Surface Area Of Porous Materials Research Articles

Elucidating the role of synthesis conditions on Zr-MOF properties and yield

Metal-organic frameworks (MOFs) are a new type of ultra-high surface area porous materials with applications in catalysis, energy storage, and gas adsorption. Compared to other MOFs, Zirconium-based MOFs (Zr-MOFs) demonstrate improved stability due to strong bonds between tetravalent zirconium and carboxylate ligands, making them applicable in real world conditions. This study aims to investigate optimal synthesis conditions for the solvothermal fabrication of Zr-MOFs by looking at two promising tetratopic ligand-based MOFs, Zr-TCPP and Zr-TPTC. By systematically investigating the impact of synthesis parameters on yield, crystallinity, and morphological characteristics, both general and specific trends were determined. The present work demonstrated that the ideal reactant ratio was twice the actual Zr:ligand ratio in the final structure. Stronger acid modulators were found to produce more crystalline samples for MOFs with flexible ligands (Zr-TPTC), where formic acid use resulted in more crystalline samples compared to acetic acid; however, this lowered the yield. The effect of temperature on yield was non-linearly dependent on the reactant ratio used for synthesising flexible Zr-TPTC. For MOFs with rigid ligands (Zr-TCPP), increasing synthesis temperature did not affect yield but decreased crystallite size and improved phase selectivity. Stability tests in water and acid were performed on both MOFs to assess the effect on crystallinity and morphology and the results showed expected trends for Zr-MOFs. The optimized synthesis parameters for Zr-TCPP resulted in a superior method of producing PCN-222 with higher yield and crystallinity. On the other hand, a new Zr-TPTC MOF with high yield and crystallinity was synthesised using the optimized parameters. This study thus elucidates the role of synthesis parameters on Zr-MOF properties and yield and furthers the understanding of MOF synthesis mechanisms, expanding the potential for their applicability in industry.

John - Sivanandan Achari Isotherm Method for the Determination of Surface Area of Porous Materials: Analysis of Granular Activated Carbons

John –Sivanandan Achari isotherm equationlog log Ce= C+n log qe,has many advantages for the structural characterization of porous materials. Linear plot of log logCe versus log qe conform to a straight line and subsequent extrapolation of amount adsorbed (qe), to the xaxis. This way one can directly determine the monolayerqm(J-SA) and hence the specific surface area (SA m2 /g) of the material.This can be analytically proved by applying the method in any type of solid-liquid equilibrium adsorption data. In this study, adsorption of methylene blue (MB) dye molecules on modified granular activated carbon (GAC) has been attempted to determine the porosity, and surface area by the new method. The solids are GAC 383 (native carbon- coconut shell based), GACO383 (native carbon oxidized) and a new carbon (GACOLaO1273). This carbon is prepared in the laboratory by steam activation after incorporating GAC383with Lanthanum(La 3+) ions. Carbons are tested in batch reactors with fixed MB concentrations by adsorptive techniques. The isotherm model behavior of the carbons are hereby reported using John - Sivanandan Achari isotherm (J-SA) equation using specific adsorption data. Porous material category as IUPAC type, constants and parameters are further evaluated with Langmuir, Freundlich, Dubinin - Radushkevich isotherms. It is seen that the isotherm followed the features of micro porous materials on using John – Sivanandan Achari (J-SA) isotherm. Porosity and surface area determined are found to give agreeing results on comparing with other isotherm models. This research is intended to highlight the significance of John and John-Sivanandan Achari (J-SA) isotherms as a tool for material characterization studies- a model originated as Indian analytical scientific skill.

