Phase-junctions between a cocatalyst and its semiconductor host are quite effective to enhance the photocatalytic activity and are widely studied, while reports on the phase-juncted cocatalyst are still rare. In this work, we report the deposition of the Pt/PtO phase-juncted nanodots as cocatalyst via NaOH modification of an interconnected meso-macroporous TiO2 network with high surface area and inner-particle mesopores to enhance the performance of photocatalytic H2 production. Our results show that NaOH modification can largely influence Pt/PtO phase-juncted nanodot formation and dispersity. Compared to the TiO2 nanoparticles, the hierarchically meso-macroporous TiO2 network containing 0.18 wt % Pt/PtO phase-juncted cocatalyst demonstrates a highest photocatalytic H2 rate of 13 mmol g–1 h–1 under simulated solar light, and possesses a stable cycling activity without obvious decrease after five cycles. Such high H2 production performance can be attributed to both the phase-juncted Pt/PtO providing more active sites while PtO suppresses the undesirable hydrogen back reaction, and the special hierarchically porous TiO2 network with inner-particle mesopores presenting short diffusion path lengths for photogenerated electrons and enhanced light harvesting efficiency. This work suggests that Pt/PtO phase-juncted cocatalyst on hierarchically porous TiO2 nanostructures is a promising strategy for advanced photocatalytic H2 production.Keywords: biomolecular self-assembly; cocatalyst; hierarchically meso-macroporous TiO2; photocatalytic H2 production; Pt/PtO phase-junction nanodots;

Owing to their immense potential in energy conversion and storage, catalysis, photocatalysis, adsorption, separation and life science applications, significant interest has been devoted to the design and synthesis of hierarchically porous materials. The hierarchy of materials on porosity, structural, morphological, and component levels is key for high performance in all kinds of applications. Synthesis and applications of hierarchically structured porous materials have become a rapidly evolving field of current interest. A large series of synthesis methods have been developed. This review addresses recent advances made in studies of this topic. After identifying the advantages and problems of natural hierarchically porous materials, synthetic hierarchically porous materials are presented. The synthesis strategies used to prepare hierarchically porous materials are first introduced and the features of synthesis and the resulting structures are presented using a series of examples. These involve templating methods (surfactant templating, nanocasting, macroporous polymer templating, colloidal crystal templating and bioinspired process, i.e. biotemplating), conventional techniques (supercritical fluids, emulsion, freeze-drying, breath figures, selective leaching, phase separation, zeolitization process, and replication) and basic methods (sol–gel controlling and post-treatment), as well as self-formation phenomenon of porous hierarchy. A series of detailed examples are given to show methods for the synthesis of hierarchically porous structures with various chemical compositions (dual porosities: micro–micropores, micro–mesopores, micro–macropores, meso–mesopores, meso–macropores, multiple porosities: micro–meso–macropores and meso–meso–macropores). We hope that this review will be helpful for those entering the field and also for those in the field who want quick access to helpful reference information about the synthesis of new hierarchically porous materials and methods to control their structure and morphology.

Solar light is widely recognized as one of the most valuable renewable energy sources for the future. However, the development of solar-energy technologies is severely hindered by poor energy-conversion efficiencies due to low optical-absorption coefficients and low quantum-conversion yield of current-generation materials. Huge efforts have been devoted to investigating new strategies to improve the utilization of solar energy. Different chemical and physical strategies have been used to extend the spectral range or increase the conversion efficiency of materials, leading to very promising results. However, these methods have now begun to reach their limits. What is therefore the next big concept that could efficiently be used to enhance light harvesting? Despite its discovery many years ago, with the potential for becoming a powerful tool for enhanced light harvesting, the slow-photon effect, a manifestation of light-propagation control due to photonic structures, has largely been overlooked. This review presents theoretical as well as experimental progress on this effect, revealing that the photoreactivity of materials can be dramatically enhanced by exploiting slow photons. It is predicted that successful implementation of this strategy may open a very promising avenue for a broad spectrum of light-energy-conversion technologies.

•BiVO4@3DOM TiO2 exhibit highly enhanced visible light photocatalytic activity.•The effect of the amount of BiVO4 as visible light sensitizer is highlighted.•The electronic interactions BiVO4/TiO2 lead to an improved charge separation.•High BiVO4 content leads to the accumulation of the electron/hole pairs at the surface of the BiVO4.A series of BiVO4/3DOM TiO2 nanocomposites have been synthesized and their photocatalytic activity was investigated under visible light irradiation using the RhB dye as model pollutant molecule in an aqueous solution. The effect of the amount of BiVO4 as visible light sensitizer on the photocatalytic activity of BiVO4/3DOM TiO2 nanocomposites was highlighted. The heterostructured composite system leads to much higher photocatalytic efficiencies than bare 3DOM TiO2 and BiVO4 nanoparticles. As the proportion of BiVO4 in BiVO4/3DOM TiO2 nanocomposites increases from 0.04 to 0.6, the photocatalytic performance of the BiVO4/3DOM TiO2 nanocomposites increases and then decreases after reaching a maximum at 0.2. This improvement in photocatalytic perfomance is related to 1) the interfacial electron transfer efficiency between the coupled materials, 2) the 3DOM TiO2 inverse opal structure with interconnected pores providing an easy mass transfer of the reactant molecules and high accessibility to the active sites and large surface area and 3) the effect of light sensitizer of BiVO4. Intensive studies on structural, textural, optical and surface properties reveal that the electronic interactions between BiVO4 and TiO2 lead to an improved charge separation of the coupled BiVO4/TiO2 system. The photogenerated charge carrier densities increase with increasing the BiVO4 content, which acts as visible light sensitizer to the TiO2 and is responsible for the enhancement in the rate of photocatalytic degradation. However, the photocatalytic activity is reduced when the BiVO4 amount is much higher than that of 3DOM TiO2. Two reasons could account for this behavior. First, with increasing BiVO4 content, the photogenerated electron/hole pairs are accumulated at the surface of the BiVO4 nanoparticles and the recombination rate increases as shown by the PL results. Second, decreasing the amount of 3DOM TiO2 in the nanocomposite decreases the surface area as shown by the BET results. Moreover, the poor adsorptive properties of the BiVO4 photocatalyst also affect the photocatalytic performance, in particular at higher BiVO4 content. The present work demonstrates that BiVO4/3DOM TiO2 is a very promising heterojunction system for visible light photocatalytic applications.The effect of the amount of BiVO4 as visible light sensitizer on the photocatalytic activity of BiVO4/3DOM TiO2 nanocomposites was highlighted. The low amount of BiVO4 nanoparticles favors the transfer of photogenerated electrons to 3DOM TiO2 while photogenerated electrons will remain at the surface of BiVO4 at high amount of BiVO4, leading to the recombination of electrons-holes and reduced photocatalytic activity.Download high-res image (254KB)Download full-size image

