Graphene-based materials have emerged as promising candidates for supercapacitor electrodes. However, their low energy density and the poor conductivity of commonly used graphene oxide remain critical challenges. In this study, we leveraged fluorographene chemistry to synthesize a graphene derivative functionalized with out-of-plane pyridine rings, covalently attached on graphene's network (G-Npyr). The resulting material exhibited a specific surface area of 230 m2 g-1 while the removal of fluorine atoms from fluorographene's lattice substantially restored graphene's conductivity. As a result, G-Npyr-based electrodes delivered an energy density of 61 Wh kg-1 at a power density of 907 W kg-1 and a volumetric energy density of 112 Wh L-1. Furthermore, the electrodes demonstrated excellent cycling stability, retaining 90% capacity after 10,000 cycles in 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4). In contrast to aqueous-based electrolytes, the latter allows the cell to operate in wider voltage window of 3.5 V. In addition to the above, the synthesis is scalable, opening the capability for real-life applications. All in all, these findings highlight the potential use of G-Npyr as a high-performance, scalable electrode material for next-generation supercapacitors.

Waste biomass, such as spent coffee grounds (SCG), presents an abundant and sustainable source of carbon for energy storage and other applications. In this study, an ultrahigh surface area carbon was synthesized from spent coffee grounds and evaluated as an electrode material for supercapacitors. Using an alkali activation process with potassium hydroxide (KOH), the produced nanoporous carbon exhibited an ultrahigh BET area (similar to 3600 m2/g) and a large pore volume (1.80 cm3 g-1), with 95% presence of micropores. These structural characteristics significantly enhanced the electrochemical performance of the material, making it suitable for use in energy storage devices. Electron spin resonance (ESR) measurements were conducted to quantify the number of radicals, aiming to shed light on the mechanism behind the formation of high surface area carbons. The activated carbon was tested in a two-electrode supercapacitor setup with an ionic liquid electrolyte, demonstrating excellent capacitive properties. It achieved high specific capacitances of 131 and 96 F g-1 at 0.5 and 4 A g-1, respectively. Furthermore, the material exhibited a gravimetric energy density of 52 W h kg-1 and a power density of 871 W kg-1 at 1 A g-1, outperforming commercially available activated carbons with an S BET of similar to 2500 m2/g. The electrochemical testing showed stable performance across a wide voltage window of up to 3.5 V, with minimal pseudocapacitive behavior, confirming its suitability for use in supercapacitors with high power and energy density demands. This work underscores the potential of converting waste biomass into high-performance energy storage materials, offering an environmentally friendly and cost-effective solution. The results highlight the advantages of using spent coffee grounds-derived activated carbon in supercapacitors, opening pathways for further development of sustainable materials for energy applications.

We report the first synthesis of metal nanoparticles and supported metal nanoparticles on carbon by using hypergolic reactions. Specifically, we report the synthesis of noble metal nanoparticles (Pt, Ag, and Au) using sodium hydride (NaH) as both an ignition trigger and a reducing agent for the corresponding metal salt precursors. In addition, we report the one-step, in situ synthesis of Pt nanoparticles supported on carbon by adding sucrose as the carbon source. The hypergolically synthesized nanoparticles display elliptical morphology and are more crystalline compared with those conventionally synthesized in solution using sodium borohydride (NaBH4). When tested as electrocatalysts, the hypergolic Pt nanoparticles exhibit more than 2 times higher specific electrochemical active surface area (ECSA) and a higher half-wave potential (E-1/2) of 0.94 V vs the reversible hydrogen electrode (RHE) compared to the conventionally synthesized ones. In addition, the electrocatalyst based on the in situ synthesized carbon that was decorated with the Pt nanoparticles synthesized hypergolically outperforms an analogous, state of the art, commercial PtC system. For example, the former shows an attractive E-1/2 (0.94 V) compared with 0.9 V for the commercial PtC. Accelerated durability tests (ADT) in an alkaline environment add another advantage. After 10 000 cycles, the hypergolically synthesized system shows a smaller reduction of E-1/2 and less degradation compared to the commercial PtC (10 mV compared to similar to 30 mV). The work described here represents the first reported synthesis using hypergolic reactions of metal nanoparticles as well as supported metal nanoparticles. The properties of the resulting electrocatalysts demonstrate the versatility and promise of the new approach in materials synthesis and open new avenues for further investigation as electrocatalysts.

