Mesoporous Nanosheets Research Articles

Alkaline Water Splitting Enhancement by MOF-Derived Fe-Co-Oxide/Co@NC-mNS Heterostructure: Boosting OER and HER through Defect Engineering and In Situ Oxidation.

Introducing defects and in situ topotactic transformation of the electrocatalysts generating heterostructures of mixed-metal oxides(hydroxides) that are highly active for oxygen evolution reaction (OER) in tandem with metals of low hydrogen adsorption barrier for efficient hydrogen evolution reaction (HER) is urgently demanded for boosting the sluggish OER and HER kinetics in alkaline media. Ascertaining that, metal-organic-framework-derived freestanding, defect-rich, and in situ oxidized Fe-Co-O/Co metal@N-doped carbon (Co@NC) mesoporous nanosheet (mNS) heterostructure on Ni foam (Fe-Co-O/Co@NC-mNS/NF) is developed from the in situ oxidation of micropillar-like heterostructured Fe-Co-O/Co@NC/NF precatalyst. The in situ oxidized Fe-Co-O/Co@NC-mNS/NF exhibits excellent bifunctional properties by demanding only low overpotentials of 257 and 112mV, respectively, for OER and HER at the current density of 10mAcm-2 , with long-term durability, attributed to the existence of oxygen vacancies, higher specific surface area, increased electrochemical active surface area, and in situ generated new metal (oxyhydr)oxide phases. Further, Fe-Co-O/Co@NC-mNS/NF (+/-) electrolyzer requires only a low cell potential of 1.58V to derive a current density of 10mAcm-2 . Thus, the present work opens a new window for boosting the overall alkaline water splitting.

Interface Engineering of Ni3Fe and FeV2O4 Coupling with Carbon-Coated Mesoporous Nanosheets for Boosting Overall Water Splitting at 1500 mA cm–2

Interface Engineering of Ni₃Fe and FeV₂O₄ Coupling with Carbon-Coated Mesoporous Nanosheets for Boosting Overall Water Splitting at 1500 mA cm^–2

In-situ derived highly active NiS2 and MoS2 nanosheets on NiMoO4 microcuboids via controlled surface sulfidation for high-current-density hydrogen evolution reaction

• In comparison with the conventional chemical vapor deposition (CVD) process, controlled surface sulfidation (CSS) is a more effective approach to tune the physical structure and surface properties of a catalyst. • Highly mesoporous nanosheets along with the copious terminal (S 2 2− )/unsaturated (S 2− ) species are successfully developed at the edge of MoS 2 via CSS, maximally exposing the active sites at the interface. • Other than the pyrite-NiS 2 and 2H-MoS 2 , a new and metastable 1T’-MoS 2 phase is identified in the CSS samples; this phase is catalytically more active than 2H-MoS 2 , further boosting the catalytic activity. • The as-fabricated noble-metal-free catalyst CSS electrode approaches today's state-of-the-arts performances, which delivers ~1Acm −2 at 264 mV with uncompensated structural and catalytic durability. In this work, we highlight the significances of Controlled Surface Sulfidation (CSS) for high-current-density hydrogen evolution reaction (HER) with bimetallic NiMoO 4 microcuboids supported on Ni foam. It reveals that a new phase 1T’-MoS 2 is derived in-situ from the surface NiMoO 4 microcuboids during CSS in addition to pyrite-phase NiS 2 and 2H-MoS 2 as obtained from full sulfidation. We denote the controlled sulfided sample as “CSS-NiS 2 /MoS 2 ” and the fully sulfided sample as “FS-NiS 2 /MoS 2 ”, respectively. The CSS-NiS 2 /MoS 2 electrode only required low overpotentials of 12, 47, 112 mV to drive -10, -20, -100 mA cm −2 , respectively, which surpasses the FS-NiS 2 /MoS 2 considerably (54, 90, 195 mV at -10, -20, -100 mA cm −2 , respectively). Notably, it delivers a high current density of -500 and -1000 mA cm −2 at low overpotentials of only 200 and 264 mV, respectively. The durability of the high-current-density activity of CSS-NiS 2 /MoS 2 is also proven over 50 h of stability test. The excellent performances of CSS-NiS 2 /MoS 2 may be synergistically contributed from the active phases and the design dual hierarchical (i.e., 2D-nano/1D-microhybrids) structure. The CSS may serve as an effective strategy to modulate the electrochemical properties of materials holding great promises for the applications of next-generation energy storage and conversion.

