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An alternative anodeto metallic sodium based on the high capacity of Sn4P3 alloy is investigated for the first time in Na–O2 batteries. This alloy is synthesised by an easy and scalable method based on ball milling which is further optimized in order to obtain the most suitable morphology while avoiding agglomeration of the material. First, the stability of Sn4P3/C composite within the battery environment is analysed and compared to that of metallic Na. Second, the electrochemical study reveals the formation of sodium superoxide on both the metallic anode and Sn4P3 alloy for the first time, which evidences the existence of O2/O2− crossover processes. Complementary impedance studies, at various voltages and as a function of cycle number, demonstrate a higher stability of the solid electrolyte interphase (SEI) throughout cycling in addition to presenting lower reactivity and greater stability than the metallic Na system. Regarding the cycling performance, although it is lower than that of metallic Na, it surpasses that exhibited by other alternative anodes under similar conditions. This work therefore demonstrates the viability of a new family of anodes, paving the way for the development of more stable and safer Na–O2 batteries. Moreover, the importance of oxygen crossover is highlighted which is a common problem regardless of the anode used.

The hard carbon puzzle: Linking material properties and electrochemical reactivity of hard carbon anodes in lithium and sodium cells. Hard carbon (HC) is the negative electrode (anode) material of choice for sodium-ion batteries (SIBs). Despite its advantages in terms of cost and sustainability, a comprehensive understanding of its microstructure is not complete yet, thus hindering a rational design of high-performance HC electrodes. In this study, rather than investigating how the precursor and synthesis method influence on the electrochemical properties of HC anodes, we examine the microstructure and surface chemistry of three optimized HC anodes obtained from different precursors by using different synthesis routes. The main goal is to evaluate the influence of the final materials properties (in their optimized state) on the electrochemical reactivity in lithium and sodium cells after a comprehensive structural characterization performed by means of X-ray photoelectron spectroscopy (XPS), wide-angle X-ray scattering (WAXS), Raman spectroscopy, scanning electron microscopy (SEM), and gas sorption measurements. The different electrochemical performance observed in terms of cycling stability and rate capability, and the stability of the solid electrolyte interphase (SEI) formed on the various HCs have been comprehensively investigated. A correlation of the material properties with their electrochemical response upon sodium and lithium uptake and release is clarified. By comparing the Na- and Li-ion storage behavior, a structure-function relation is identified., publishedVersion

In this work we report a framework to understand the role of solvent-salt interactions and how they mediate the performance of sodium-air/O2 batteries. The utilization of suitable electrolyte materials remains a point of major concern within the research community, as their stability and decomposition pathways during cycling are intimately connected with capacity and cycle life. Glyme based solvents have been widely utilized in Na–O2 batteries, however, to date no clear correlation between solvent/electrolyte properties and battery performance has been given. Herein, we have examined the effect of glyme chain length (ethylene glycol dimethyl ether DME; diethylene glycol dimethyl ether, DEGDME; and tetraethylene glycol dimethyl ether, TEGME) on the cycling behaviour of Na–O2 batteries and conclude that overall cell performance is highly dependent on solvent selection, salt concentration and rate of discharge/charge. We demonstrate how solvent selection helps define cell chemistry and performance by linking salt-solvent interactions to enthalpy of dissolution - and subsequently to sodium battery electrolyte properties - through the combination of both experimental and theoretical methodologies. The approaches detailed in this study could be used to predictively prepare electrolytes for Li-air batteries, other glyme-based electrochemical systems and low temperature applications.

One of the main technological challenges oxide-based solid-state batteries face today is the densification of their components to reach good interfacial contact. The most common approach requires co-sintering of the different components (electroactive material, catholyte and conducting additive) at high temperatures which often results in the inter-diffusion of elements that deteriorate the overall cathode performance. In this work, the impact of different carbon grades in the thermal response of LATP-NMC622-Carbon electrodes is evaluated and shown to significantly influence the chemical compatibility between components. By means of a combination of bulk and surface characterization techniques including gas adsorption, X-ray diffraction, X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy and thermogravimetric analysis, it is shown that carbons with low surface area are more adequate as result in higher oxidation temperatures and hence are less reactive.