Surface area per volumetric loading and its practical significance

The surface area of porous materials is a widely-used parameter in catalysis and adsorption. The most-commonly applied model, Brunauer–Emmett–Teller (BET), bases the parameter to the mass of material. Though the model does have its limitations, comparisons among materials are widely done to rank them from low to high surface areas, and to make correlations with other properties. However, in practical terms volume is often more appropriate since the design of reactors and adsorption columns aims at minimizing their volume. Thus, in such cases the surface areas can be better expressed per material bed volume using the bulk density. In this communication, we discuss the concept of volumetric surface area as m2/cm3MatBed, showing remarkable new insights. We applied this concept to two mesoporous silica-based materials with comparable pore size and C values. A material which was far superior in terms of conventional surface area (561 versus 227 m2/gMat), they both became comparable in terms of m2/cm3MatBed (ca. 110 both) due to the much lower density of the former material. In other words, being superior in gravimetric terms does not guarantee to be volumetrically superior. The results highlight the importance of considering the material bulk density when comparing surface areas of porous materials for applications where volume is critical.

Simulation of martensitic transformation in porous alloys based on phase-field method

Porous materials, characterized by the presence of interconnected pores, have been found to exhibit unique properties that differ from their bulk counterparts. One area of interest is the influence of pores on the martensitic transformation in shape memory alloys (SMAs), which directly affects the material's shape memory effect and mechanical properties. The martensitic transformation is accompanied by the formation of different martensitic variants, which determine the overall morphology, distribution, and self-accommodation effect of the transformed regions. Previous experimental studies have shown that the presence of pores, particularly at the metal-air interface, can significantly impact the martensitic variant structure, leading to its thinning. This thinning effect has been found to enhance the damping performance of the alloy. Experimental observations have indicated that there is no relief of martensitic variants around the metal-air interface, and there is non-transformed regions present. These observations suggest that the metal-air interface in porous materials is not a free surface and plays a crucial role in influencing the martensitic transformation. To further investigate the effect of martensitic variant self-accommodation on different constrained interfaces in porous materials, a three-dimensional phase-field model based on the Time Dependent Ginzburg Landau (TDGL) function is proposed in this study. The phase-field model allows for a comprehensive understanding of the evolution of martensitic variants and their interaction with the constrained interfaces. Remarkably, the simulation results align well with the experimental findings, demonstrating the presence of fine martensitic variants near the metal-air interface. The simulations under different interface constraint conditions reveal that increasing the specific surface area of porous materials is an effective strategy to obtain a more refined martensitic variant structure. The system's total energy is minimized by reducing the strain energy, which leads to the formation of a greater number of fine martensitic variants. This finding suggests that controlling the specific surface area of porous materials can be a promising approach to tailor the mechanical properties of SMAs for specific applications. In conclusion, the presence of metal-air interface in porous materials significantly influences the evolution of the martensitic transformation in SMAs. Experimental observations have shown that the introduction of pore can modify the martensitic variant structure, resulting in improved damping performance. The proposed phase-field model successfully captures the behavior of martensitic variants near constrained interfaces. The simulation results emphasize the importance of specific surface area in obtaining fine martensitic variant structures. These findings contribute to a deeper understanding of the role of porous materials in shaping the properties of SMAs and provide valuable insights for their design and application in various fields.

How to Read and Determine the Specific Surface Area of Inorganic Materials using the Brunauer-Emmett-Teller (BET) Method

The specific surface area of inorganic materials is a crucial parameter that influences their performance in various applications. The Brunauer-Emmett-Teller (BET) method is widely used for accurately determining the surface area of porous materials. This study presents a comprehensive guide to determining the specific surface area of inorganic materials using the BET method. The paper outlines the theoretical background of the BET method, the experimental procedures involved, and the data analysis techniques. Additionally, we discuss the limitations and potential sources of errors in the BET method. The proposed guide aims to provide researchers and practitioners with a systematic approach to accurately measure the specific surface area of inorganic materials, enabling informed decision-making and enhancing material design and optimization processes.

Brunauer-Emmett-Teller Areas from Nitrogen and Argon Isotherms Are Similar.