Ultra-Thin Mesoporous LiV3O8 Nanosheet with Exceptionally Large Specific Area for Fast and Reversible Li Storage in Lithium-Ion Battery Cathode

LiV3O8 is considered as a promising cathode material for lithium-ion batteries (LIBs) because of its high specific capacity and good safety. However, the poor cycling stability and low rate capability of LiV3O8 electrode seriously hinder its application in long lifespan and high power LIBs. In the present work, an ultra-thin mesoporous LiV3O8 nanosheet is synthesized on the basis of efficient reduction-oxidation and freeze-dried strategy. The mesoporous nanosheet with a very small thickness of about 1.36 nm has an exceptionally large surface area of 397 m2 g−1 (8–20 times of LiV3O8 reported). The electrochemical test results indicate that the nanosheet cathode can deliver a reversible capacity of 301 mA h g−1 at current density of 100 mA g−1 in the potential range of 2.0–4.0 V and retain 87.1% of the starting discharge capacity after 550 discharge/charge cycles at 2000 mA g−1. The excellent lithium storage performances are ascribed to its unique flexible ultra-thin mesoporous nanosheet structure, which can increase the surface pseudocapacitive lithium storage, reduce the charge transfer resistance, improve the diffusion coefficient of lithium ion, and accommodate the volume changes of LiV3O8 in the discharge-charge processes. These results demonstrate a great potential of ultra-thin mesoporous LiV3O8 nanosheet for large capacity, long life and high power LIBs.

Interface-strain-confined synthesis of amorphous TiO2 mesoporous nanosheets with stable pseudocapacitive lithium storage

• A largescale salt-template method is developed to prepare conformable amorphous TiO 2 mesoporous nanosheets. • Interfacial strain between salt and TiO 2 is revealed to assist to suppress the amorphous-to-crystalline transformation. • This amorphous TiO 2 possesses ultrathin structure and rich mesopores that are beneficial for fast lithium-storage. • Remarkable high-rate long-term cycling stability (103 mA h g −1 at 6 A g −1 after 1000 cycles) are demonstrated. Amorphous nanomaterials recently have been demonstrated as a new type of high-power electrodes for many electrochemical energy-storage devices owing to their structural advantages of large surface area, shortened ion-diffused pathway, rich surficial defects and loosely packed structure; However, it is still challenging to prepare amorphous nanomaterials on a large scale via low-cost sol–gel method due to the easy amorphous-to-crystalline transformation upon post calcination process. Herein, we develop a simple and scalable approach to prepare amorphous TiO 2 mesoporous nanosheets by using the potassium chloride (KCl) as the template. The experimental results combined with density functional theory (DFT) calculations have revealed that the interfacial strain between the KCl and TiO 2 suppresses the crystallization of TiO 2 , which maintains amorphous characteristics even at a relative high temperature of 400 °C. Benefiting from short Li + -diffused distance, accessible mesoporous structure, and surface pseudo-capability, the amorphous TiO 2 nanosheet electrode exhibits fast and durable lithium-storage/-release ability, such as delivering a high reversible capacity of 103 mA h g −1 at 6 A g −1 after 1000 cycles. This study may pave a new way for the design of amorphous nanoarchitectures, and highlight the function of the templates, not only leading to the formation of various morphologies, but also affecting the surface microstructure.