Anthropogenic activities related to population growth, economic development, technological advances, and changes in lifestyle and climate patterns result in a continuous increase in energy consumption. At the same time, the rare metal elements frequently deployed as catalysts in energy related processes are not only costly in view of their low natural abundance, but their availability is often further limited due to geopolitical reasons. Thus, electrochemical energy storage and conversion with earth-abundant metals, mainly in the form of single-atom catalysts (SACs), are highly relevant and timely technologies. In this review the application of earth-abundant SACs in electrochemical energy storage and electrocatalytic conversion of chemicals to fuels or products with high energy content is discussed. The oxygen reduction reaction is also appraised, which is primarily harnessed in fuel cell technologies and metal-air batteries. The coordination, active sites, and mechanistic aspects of transition metal SACs are analyzed for two-electron and four-electron reaction pathways. Further, the electrochemical water splitting with SACs toward green hydrogen fuel is discussed in terms of not only hydrogen evolution reaction but also oxygen evolution reaction. Similarly, the production of ammonia as a clean fuel via electrocatalytic nitrogen reduction reaction is portrayed, highlighting the potential of earth-abundant single metal species.

We report a family of carbon sorbents synthesized by integrating hypergolics with activation reactions on a templated substrate. The materials design leads to nanoporous carbons with a BET area of 4800 m2 g-1 with an impressive total pore volume of 2.7 cm3 g-1. To the best of our knowledge, this BET area value is the highest reported in the literature. Electron spin resonance (ESR) measurements determined the number of radicals in an effort to provide a mechanistic understanding of the formation of ultrahigh surface area carbons. In combination with XPS, we propose a mechanism based on the synergistic effect between rim-based pentagonal rings and carbon radicals, which we believe can be exploited to produce other highly porous carbons. The CO2 capture capacity of the hyperporous carbon tested under dynamic CO2 capture conditions was ∼1.25 mmol g-1 versus 0.66 mmol g-1 of a conventionally activated carbon under similar conditions. The CO2 capture kinetics were extremely fast and reached 99% of the total capacity within 120 s. Lastly, supercapacitor electrodes deliver a high volumetric energy density of ∼60 W h L-1 and a volumetric power density of 1 kW L-1, which is the highest reported value for activated carbon.

The development of advanced electrode materials for the next generation of electrochemical energy storage (EES) solutions has attracted profound research attention as a key enabling technology toward decarbonization and electrification of transportation. Since the discovery of graphene's remarkable properties, 2D nanomaterials, derivatives, and heterostructures thereof, have emerged as some of the most promising electrode components in batteries and supercapacitors owing to their unique and tunable physical, chemical, and electronic properties, commonly not observed in their 3D counterparts. This review particularly focuses on recent advances in EES technologies related to 2D crystals originating from non-layered 3D solids (non-van der Waals; nvdW) and their hallmark features pertaining to this field of application. Emphasis is given to the methods and challenges in top-down and bottom-up strategies toward nvdW 2D sheets and their influence on the materials' features, such as charge transport properties, functionalization, or adsorption dynamics. The exciting advances in nvdW 2D-based electrode materials of different compositions and mechanisms of operation in EES are discussed. Finally, the opportunities and challenges of nvdW 2D systems are highlighted not only in electrochemical energy storage but also in other applications, including spintronics, magnetism, and catalysis.