•An alkali modification process produces highly dispersed ultrafine Pt nanoclusters.•Ultrafine Pt nanoclusters have metallic Pt0 and oxidized Pt2+ species.•NYTiO2 as a model photocatalyst for H2 production.•NYTiO2-Pt with Pt0 and Pt2+ species as light harvesting reactor for efficient H2 production.We demonstrate an alkali modification process to produce highly dispersed ultrafine Pt nanoclusters with metallic Pt0 and oxidized Pt2+ species as co-catalyst anchored on nanosheet-constructed yolk-shell TiO2 (NYTiO2-Pt) acting as light harvesting reactor for highly efficient photocatalytic H2 production. Benefiting from the high surface area, highly dispersed ultrafine Pt nanoclusters (~0.6 nm) with Pt0 and Pt2+ species and special nanosheet-constructed yolk-shell structure, this novel light harvesting reactor exhibits excellent performance for photocatalytic H2 production. The NYTiO2-Pt-0.5 (0.188 wt% Pt) demonstrates an unprecedentedly high H2 evolution rate of 20.88 mmol h−1 g−1 with excellent photocatalytic stability, which is 87 times than that of NYTiO2-Pt-3.0 (0.24 mmol h−1 g−1, 1.88 wt% Pt), and also much higher than those of other TiO2 nanostructures with the same Pt content. Such H2 evolution rate is the highest reported for photocatalytic H2 production with such a low Pt content under simulated solar light. Our strategy here suggests that via alkali modifying the photocatalysts, we can not only enhance the H2 production for solar energy conversion but also significantly decrease the noble metal content for cost saving.An alkali modified nanosheet-constructed yolk-shell NYTiO2-Pt light harvesting reactor has been designed for highly efficient photocatalytic H2 production under simulated solar light. Owing to the high surface area, highly dispersed Pt nanoclusters with metallic Pt0 and oxidized Pt2+ species and special yolk-shell structure, the NYTiO2-Pt-0.5 (0.188 wt% Pt) demonstrates an H2 evolution rate of (20.88 mmol h−1 g−1) with excellent photocatalytic stability under simulated solar light.Download high-res image (191KB)Download full-size image

Lithium–sulfur (Li–S) batteries are receiving significant attention as an alternative power system for advanced electronic devices because of their high theoretical capacity and energy density. In this work, we have designed manganese dioxide (MnO2) nanosheet functionalized sulfur@poly(3,4-ethylenedioxythiophene) core–shell nanospheres (S@PEDOT/MnO2) for high performance lithium–sulfur (Li–S) batteries. A PEDOT layer is used to address the low electrical conductivity of sulfur and acts as a protective layer to prevent dissolution of polysulfides. The MnO2 nanosheets functionalized on PEDOT further provide a high active contact area to enhance the wettability of the electrode materials with electrolytes and further interlink the polymer chains to improve the conductivity and stability of the composite. As a result, S@PEDOT/MnO2 exhibits an improved capacity of 827 mA h g−1 after 200 cycles at 0.2C (1C = 1673 mA g−1) and a further ∼50% enhancement compared to S@PEDOT (551 mA h g−1) without MnO2 functionalization. In particular, the discharge capacity of S@PEDOT/MnO2 is 545 mA h g−1 after 200 cycles at 0.5C. Our demonstration here indicates that the functionalization of inorganic nanostructures on conducting polymer coated sulfur nanoparticles is an effective strategy to improve the electrochemical cycling performance and stability of sulfur cathodes for Li–S batteries.

Unique walnut-shaped porous MnO2/carbon nanospheres (P-MO/C-NSs) with high monodispersity have been designed and prepared for lithium storage via in situ carbonization of amorphous MnO2 nanospheres. Polyvinylpyrrolidone (PVP) is utilized as both the surfactant for morphology control and carbon source for carbon scaffold formation accompanied with MnO2 crystallization. Such a unique walnut-shaped porous nanostructure with an intimate carbon layer provides a large contact area with the electrolyte, short transport path length for Li+, low resistance for charge transfer and superior structural stability. The P-MO/C-NS electrode demonstrates high lithium storage capacity (1176 mA h g−1 at 100 mA g−1), very good cycling stability (100% capacity retention versus the second cycle) and excellent rate capability (540 mA h g−1 at 1000 mA g−1). We propose that it is the deep oxidation of Mn2+ to Mn3+ in P-MO/C-NSs, which results in an extraordinarily high capacity of 1192 mA h g−1 at a current density of 1000 mA g−1 after a long period of cycling, very close to the maximum theoretical reversible capacity of MnO2 (1230 mA h g−1). This is the highest value ever observed for MnO2-based electrodes at such a rate. The high lithium storage capacity and rate capability can be attributed to the enhanced reaction kinetics owing to the walnut-shaped porous nanostructure with an intimate carbon layer. This work provides a meaningful demonstration of designing porous nanostructures of carbon-coated metal oxides undergoing deep conversion reactions for enhanced electrochemical performances.

Three-dimensional (3D) macro–mesoporous structures demonstrate effective performance for gas sensing. In this work, we have designed and successfully prepared aperture-controllable three-dimensional interconnected macro–mesoporous ZnO (3D-IMM-ZnO) nanostructures by template-based layer-by-layer filtration deposition. XRD, SEM, and TEM have been used to characterize the obtained hexagonal wurzite 3D-IMM-ZnO nanostructures. Owing to its special 3D interconnected hierarchically porous structure, the 3D-IMM-ZnO nanostructures exhibit excellent gas sensing performances toward acetone and methanol. The 3D-IMM-ZnO nanostructure with the largest macropore demonstrates the best gas sensitivity owing to its largest cavity providing enough space for gas diffusion. On the basis of the results and analyses, we propose that the synergistic effect of electron liberation and electron density of acetone and the special structure make the 3D-IMM-ZnO nanostructures demonstrate better gas sensing properties than many other porous ZnO nanostructures and preferred selectivity to acetone.Keywords: 3D interconnected macro−mesoporous ZnO; acetone; gas sensor; methanol; selectivity