Facile synthesis of ultrathin two-dimensional graphene-like CeO2–TiO2 mesoporous nanosheet loaded with Ag nanoparticles for non-enzymatic electrochemical detection of superoxide anions in HepG2 cells

Here we presented a new facile strategy to fabricate ultrathin two-dimensional (2D) metal oxide nanosheets, by using polydopamine-coated graphene (rGO@PDA) as a template under simply wet-chemical conditions. Based on the strategy, graphene-like CeO2–TiO2 mesoporous nanosheet (MNS-CeO2-TiO2) was prepared and was loaded with dispersive Ag nanoparticles (AgNPs) to obtain effective electrocatalysts (denoted as Ag/MNS-CeO2-TiO2) for electrochemical detection of superoxide anion (O2•−). Characterizations demonstrated that MNS-CeO2-TiO2 exhibited ultrathin thickness, larger specific surface area, and pore volume in comparison with its bulk counterpart. The above properties of MNS-CeO2-TiO2 shorten electron transmission distance, promotes mass transfer, and is conducive to the dispersion of post-modified AgNPs. Therefore, the recommended Ag/MNS-CeO2-TiO2 sensors (denoted as Ag/MNS-CeO2-TiO2/SPCE) exhibited satisfactory properties, including the sensitivity of 737.1 μA cm−2 mM−1, the detection limit of 0.0879 μM (S/N = 3), and good selectivity. Meanwhile, the sensors also successfully realized in the online monitoring of O2•− released from HepG2 cells, meaning the prepared sensors had practical application potential towards the analysis of O2•− in biological samples.

Nitrogen-doped graphene quantum dots-modified mesoporous SnO2 hierarchical hollow cubes for low temperature detection of nitrogen dioxide

Abstract The exploration of nitrogen dioxide (NO2) gas sensor with high response, fast response and recovery speed, and low working temperature is still an urgent challenge. In this work, a novel SnO2 hierarchical hollow cube composed of ultrathin mesoporous nanosheets was successfully prepared via a simple sulfidation-oxidation method, and nitrogen-doped graphene quantum dots (N-GQDs) were evenly modified on the surface of SnO2. The prepared N-GQDs modified SnO2 (NG/Snx) shows an improved response, and the optimal sample (NG/Sn1.5) response (Rg/Ra = 417) toward 1 ppm NO2 is approximately 2.2 times that of pure SnO2 at 130 °C. Moreover, the NG/Sn1.5 sensing material exhibits fast response and recovery speed, good selectivity, repeatability, and long-term stability. More attractively, the NG/Sn1.5 sensor has outstanding detection ability (Rg/Ra = 25.3) for low concentration NO2 (100 ppb). The significantly improved NO2 sensing performance of NG/Sn1.5 sensing material is mainly attributed to the zero-dimensional/three-dimensional (0D/3D) heterostructure construction and N doping, which increases the space charge modulation depth and NO2 adsorption active sites of the composite material. In addition, the mesoporous hierarchical cubic structure is beneficial to the improvement of NO2 sensing performance due to its stable gas diffusion channels, large specific surface area, and abundant nanoscale grain boundaries. The results obtained herein may provide new ideas for the preparation of high performance NO2 sensors at low temperatures.

Magnetic mesoporous carbon nanosheets derived from two-dimensional bimetallic metal-organic frameworks for magnetic solid-phase extraction of nitroimidazole antibiotics

We prepared two-dimensional (2D) bimetallic metal-organic frameworks (Ni-ZIF-8) nanosheets by a simple solvent-free method at room temperature. The morphology and composition of Ni-ZIF-8 can be controlled through adding different amounts of Ni. And then, the 2D magnetic mesoporous nanosheets (Ni/ZnO@C) were synthesized by directly pyrolyzing Ni-ZIF-8 under argon atmosphere and explored as magnetic solid phase extraction (MSPE) adsorbents for the determination of nitroimidazole antibiotics (NIABs). Magnetic Ni nanoparticles embedded in carbon nanosheets uniformly resulted in high magnetization saturation of Ni/ZnO@C for easy separation. The Ni/ZnO@C can form hydrogen bond and π-π interaction with three NIABs resulting from their rich N-H containing imidazole, π-electron. Due to the high specific surface area and high mass transfer rate of 2D Ni/ZnO@C, the materials showed satisfactory adsorption capacity and rapid adsorption kinetics for NIABs. A rapid and effective method of Ni/ZnO@C-MSPE combined with high-performance liquid chromatography was proposed for the determination of NIABs. Several main parameters affecting MSPE were investigated. Under the optimal conditions, wide linear was achieved ranging from 0.1 to 500 µg⋅L−1 with a low detection limit of 0.025-0.05 µg⋅L−1. The established method has been successfully applied to analyze NIABs from environmental water samples with satisfactory recovery from 74.33 to 105.71%.