Secondary zinc-air batteries (ZABs) offer a promising alternative for the future of sustainable energy storage. However, the current capability of secondary ZABs is far from satisfactory. The limitations for achieving high reversibility are mainly related to the bifunctional air electrodes as it severely hampers practical applications and commercialization of secondary ZABs. Many efforts have been devoted to the development of efficient and corrosion resistant bifunctional electrocatalysts towards oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). In ZABs, carbon is commonly used as conductive additive, however, it has been observed that carbon materials are not resistant to the high positive voltages applied in electrical recharge. In this work, the use of metallic nickel as alternative conductive additive in bifunctional air electrodes is explored and compared with carbon nanotubes (CNT). We demonstrate that the chemical resistance of CNT does not limit the electrode performance; but the density of the additive as well as its interaction with the active material is crucial for achieving long cycle life. The use of Ni as conductive agent in secondary ZABs boosted the cycle life by delivering more than 2,400 cycles, in contrast to the 88 cycles delivered by the analogous carbon-based battery. This work was supported by CDTI (ALMAGRID of the “CERVERA Centros Tecnológicos” program, CER-20191006), the Basque Country Government (CIC energiGUNE’20 of the ELKARTEK program, N° Exp. KK-2020/0078), the European Commission through the project ZABCAT “A New Zn-Air Battery Prototype to Overcome Cathode Degradation Through Catalyst Confinement” (grant agreement 966743) and the Ministerio de Ciencia e Innovación through the project AVANZA “Advanced Zn-Air Battery Prototype for the Energy Transition Horizon” (TED2021-131451B-C22). N. Ortiz-Vitoriano thanks Ramon y Cajal grant (RYC-2020-030104-I) funded by MCIN/AEI/10.13039/501100011033 and by FSE invest in your future.

Sodium-oxygen batteries (SOBs) have the potential to provide energy densities higher than the state-of-the-art Li-ion batteries. However, controlling the formation of sodium superoxide (NaO2) as the sole discharge product on the cathode side is crucial to achieve durable and efficient SOBs. In this work, the discharge efficiency of two graphene-based cathodes was evaluated and compared with that of a commercial gas diffusion layer. The discharge products formed at the surface of these cathodes in a glyme-based electrolyte were carefully studied using a range of characterization techniques. NaO2 was detected as the main discharge product regardless of the specific cathode material while small amounts of Na2O2⋅2H2O and carbonate-like side-products were detected by X-ray diffraction as well as by Raman and infrared spectroscopies. This work leverages the use of X-ray diffraction to determine the actual yield of NaO2 which is usually overlooked in this type of batteries. Thus, the proper quantification of the superoxide formed on the cathode surface is widely underestimated; even though is crucial for determining the efficiency of the battery while eliminating the parasitic chemistry in SOBs. Here, we develop an ex-situ analysis method to determine the amount of NaO2 generated upon discharge in SOBs by transmission X-ray diffraction and quantitative Rietveld analysis. This work unveils that the yield of NaO2 depends on the depth of discharge where high capacities lead to very low discharge efficiency, regardless of the used cathode. We anticipate that the methodology developed herein will provide a convenient diagnosis tool in future efforts to optimize the performance of the different cell components in SOBs., M.E., L.M and N.O.-V. thank the European Union (Graphene Flagship-Core 3, Grant number 881603) for the financial support of this work. J.I.P. acknowledges funding by the Spanish Ministerio de Ciencia, Innovación y Universidades (MICINN), Agencia Estatal de Investigación (AEI) and the European Regional Development Fund (ERDF) through project RTI2018-100832-B-I00. R.Y. acknowledges financial support from StandUp for Energy and the Swedish Energy Agency.

Graphene aerogels derived from a biomolecule‐assisted aqueous electrochemical exfoliation route are explored as cathode materials in sodium–oxygen (Na–O2) batteries. To this end, the natural nucleotide adenosine monophosphate (AMP) is used in the multiple roles of exfoliating electrolyte, aqueous dispersant, and functionalizing agent to access high quality, electrocatalytically active graphene nanosheets in colloidal suspension (bioinks). The surface phenomena occurring on the electrochemically derived graphene cathode is thoroughly studied to understand and optimize its electrochemical performance, where a cooperative effect between the nitrogen atoms and phosphates from the AMP molecules is demonstrated. Moreover, the role of the nitrogen atoms in the adenine nucleobase of AMP and short‐chain phosphate is unraveled. Significantly, the use of such cathodes with a proper amount of AMP molecules adsorbed on the graphene nanosheets delivers a discharge capacity as high as 9.6mAhcm−2and performs almost 100 cycles with a considerably reduced cell overpotential and a coulombic efficiency of≈97% at high current density (0.2mAcm−2). This study opens a path toward the development of environmentally friendly air cathodes by the use of natural nucleotides which offers a great opportunity to explore and manufacture bioinspired cathodes for metal–oxygen batteries.

Graphene aerogels derived from a biomolecule-assisted aqueous electrochemical exfoliation route are explored as cathode materials in sodium-oxygen (Na-O

Fundamental understanding of the physical phenomena and electrochemical reactions occurring in metal–air batteries is critical for developing rational approaches towards high-performing Na–O2 battery cathodes. In this context, air cathode porosity plays a key role in battery performance, influencing oxygen supply and hence oxygen reduction and evolution reaction kinetics (ORR/OER). Graphene-based aerogels offer great versatility as air-cathodes due to their low density, high electronic conductivity and adjustable porosity. Reduced graphene aerogels with different porosities are examined where high meso-macroporosity and a narrow macropore size arrangement exhibit the best electrode performance among all studied materials (6.61 mA h cm−2). This is ascribed to the particular macroporous 3D structure of graphene-based electrodes, which favours the diffusion of oxygen to the defect sites in graphene sheets. An outstanding cycle life is achieved by using the pore-tuned cathode, leading to 39 cycles (486 h) at 0.5 mA h cm−2 with very low overpotential (250 mV) and efficiency over 95%. The cyclability is further increased to 745 h (128 cycles) by decreasing the capacity cut-off. This study shows that tuning of material porosity opens a new avenue of research for achieving Na–O2 batteries with high performance by maximizing the effective area of the electrodes for the ORR/OER.