Hierarchically porous TiO2/carbon hollow spheres (TiO2/C-HS) have been designed and prepared through a facile one-pot template-free hydrothermal route using sucrose as a carbon source, TiO2 solid spheres as a TiO2 source and NH4F as a structure-directing reagent. The nanocrystal constructed hierarchically porous hollow spherical structure offers enough space for electrolyte penetration and storage and a short path length for Li+ diffusion and e− transport. The carbon layer on TiO2 surface improves its conductivity as well as the structure stability. As a result, such a special hollow structure with carbon layers exhibits enhanced lithium storage properties comparing with the solid spheres. The TiO2/C-HS anode exhibits discharge capacities of 286, 235, 197, 164 and 127 mA h g−1 at various rates of 0.2, 0.5, 1, 2 and 5C (1C = 168 mA g−1), respectively. A capacity of 175 mA h g−1 still remains after 200 cycles at 1C, demonstrating a very high lithium insertion coefficient of 0.52, a little higher than the theoretical value of 0.5. SEM, TEM, HRTEM and electrochemical impedance spectra (EIS) techniques have been utilized to understand the Li+ insertion process and structural stability. Our results reveal that the high electrochemical performance of the TiO2/C-HS anode can be attributed to the synergy of the hierarchically porous hollow structure, carbon layer and newly formed numerous ∼5 nm Li2Ti2O4 on the surface of the TiO2 nanocrystals.

Biomolecular self-assembly is an effective synthesis strategy for material fabrication with unique structural complexity and properties. For the first time, we integrate inner-particle mesoporosity in a three-dimensional (3D) interconnected macroporous TiO2 structure via the mediation of biomolecular self-assembly of the lipids and proteins from rape pollen coats and Pluronic P123 to optimize the structure for high performance lithium storage. Benefitting from the hierarchically 3D interconnected macro-mesoporous structure with high surface area, small nanocrystallites and good electrolyte permeation, such a unique porous structure demonstrates superior electrochemical performance, with high initial coulombic efficiency (94.4% at 1C) and a reversible discharge capacity of 161, 145, 127 and 97 mA h g−1 at 2, 5, 10 and 20C for 1000 cycles, with 79.3%, 89.9%, 90.1% and 87.4% capacity retention, respectively. Using SEM, TEM and HRTEM observations on the TiO2 materials before and after cycling, we verify that the inner-particle mesoporosity and the Li2Ti2O4 nanocrystallites formed during the cycling process in interconnected macroporous structure greatly enhance the cycle life and rate performance. Our demonstration here offers opportunities towards developing and optimizing hierarchically porous structures for energy storage applications via biomolecular self-assembly.

A uniform, hierarchical porous vaterite calcium carbonate microsphere stacked from nanoparticles is synthesized in dimethylformamide–water (DMF–H2O) mixed solvent without template. We propose a solvent-reaction assisted synthesis of the product by a mesoscale growth pathway. The product shows large removal capacity towards Pb2+, Cd2+ and Zn2+, of 1960 mg g−1, 1040 mg g−1 and 587.3 mg g−1, respectively. It also exhibits efficient and selective adsorption of Congo red (272 mg g−1, 5 min for equilibrium), which is reported for the first time on calcium carbonate. The removal mechanism is demonstrated to be the precipitation transformation for the heavy metal ion sequestration, and adsorption mechanism for the removal of the organic dyes. The good performance of the product is ascribed to the large amount of active adsorption sites provided by the nanoscale building blocks and mesopores, and the short pathway provided by the sunken poles and the hierarchical structure with enhanced mass transfer and decreased blocking of channels.

•High-performance supercapacitor-like Li-ion battery concept has been proposed.•3 nm NiO nanodots have been deposited on macroporous nickel foam by self-assembly method.•Binder-free three-dimensional (3D) hierarchically macro-mesoporous electrodes have been prepared.•This electrode architecture simultaneously enables rapid ion transfer and ultra-short solid-phase ion diffusion.•The electrode exhibits supercapacitor-like high rate capabilities with high lithium battery capacities.We report a binder-free three-dimensional (3D) macro-mesoporous electrode architecture via self-assembly of 3 nm NiO nanodots on macroporous nickel foam for high performance supercapacitor-like lithium battery. This electrode architecture provides a hierarchically 3D macro-mesoporous electrolyte-filled network that simultaneously enables rapid ion transfer and ultra-short solid-phase ion diffusion. Benefitting from the structural superiority owing to the interconnected porous hierarchy, the electrode exhibits supercapacitor-like high rate capabilities with high lithium battery capacities during the discharge-charge process: a very high capacity of 518 mA h g−1 at an ultrahigh current density of 50 A g−1. It exceeds at least ~10 times than that of the state-of-the-art graphite anode, which shows only ~50 mA h g−1 at ~2 to 3 A g−1 as anode for Li-ion batteries. The preparation method of 3D interconnected hierarchically macro-mesoporous electrode presented here can provide an efficient new binder-free electrode technique towards the development of high-performance supercapacitor-like Li-ion batteries.A binder-free 3D interconnected macro-mesoporous NiO electrode for rapid ion transfer and ultra-short solid-phase ion diffusion has been developed via self-assembly of 3 nm NiO nanodots on macroporous nickel foam. The electrode enables Li-ion storage battery working with supercapacitor rate capability while maintaining high battery capacity. This work described here highlights a new approach to fabricate high-performance electrochemical energy storage devices with both high power as well as energy density.