Porous Carbon Nanosheets Derived from ZIF‐8 Treated with KCl as Highly Efficient Electrocatalysts for the Oxygen Reduction Reaction

Developing advanced electrocatalysts for the oxygen reduction reaction (ORR) is a critical reaction in fuel cells. Metal–organic framework (MOF)‐derived nitrogen‐doped carbons have been widely reported as promising electrocatalysts for ORR. Herein, a KCl‐assisted pyrolysis method is reported to prepare N‐doped porous carbon nanosheets (NCNS). During pyrolysis preparation, KCl crystals act as templates and activator, penetrating the ZIF‐8‐derived carbon material via capillarity, which facilitates the formation of micro‐ and mesopores carbon nanosheets. By adjusting the KCl dosage and pyrolysis temperature, the carbon material structure, nitrogen species, and graphitization degree are effectively controlled. The optimal NCNS‐10‐900 catalyst exhibits a higher half‐wave potential (≈0.88 V) in alkaline solution, which is even better than Pt/C (≈0.86 V). The NCNS‐10‐900 also exhibits outstanding long‐term stability with an only 17 mV shift in half‐wave potential after a 10K cycle durability test. All of these high properties are ascribed to the high specific surface area, the abundant microporous and mesoporous nanosheet structure, and the synergistic effects of the N species with intrinsic activity. This strategy of using a KCl‐assisted pyrolysis MOF provides a feasible method to explore highly efficient and robust non‐noble metal catalysts for energy‐conversion reactions.

N-Doped Graphene-Decorated NiCo Alloy Coupled with Mesoporous NiCoMoO Nano-sheet Heterojunction for Enhanced Water Electrolysis Activity at High Current Density

HighlightsN-doped graphene-coated structure and mesoporous nano-sheet can efficiently boost active sites and stability for hydrogen and oxygen evolution reaction.NiCo@C-NiCoMoO/NF exhibits low overpotentials for HER (266 mV) and OER (390 mV) at ± 1000 mA cm−2.For water electrolysis, it can hold at 1000 mA cm−2 for 43 h in 6.0 M KOH + 60 °C condition.

V2O3-Decorated Spinel CoFe2O4 with Carbon-Encapsulated Mesoporous Nanosheets for Efficient Water Splitting

A lot of research has been going on to develop efficient nonprecious bifunctional catalysts for electrochemical water splitting. Here, we synthesize a V2O3-decorated spinel CoFe2O4 catalyst self-supported on nickel foam (NF) with a carbon-encapsulated mesoporous nanosheet structure [(V2O3–CoFe2O4)@C/NF] through a hydrothermal method and high-temperature annealing. It exhibits lower overpotentials for hydrogen evolution reaction (61 and 301 mV) and oxygen evolution reaction (226 and 310 mV) at ±10 and ±500 mA cm–2 and can hold at ±500 mA cm–2 for 80 h. As for overall water splitting, it needs 1.53 V to produce 10 mA cm–2 and maintains 80 h at 100 mA cm–2, suggesting good stability. This high performance originated from the V2O3-decorated spinel CoFe2O4, carbon-encapsulated structure and the self-supported mesoporous nanosheets. Therefore, this work provides a convenient, green, and promising method to design non-noble, low-cost, and high-efficient catalysts for water splitting.

Surface-reconstructed formation of hierarchical TiO2 mesoporous nanosheets with fast lithium-storage capability

A simple dual-templated synthesis method was used to produce novel porous TiO2 nanosheets with a surficial nanoarchitecture that deliver high lithium-storage capacity at high rates.

Emulsion-template synthesis of mesoporous nickel oxide nanoflowers composed of crossed nanosheets for effective nitrogen reduction.