More than 14 billion pencils are manufactured and used globally every year. On average, a pencil is discarded after 60% of its original length has been depleted. In the present work we propose a simple and affordable way of converting this non-neglectable amount of waste into added value carbon product. In particular, we demonstrate the microwave synthesis of carbon from the wood pencil with and without chemical activation. This could be a process stage before the final recycling of the expensive graphite core. In the latter case, irradiation of the wood pencil in a domestic microwave oven heats up the pencil’s graphite core, thus inducing carbonization of its wood casing. The carbonized product consists of amorphous carbon nanosheets having relatively low surface area. However, if the wood pencil is soaked in 50% KOH aqueous solution prior to microwave irradiation, a significantly higher surface area of carbon is obtained, consisting of irregular-shaped porous particles. Consequently, the obtained carbon can easily decolorize a methylene blue aqueous solution, can be used to make pocket warmers or gunpowder, and lastly, serves as an excellent adsorbent towards Cr(VI) removal from water, showing a maximum adsorption capacity of 70–75 mg/g within 24 h at 23 °C, pH = 3.

Graphene derivatives are an emerging and important class of promising materials because they can bear a wide variety of functional groups, rendering them suitable for a plethora of applications, ranging from energy storage to sensorics. Further functionalisation of these materials requires a thorough understanding of their reactivity at the molecular level because the organic functional groups are close to an effectively infinite surface, which may affect their reactivity. Nitrile groups grafted on a graphene can be easily hydrolysed to carboxyl groups, but they are resistant to reduction by LiAlH4. Here, we combine theoretical and experimental methods to explain the resistance of CN groups grafted on the graphene surface in terms of the limited accessibility of these groups for the reduction agent. We highlight that such mechanistic aspects, i.e., steric hindrance of the reaction centres and surface-solvent interactions, play a crucial role in the reactivity of 2D materials.

In a previous work we have demonstrated the carbonization of biomass waste, such as stale bread, spent coffee and cardboard, in piranha solution towards the formation of hypergolic carbons that could be exploited as solid fuels in rocket engines. These cases simply aimed to provide some interesting examples of waste valorization towards a new class of carbon-based rocket fuels rather unique to the piranha solution treatment. In an effort to further strengthen this concept with additional examples herein we report the carbonization of waste tea in piranha solution towards the formation of hypergolic carbons at decent yield. Likewise bread, coffee and cardboard waste, spent tea is also produced in large quantities worldwide every year, thus meriting further attention in this context. Consistently with the previously reported results, the piranha solution-mediated carbonization of waste tea produces carbon nanosheets that spontaneously ignite upon contact with fuming nitric acid HNO3 at ambient conditions. Interestingly, intercalation of the nanosheets with certain ignitable molecules further boosts carbon hypergolicity upon contact with fuming nitric acid HNO3. These findings come to confirm the versatile character of the method in diverting biomass waste into valuable energetic carbons by piranha solution.

In the present work we report for the first time the carbonization of biomass waste, such as stale bread and spent coffee, in piranha solution (H2SO4-H2O2) at ambient conditions. Carbonization is fast and exothermic, resulting in the formation of carbon nanosheets at decent yields of 25–35%, depending on the starting material. The structure and morphology of the nanosheets were verified by X-ray diffraction, Raman, X-ray photoelectron and microscopy techniques. Interestingly, the obtained carbon spontaneously ignites upon contact with fuming nitric acid HNO3 at ambient conditions, thus offering a rare example of hypergolicity involving carbon as the solid fuel (i.e., hypergolic carbon). Based on the relatively large interlayer spacing of the as-produced carbons, a simple structural model is proposed for the observed hypergolicity, wherein HNO3 molecules fit in the gallery space of carbon, thus exposing its basal plane and defect sites to a spontaneous reaction with the strong oxidizing agent. This finding may pave the way towards new type hypergolic propellants based on carbon, the latter exclusively obtained by the carbonization of biomass waste in piranha solution.