Despite recommendations from the 2015 International Union of Pure and Applied Chemistry (IUPAC) technical report, surface areas of porous materials continue to be characterized by an N2 adsorption isotherm using the Brunauer-Emmett-Teller (BET) method. In this study, we provide the basis for such a practice by carrying out systematic large-scale molecular simulations on homogeneous and heterogeneous model surfaces. Specifically, we investigated the purported "orientational effect" of the N2 molecule on these surfaces. Grand canonical Monte Carlo (GCMC) simulation results from 257 diverse metal-organic frameworks show that the BET areas from Ar and N2 are similar in the range of 250-7500 m2/g with a mean deviation of 4%. Detailed analyses based on the consistency criteria for BET equations reveal that the large deviation (>10%) between the BET areas from Ar and N2 are materials specific and more prone to materials that are not able to satisfy the 3 and 4 consistency criteria. For materials that satisfy all four consistency criteria, the BET areas predicted from Ar and N2 isotherms are comparable.

High hydrogen release by cryo-adsorption and compression on porous materials

Although hydrogen is a promising energy carrier to replace fossil fuels and reduce CO 2 emissions, its low volumetric energy density remains a major drawback. Indeed, hydrogen storage is one of the main technical obstacles limiting the large-scale use of hydrogen in fuel cell vehicles (FCVs). To solve this problem, there are different technical approaches such as: (i) compression in gas cylinders, (ii) liquefaction in cryogenic tanks, (iii) cryo-compression; and (iii) absorption or adsorption into solids. Cryogenic adsorption pressure systems are a promising approach to hydrogen storage because they require less resistant materials than those needed for compression at 70 MPa at room temperature, and can avoid the gas loss associated with boiling in liquid hydrogen storage systems. In this manuscript, we have reviewed different solutions for hydrogen storage, with a particular focus on hydrogen adsorption at cryogenic temperatures and moderate pressures on high surface area porous materials, namely: activated carbons, hyper-crosslinked polymers and metal organic frameworks. In addition, we discuss the elements involved in the design of rapidly rechargeable, compact, lightweight and cost-effective hydrogen storage systems. We also provide not only hydrogen storage capacities but hydrogen release capacities considering hydrogen at 10 MPa a discharge at 0.5 MPa. • Hydrogen storage by compression, liquefaction and cryo-compression is reviewed. • Hydrogen storage enhancement by adsorption in cryo-compression systems is discussed. • Cryo-adsorption of hydrogen on high surface materials is thoroughly reviewed. • The pros and cons of high surface area polymers, carbons and MOFs are presented. • Data on useable hydrogen in cryo-adsorption systems are reported.

Liquid Cavitation during Nitrogen Sorption on Soils

The nitrogen sorption isotherm is conventionally used to deduce the specific surface area of porous materials. However, it often exhibits a sharp drop around 0.5 relative pressure. A theory explicitly accounting for intermolecular-scale pressure, instead of classical theories of constant disjoining pressure in condensed liquid, is constructed and used to determine cavitation during desorption. Intermolecular-scale liquid pressure distribution is quantified using a recently developed soil sorptive potential framework, showing compressive liquid nitrogen pressure decaying nonlinearly with increasing distance to the particle surface. A range of cavitation pressure is predicted by classical nucleation theory and the van der Waals equation of state. Cavitation is shown to be triggered when nitrogen’s global minimum liquid pressure falls within the cavitation threshold. It is shown that this criterion is valid for all tested soils. Computed minimum liquid pressure always occurs at 0.5 relative pressure, which is in accordance with experimental isotherm data and further indicates the validity of the cavitation onset criterion.

Learning the Use of Artificial Intelligence in Heterogeneous Catalysis

We describe the use of artificial intelligence techniques in heterogeneous catalysis. This description is intended to give readers some clues for the use of these techniques in their research or industrial processes related to hydrodesulfurization. Since the description corresponds to supervised learning, first of all, we give a brief introduction to this type of learning, emphasizing the variables X and Y that define it. For each description, there is a particular emphasis on highlighting these variables. This emphasis will help define them when one works on a new application. The descriptions that we present relate to the construction of learning machines that infer adsorption energies, surface areas, adsorption isotherms of nanoporous materials, novel catalysts, and the sulfur content after hydrodesulfurization. These learning machines can predict adsorption energies with mean absolute errors of 0.15 eV for a diverse chemical space. They predict more precise surface areas of porous materials than the BET technique and can calculate their isotherms much faster than the Monte Carlo method. These machines can also predict new catalysts by learning from the catalytic behavior of materials generated through atomic substitutions. When the machines learn from the variables associated with a hydrodesulfurization process, they can predict the sulfur content in the final product.

