Fe-S/NiFe_(2)O_(4)||Ni1/2Fe-S/NiFe_(2)O_(4) is only approximately 3.91 V at an industrial current density of 500 mA/cm^(2),which is lower than that of the 20wt%Pt/C||IrO_(2)-Ta_(2)O_(5) electrolyzer(i.e.,approximately 4.79 V).This work provides a promising strategy to develop excellent bifunctional electrocatalysts for fluctuating overall water splitting.

Recent advances in the synthesis of nanoscale hierarchically porous metal–organic frameworks

Nanoscale hierarchically porous metal–organic frameworks(NHP-MOFs)have received unprecedented attention in many fields owing to their integration of the strengths of nanoscale size(<1μm)and hierarchical porous structure(micro-,meso-and/or macro-pores)of MOFs.This review focuses on recent advances in the main synthetic strategies for NHP-MOFs based on different metal ions(e.g.,Cu,Fe,Co,Zn,Al,Zr,and Cr),including the template method,composite technology,post-synthetic modification,in situ growth and the grind method.In addition,the mechanisms of synthesis,regulation techniques and the advantages and disadvantages of various methods are discussed.Finally,the challenges and prospects of the commercialisation of promising NHP-MOFs are also presented.The purpose of this review is to provide a road map for future design and development of NHP-MOFs for practical application.

Nitrogen and sulfur co-doped graphene aerogel with hierarchically porous structure for high-performance supercapacitors

Supercapacitors with unique performance have been widely utilized in many fields. Herein, we report a nitrogen and sulfur co-doped graphene aerogel(N/S-GA-2) prepared using a low toxic precursor for high-performance supercapacitors. The as-obtained material possesses a hierarchically porous structure and a large number of electrochemical active sites. At a current density of 1 Ag^-1, the specific capacitance of the N/S-GA-2 for supercapacitors with the ionic liquid as the electrolyte is 169.4 Fg^-1, and the corresponding energy density is 84.5 Wh kg^-1.At a power density of 8.9 k W kg^-1, the energy density can reach up to 75.7 Wh kg^-1, showing that the N/S-GA-2 has an excellent electrochemical performance. Consequently, the N/S-GA-2 can be used as a promising candidate of electrode materials for supercapacitors with high power density and high energy density.

Nitrogen-rich hierarchically porous carbon foams as high-performance electrodes for lithium-based dual-ion capacitor

Nitrogen-rich porous carbonaceous materials have shown great potential in energy storage and conversion applications due to their facile fabrication,high electronic conductivity,and improved hydrophilic property.Herein,three-dimensional porous N-rich carbon foams are fabricated through a one-step carbonization-activation method of the commercial melamine foam,and displaying hierarchically porous structure(macro-,meso-,and micro-pores),large surface area(1686.5 m2 g^-1),high N-containing level(3.3 at%),and excellent compressibility.The as-prepared carbon foams as electrodes for quasi-solid-state supercapacitors exhibit enhanced energy storage ability with 210 F g^-1 and 2.48c at 0.1 A g^-1,and150 F g^-1 and 1.77 F cm^-2 at 1 A g^-1,respectively.Moreover,as an electrode for lithium-based dual-ion capacitor,this distinctive porous carbon also delivers remarkable specific capacitance with 143.6 F g^-1 at0.1 A g^-1 and 116.2 F g^-1 at 1 A g^-1.The simple preparation method and the fascinating electrochemical performance endow the N-rich porous carbon foams great prospects as high-performance electrodes for electrochemical energy storage.

Cocoon Silk-Derived, Hierarchically Porous Carbon as Anode for Highly Robust Potassium-Ion Hybrid Capacitors

Potassium-ion hybrid capacitors(KIHCs) have attracted increasing research interest because of the virtues of potassium-ion batteries and supercapacitors.The development of KIHCs is subject to the investigation of applicable K+storage materials which are able to accommodate the relatively large size and high activity of potassium.Here,we report a cocoon silk chemistry strategy to synthesize a hierarchically porous nitrogen-doped carbon(SHPNC).The as-prepared SHPNC with high surface area and rich N-doping not only offers highly efficient channels for the fast transport of electrons and K ions during cycling,but also provides sufficient void space to relieve volume expansion of electrode and improves its stability.Therefore,KIHCs with SHPNC anode and activated carbon cathode afford high energy of 135 Wh kg-1(calculated based on the total mass of anode and cathode),long lifespan,and ultrafast charge/slow discharge performance.This study defines that the KIHCs show great application prospect in the field of high-performance energy storage devices.