Graphene and graphene-based materials have shown great promise in many technological applications, but their large-scale production and processing by simple and cost-effective means still constitute significant issues in the path of their widespread implementation. Here, we investigate a straightforward method for the preparation of a ready-to-use and low oxygen content graphene material that is based on electrochemical (anodic) delamination of graphite in aqueous medium with sodium halides as the electrolyte. Contrary to previous conflicting reports on the ability of halide anions to act as efficient exfoliating electrolytes in electrochemical graphene exfoliation, we show that proper choice of both graphite electrode (e.g., graphite foil) and sodium halide concentration readily leads to the generation of large quantities of single-/few-layer graphene nanosheets possessing a degree of oxidation (O/C ratio down to ∼0.06) lower than that typical of anodically exfoliated graphenes obtained with commonly used electrolytes. The halide anions are thought to play a role in mitigating the oxidation of the graphene lattice during exfoliation, which is also discussed and rationalized. The as-exfoliated graphene materials exhibited a three-dimensional morphology that was suitable for their practical use without the need to resort to any kind of postproduction processing. When tested as dye adsorbents, they outperformed many previously reported graphene-based materials (e.g., they adsorbed ∼920 mg g

The mechanisms behind enhanced charge storage of P-functionalized carbons are unraveled for the first time using non-porous graphene oxide treated with phosphoric acid and annealed at either 400 or 800 degrees C. The electrochemical study in 1 M H2SO4 reveals that phosphorus groups boost charge storage and electrochemical stability, with more effect for the higher annealing temperature. Annealing at 800 degrees C also leads to the material withstanding 60,000 charge-discharge cycles with no capacitance loss at 1.5 V. The improvement in the electrochemical performance is shown to be mainly governed by the change in surface chemistry comprehensively studied with NMR, FTIR and XPS characterization techniques. The collective analysis of electrochemical response and surface chemistry demonstrates that enhanced charge storage by phosphorus-functionalized graphene materials is made possible due to the following synergistic mechanisms: i) non-Faradaic charging; ii) nascent hydrogen storage in the interlayer; iii) benzoquinoneto-hydroquinone redox processes; iv) phosphate-to-phosphonate like transformation. From the practical perspective, the stored charge can be boosted due to the higher capacitance upon prior electrochemical activation in the vicinity of oxygen evolution potential and the wider usable electrochemical window enabled by phosphorus-related groups. (C) 2020 The Author(s). Published by Elsevier Ltd. The authors thank the European Union (Graphene Flagship, Core 2, Grant number 785219) and the Spanish Ministry of Science and Innovation (MICINN/FEDER) (RTI2018-096199-B-I00) for the financial support of this work. J. L. G. U. is very thankful to the Spanish Ministry of Education, Science and Universities (MICINN) for the FPU grant (16/03498). We also want to acknowledge the company GRAPHENEA for supplying the graphene oxide used in this work and Yan Zhang from CIC Energigune for collecting FTIR spectra.

Graphene aerogels derived from a biomolecule‐assisted aqueous electrochemical exfoliation route are explored as cathode materials in sodium–oxygen (Na–O2) batteries. To this end, the natural nucleotide adenosine monophosphate (AMP) is used in the multiple roles of exfoliating electrolyte, aqueous dispersant, and functionalizing agent to access high quality, electrocatalytically active graphene nanosheets in colloidal suspension (bioinks). The surface phenomena occurring on the electrochemically derived graphene cathode is thoroughly studied to understand and optimize its electrochemical performance, where a cooperative effect between the nitrogen atoms and phosphates from the AMP molecules is demonstrated. Moreover, the role of the nitrogen atoms in the adenine nucleobase of AMP and short‐chain phosphate is unraveled. Significantly, the use of such cathodes with a proper amount of AMP molecules adsorbed on the graphene nanosheets delivers a discharge capacity as high as 9.6 mAh cm−2 and performs almost 100 cycles with a considerably reduced cell overpotential and a coulombic efficiency of ≈97% at high current density (0.2 mA cm−2). This study opens a path toward the development of environmentally friendly air cathodes by the use of natural nucleotides which offers a great opportunity to explore and manufacture bioinspired cathodes for metal–oxygen batteries., M.E., J.L.G.‐U., D.C., and N.O.‐V. thank the European Union (Graphene Flagship‐Core 3, Grant number 881603) and the Spanish Ministry of Science and Innovation (MICINN/FEDER) (RTI2018‐096199‐B‐I00) for the financial support of this work. J.M.M., J.I.P., and S.V.‐R. gratefully acknowledge funding by the Spanish Ministerio de Ciencia, Innovación y Universidades (MICINN), Agencia Estatal de Investigación (AEI), and the European Regional Development Fund (ERDF) through project RTI2018‐100832‐B‐I00, as well as Plan de Ciencia, Tecnología e Innovación (PCTI) 2013‐2017 del Principado de Asturias and the ERDF (project IDI/2018/000233). J.L.G.‐U. is very thankful to the Spanish Ministry of Education, Science and Universities (MICINN) for the FPU grant (16/03498)