•Polyhedral oligosilsesquioxanes are assembled into hierarchically porous carbons.•The carbons contain uniform micropores interconnected with highly ordered mesopores.•Nitrogen functionalities can spontaneously be incorporated into the carbon materials.•The porous carbons have desired structural characteristics towards supercapacitors.Polyhedral oligosilsesquioxanes (POSS), regarded as the smallest possible particles of silica, are used as carbon source and assembled into hierarchically porous carbon structures by a block copolymer-assisted method. The obtained carbon materials with high specific surface area of over 2000 m2 g−1 and large pore volume of over 1.19 cm3 g−1 possess both quite uniform micropores with the size of ~1 nm and highly ordered mesopores with the size of ~4 nm, owing to the molecular-scale templating effect of POSS siloxane cages as well as the good assembly compatibility between the block copolymers and the aminophenyl-functionalized POSS used. The mesopore arrangement can be two-dimensionally hexagonal (p6m) or body-centered cubic (Im  3¯m) by simply adjusting different block copolymers. Nitrogen functionalities with a relatively high content (~4 wt%) can spontaneously be incorporated into those carbon materials. Benifiting from the uniform microporosity and the nitrogen doping, the specific capacitance of the POSS-derived hierarchically porous carbons can reach ~160 F g−1 in ionic liquid electrolyte and ~210 F g−1 in 1 M H2SO4 aqueous electrolyte, when measured at a current density of 0.25 A g−1 in a symmetrical two-electrode cell. More importantly, the highly ordered mesopores can facilitate ions fast transportion to the fine micropores to achieve the excellent power performance. The hierarchial carbon sample with a hexagonal mesostructure and a high mesoporosity displays the best rate capability with 94% and 97% of capacitance retention in ionic liquid and 1 M H2SO4, respectively, with the current density range from 0.25 to 10 A g−1. By combining self-assembly strategy with rich POSS chemistry, we believe that many other hierarchical hybrid materials or carbon materials with unique electrochemical properties can be synthesized.

A hierarchical nanosheet-constructed yolk–shell TiO2 (NYTiO2) porous microsphere is synthesized through a well-designed, one-pot, template-free solvothermal alcoholysis process using tetraethylenepentamine (TEPA) as the structure directing reagent. Such a yolk–shell structure with a highly porous shell and dense mesoporous core is quite advantageous as an anode material for lithium ion batteries (LIBs). The outer, 2D nanosheet-based porous (15 nm) shell and the nanocrystal-based inner mesoporous (3 nm) core provide a stable, porous framework, effective grain boundaries and a short diffusion pathway for Li+ and electron transport, facilitating lithium insertion/extraction. The voids between the core and the shell can not only store the electrolyte due to capillary and facilitate charge transfer across the electrode/electrolyte interface but also buffer the volume change during the Li+ insertion/extraction. As a result, NYTiO2 demonstrates excellent Li+ capacity with outstanding cycle performance and superior rate capability at different rates for >700 cycles, retaining a 225 mA h g−1 reversible capacity after 100 cycles at 1 C. In particular, the reversible capacity can still be maintained at 113 mA h g−1 after 100 cycles at 10 C. We also observe the formation of homogeneously distributed 5–10 nm Li2Ti2O4 nanocrystallites on the surface of the nanosheets during the discharge–charge process. The synergy of the yolk–shell structure with dual mesopores in the shell and core and the Li2Ti2O4 nanocrystallites endow the hierarchical NYTiO2 with high reversible capacity, excellent rate capability and outstanding cycle performance.

Hollow Cu2O microspheres (0.7 to 4 μm in diameter) with two active {111} and {110} facets have been prepared in water/ethylene glycol (H2O/EG) solution via a fast hydrothermal route in only 1 h. Due to the dangling “Cu” atoms in the highly active {111} and {110} facets, the microspheres demonstrate preferential selective adsorption and photodegradation for negatively charged methyl orange (MO), comparing to cationic rhodamine B (RhB) and neutral phenol. The 0.7 μm hollow Cu2O microspheres show the best adsorption capacity and photodegradation performance for MO removal: 49% MO can be adsorbed in 60 min and 99.8% MO can be fully removed under visible light illumination in 80 min, owing to the two active {110} and {111} facets and hollow structure. To exactly evaluate the photocatalytic efficiency, a new methodology is proposed by deducting the adsorption effect. The results show that in spite of 99.2% MO is removed from the solution under visible light illumination in 60 min, 14% MO is still adsorbed on the catalyst, which can be totally removed under further 20 min illumination. Our synthesis strategy presents a new opportunity for the preparation of hollow structures with high active facets. And the proposed accurate evaluation methodology may be extended to other photocatalysts with high adsorption capability for organic pollutants.

Tunable macro–mesoporous ZnO (M/m-ZnO) nanostructures with a wurtzite hexagonal structure have been successfully synthesized using polymer colloids as a hard template and 20–40 nm ZnO nanoparticles as a precursor via controlling the ratios of colloids and ZnO nanoparticles. The as-prepared macro–mesoporous ZnO nanostructures are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. Gas sensing performance is carried out for ethanol and acetone at different temperatures and concentrations. The gas sensing results show that the tunable M/m-ZnO nanostructures exhibit excellent gas sensing performances because the hierarchical macro–mesopores provide a large contacting surface area for electrons, oxygen and target gas molecules, offer smooth transport channels for target gas diffusion and finally enhance the gas molecular diffusion kinetics. The M/m-ZnO-600 nm demonstrates the best performance for ethanol and acetone detection. In addition, the sensor based on M/m-ZnO-600 nm gives obvious tendencious selectivity and a good repeatability and long-term stability to acetone at the optimum temperature of 300 °C. This work suggests that the macro–mesoporous ZnO is a potential material for advanced gas sensing.

•Hierarchical nanorods chains constructed TiO2 hollow microspheres (HNC-TiO2-HMSs) have been designed and prepared.•Innovative synthesis strategy to engineer the formation of HNC-TiO2-HMSs.•Excellent Li+ storage capacity with outstanding cycle performance and superior rate capability.•Self-improving phenomenon of cycle performance and storage capacity.•in-situ XRD study on the Li+ insertion process and the phase transformation.Hierarchical nanorods chains-constructed TiO2 hollow microspheres (HNC-TiO2-HMSs) have been designed and prepared through a facile one-pot fluorine-free solvothermal alcoholysis route using TiCl4 and isopropanol reaction system. Owing to the assembly of radially oriented nanorods chains leading to the formation of the shell of the hollow spheres, a large series of straight channels along nanorods chains are formed. Such highly porous hollow microspheres with hollow cavity, straight nanorods chains and straight nanochannels are highly desirable for Li ions batteries because such structure can easily store the electrolyte, facilitate the charge diffusion and Li+ insertion and buffer the volume change during the Li+ insertion/extraction process. One of the key innovation of the present work is the fine tuning of water amount released from the esterification of alcohol to induce in a well controlled hydrolysis of TiCl4 and engineer precisely HNC-TiO2-HMSs formation. Most importantly, the released Cl− ions direct the nanorods growing along (001) crystal plane and self-assembling along the radial direction accompanying with nanorods size controlling to form HNC-TiO2-HMSs. The obtained TiO2 anode material with such special structure demonstrates excellent Li+ storage capacity with outstanding cycle performance and superior rate capability at different rates over 700 cycles: a reversible capacity of 216 mA h g−1 is obtained after 100 cycles at 1 C and a reversible capacity of 112 mA h g−1 is retained after 100 cycles at 10 C. The SEM, TEM, HRTEM and in-situ XRD techniques have been utilized to shed light on the Li+ insertion process and the phase transformation. Most importantly, a self-improving phenomenon of cycle performance and storage capacity was observed owing to the formation of numerous ~5 nm Li2Ti2O4 nanocrystals formed on the surface of the nanorods chains. The results reveal that the high performance of the as-prepared HNC-TiO2-HMSs in terms of storage capacity, cycle performance and rate capability can be attributed to the synergy of the special structure and the self-improving phenomenon. Our simple reaction system may provide a concrete example on the construction of novel hollow spherical porous anode materials for high performance lithium batteries.