The Brunauer–Emmett–Teller model on alumino-silicate mesoporous materials. How far is it from the true surface area?

Determining the surface area of porous materials through the Brunauer–Emmett–Teller (BET) model is a common practice. The method is generally applied in commercial software packages, where the assumptions are sometimes accepted by the experimenter whilst they may sometimes require a deeper analysis. One element of debate is the molecular cross-sectional area of the adsorptive. There is not yet agreement about the correctness of the BET model using a certain value for cross-sectional area of N2; the conventionally-used parameter seems to overestimate the surface areas. In this work, a preliminary study of a modified method is presented, which introduces an ‘apparent’ cross-sectional area for N2, which is smaller to the typically-used value. This value was obtained after measuring a number of relevant mesoporous materials in N2 and Ar, using a model that considers an apparent value for the cross-sectional area. The model predicts outcomes very close to the Ar-based measurements in terms of low relative error. Then, we went one step further and looked into the geometrical surface areas, also referred to as true surface areas. By combining prior studies with our work, it was found that the surface area, using N2 and the conventionally-used cross section, can be ca. 50% higher than the geometrical surface area. Therefore, the significance of the BET surface area seems to be far from well understood, though it is widely applied. This approach also allowed to define an ‘effective’ cross section for N2, that relates it to the geometrical surface area. Its value agrees with prior considerations for an epitaxial orientation of the N2 molecule with a hydroxylated silica surface. As a final recommendation, critical thinking is needed about the default settings in standardised calculations, which may not represent a reliable measure of the true surface area.

Metallic Porous Iron Nitride and Tantalum Nitride Single Crystals with Enhanced Electrocatalysis Performance.

Altering a material's catalytic properties would require identifying structural features that deliver electrochemically active surfaces. Single-crystalline porous materials, combining the advantages of long-range ordering of bulk crystals and large surface areas of porous materials, would create sufficient active surfaces by stabilizing 2D active moieties confined in lattice and may provide an alternative way to create high-energy surfaces for electrocatalysis that are kinetically trapped. Here, a radical concept of building active metal-nitrogen moieties with unsaturated nitrogen coordination on a porous surface by directly growing metallic porous metal nitride (Fe3 N and Ta5 N6 ) single crystals at unprecedented 2 cm scale is reported. These porous single crystals demonstrate exceptionally high conductivity of 0.1-1.0 × 105 S cm-1 , while the atomic surface layers of the porous crystals are confirmed to be an Fe termination layer for Fe3 N and a Ta termination layer for Ta5 N6 . The unsaturated metal-nitrogen moieties (Fe6 -N and Ta5 -N3 ) with unique electronic structures demonstrate enhanced electrocatalysis performance and durability.

Supported Porous Nanomaterials as Efficient Heterogeneous Catalysts for CO2 Fixation Reactions.

CO2 is a major greenhouse gas responsible for global warming and can act as an abundant and inexpensive C1 source for enhancing the chain length/functionalization of a wide range of reactive organic molecules. It is moderately reactive, nontoxic and renewable. Thus, CO2 fixation reactions are important to meet the global challenges, that is, to mitigate the concentration of CO2 in the atmosphere through its fruitful utilization, which is of great interest from economic and environmental perspectives. Various metallic nanoparticles as well as metal oxides can be supported over high surface area porous materials and the resulting nanomaterial can act as heterogeneous and reusable solid catalyst for CO2 fixation reactions for the synthesis of a large number of fuels, natural products agrochemicals, and pharmaceutical compounds. Here we present an overview of the recent progress as well as promising future of metal/metal oxide nanoparticles supported over porous nanomaterials as heterogeneous catalysts for a wide spectrum of these CO2 fixation reactions.