Enhanced stability of highly-dispersed copper catalyst supported by hierarchically porous carbon for long term selective hydrogenation

Copper based catalysts have high potential for the substituent of noble-metal based catalysts as their high selectivity and moderate activity for selective hydrogenation reaction;however,achieving further high catalytic stability is very difficult.In this work,the carbonization process of Cu-based organic frameworks was explored for the synthesis of highly-dispersed Cu supported by hierarchically porous carbon with high catalytic performance for selective hydrogenation of 1,3-butadiene.The porous hierarchy of carbon support and the dispersion of copper nanoparticles can be precisely tuned by controlling the carbonization process.The resultant catalyst carbonized at 600°C exhibits a rather low reaction temperature at 75°C for 100%butadiene conversion with 100%selectivity to butenes,due to its reasonable porous hierarchy and highly-dispersed copper sites.More importantly,unprecedentedly stability of the corresponding Cu catalyst was firstly observed for selective 1,3-butadiene hydrogenation,with both 100%butadiene conversion and 100%butenes selectivity over 120 h of reaction at 75°C.This study verifies that a simply control the carbonization process of metal organic frameworks can be an effective way to obtain Cu-based catalysts with superior catalytic performance for selective hydrogenation reaction.

Rambutan-like hierarchically porous carbon microsphere as electrodematerial for high-performance supercapacitors

Used as high-performance electrodes,both structural and compositional alterations of carbon materials play very important roles in energy conversion/storage devices.Especially in supercapacitors,hierarchical pores and heteroatom doping in carbon materials are indispensable.Here the rambutan-like hierarchically porous carbon microspheres(PCMs)have been constructed via a hydrothermal treatment,followed by carbonization/activation.The hierarchically porous microstructure is composed of three-dimensional porous carbon networks,which give rise to a large surface area.Moreover,N and O functional groups are introduced in the as-prepared samples,which could generate the extra pseudocapacitance.Benefitting from the interconnected hierarchical and open structure,PCM exhibits outstanding capacitive performance,for example,superior specific capacitance and rate capability(397 and 288 F g^(−1) at 0.5 and 20A g^(−1),respectively),as well as long cycling stability(about 95%capacitance retention after 10,000 cycles).These encouraging results may pave an efficient way to fabricate advanced supercapacitors in the future.

Three-dimensional ordered hierarchically porous carbon materials for high performance Li-Se battery

Developing host materials with high specific surface area, good electron conductivity, and fast ion transportation channel is critical for high performance lithium-selenium(Li-Se) batteries. Herein, a series of three dimensional ordered hierarchically porous carbon(3D OHPC) materials with micro/meso/macropores are designed and synthesized for Li-Se battery. The porous structure is tuned by following the concept of the generalized Murray’s law to facilitate the mass diffusion and reduce ion transport resistance.The optimized 3D Se/OHPC cathode exhibits a very high 2 nd discharge capacity of 651 m Ah/g and retains 361 m Ah/g after 200 cycles at 0.2 C. Even at a high current rate of 5 C, the battery still shows a discharge capacity as high as 155 m Ah/g. The improved electrochemical performance is attributed to the synergy effect of the interconnected and well-designed micro, meso and macroporosity while shortened ions diffusion pathways of such Murray materials accelerate its ionic and electronic conductivities leading to the enhanced electrochemical reaction. The diffusivity coefficient in Se/OHPC can reach a very high value of 1.3 × 10^(-11)cm^(2)/s, much higher than those in single pore size carbon hosts. Their effective volume expansion accommodation capability and reduced dissolution of polyselenides ensure the high stability of the battery. This work, for the first time, established the clear relationship between textural properties of cathode materials and their performance and demonstrates that the concept of the generalized Murray’s law can be used as efficient guidance for the rational design and synthesis of advanced hierarchically porous materials and the great potential of 3D OHPC materials as a practical high performance cathode material for Li-Se batteries.

Seaweed-Derived Hierarchically Porous Carbon for Highly Efficient Removal of Tetracycline

Herein we present a facile approach for the preparation of a novel hierarchically porous carbon,in which seaweeds serve as carbon source and KOH as activator.The fabricated KOH-activated seaweed carbon(KSC)displays strong affinity towards tetracycline with maximum uptake quantity of 853.3 mg/g,significantly higher than other tetracycline adsorbents.The superior adsorption capacity ascribes to large specific surface area(2614 m^(2)/g)and hierarchically porous structure of K-SC,along with strongπ-πinteractions between tetracycline and KSC.In addition,the as-prepared K-SC exhibits fast adsorption kinetics,capable of removing99%of tetracycline in 30 min.Meanwhile,the exhausted K-SC can be regenerated for four cycling adsorption without an obvious degradation in capacities.More importantly,p H and ionic strengths barely affect the adsorption performance of K-SC,implying electrostatic interactions hardly play any role in tetracycline adsorption process.Furthermore,the K-SC packed fixed-bed column(0.1 g of adsorbents)can continually treat 2780 m L solution spiked with 5.0 mg/g tetracycline before reaching the breakthrough point.All in all,the fabricated K-SC equips with high adsorption capacity,fast adsorption rate,glorious anti-interference capability and good reusability,which make it hold great feasibilities for treating tetracycline contamination in real applications.