•New lamellar manganese alkoxide (Mn-DEG) microspheres were synthesized via solution-phase reaction.•DEG acts as both solvent and structure-directing reagent.•The HM-MO/C-MS are from the in situ carbonization of Mn-DEG.•The HM-MO/C-MS combine various advantages to improve lithium storage.•The HM-MO/C-MS deliver highly enhanced lithium battery performance.•The synthesis strategy can be broadened to other metal oxides/carbon composites.Two types of hierarchical mesoporous urchin-like Mn3O4/carbon microspheres (HM-MO/C-MS) have been prepared via the in situ carbonization of the newly synthesized lamellar manganese alkoxide (Mn-DEG) along with the crystallization of Mn3O4 in air (MO-A) and nitrogen (MO-N), respectively. Such unique HM-MO/C-MS with high surface area provides obvious advantages including a large contact area with electrolyte, a short transport path for Li+ ions, a low resistance for charge transfer, and a superior structural stability. When used as an anode material for lithium ion batteries in the voltage range of 0.01–3 V, the HM-MO/C-MS obtained in nitrogen (MO-N) exhibits high lithium storage capacity (915 mA h g−1 at 100 mA g−1 for 50 cycles), great cycling stability (94.5% capacity retention versus the second cycle) and excellent rate capability (510 mA h g−1 at 1000 mA g−1). In particular, when cycling at a high current density of 1500 mA g−1, the reversible capacity of the MO-N sample can still be maintained as high as 480 mA h g−1 with a high capacity retention of 93.7% after 200 cycles. Even in a narrower voltage range of 0.01–1.5 V, the lithium storage capacity of the MO-N sample can reach 556 mA h g−1 at 100 mA g−1 with a very good cycling stability (over 91% capacity retention from the second cycle) and have an excellent rate capability of 269 mA h g−1 at 1000 mA g−1. Both MO-N and MO-A samples present a very high volumetric capacity of 741.2 mA h cm−3 and 647.4 mA h cm−3 at 100 mA g−1, respectively. Such high performances both in the voltage ranges of 0.01–3 V and 0.01–1.5 V are among the highest reported. Ex-situ SEM images showed clearly the excellent morphological and structural stability of our materials. The results demonstrate that the unique hierarchical mesoporous microspheres/carbon structure is favorable for improving the cyclability and rate capability in energy storage applications. Our effective synthesis strategy can be broadened to construct other mesoporous metal oxides/carbon composites for high-performance lithium ion batteries.

As anode materials for lithium ion batteries, two three dimensionally ordered macroporous TiO2, one with disordered inter-particle mesopores formed by the aggregation of nanoparticles (3DOM) and another with inner-particle mesopores generated by a surfactant templating strategy (3DOMM), have been synthesized using poly(styrene-methyl methacrylate-3-sulfopropyl methacrylate potassium) (P(St-MMA-SPMAP)) spheres as a hard template and their electrochemical properties are compared. SEM and TEM observations reveal that both 3DOM TiO2 and 3DOMM TiO2 have well-ordered macropores and interconnected macropore walls with a regular periodicity. 3DOMM TiO2 demonstrates a specific surface area of 139 m2 g−1, which is higher than that of 3DOM TiO2 (99 m2 g−1) due to the smaller crystallite size and inner-particle mesopores. The electrolyte adsorption results show that both 3DOM TiO2 and 3DOMM TiO2 have similar adsorption capacities despite a difference in the surface area. Electrochemical impendence spectroscopy analysis shows that 3DOMM TiO2 has a lower charge transfer resistance and faster Li+ diffusion coefficient than 3DOM TiO2. Moreover, both 3DOM TiO2 and 3DOMM TiO2 possess excellent initial capacity of 248 mA h g−1 and 235 mA h g−1 at 0.2 C and 208 mA h g−1 and 202 mA h g−1 at 1 C, respectively. The reversibility study demonstrates that the 3DOMM TiO2 displays higher cycling capacity, superior rate behavior and higher Coulombic efficiency because the higher surface area provides more active sites and the presence of the inner-particle mesopores in the walls of macropores serve as a bicontinuous transport path and affords a shorter path length for diffusion of Li ions compared with the 3DOM TiO2 and its crystallite aggregated mesopores. The reversible capacity of 106 mA h g−1 observed for the 3DOMM TiO2 can be retained after 200 charge–discharge cycles at a relatively high current rate of 4 C. This cycle stability performance can be equally attributed to the crystallite size and inner-particle mesopores in the 3DOMM TiO2. Moreover, the existence of a bicontinuous porous structure in the 3DOMM TiO2 can further enhance the lithium insertion/extraction capacity at high rates. We believe that this study can shed light on the 3DOMM structure as a promising material for highly enhanced performance in lithium ion batteries.