A novel emulsion-template synthesis approach was developed for the preparation of nickel oxide nanoflowers (NiO-NFs) composed of crossed mesoporous nanosheets. The interface assembly process was regulated by tuning the dosage of NH3·H2O, resulting in the tunability of thickness and size of mesoporous NiO nanosheets. The as-prepared NiO-NFs were characterized by field emission scanning electron microscopy, transmission electron microscopy, Brunauer-Emmett-Teller analysis, X-ray diffraction, and X-ray photoelectron spectroscopy (XPS). The results indicate that NiO-NFs have a mesopore size of about 9.5-15 nm and a crossed nanosheet thickness of about 12.4-50 nm. XPS results demonstrated that all NiO-NF samples consisted of Ni2+ and Ni3+. Electrochemical nitrogen reduction reaction (NRR) measurements revealed that NiO-NF-3.0 showed an optimal NRR performance of NH3 yield and faradaic efficiency (16.16 μg h-1 mg-1cat. and 9.17% at -0.4 V vs. RHE) in 0.1 M Na2SO4. Interestingly, NiO-NF-3.0 also displayed the highest Ni3+ content, which correlates with the order of electrochemical NRR performance. This can be attributed to the fact that Ni3+ promotes the electropositivity of NiO-NFs, resulting in more facile adsorption of N2 gas than Ni2+, and leading to enhanced electrocatalytic properties. These enhanced NRR performances are comparable or superior to those of reported noble-metal catalysts. This study provides a novel method for the fabrication of low-cost metal oxide nanomaterials that allows the construction of electrochemical NRR catalysts to meet the needs of industrial production. Also, it provides a new approach to improve the electrochemical properties by increasing the content of high-valent metal ions in a metal oxide.

Cytosine-Co assemblies derived CoNx rich Co-NCNT as efficient tri-functional electrocatalyst

Carbon-metal composites are promising multifunctional electrocatalysts, but it is still challenging to prepare carbon-metal composites with tunable structure and strong metal-carbon interactions. Here, we present a unique gas-foaming assembly strategy to prepare cytosine-Co chelate derived Co and N codoped carbon nanotube (Co-NCNT). The structure for Co-NCNTs could be easily controlled by regulating cytosine-Co coordination or the carbonization temperature. The optimal Co-NCNT possesses homogeneous distributed NCNTs (10 nm), CoOx (5 nm) and CoNx moieties to synergistically boost electrochemical processes, and offer mesoporous nanosheet architecture to guarantee fast mass migrate and electron transfer. As a result, Co-NCNT shows remarkable ORR performance (onset potential of 0.93 V in 0.1 M KOH electrolyte) along with significant OER and HER activity. More important, it was found that CoNx moieties are responsible for the remarkable electrocatalytic activity in Co-NCNTs, because CoNx could alter active center, enhance metal-carbon synergy, decrease interfacial resistance and reinforce the strength of composites. Therefore, this paper not just demonstrates an advanced multi-functional electrocatalyst, but could also give deep understanding on the designing of multifunctional electrocatalysts.

The enhanced P-nitrophenol degradation with Fe/Co3O4 mesoporous nanosheets via peroxymonosulfate activation and its mechanism insight

In current work, iron doping Co3O4 (Fe/Co3O4) mesoporous nanosheets with different iron ratios were successfully prepared to degrade P-nitrophenol (PNP) via peroxymonosulfate (PMS) activation. The obtained optimal 0.15Fe/Co3O4 exhibited the best PMS activation performance, almost 100% of PNP can be removed at pH = 5.5 in 60 min with negligible Co leaching. The excellent PMS activation performance of 0.15Fe/Co3O4 was mainly attributed to the enhanced electron transfer efficiency of Co2+/Co3+ and Fe2+/Fe3+ cycles and abundant oxygen vacancies, which benefiting in promoting more hydroxyl radical (•OH), sulfate radical (SO4•−), and singlet oxygen (1O2) generation. And the intimate relationship between PNP degradation efficiency and the contents of Co2+, Fe2+, Ovac in xFe/Co3O4 was obseved. Meanwhile, the mechanism for improved PMS activation efficiency was proposed based on ROSs quenching, XPS, and ESR results. In addition, the degradation pathway of PNP was explored based on the intermediates determined via the gas chromatography-mass spectrometer (GC-MS). This study can provide an effective strategy to obtain Co based catalysts with excellent PMS activation for recalcitrant pollutants degradation.