Lithium-Sulfur Batteries is promising energy storage systems due to their superior capacity and energy density. A promising solution for drawbacks such as low sulfur utilization and cycling stability is the use of porous carbon as sulfur carrier. On the other hand, cyclic economy and green ideas is of great importance nowadays. Carbon-sulfur cathodes from waste valorization, abundant, and low-cost precursors is an attractive approach. Herein, an activated carbon (AC-Poc) derived from "Posidonia oceanica" sea-waste, was studied as a matrix for the development of a novel carbon-sulfur composite cathode (AC-Poc/S) for the first time. AC-Poc can be used as an effective sulfur host, due to its high specific BET surface area (1264 m(2).g(-1)) hierarchical porous structure, and total pore volume 0.81 cm(3).g(-1). AC-Poc/S reveals an outstanding initial capacity of 1539 mAh.g(-1) as cathode material, combined with high reversible capacity at 0.2 C. Furthermore, the discharge capacity of 390 mAh/g at 2 C reveals good rate capability, even at increased C-rate. AC-Poc/S composite exhibits excellent sulfur utilization (92 %) alongside with sufficiently well electrochemical performance. These results combined with the easy synthesis method of the activated carbon from an abundant and low-cost precursor make AC-Poc/S a very promising material for LSBs applications.

Metal-organic frameworks (MOFs) materials constructed by the coordination chemistry of metal ions and organic ligands are important members of the crystalline materials family. Owing to their exceptional properties, for example, high porosity, tunable pore size, and large surface area, MOFs have been applied in several fields such as gas or liquid adsorbents, sensors, batteries, and supercapacitors. However, poor conductivity and low stability hamper their potential applications in several attractive fields such as energy and gas storage. The integration of MOFs with carbon nanotubes (CNTs), a well-established carbon allotrope that exhibits high conductivity and stability, has been proposed as an efficient strategy to overcome such limitations. By combining the advantages of MOFs and CNTs, a wide variety of composites can be prepared with properties superior to their parent materials. This review provides a comprehensive summary of the preparation of CNT@MOF composites and focuses on their recent applications in several important fields, such as water purification, gas storage and separation, sensing, electrocatalysis, and energy storage (supercapacitors and batteries). Future challenges and prospects for CNT@MOF composites are also discussed.

Hybrid Materials In article number 2104628, Demetrios D. Chronopoulos, Kolleboyina Jayaramulu, Michal Otyepka, and co-workers review the integration of carbon nanotubes with metal–organic frameworks into hybrid materials with augmented properties, otherwise difficult to accomplish by a single class of materials. The authors map the growth, structure, synthetic strategies, properties, and specific applications including water purification, gas storage and separation, sensing, electrocatalysis, supercapacitors, and batteries.

Sulfur represents a low‑cost, sustainable, and high theoretical capacity cathode material for lithium–sulfur batteries, which can meet the growing demand in portable power sources, such as in electric vehicles and mobile information technologies. However, the shuttling effect of the formed lithium polysulfides, as well as their low conductivity, compromise the electrochemical performance of lithium–sulfur cells. To tackle this challenge, a so far unexplored cathode, composed of sulfur covalently bonded directly on graphene is developed. This is achieved by leveraging the nucleophilicity of polysulfide chains, which react readily with the electrophilic centers in fluorographene, as experimental and theoretical data unveil. The reaction leads to the formation of carbon–sulfur covalent bonds and a particularly high sulfur content of 80 mass%. Owing to these features, the developed cathode exhibits excellent performance with only 5 mass% of conductive carbon additive, delivering very high full‑cathode‑mass capacities and rate capability, combined with superior cycling stability. In combination with a fluorinated ether as electrolyte additive, the capacity persists at ≈700 mAh g−1 after 100 cycles at 0.1 C, and at ≈644 mAh g−1 after 250 cycles at 0.2 C, keeping ≈470 mAh g−1 even after 500 cycles.