Low electron transportation and lithium ion diffusion coefficient in laminar vanadium oxide nanostructures limit their electrochemical performance for lithium ion batteries. In this work, V2O5 nanowires and VOx nanotubes were obtained via heat treatment of the pristine vanadium oxide nanotubes at different temperatures under air and nitrogen atmospheres, respectively, and then used as cathode materials for lithium ion batteries. It is interesting to note that the pristine vanadium nanotubes were transformed to V2O5 nanowires under an ambient atmosphere while the nanotube morphology can be maintained under an inert N2 atmosphere. The electrochemical results show that the V2O5 nanowires obtained at 400 °C deliver the best cycling performance with an initial discharge capacity as high as 278 mA h g−1 and the best rate capability with a discharge capacity of 115 mA h g−1 at 500 mA g−1. The VOx nanotubes obtained at 400 °C show the highest lithium storage capacity of 218 mA h g−1 with excellent capability retention and the best rate capability among all the nanotube samples. The improvement of electrochemical properties of V2O5 nanowires and VOx nanotubes can be attributed to the synergy of the enhanced surface area and better crystallinity. The different electrochemical properties reveal the existence of four different modes of Li ion intercalation/de-intercalation behaviors in V2O5 nanowires and VOx nanotubes. It is very interesting to note that the Li ion intercalation/de-intercalation in amorphous VOx nanotubes (VOx + yLi+ + ye− → LiyVOx) can induce a phase transformation from amorphous matrix to layered crystalline structure. This present work reveals that the electrochemical properties, in particular the cycling stability of vanadium oxide nanostructures, can be improved by tuning the one-dimensional structures' crystallinity. Furthermore, the phase transformation from amorphous matrix to layered crystalline structure of VOx nanotubes may open an exciting door for all the amorphous nanostructures for the application of LIBs.

Highly ordered, dense and continuous ZnO inverse opal (ZnO-IO) films with different air sphere sizes have been successfully prepared by a metal salt-based sol–gel infiltration method and used to prove and demonstrate the slow photon effect occurrence to enhance the photocatalytic activity. The obtained ZnO-IO films have a pure wurzite structure with similar crystallite size according to the XRD experiments and show very ordered macroporous structures from SEM and TEM analyses. The ZnO-IO films present a photoinduced surface wettability conversion phenomenon and the wettability of the ZnO film can be tuned from superhydrophobicity to hydrophilicity after UV-vis irradiation. Compared with the ZnO film without inverse opal structure, both ZnO-IO films demonstrate highly enhanced photocatalytic activities due to the hierarchically macro–mesoporous structure and particularly the slow photon enhanced light absorption. The synergy of the slow photon effect and hierarchically porous structure of inverse opal itself results in the highest photocatalytic activity at an incident light angle of θ = 40°. Moreover, our results suggest that the slow photon effect occurring at the red edge of PBG exhibits a higher photocatalytic reaction rate than that at the blue edge of PBG. The extraordinary enhancement of the photocatalytic activity via changing the incident light angle reveals that the slow photon effect does take place and further dramatically enhance the photocatalytic activity of ZnO-IO films. This work may open an exciting door to all the fields related to light absorption, such as solar cells, and optical and electro-optical devices.

The photonic effect on the photocatalytic activity of the continuous titania inverse opal (TiO2-IO) films differing only by the air sphere size (185 and 165 nm) and prepared by a colloid crystal template approach and annealing at different temperatures (700 and 800 °C) has been investigated by aqueous solution degradation of dye pollutants using mesoporous TiO2 thin films as the reference. The high quality of TiO2 inverse opal films has been confirmed by a blue shift of the Photonic Band Gap (PBG) with increasing light incident angle. Excellent agreement was found between theoretical and experimental reflectance spectra, confirming the photonic crystal structure of the samples. The slow photon light absorption enhancement effect inducing highly improved photocatalytic degradation of dye pollutants has been revealed in an aqueous reaction system. When compared with the mesoporous (m-TiO2) films obtained under the same conditions, all the TiO2-IO films demonstrate a much higher photocatalytic activity. At a light incident angle of 0°, the TiO2-IO-700 film (air sphere size: 185 nm) showed a better photocatalytic activity than that of TIO2-IO-800 (air sphere size: 165 nm). Most importantly, with increasing light incident angle, the photocatalytic activity of the TiO2-IO-700 film decreases whilst that of the TiO2-IO-800 film increases sharply due to the enhancement of light absorption related to a slow photon effect, generating more electron-holes. The present work revealed that photocatalytic activity can be dramatically enhanced by utilizing slow photons located at the PBG edges with energies close to the electronic bandgap of the semiconductor. The study using the slow-photon effect on the basis of photonic crystals to improve the photocatalytic activity by enhancing the light absorption could be an important future research direction. The slow-photon effect can open a new exciting avenue to all the fields related to light absorption including solar cells, optical telecommunications and optical computing.

Hierarchical core–corona porous γ-Al2O3 nanostructures have been synthesized through the reaction of toluene diluted TMA with water by controlling the methane leaching. The obtained γ-Al2O3 core–corona nanostructures exhibit high thermal stability and excellent performance for polluted water treatment.

We report on one-pot synthesis of various morphologies of CuO nanostructures. PEG200 as a structure directing reagent under the synergism of alkalinity by hydrothermal method has been employed to tailor the morphology of CuO nanostructures. The CuO products have been characterized by XRD, SEM, and TEM. The morphologies of the CuO nanostructures can be tuned from 1D (nanoseeds, nanoribbons) to 2D (nanoleaves) and to 3D (shuttle-like, shrimp-like, and nanoflowers) by changing the volume of PEG200 and the alkalinity in the reaction system. At neutral and relatively low alkalinity (OH−/Cu2+ ≤ 3), the addition of PEG200 can strongly influence the morphologies of the CuO nanostructures. At high alkalinity (OH−/Cu2+ ≥ 4), PEG200 has no influence on the morphology of the CuO nanostructure. The different morphologies of the CuO nanostructures have been used for the photodecomposition of the pollutant rhodamine B (RhB) in water. The photocatalytic activity has been correlated with the different nanostructures of CuO. The 1D CuO nanoribbons exhibit the best performance on the RhB photodecomposition because of the exposed high surface energy {−1 2 1} crystal plane. The photocatalytic results show that the high energy surface planes of the CuO nanostructures mostly affect the photocatalytic activity rather than the morphology of the CuO nanostructures. Our synthesis method also shows it is possible to control the morphologies of nanostructures in a simple way.Graphical abstractHighlights► Various morphologies of CuO nanostructures were synthesized by hydrothermal method. ► PEG200 act as structure directing reagent with the synergism of alkalinity. ► The method provides a way to transform 1D to 2D and to 3D nanostructures. ► The morphology is not the factor to determine the photocatalytic performance. ► The high surface energy {−1 2 1} facets dominate the high photocatalytic performance.