The depletion of fossil fuels, the rapid evolution of the global economy, and high living standards require the development of new energy‐storage systems that can meet the needs of the world's population. Metal–oxygen batteries (M=Li, Na) arise, therefore, as promising alternatives to widely used lithium‐ion batteries, due to their high theoretical energy density, which approaches that of gasoline. Although significant progress has been made in recent years, there are still several challenges to overcome to reach the final commercialization of this technology. One of the most limiting and challenging factors is the development of bifunctional cathodes towards oxygen reduction and evolution reactions. In this sense, graphene, which is very promising and tunable, has been widely explored by the research community as a key material for this technology. Herein, a wide literature overview is presented and analyzed with the aim of guiding future research in this field., Future is flat: Graphene is a very versatile and promising air cathode in M–O2 (M=Li, Na) batteries due to its high electronic conductivity, large specific surface area, high mechanical strength, low density, and intrinsic catalytic activity towards oxygen reduction and reactions.

Integrated approaches that expedite the production and processing of graphene into useful structures and devices, particularly through simple and environmentally friendly strategies, are highly desirable in the efforts to implement this two-dimensional material in state-of-the-art electrochemical energy storage technologies. Here, we introduce natural nucleotides (e.g., adenosine monophosphate) as bifunctional agents for the electrochemical exfoliation and dispersion of graphene nanosheets in water. Acting both as exfoliating electrolytes and colloidal stabilizers, these biomolecules facilitated access to aqueous graphene bio-inks that could be readily processed into aerogels and inkjet-printed interdigitated patterns. Na-O2 batteries assembled with the graphene-derived aerogels as the cathode and a glyme-based electrolyte exhibited a full discharge capacity of ∼3.8 mAh cm–2 at a current density of 0.2 mA cm–2. Moreover, shallow cycling experiments (0.5 mAh cm–2) boasted a capacity retention of 94% after 50 cycles, which outperformed the cycle life of prior graphene-based cathodes for this type of battery. The positive effect of the nucleotide-adsorbed nanosheets on the battery performance is discussed and related to the presence of the phosphate group in these biomolecules. Microsupercapacitors made from the interdigitated graphene patterns as the electrodes also displayed a competitive performance, affording areal and volumetric energy densities of 0.03 μWh cm–2 and 1.2 mWh cm–3 at power densities of 0.003 mW cm–2 and 0.1 W cm–3, respectively. Taken together, by offering a green and straightforward route to different types of functional graphene-based materials, the present results are expected to ease the development of novel energy storage technologies that exploit the attractions of graphene., Funding by the Spanish Ministerio de Economía y Competitividad (MINECO) and the European Regional Development Fund (ERDF) through project MAT2015-69844-R and by the Spanish Ministerio de Ciencia, Innovación y Universidades and ERDF through project RTI2018-100832-B-I00 is gratefully acknowledged. Partial funding by Plan de Ciencia, Tecnología e Innovación (PCTI) 2013-2017 del Principado de Asturias and the ERDF through project IDI/2018/000233 is also acknowledged. J.M.M. is grateful to the Spanish Ministerio de Educación, Cultura y Deporte (MECD) for his pre-doctoral contract (FPU14/00792). J.N.C. acknowledges the ERC Adv. Gr. FUTUREPRINT. This work was also financially supported by the European Union (Graphene Flagship, Core 2, Grant number 785219).

The depletion of fossil fuels, the rapid evolution of the global economy and high life standards require the development of new energy storage systems that can meet the needs of world´s population. Metal‐oxygen batteries (M = Li, Na) arise, therefore, as promising alternatives to wide‐extended lithium‐ion batteries, due to their high theoretical energy density which approaches that of gasoline. Although significant progress has been made in the last years, there are still several challenges to overcome in order to reach the final commercialization of this technology. One of the most limiting and challenging factors is the development of bifunctional cathodes towards oxygen reduction and evolution reactions. In this sense, graphene‐ very promising and tunable ‐ has been widely explored by the research community as a key material for this technology. Herein, a wide literature overview is presented and analyzed with the aim of guiding future research in this field.