Hypergolic systems rely on organic fuel and a powerful oxidizer that spontaneously ignites upon contact without any external ignition source. Although their main utilization pertains to rocket fuels and propellants, it is only recently that hypergolics has been established from our group as a new general method for the synthesis of different morphologies of carbon nanostructures depending on the hypergolic pair (organic fuel-oxidizer). In search of new pairs, the hypergolic mixture described here contains polyaniline as the organic source of carbon and fuming nitric acid as strong oxidizer. Specifically, the two reagents react rapidly and spontaneously upon contact at ambient conditions to afford carbon nanosheets. Further liquid-phase exfoliation of the nanosheets in dimethylformamide results in dispersed single layers exhibiting strong Tyndall effect. The method can be extended to other conductive polymers, such as polythiophene and polypyrrole, leading to the formation of different type carbon nanostructures (e.g., photolumincent carbon dots). Apart from being a new synthesis pathway towards carbon nanomaterials and a new type of reaction for conductive polymers, the present hypergolic pairs also provide a novel set of rocket bipropellants based on conductive polymers.

Herein, we present an interesting route to carbon derived from ferrocene without pyrolysis. Specifically, the direct contact of the metallocene with liquid bromine at ambient conditions released rapidly and spontaneously carbon soot, the latter containing dense spheres, nanosheets, and hollow spheres. The derived carbon carried surface C-Br bonds that permitted postfunctionalization of the solid through nucleophilic substitution. For instance, treatment with diglycolamine led to covalent attachment of the amine onto the carbon surface, thus conferring aqueous dispersability to t he solid. The dispersed solid exhibited visible photoluminescence under UV irradiation as a result of surface passivation by the amine. Hence, the present method not only allowed a rapid and spontaneous carbon formation at ambient conditions, but also surface engineering of the particles to impart new properties (e.g., photoluminescence).

A new two-electron photosensitizer, H2BBQ2+[ZnCl4]2-/[(ZnCl)2(μ-BBH)] (BBQ stands for 2,5-bis[bis(pyridin-2-ylmethyl)amino]-1,4-quinone and BBH stands for 2,5-bis[bis(pyridin-2-ylmethyl)amino]-1,4-hydroquinone), has been synthesized and the oxidation state of the ligand was determined by X-ray crystallography and NMR spectroscopy. Under light illumination the H2BBQ2+[ZnCl4]2- + ZnCl2 is reduced quantitatively to [(ZnCl)2(μ-BBH)] (pH ∼ 5) oxidizing H2O to H2O2 as is evident by trap experiments. Electrochemistry gave a reversible two-electron ligand-centered redox wave for [(ZnCl)2(μ-BBH)]. UV-Vis, luminescence and EPR spectroscopies reveal the slow formation of a stable quinone diradical, intermediate of the reaction. DFT calculations are in agreement with the proposed mechanism. Based on this property an aqueous {[(ZnCl)2(μ-BBH)]||H2O2} solar rechargeable galvanic cell has been constructed.

Nanoparticulate titania was synthesized by flame spray pyrolysis and was used to construct photoanodes for photoelectrochemical cells and quantum dot sensitized solar cells. Powders obtained by flame spray pyrolysis were composed of smaller nanoparticles and had higher specific surface areas than common commercial types of titania and this was carried over to the structure of the photoanodes and reflected on the photoelectrocatalytic and solar cell behavior of the photoanodes. The highest specific surface area and the smallest nanoparticle size produced in this work were 249 m(2) g(-1) and 7 nm, respectively. CdS-sensitized photoanodes were affected by the amount of the deposited sensitizer, which was the largest in the case of the powder with the highest specific surface area. When, however, the photoanodes were loaded with a relatively large amount of CdSe sensitizer, the role of the latter increased and the differences between the different forms of titania diminished. (C) 2015 Elsevier B.V. All rights reserved.