•PANI@CdS core-shell nanospheres via a proton doped in-situ polymerization technique.•PANI@CdS core-shell nanospheres demonstrate highly enhanced photocorrosion inhibition and photocatalytic hydrogen production.•CS and/or NCd bonds are newly formed between PANI shell and CdS core, leading to enhanced photocorrosion inhibition.•The photogenerated holes migrate from VB of CdS to HOMO of PANI, leading to enhanced photocatalytic hydrogen production.CdS is a very good visible-light responsive photocatalyst for hydrogen production. However, the fast recombination of photogenerated electron-hole pairs and quick photocorrosion limit its application in photocatalysis. To address these problems, we herein have designed and synthesized monodisperse polyaniline@cadmium sulfide (PANI@CdS) core-shell nanospheres to probe the mechanisms of photocorrosion inhibition and photocatalytic H2 production. All the PANI@CdS core-shell nanospheres demonstrate highly enhanced photocorrosion inhibition and photocatalytic hydrogen production comparing to the pure CdS nanospheres. Particularly, the PANI@CdS core-shell nanospheres with the thinnest PANI shell possess the highest hydrogen production rate of 310 μmol h−1 g−1 in 30 h without deactivation. Our results reveal that the newly formed CS and/or NCd bonds in PANI@CdS prevent the reduction of the surface sulfide ions to sulphur, leading to effective photocorrosion inhibition. Our results also verify that the photogenerated holes migrating from valence band (VB) of CdS to the highest occupied molecular orbital (HOMO) of PANI leads to the enhanced photocatalytic hydrogen production. This work can shed some light on the mechanism of conducting polymers modifying metal sulfides for effective photocorrosion inhibition and highly enhanced photocatalytic activities.

Highly ordered, dense and continuous ZnO inverse opal (ZnO-IO) films with different air sphere sizes have been successfully prepared by a metal salt-based sol–gel infiltration method and used to prove and demonstrate the slow photon effect occurrence to enhance the photocatalytic activity. The obtained ZnO-IO films have a pure wurzite structure with similar crystallite size according to the XRD experiments and show very ordered macroporous structures from SEM and TEM analyses. The ZnO-IO films present a photoinduced surface wettability conversion phenomenon and the wettability of the ZnO film can be tuned from superhydrophobicity to hydrophilicity after UV-vis irradiation. Compared with the ZnO film without inverse opal structure, both ZnO-IO films demonstrate highly enhanced photocatalytic activities due to the hierarchically macro–mesoporous structure and particularly the slow photon enhanced light absorption. The synergy of the slow photon effect and hierarchically porous structure of inverse opal itself results in the highest photocatalytic activity at an incident light angle of θ = 40°. Moreover, our results suggest that the slow photon effect occurring at the red edge of PBG exhibits a higher photocatalytic reaction rate than that at the blue edge of PBG. The extraordinary enhancement of the photocatalytic activity via changing the incident light angle reveals that the slow photon effect does take place and further dramatically enhance the photocatalytic activity of ZnO-IO films. This work may open an exciting door to all the fields related to light absorption, such as solar cells, and optical and electro-optical devices.

As anode materials for lithium ion batteries, two three dimensionally ordered macroporous TiO2, one with disordered inter-particle mesopores formed by the aggregation of nanoparticles (3DOM) and another with inner-particle mesopores generated by a surfactant templating strategy (3DOMM), have been synthesized using poly(styrene-methyl methacrylate-3-sulfopropyl methacrylate potassium) (P(St-MMA-SPMAP)) spheres as a hard template and their electrochemical properties are compared. SEM and TEM observations reveal that both 3DOM TiO2 and 3DOMM TiO2 have well-ordered macropores and interconnected macropore walls with a regular periodicity. 3DOMM TiO2 demonstrates a specific surface area of 139 m2 g−1, which is higher than that of 3DOM TiO2 (99 m2 g−1) due to the smaller crystallite size and inner-particle mesopores. The electrolyte adsorption results show that both 3DOM TiO2 and 3DOMM TiO2 have similar adsorption capacities despite a difference in the surface area. Electrochemical impendence spectroscopy analysis shows that 3DOMM TiO2 has a lower charge transfer resistance and faster Li+ diffusion coefficient than 3DOM TiO2. Moreover, both 3DOM TiO2 and 3DOMM TiO2 possess excellent initial capacity of 248 mA h g−1 and 235 mA h g−1 at 0.2 C and 208 mA h g−1 and 202 mA h g−1 at 1 C, respectively. The reversibility study demonstrates that the 3DOMM TiO2 displays higher cycling capacity, superior rate behavior and higher Coulombic efficiency because the higher surface area provides more active sites and the presence of the inner-particle mesopores in the walls of macropores serve as a bicontinuous transport path and affords a shorter path length for diffusion of Li ions compared with the 3DOM TiO2 and its crystallite aggregated mesopores. The reversible capacity of 106 mA h g−1 observed for the 3DOMM TiO2 can be retained after 200 charge–discharge cycles at a relatively high current rate of 4 C. This cycle stability performance can be equally attributed to the crystallite size and inner-particle mesopores in the 3DOMM TiO2. Moreover, the existence of a bicontinuous porous structure in the 3DOMM TiO2 can further enhance the lithium insertion/extraction capacity at high rates. We believe that this study can shed light on the 3DOMM structure as a promising material for highly enhanced performance in lithium ion batteries.

Low electron transportation and lithium ion diffusion coefficient in laminar vanadium oxide nanostructures limit their electrochemical performance for lithium ion batteries. In this work, V2O5 nanowires and VOx nanotubes were obtained via heat treatment of the pristine vanadium oxide nanotubes at different temperatures under air and nitrogen atmospheres, respectively, and then used as cathode materials for lithium ion batteries. It is interesting to note that the pristine vanadium nanotubes were transformed to V2O5 nanowires under an ambient atmosphere while the nanotube morphology can be maintained under an inert N2 atmosphere. The electrochemical results show that the V2O5 nanowires obtained at 400 °C deliver the best cycling performance with an initial discharge capacity as high as 278 mA h g−1 and the best rate capability with a discharge capacity of 115 mA h g−1 at 500 mA g−1. The VOx nanotubes obtained at 400 °C show the highest lithium storage capacity of 218 mA h g−1 with excellent capability retention and the best rate capability among all the nanotube samples. The improvement of electrochemical properties of V2O5 nanowires and VOx nanotubes can be attributed to the synergy of the enhanced surface area and better crystallinity. The different electrochemical properties reveal the existence of four different modes of Li ion intercalation/de-intercalation behaviors in V2O5 nanowires and VOx nanotubes. It is very interesting to note that the Li ion intercalation/de-intercalation in amorphous VOx nanotubes (VOx + yLi+ + ye− → LiyVOx) can induce a phase transformation from amorphous matrix to layered crystalline structure. This present work reveals that the electrochemical properties, in particular the cycling stability of vanadium oxide nanostructures, can be improved by tuning the one-dimensional structures' crystallinity. Furthermore, the phase transformation from amorphous matrix to layered crystalline structure of VOx nanotubes may open an exciting door for all the amorphous nanostructures for the application of LIBs.