Integrated approaches that expedite the production and processing of graphene into useful structures and devices, particularly through simple and environmentally friendly strategies, are highly desirable in the efforts to implement this two-dimensional material in state-of-the-art electrochemical energy storage technologies. Here, we introduce natural nucleotides (e.g., adenosine monophosphate) as bifunctional agents for the electrochemical exfoliation and dispersion of graphene nanosheets in water. Acting both as exfoliating electrolytes and colloidal stabilizers, these biomolecules facilitated access to aqueous graphene bio-inks that could be readily processed into aerogels and inkjet-printed interdigitated patterns. Na-O2 batteries assembled with the graphene-derived aerogels as the cathode and a glyme-based electrolyte exhibited a full discharge capacity of ∼3.8 mAh cm–2 at a current density of 0.2 mA cm–2. Moreover, shallow cycling experiments (0.5 mAh cm–2) boasted a capacity retention of 94% after 50 cycles, which outperformed the cycle life of prior graphene-based cathodes for this type of battery. The positive effect of the nucleotide-adsorbed nanosheets on the battery performance is discussed and related to the presence of the phosphate group in these biomolecules. Microsupercapacitors made from the interdigitated graphene patterns as the electrodes also displayed a competitive performance, affording areal and volumetric energy densities of 0.03 μWh cm–2 and 1.2 mWh cm–3 at power densities of 0.003 mW cm–2 and 0.1 W cm–3, respectively. Taken together, by offering a green and straightforward route to different types of functional graphene-based materials, the present results are expected to ease the development of novel energy storage technologies that exploit the attractions of graphene.

Herein, we report a simple approach for the preparation of phosphate-functionalized carbonaceous graphene-based composites. The homogeneous deposition of a thin layer of phenolic resin on the surface of graphene oxide (GO) sheets was achieved using phosphoric acid as the polymerization catalyst and functionalization agent. Subsequent pyrolysis of the composite yielded homogeneous lamellar-shaped microstructured porous carbon-graphene composites combining enhanced molecular diffusion and high electron transfer. In order to elucidate the effect of GO and porosity on the supercapacitor performance, a graphene free sample and a KOH-activated composite were also prepared and tested in a two-electrode configuration using aqueous and organic electrolytes. It was found that the presence of GO and the KOH activation lead to an increase in the specific surface area combined with a progressive widening of the pores. As a result, the KOH-activated composite reached specific capacitances of 211 and 105 F g(-1) when using 1 M H2SO4 and 1.5 M Et4NBF4 electrolytes, respectively. It was also found that phosphorus-functionalization of electrodes leads to an operating voltage of 1.3 V in the aqueous electrolyte, resulting in a considerable increase of the energy density of the cell. Finally, both non-activated and activated graphene-based composites provide excellent capacitance retention, energy and power densities and cycling stability. We thank the European Union (Graphene Flagship, Core 2, Grant number 785219), the Spanish Ministry of Science and Innovation (MICINN/FEDER) (MAT2015-64617-C2-2-R and RTI2018-096199-B-I00) and the Basque Government (Elkartek 2018) for the financial support of this work. J. L. G. U. is very thankful to the "Ministerio de ciencia, innovacion y universidades" for the FPU grant (16/03498). We also want to acknowledge the company GRAPHENEA for supplying the graphene oxide used in this work and Dr M. A. Munoz for the acquisition of the XPS spectrum.

A series of electrospun binder-free carbon nanofiber (CNF) mats have been studied as air cathodes for Na-oxygen batteries using a pyrrolidinium-based electrolyte and compared with the commercial air cathode Toray 090. A tenfold increase in the discharge capacity is attained when using CNFs in comparison with Toray 090, affording a discharge capacity of 1.53 mAh cm-2 at a high discharge rate of 0.63 mA cm-2 . The good specific discharge and charge capacities of these CNFs are determined by the void space and the highly accessible surface of the carbon fiber. Furthermore, a threefold increase has been attained in terms of specific capacity by controlling the flooding of the air cathode and hence the location of the three-phase boundary within the CNF mat. The enhancement in performance has been correlated to the morphology, composition, distribution, and location of the discharge products. Sodium superoxide and peroxide were identified as the discharge products and, more importantly, the common side reaction discharge products, which are known to be detrimental to battery performance (including sodium fluoride, sodium hydroxide, and formate), were not observed, exemplifying the stability of the pyrrolidinium-based electrolyte and these binder-free CNF air cathodes.

Glucose-derived carbon/carbon nanotube (CNT) hybrid materials were prepared by hydrothermal carbonization of glucose in the presence of CNTs and subsequent carbonization, physical activation, or chemical activation. The proportion of CNTs added during the hydrothermal polymerization of glucose was varied to ascertain the optimum dose to maximize the performance of the carbon hybrids in supercapacitor applications. Both the thermal treatment applied and the addition of CNTs lead to changes in the textural and chemical properties of the activated carbons. It was observed that samples bearing CNTs exhibit higher number of nucleation centers for glucose oligomers to polymerize, and consequently, the behavior of the hydrothermal carbon toward activation differs according to the activating agent employed. Moreover, the initial chemical speciation dominated by acidic groups shifts to more basic functionalities (quinones and carbonyl groups) with the addition of CNTs. The effect of the different physicochemical properties of the prepared carbons on their electrochemical behavior was evaluated. The addition of 2 wt % of CNTs and subsequent chemical activation leads to electrode materials yielding 206 F g-1 and 78% of capacitance retention up to 0.8 V and 20 A g-1 and high rate cyclability (97% after 5000 cycles). The outstanding performance is ascribed to the high surface area, narrow mesopores, and phenol/carbonyl surface functionalities, which enhance molecular diffusion, the amount of stored energy, and electronic transportation, respectively.