Natural Fresh Proteins Directed Hierarchically Porous Nitrogen-doped TiO_(2) as with High Performance as Photocatalyts and Electrode Materials

Fresh EPF proteins from Liangzi Lake were employed as a template to synthesize hierarchically porous nitrogen-doped TiO_(2) in a single process.The experimental results show that N-TiO_(2) sample exhibits significantly enhanced visible-light photocatalytic activity in both chemical waste treatment and hydrogen production,and the visible-light photocatalytic activities vary with the concentrations of EPF proteins.The optimal concentration of protein is 600 mg·mL^(-1) and the degradation of RhB could be almost completed in just 25 min.Furthermore,the performance of as-synthesized TiO2 as an electrode for Li-ion battery can be also regulated by the EPF proteins.Natural extrapallial fluid(EPF)proteins extracted from the same kind of mussels living in different regions have significantly different effects on the performances of TiO_(2) as electrode materials for Li-ion battery.The present work highlights the unimaginable effects of natural organic matrix on the synthesis of advanced materials with optimized functional properties.

Ultra-stable and High-rate Lithium Ion Batteries Based on Metal-organic Framework-derived ln2O3 Nanocrystals/Hierarchically Porous Nitrogen-doped Carbon Anode

Exploring electrode materials with attractive specific capacity and prominent cyclic durability is of the essence for promoting lithium ion batteries(LIBs).In2O3 has shown an extraordinary promise for LIBs with advantageous gravimetric capacity(theoretically 965 mA h g-1) and low working voltage.However,In2O3 still suffers from the inherent weaknesses of metal oxides in practical application,especially low conductivity and incorrigible volume expansion upon the cycling process.Here,we demonstrate the architecture of metal-organic framework(MOF)-derived In2O3 nanocrystals/hierarchically porous nitrogen-doped carbon composite(In2O3/HPNC) for ultra-stable LIBs anode.This hierarchically porous structure(micro/meso/macro-pores) with nitrogen doping not only ensures exceptional mechanical strength and accommodates the volume expansion of In2O3 nanocrystals,but also offers electrons and lithium ions efficient interpenetrating pathways to migrate rapidly during charge/discharge processes.Thus,In2O3/HPNC exhibits excellent cyclic stability with a high specific capacity of 623 mA h g-1 over2000 cycles at 1000 mA g-1,corresponding to an ultra-low specific capacity decay of 0.017% per cycle(the best among the ln203-based anode for LIBs),and outstanding rate performance,suggesting a critical step toward achieving long-life and high-rate LIBs in practical devices.

Hierarchically porous Fe_2O_3 /CuO composite monoliths:Synthesis and characterization

In this paper,hierarchically porous Fe2O3 /CuO composite monoliths were first successfully synthesized by a mild method using silica monoliths as templates.The structure of composite monoliths was characterized by X-ray diffraction,scanning electron microscopy,nitrogen adsorption-desorption.The results indicated that the molar ratio of Fe to Cu had a great influence on the crystal phase of Fe2O3,pore size and the structure of the macroporous wall.The Fe2O3 /CuO composite monoliths consist of hierarchically macroporous and mesoporous structure,while the sample with the Fe/Cu molar ratio of 2：1 possesses tighter wall structure than other samples.It is expected that asprepared Fe2O3/CuO composite monoliths have potential applications in several fields as catalysts,catalyst supports,chemical sensors and high-performance liquid chromatography （HPLC）.

Boosting ethanol oxidation over nickel oxide through construction of quasi-one-dimensional morphology and hierarchically porous structure

Quasi-one-dimensional NiO with a hierarchically porous structure was synthesized through a facile coordination−precipitation method with the coupling effect of ammonia and a post-calcination treatment.The electrocatalytic properties of NiO fibers for the oxidation of ethanol were compared with those of NiO spheres.The results show that the fibrous NiO possesses a larger specific surface area of 140.153 m2/g and a lower electrical resistivity of 4.5×105Ω·m,leading to an impressively superior electrocatalytic activity to spherical NiO for ethanol oxidation in alkaline media.The current decay on fibrous NiO at 0.6 V in 100−900 s was 0.00003%,which is much lower than that of spherical NiO,indicating its better stability.The unique morphology and hierarchically porous structure give the fibrous NiO great potential to be used as an anodic electrocatalyst for direct ethanol fuel cells.

3D hierarchically porous NiO/Graphene hybrid paper anode for long-life and high rate cycling flexible Li-ion batteries

With the rapid emergence of wearable devices, flexible lithium-ion batteries(LIBs) are much more needed than ever. Free-standing graphene-based composite paper electrodes with various active materials have appealed wide applications in flexible LIBs. However, due to the prone-to-restacking feature of graphene layers, a long cycle life at high current densities is rather difficult to be achieved. Herein, a unique threedimensional(3D) hierarchically porous NiO micro-flowers/graphene paper(fNiO/GP) electrode is successfully fabricated. The resulting fNiO/GP electrode shows superior long-term cycling stability at high rates(e.g., storage capacity of 359 mAh/g after 600 cycles at a high current density of 1 A/g). The facile 3D porous structure combines both the advantages of the graphene that is highly conductive and flexible to ensure rapid electrons/ions transfer and buffer the volume expansion of NiO during charge/discharge,and of the micro-sized NiO flowers that induces hierarchical between-layer pores ranging from nanomicro meters to promote the penetration of the electrolyte and prevent the re-stacking of graphene layers. Such structural design will inspire future manufacture of a wide range of active materials/graphene composite electrodes for high performance flexible LIBs.