N-Heptane catalytic cracking on ZSM-5 zeolite nanosheets: Effect of nanosheet thickness

To explore the effect of channel properties on catalytic activity, ZSM-5 zeolite nanosheets were synthesized with di-quaternary ammonium-type surfactant and used in n-heptane cracking reaction. Nanosheet thickness was changed from around 4 nm–20 nm by adjusting the ratio of surfactant to tetraethyl orthosilicate (TEOS). The synthesized zeolite nanosheets were characterized by physical and chemical adsorption, electron microscopy, X-ray diffraction (XRD), pyridine infrared (Py-IR), Thermogravimetric analysis (TGA) and Raman spectra. The results showed that zeolite with thicker nanosheets had more microporosity and was more conducive to remarkably improving the selectivity of light olefins. High mesoporosity of zeolite nanosheets greatly reduces the diffusion resistance and accelerates mass transfer which even increases the direct diffusion of insufficiently cracked intermediates. Thicker zeolite nanosheets with more micropores prolong the reaction time and thus improve the selectivity of target products. • Ordered mesoporous nanosheet zeolites were synthesized and used in catalytic cracking reaction. • Nanosheet thickness was regulated from around 4 nm–20 nm through the change of template concentration in synthetic gel. • Thicker nanosheet zeolite with more micropores was conducive to the production of ethylene and propylene. • A well linear dependence was found between total selectivity and HFʺ.

Recyclable nanocellulose-confined palladium nanoparticles with enhanced room-temperature catalytic activity and chemoselectivity

We describe the synthesis of even-dispersed palladium nanoparticles (Pd NPs) confined within a cellulose nanofiber (CNF) matrix for developing a high-performance and recyclable catalyst. The CNF matrix was composed of CNF-assembled mesoporous nanosheets and appeared as soft and hydrophilic foam. Ultrafine Pd NPs (∼6 nm) with high-loading (9.6 wt%) were in situ grown on these mesoporous nanosheets, and their dense spatial distributions were likely to generate nano-confinement catalytic effects on the reactants. Consequently, the CNF-confined Pd NPs (CNF-Pd) exhibited an enhanced room-temperature catalytic activity on the model reaction of 4-nitrophenol hydrogenation with a highest rate constant of 8.8×10−3 s−1 and turnover frequency of 2640 h The CNF Pd catalyst possessed good chemical stability and recyclability in aqueous media which could be reused for at least six cycles without losing activity. Moreover, chemoselective reduction of 3 nitrostyrene was achieved with high yield (80%–98%) of 3-aminostyrene in alcohol/water cosolvent. Overall, this work demonstrates a positive nanoconfinement effect of CNFs for developing stable and recyclable metal NP catalysts.

Efficient CO2 Separation of Multi-Permselective Mixed Matrix Membranes with a Unique Interfacial Structure Regulated by Mesoporous Nanosheets.

A facile strategy to elevate gas separation performances of polymers is to introduce a versatile particle. In this study, the novel F-Ce nanosheets are synthesized, and then F-Ce is functionalized with 1-ethyl-3-methylimidazole thiocyanate (ionic liquids, ILs), obtaining multifunctional f-F-Ce nanosheets by the facile and environment-friendly methods. The multifunctional f-F-Ce nanosheets are incorporated into the Pebax (Pebax 1657) matrix to fabricate mixed matrix membranes (MMMs) for efficient CO2 separation. The f-F-Ce nanosheets play versatile parts in elevating membrane gas separation performance. On the one hand, f-F-Ce tends to arrange horizontally and constructs a unique interfacial structure for cross-layer CO2 transport in MMMs. On the other hand, the abundant mesopores from f-F-Ce construct high-speed CO2 transport channels in MMMs and notably elevate the gas permeability. Moreover, the as-prepared MMMs separate CO2 efficiently due to the comprehensive improvements of diffusivity selectivity, solubility selectivity, and reactivity selectivity. First, the high aspect ratio of f-F-Ce provides the tortuous pathways for gas transport and generates the rigid interface between the Pebax matrix and f-F-Ce nanosheets, increasing the diffusivity selectivity. Second, SCN- groups from ILs show excellent affinity to CO2, enhancing the solubility selectivity. Third, amine groups from ILs with abundant methylimidazole generate reversible reaction with CO2 to elevate reactivity selectivity. Consequently, the f-F-Ce-doped MMMs display excellent CO2 permeability and CO2/CH4 selectivity. In particular, the MMM incorporated with 8 wt % f-F-Ce displays a CO2 permeability of 1823 Barrer and a CO2/CH4 selectivity of 35, overcoming the Robeson upper bound line (2008).