Porous carbons derived from metal-organic frameworks (MOFs) are promising materials for a number of energy- and environment-related applications, but their almost exclusively microporous texture can be an obstacle to their performance in practical uses. Here, we introduce a novel strategy for the generation of very uniform mesoporosity in a prototypical MOF, namely, zeolitic imidazolate framework-8 (ZIF-8). The process, referred to as "nanopore lithography", makes use of graphene oxide (GO) nanosheets enclosing ZIF-8 particles as masks or templates for the transfer of mesoporous texture to the latter. Upon controlled carbonization and activation, nanopores created in the GO envelope serve as selective entry points for localized etching of carbonized ZIF-8, so that such nanopores are replicated in the MOF-derived carbonaceous structure. The resulting porous carbons are dominated by uniform mesopores ∼3-4 nm in width and possess specific surface areas of ∼1300-1400 m2 g-1. Furthermore, we investigate and discuss the specific experimental conditions that afford the mesopore-templating action of the GO nanosheets. Electrochemical characterization revealed an improved capacitance as well as a faster, more reversible charge/discharge kinetics for the ZIF-8-derived porous carbons obtained through nanopore lithography, relative to those for their counterparts with standard activation (no GO templating), thus indicating the potential practical advantage of the present approach in capacitive energy storage applications.

Correction for ‘Flat-shaped carbon–graphene microcomposites as electrodes for high energy supercapacitors’ by Gelines Moreno-Fernández et al., J. Mater. Chem. A, 2019, 7, 14646–14655.

The objective of this work was to produce carbons with controllable bimodal porosity in the micro-mesopore range. Hierarchical micro-mesoporous carbons were prepared by direct replication, using bimodal Y zeolite core/MCM-48 silica shell aluminosilicates as templates. Different variables of the chemical vapor deposition (CVD) process were studied in order to achieve a suitable infiltration of both meso and micropores of the templates. Thus, one-step infiltration with acetylene and also two-step infiltration with acetylene and propylene were performed to further investigate the effect of the precursor and CVD steps duration. One-step acetylene CVD gave the best results since the obtained carbons exhibited high specific surfaces areas of 1000–1323 m 2 /g, and their X-ray diffraction and transmission electron microscopy analysis revealed that they faithfully replicated the hierarchical core–shell structure of the parent template. When propylene was used as carbon source a better replication of the mesoporous shell was achieved, but as a counterpoint, the replication of the microporous core failed.

Electrically rechargeable zinc-air batteries have gained great attention in recent years due to their capacity to provide high energy density. The electrolyte has played a key role in the advancement of this technology and recently, aqueous chloride-based electrolytes have been demonstrated as a possible alternative to the traditional alkaline system. This study investigates, for the first time, the selection of an optimal bifunctional air electrode (BAE) formulation in two aqueous chloride-based electrolytes (pH4 and pH8) for zinc-air batteries. The effect of different MnxOy-based catalysts and carbon materials with different electrode formulations are electrochemically analyzed in the two electrolytic systems. The BAE formulation containing 20 wt% γ-MnO2, 70 wt% carbon nanotubes (CNT) and 10 wt% PTFE demonstrated the lowest overpotential, among all studied formulations, in both electrolytes. The cycling tests carried out using the selected electrode formulation, at both pH4 and pH8, reveal stable discharge-charge cycling over 400 h with an overpotential lower than 1.1 V. Moreover, the absence of manganese dissolution for the pH8 electrolyte is confirmed by ICP analysis, which overcomes the issue concerning the dissolution of manganese in more acidic media. Contrary to what is stated in conventional alkaline zinc-air batteries, where α-MnO2 is the most promising catalyst, this study highlights the potential of γ-MnO2-based BAEs when using aqueous chloride-based electrolyte.

Two CeO2/carbon nanotube composites were prepared in both basic and neutral medium thus using different deposition procedures of the cerium oxide. The modification of the synthesis conditions varied the hydrolysis rate of the cerium oxide precursor, leading to materials with different morphology, texture and surface chemistry, significantly changing their electrochemical performance. The different mechanisms of charge storage occurring on the surface of the materials were thoroughly studied to investigate the origin of the observed changes in the electrochemical properties. To that end, a combination of sweep wave voltammetry and deconvolution analysis in acid (1 M H2SO4), basic (1 M NaOH) and neutral (1 M Na2SO4) electrolytes was conducted. The faradaic activity of the composite prepared by slow hydrolysis (containing well-dispersed and small ceria particles) is enhanced as compared with the composite prepared by fast hydrolysis, which originates bulky particles.