Functionalized and metal-doped biomass-derived activated carbons for energy storage application

The development of a viable hydrogen storage system is one of the key challenges which must be solved prior to the establishment of a hydrogen economy. One of the envisaged options to store hydrogen is adsorption on high surface area porous materials such as activated carbons (ACs). The aim of the present study is to develop a low cost hydrogen storage material and to improve its uptake capacity at room temperature. First, an activated carbon has been prepared from olive pomace through chemical activation procedure. Then, the carbon surface has been decorated with oxygen functional groups and with metal nanoparticles. A careful textural characterizations show that, in contrast to other gases, oxygenated groups hindered H2 access to active adsorption sites. Hence acid activation should be avoided for hydrogen adsorbent preparation. While, the insertion of metal nanoparticles improve the H2 adsorption performance of AC via spillover mechanism at room temperature, unless the metal content and the catalyst preparation method were optimized.

A comprehensive analysis of the BET area for nanoporous materials

The Brunauer‐Emmett‐Teller (BET) method has been used extensively to characterize the surface areas of porous materials by semiempirical fitting of gas‐adsorption isotherms. However, questions often arise concerning the applicability and the exact meaning of the BET areas. In particular, there has been much debate about whether the BET method provides a faithful description of the geometrical areas of porous materials if the atomic structures are exactly known. In this work, we provide a comprehensive analysis of the BET areas for both model slit pores and crystalline porous materials using the grand canonical Monte Carlo simulation. Based on extensive simulation data for nitrogen adsorption at 77 K and the conventional models of materials characterization, we find no simple correlation between the BET and geometrical surface areas. For materials with the same BET area, their geometric surface areas may vary over one order of magnitude. © 2017 American Institute of Chemical Engineers AIChE J, 63: 286–293, 2018

Facile Synthesis of Three-Dimensional Mg-Al Layered Double Hydroxide/Partially Reduced Graphene Oxide Nanocomposites for the Effective Removal of Pb2+ from Aqueous Solution.

A series of three-dimensional (3D) porous nanocomposites, comprised of partially reduced graphene oxide (pRGO) and CO32- containing Mg-Al layered double hydroxide, were synthesized in two steps. In the first step, graphene oxide (GO) was fabricated by a modified Hummers' method, and, subsequently, in the second step layered double hydroxide (LDH) nanosheets were homogeneously grown on the surface of the GO sheets by an in situ crystallization approach, involving a facile coprecipitation technique. The alkaline medium used for the in situ growth of LDH on the GO surface resulted in the partial reduction of GO to pRGO, which was confirmed by XRD. XRD also revealed the successful formation of crystalline LDH nanosheets on the surface of pRGO, whereas FTIR spectroscopy confirmed the presence of different functional groups in the nanocomposites. Nitrogen adsorption-desorption studies of the prepared nanocomposites revealed them as high surface area porous materials. Electron microscopic techniques, like TEM and SEM, confirmed that the architectures of the prepared nanocomposites displayed an interconnected 3D network, where a number of LDH nanosheets were interwoven on the surface of pRGO. The elemental mapping and EDX analysis qualitatively confirmed the presence of all of the expected elements in the fabricated nanocomposites. Because of the unique 3D porous network and the presence of a large number of oxygen-containing functional groups, the prepared nanocomposites proved suitable for the adsorption of Pb2+ ions from aqueous solution with a maximum adsorption capacity of 116.2 mg g-1. Equilibrium was achieved after 180 min on conducting the adsorption experiments at pH 4.5. Desorption experiments established the possibility of recovering the metal ions as well as the regeneration of adsorbents for repeated use.

Promoting and Tuning Porosity of Flexible Ether-Linked Phthalazinone-Based Covalent Triazine Frameworks Utilizing Substitution Effect for Effective CO2 Capture.