Honeycombed-like nanosheet array composite NiCo2O4/rGO for efficient methanol electrooxidation and supercapacitors

A series of novel honeycombed-like composites NiCo2O4/rGO-T (rGO: reduced graphene oxide, T: 200, 250 and 300 °C) were obtained by a pre-adjusted pH value aq. phase coprecipitation strategy assisted by citric acid, followed annealing in N2 flow. The NiCo2O4/rGO-250 shows the most uniformly highly-ordered honeycombed-like nanosheet array morphology consisting of ultrathin mesoporous nanosheets (~110 nm × 12 nm) interdigitated vertically grown on the rGO surface in both sides with the highest crystallinity, higher surface area (145 m2 g−1), bimodal pore size distribution (3.4 and 12.5 nm) along with the highly open macroporous networks. The NiCo2O4/rGO-250 electrode exhibits the highest current density for methanol oxidation reaction of 90 A g−1 at 0.6 V, as well as high cycling stability (94% after 500 cycles, returned to 98% with fresh electrolyte), which is the best one so far among reported catalysts with similar compositions. Simultaneously, NiCo2O4/rGO-250 electrode exhibits considerable specific capacitance of 1380 F g−1 at 1 A g−1, high rate performance (10 A g−1, 967 F g−1), and good cycling stability which remains 90% at 5 A g−1 after 1000 charge–discharge cycles for supercapacitor. The excellent electrochemical performance of the NiCo2O4/rGO-250 electrode can be attributed to the highly-ordered honeycombed-like mesoporous nanosheet array along with the greatly increased specific surface area exposing more active sites, the highly open macroporous networks formed by adjacent ultrathin NiCo2O4 nanosheets providing more ion/electron diffusion paths and effective contact area of electrolyte, and the strong NiCo2O4– rGO synergy endowing excellent conductivity and structural robustness, thus greatly facilitate the transfer of electrons and ions in electrode and at the electrolyte/electrode interface.

NiCo2 O4 -Based Nanosheets with Uniform 4 nm Mesopores for Excellent Zn-Air Battery Performance.

Herein, a strategy is reported for the fabrication of NiCo2 O4 -based mesoporous nanosheets (PNSs) with tunable cobalt valence states and oxygen vacancies. The optimized NiCo2.148 O4 PNSs with an average Co valence state of 2.3 and uniform 4 nm nanopores present excellent catalytic performance with an ultralow overpotential of 190 mV at a current density of 10 mA cm-2 and long-term stability (700 h) for the oxygen evolution reaction (OER) in alkaline media. Furthermore, Zn-air batteries built using the NiCo2.148 O4 PNSs present a high power and energy density of 83 mW cm-2 and 910 Wh kg-1 , respectively. Moreover, a portable battery box with NiCo2.148 O4 PNSs as the air cathode presents long-term stability for 120 h under low temperatures in the range of 0 to -35 °C. Density functional theory calculations reveal that the prominent electron exchange and transfer activity of the electrocatalyst is attributed to the surface lower-coordinated Co-sites in the porous region presenting a merging 3d-eg -t2g band, which overlaps with the Fermi level of the Zn-air battery system. This favors the adsorption of the *OH, and stabilized *O radicals are reached, toward competitively lower overpotential, demonstrating a generalized key for optimally boosting overall OER performance.