Owing to their immense potential in energy conversion and storage, catalysis, photocatalysis, adsorption, separation and life science applications, significant interest has been devoted to the design and synthesis of hierarchically porous materials. The hierarchy of materials on porosity, structural, morphological, and component levels is key for high performance in all kinds of applications. Synthesis and applications of hierarchically structured porous materials have become a rapidly evolving field of current interest. A large series of synthesis methods have been developed. This review addresses recent advances made in studies of this topic. After identifying the advantages and problems of natural hierarchically porous materials, synthetic hierarchically porous materials are presented. The synthesis strategies used to prepare hierarchically porous materials are first introduced and the features of synthesis and the resulting structures are presented using a series of examples. These involve templating methods (surfactant templating, nanocasting, macroporous polymer templating, colloidal crystal templating and bioinspired process, i.e. biotemplating), conventional techniques (supercritical fluids, emulsion, freeze-drying, breath figures, selective leaching, phase separation, zeolitization process, and replication) and basic methods (sol–gel controlling and post-treatment), as well as self-formation phenomenon of porous hierarchy. A series of detailed examples are given to show methods for the synthesis of hierarchically porous structures with various chemical compositions (dual porosities: micro–micropores, micro–mesopores, micro–macropores, meso–mesopores, meso–macropores, multiple porosities: micro–meso–macropores and meso–meso–macropores). We hope that this review will be helpful for those entering the field and also for those in the field who want quick access to helpful reference information about the synthesis of new hierarchically porous materials and methods to control their structure and morphology.

The photonic effect on the photocatalytic activity of the continuous titania inverse opal (TiO2-IO) films differing only by the air sphere size (185 and 165 nm) and prepared by a colloid crystal template approach and annealing at different temperatures (700 and 800 °C) has been investigated by aqueous solution degradation of dye pollutants using mesoporous TiO2 thin films as the reference. The high quality of TiO2 inverse opal films has been confirmed by a blue shift of the Photonic Band Gap (PBG) with increasing light incident angle. Excellent agreement was found between theoretical and experimental reflectance spectra, confirming the photonic crystal structure of the samples. The slow photon light absorption enhancement effect inducing highly improved photocatalytic degradation of dye pollutants has been revealed in an aqueous reaction system. When compared with the mesoporous (m-TiO2) films obtained under the same conditions, all the TiO2-IO films demonstrate a much higher photocatalytic activity. At a light incident angle of 0°, the TiO2-IO-700 film (air sphere size: 185 nm) showed a better photocatalytic activity than that of TIO2-IO-800 (air sphere size: 165 nm). Most importantly, with increasing light incident angle, the photocatalytic activity of the TiO2-IO-700 film decreases whilst that of the TiO2-IO-800 film increases sharply due to the enhancement of light absorption related to a slow photon effect, generating more electron-holes. The present work revealed that photocatalytic activity can be dramatically enhanced by utilizing slow photons located at the PBG edges with energies close to the electronic bandgap of the semiconductor. The study using the slow-photon effect on the basis of photonic crystals to improve the photocatalytic activity by enhancing the light absorption could be an important future research direction. The slow-photon effect can open a new exciting avenue to all the fields related to light absorption including solar cells, optical telecommunications and optical computing.

Lithium–sulfur (Li–S) batteries are receiving significant attention as an alternative power system for advanced electronic devices because of their high theoretical capacity and energy density. In this work, we have designed manganese dioxide (MnO2) nanosheet functionalized sulfur@poly(3,4-ethylenedioxythiophene) core–shell nanospheres (S@PEDOT/MnO2) for high performance lithium–sulfur (Li–S) batteries. A PEDOT layer is used to address the low electrical conductivity of sulfur and acts as a protective layer to prevent dissolution of polysulfides. The MnO2 nanosheets functionalized on PEDOT further provide a high active contact area to enhance the wettability of the electrode materials with electrolytes and further interlink the polymer chains to improve the conductivity and stability of the composite. As a result, S@PEDOT/MnO2 exhibits an improved capacity of 827 mA h g−1 after 200 cycles at 0.2C (1C = 1673 mA g−1) and a further ∼50% enhancement compared to S@PEDOT (551 mA h g−1) without MnO2 functionalization. In particular, the discharge capacity of S@PEDOT/MnO2 is 545 mA h g−1 after 200 cycles at 0.5C. Our demonstration here indicates that the functionalization of inorganic nanostructures on conducting polymer coated sulfur nanoparticles is an effective strategy to improve the electrochemical cycling performance and stability of sulfur cathodes for Li–S batteries.

Unique walnut-shaped porous MnO2/carbon nanospheres (P-MO/C-NSs) with high monodispersity have been designed and prepared for lithium storage via in situ carbonization of amorphous MnO2 nanospheres. Polyvinylpyrrolidone (PVP) is utilized as both the surfactant for morphology control and carbon source for carbon scaffold formation accompanied with MnO2 crystallization. Such a unique walnut-shaped porous nanostructure with an intimate carbon layer provides a large contact area with the electrolyte, short transport path length for Li+, low resistance for charge transfer and superior structural stability. The P-MO/C-NS electrode demonstrates high lithium storage capacity (1176 mA h g−1 at 100 mA g−1), very good cycling stability (100% capacity retention versus the second cycle) and excellent rate capability (540 mA h g−1 at 1000 mA g−1). We propose that it is the deep oxidation of Mn2+ to Mn3+ in P-MO/C-NSs, which results in an extraordinarily high capacity of 1192 mA h g−1 at a current density of 1000 mA g−1 after a long period of cycling, very close to the maximum theoretical reversible capacity of MnO2 (1230 mA h g−1). This is the highest value ever observed for MnO2-based electrodes at such a rate. The high lithium storage capacity and rate capability can be attributed to the enhanced reaction kinetics owing to the walnut-shaped porous nanostructure with an intimate carbon layer. This work provides a meaningful demonstration of designing porous nanostructures of carbon-coated metal oxides undergoing deep conversion reactions for enhanced electrochemical performances.