Hierarchical ordered porous carbons show a better behavior as electric double layer capacitors (EDLCs) than disordered carbons especially at high rates thanks to their unique architectural design. In the present work, we demonstrate that mesostructural order is a key factor for the performance of carbons at high rates. For that, two series of hierarchical micro–mesoporous carbons were prepared by chemical activation with KOH following two different procedures. SBA-15 silica was infiltrated by chemical vapor deposition of propylene and the resulting carbon–silica composite was split into two halves. One part was directly activated and, subsequent to the activation process, the template was eliminated. The second part was first subjected to the template removal and the resulting CMK-3 type carbon was further activated. Thus, carbons obtained by both these methods present bimodal pore size distributions and different mesostructural order as a function of the activation conditions. Carbons prepared from the direct activation of the composite present a high conservation of the ordered mesoporous structure. The electrochemical performance of both carbon series was tested in an acid aqueous electrolyte (1 M H2SO4) by cyclic voltammetry and impedance spectroscopy. A highly ordered mesoporous structure significantly improves the specific capacitance at high scan rates due to enhancement in the diffusion of molecules.

A simple procedure to obtain hierarchical micro-mesoporous aluminosilicate composites was developed by growing MCM-48 silica over commercial Y zeolite. The obtained hierarchical composites have a microporous core and a mesoporous shell. The process consists in assembling dispersed Y zeolite with a mesoporous silica phase that is formed “in situ” by “soft-templating” with cetryltrimethylammonium bromide (CTAB) as surfactant. The Y zeolite/MCM-48 silica ratio and aging time were varied to study their effects on the final porosity and structure of the hierarchical composites. The pore textural and structural characteristics of the composites did not match those of the corresponding Y zeolite/MCM-48 silica physical mixtures. This implies that the synthesized composites integrate micropores and mesopores in the same bulk. The obtained composites exhibited micropore and mesopore volumes ranging between 0.15–0.31 and 0.30–0.51 cm3/g, respectively. X-ray diffraction and N2 adsorption results revealed that the presence of zeolite in the reaction medium favors the formation of mesopores in the obtained materials, especially for short hydrothermal treatments. TEM results showed that the obtained adsorbents are constituted by an integrated micro-mesoporous bimodal system in which Y zeolite is surrounded by a thin cover of MCM-48 silica.

Hierarchical micro-mesoporous carbons have been obtained by a simple one-pot procedure by adjusting the hydrogen bond interaction between Pluronic 123 surfactant, carbon precursor and tetraethoxysilane (TEOS) in acidic media through changes in carbon precursor nature and concentration. This has resulted in modifications in the packing of surfactant micelles, leading to silicas and carbons with different textural and structural characteristics. Conventional soft templating with SBA-15 type silica was carried out but two new variables were included, namely the addition of organic molecules of different nature and size to the reaction medium and the use of H 2 SO 4 instead of HCl to promote dehydration and polymerization of carbon precursors. Due to the TEOS-carbon precursor interaction an “in situ” infiltration of the latter occurred simultaneously to SBA-15 formation. This fact avoids the pre-synthesis of hard template and post-synthesis treatments of mesoporous carbons to generate microporosity. BET surface areas between 800 and 1000 m 2 /g were obtained, with micropore and mesopore volumes up to 0.35 and 1.13 cm 3 /g, respectively. Even thought we had to face the difficulty of suitable infiltration and consequently replication of the mesoporous template, long-range order was observed for some carbons as evidenced by means of Transmission Electron Miscroscopy and X-ray Diffraction.

Activated carbon xerogels with a cellular morphology were obtained from hydrothermally carbonized glucose-graphene oxide (GO) hybrids and tested as supercapacitor electrodes. The effect of the chemical activation (using KOH) on the nanometer-scale morphology, local structure, porous texture and surface chemistry of the resulting carbon materials was investigated and correlated with their electrochemical behaviour. The electrochemical performance of the activated xerogels was studied in a three-electrode cell using 1 M H2SO4 as the electrolyte. The results underlined the relevant role played by the xerogel nanomorphology; more specifically, xerogels with cellular structures exhibiting well-connected, continuous and very thin (∼5–15 nm) carbon walls (prepared with lower amounts of activating agent) favored ionic diffusion and electronic conduction compared to materials with broken, thicker walls (obtained from higher amounts of activating agent). The effect of nanomorphology and local structure was also made apparent when the xerogels were used as actual supercapacitor electrodes. Particularly, a symmetric capacitor assembled from a carbon xerogel with very thin walls and relatively high graphitic character delivered a much higher specific capacitance than that of a commercial activated carbon (223 vs 153 F g−1 at 100 mA g−1) as well as a significantly improved retention of capacitance at high current densities., This work was financed by QREN, ON2, FCT and FEDER (Project NORTE-07-0124- FEDER-000015 and NORTE-07-0162-FEDER-000050), and co-financed by FCT and FEDER through COMPETE 2020 (Project UID/EQU/50020/2013 - POCI-01-0145- FEDER-006984). Partial funding of this work by the Spanish MINECO and the European Regional Development Fund (projects MAT2015-69844-R and MAT2012- 34011) is also gratefully acknowledged.