Five porous ether-linked phthalazinone-based covalent triazine frameworks (PHCTFs) were successfully constructed via ionothermal polymerizations from flexible dicyano monomers containing asymmetric, twisted, and N-heterocyclic phthalazinone structure. All the building blocks could be easily prepared by simple and low-cost aromatic nucleophilic substitution reactions, showing the large-scale application potential of thermal stable phthalazinone structure in constructing porous materials. Generally, the flexible building blocks are avoided to prevent the networks from collapsing in constructing high surface area porous materials. Our experimental results revealed that the introduction of the substituents can effectively decrease the probability of the network interpenetration from the longer struts and the intermolecular/intramolecular intercalation from the increased degree of conformation freedom in the flexible ether-linkage, the BET surface areas of PHCTFs increasing from 676 to 1270 m2 g-1. Meanwhile, the effects of introducing different sizes (methyl or phenyl group) and amounts (one or two) of substituents on the porosities of the target polymer networks were also investigated in detail. The high CO2 adsorption capacity of 10.3 wt % (273 K, 1 bar) can be ascribed to the strong affinity of the electron-rich N,O-containing networks with CO2. Excitingly, PHCTF-5 demonstrates the high CO2/N2 selectivity up to 138 (273 K, 1 bar), according to the ideal adsorbed solution theory (IAST) for the higher proportion of Vmicro accompanied the electron-rich heteroatoms characteristic. Such high CO2 adsorption capacity and good separation properties are superior to those of many other microporous organic polymers. These properties along with easily up-scalable synthesis make porous PHCTFs promising candidates applied in gas sorption and separation field.

Evaluation of adhesion of asphalt binders using wicking experiments

The objective of this study was to develop a methodology to evaluate the adhesion of liquids to porous by solids using wetting/wicking experiments. The surface area of porous materials significantly increases compared with that of their solid analogs. Hence, pores play an important role in the adhesion of resins and binders to solids. The authors developed an experimental protocol allowing one to evaluate the work of adhesion, a characteristic thermodynamic parameter of the liquid/porous solid pair. It is shown that for the determination of the work of adhesion, one needs to know the pore size distribution, the wicking constant of the wetting liquid and the surface tension of the liquid. Asphalt binders and different rocks were studied to illustrate the methodology.

Modeling Growth Kinetics of Gas Hydrate in Porous Media: Experimental Validation

In this contribution, a rigorous kinetic model is proposed for carbon dioxide (CO2) based gas hydrate formation in porous media in the presence of a promoter. This model introduces the difference in chemical potential between the water in hydrate phase and liquid phase as the driving force. The effective surface area of porous material is proposed for the growth of CO2 hydrate, and this parameter plays a major role in making the model different with the existing kinetic models. A parameter set is identified for each of the porous materials used involving a system with various components at a reasonably high pressure. The proposed kinetic model is finally evaluated for four different porous materials (cellulose foam, silica gel, silica sand, and polyurethane foam) by comparing it with the available models with reference to the experimental data sets taken from the literature. It is investigated that this kinetic model consistently outperforms the existing models for a wide variety of conditions.

Environmental Aspects of Using Metallic Organic Frameworks As Adsorbents in Natural Gas Storage Systems

The use of natural gas (NG) for automotive industry has gained renewed interest due to its growing supplies in the United States, relatively low cost compared to gasoline and diesel fuels and reduced emissions of carbon and particulate per equivalent. Because of its relatively low energy density NG must be stored at high pressure, 3,600 psi service pressure in the United States, in order to achieve an energy density suitable for vehicular use. Compressed NG cylinders are available in four types. Type 1, all metal (steel or aluminum) are the most widely used CNG cylinders in the world. Type 2 cylinders are metal liner reinforced by composite wrap (glass or carbon fiber) around the middle. Metal liner reinforced by composite wrap around the entire tank constitutes Type 3. While Type 4 cylinders are made of plastic gas-tight liner reinforced by composite wrap around the entire tank. Utilization of CNG storage systems in light duty vehicles has limited market penetration because of the cost of the pressure vessel and its occupancy of cargo space. Adsorbents materials are becoming an attractive option to develop low pressure and conformable NG storage system. Adsorbed NG storage relies on physisorption, i.e. weak gas-solid interactions between the fuel and the adsorbent surface. While research into adsorbents has focused on assessing their storage capabilities there is, to our knowledge, no reported data on their compatibility with the storage vessel and components in NG environment. High surface area porous materials such as Activated Carbons and Metal Organic Frameworks (MOF) are considered as the most promising adsorbents. The Cu3(btc)2 MOF, copper benzene-1,3,5-tricarboxylate also known as HKUST-1, has been extensively studied for gas storage. Herein we report its compatibility in NG environment with the pressure vessel, more particularly with the metal liner. We show that not only the stability of the adsorbent but also the integrity of the metallic liner can be drastically affected.