Hierarchical micro–mesoporous carbons with high porosity development and ordered structure were prepared. The innovative proposal consists in developing microporosity in ordered mesoporous carbon by chemical activation in template presence in order to minimize the structural damage. Thus, we have directly carried out the chemical activation of a mesoporous carbon/silica composite with KOH. The effect on mesoporous ordered structure of both KOH/carbon ratio and activation temperature has been studied. Following chemical activation the specific surface area is increased from 341 to 1757 m 2 /g and the micropore volume becomes almost six times larger than initial value. Although a slight widening of the mesopore distribution and an increase in the mesopore volume has been observed during activation, TEM and XRD results reveal an excellent conservation of the ordered mesoporous structure during activation even at conditions well above the limits that a CMK-3 type carbon can resist.

Ordered mesoporous carbon (OMC) with hexagonal arrays of tubes (CMK-3) was synthesized by direct replication, using SBA-15 as template and propylene as carbon source. Microporosity was developed in these OMCs with either carbon dioxide or potassium hydroxide as activating agents; effects of these activation treatments on their pore structure were discussed. Porous texture was characterized by gas adsorption, morphology was examined by SEM and the degree of order of porous structure was evaluated by X-ray diffraction and TEM micrography. The specific surface area, microporous volume and total pore volume were markedly enhanced upon activation of CMK-3, but the long-range ordered structure gradually became more disordered. Potassium hydroxide activation develops the materials microporosity in a greater extent than with CO2, nevertheless moderate temperatures and activating agent proportions must be used in order to preserve the ordered mesoporous structure.

Cerium oxide/multiwalled carbon nanotube composites with different oxide loadings (5–60 wt. %) were prepared by sol-gel deposition of the oxide onto the carbon support. The morphology, texture and surface properties of the prepared materials were studied and correlated with their electrochemical behavior. The different charge storage mechanisms occurring on the surface of the composites were successfully identified by a newly developed electrochemical method, namely the combination of sweep wave voltammetry with deconvolution analysis in 1 M H 2 SO 4 . The deposition of moderate oxide loadings (up to 10 wt. %) leads to small and well distributed oxide particles on the nanotubes surface. Therefore, the appearance of defects on the oxide structure is favored, promoting both electronic conduction and faradaic activity. Curiously, cerium oxide loadings above 10 wt. % induce a higher dispersion of the carbon support. This convenient synergism enhances the electroactive area of the composites by increasing molecular diffusion.

Nanostructured mesoporous carbons are widely used in catalysis, adsorption and energy storage. Unlike conventional carbons, the textural properties of nanostructured carbons can be easily adjusted during synthesis. This design of the mesostructure allows to process large molecules by addressing the diffusional limitations/pore blockage which might occur in purely microporous carbon materials. Many synthetic approaches have been reported for the synthesis of mesoporous materials, either with a disordered mesoporosity (carbon gels), or with ordered porous systems (templated carbons). Carbon gels are synthesized by sol-gel processing through the polymerization of hydroxybenzenes and aldehydes. On the other hand, carbons with a periodically arranged mesoporous network can be obtained from the same precursors in the presence of templates, which may be rigid inorganic solids (hard-templating) or supramolecular assemblies (soft-templating). Controlling the surface chemistry is also a critical step in the development of high-performance materials; this can be achieved by doping with heteroatoms and functionalization with surface groups. The design of both texture and surface chemistry allows tuning the properties, thus leading to materials that meet the requirements of the targeted applications. The fundamentals, recent advances and the main challenges related to the preparation of nanostructured mesoporous carbon materials are presented in this review. (c) 2016 Elsevier Ltd

Hierarchical carbons with different boron contents (from 0.42 to 2.37 wt.%) were prepared by combination of soft-templating and hydrothermal approaches. This newly developed strategy enables adequate control of the chemical state of the boron functionalities in carbon materials since the self-generated pressures favour B–C bond formation. The total content of oxygen increases simultaneously with the boron content, and its speciation is also influenced by the boron chemical state distribution: the presence of C–B–C (BC 3 and BC 2 O) species induces the oxidation of phenols to carbonyls. The electrochemical performance of the prepared carbons was tested in a three-electrode cell configuration (1 M H 2 SO 4 ) showing good specific capacitances per BET specific surface area (20–36 μF/cm 2 ). The presence of boron on the carbon backbone improves both the charge propagation and the pseudocapacitive properties. Nevertheless, the electrochemical properties are only enhanced up to some level of boron doping (around 1.8 wt.%). A two-electrode supercapacitor built with a carbon prepared by a mild hydrothermal synthesis (50 °C during 28 h) delivered energy densities similar to those of commercial activated carbons. This could lead to high volumetric capacitance, since the boron doped carbons present much higher density.