Synthesis and Electrochemical Properties of IrO2 Nanosheets

1. Introduction IrO2 is known as one of the most highly active and stable OER catalysts. It is essential that high surface area materials are used, either by preparing porous architectures or dispersing nanoparticles on conducting supports since Ir is a precious metal. Two-dimensional nanosheets have recently attracted increased interest as building blocks for high surface area porous materials. Nanosheets with electronic conductivity, for example, RuO2 nanosheets find application in transparent conductive electrodes as well as electrochemical energy storage and conversion.1,2) IrO2 is analogous to RuO2in many aspects; both possess the rutile structure and are room-temperature metallic conductors. Here we report the successful synthesis of an ion exchangeable layered iridium oxide which can be exfoliated into elemental nanosheets and subsequently used as an electrocatalyst. 2. Experimental Layered K0.30Ir0.93O2•nH2O was prepared by solid-state reaction of a 1:2 mixture of K2CO3 and IrO2 under inert atmosphere. Proton exchange was conducted by reaction in 1 M HCl for 3 days. Chemical exfoliation was conducted by shaking H0.30Ir0.93O2•nH2O in an aqueous solution of tetrabutylammonium hydroxide for 1 week. Electrochemical properties were studied in H2SO4 and HClO4. Results and discussion The Ir0.93O2 nanosheets (typical AFM image given in Fig. 1 inset) have an average thickness of c.a. 1.5 nm. The sharp edges suggest that the nanosheets are highly crystalline. Cyclic voltammograms of the Ir0.93O2 nanosheet electrode in 0.5 M H2SO4 is shown in Fig. 1. Three distinct redox peaks are observed. The E 1/2=0.95 and 1.19 peaks are typical of IrO2 3) and assigned to the Ir3+/Ir4+ and Ir4+/Ir5+ couple. The peaks at E 1/2=0.83 is observed only for IrO2 nanosheet, and shifts in HClO4; this peak is attributed to ad/desorption of anion. The onset of OER is observed at a potential similar to IrO2 nanoparticles.4) The specific capacitance between 0.2 and 1.2 V vs RHE at 2 mV s-1 was 93 kF mol-1, or 432 F g-1, which is the highest reported value for IrO2-based materials. It also closely matches the value of 88 kF mol-1 for RuO2nanosheet. Thus, almost all of the nanosheets surface is electrochemically accessible, and thus should provide unprecedented high utilization of the precious metal. 1) W. Sugimoto, H. Iwata, Y. Yasunaga, Y. Murakami, Y. Takasu, Angew. Chem. Int. Ed., 42, 4092 (2003). 2) K. Fukuda, T. Saida, J. Sato, M. Yonezawa, Y. Takasu, W. Sugimoto, Inorg. Chem., 49, 4391 (2010). 3) H. Andreas, H. Elzanowska, I. Serebrennikova, V.J. Birss. J. Electrochem. Soc., 147, 4598 (2000). 4) Y. Lee, J. Suntivich, K.J. May, E.E. Perry, Y. Shao-Horn, J. Phys. Chem. Lett. 3, 399 (2012). Figure 1. Cyclic voltammograms of IrO2 nanosheet electrodes in 0.5 M H2SO4 at 50 mV -1 (inset shows a typical AFM image of nanosheets on Si). Figure 1