Search

Over the past 150 years, our ability to produce and transform engineered materials has been responsible for our current high standards of living, especially in developed economies. However, we must carefully think of the effects our addiction to creating and using materials at this fast rate will have on the future generations. The way we currently make and use materials detrimentally affects the planet Earth, creating many severe environmental problems. It affects the next generations by putting in danger the future of the economy, energy, and climate. We are at the point where something must drastically change, and it must change now. We must create more sustainable materials alternatives using natural raw materials and inspiration from nature while making sure not to deplete important resources, i.e. in competition with the food chain supply. We must use less materials, eliminate the use of toxic materials and create a circular materials economy where reuse and recycle are priorities. We must develop sustainable methods for materials recycling and encourage design for disassembly. We must look across the whole materials life cycle from raw resources till end of life and apply thorough life cycle assessments (LCAs) based on reliable and relevant data to quantify sustainability. We need to seriously start thinking of where our future materials will come from and how could we track them, given that we are confronted with resource scarcity and geographical constrains. This is particularly important for the development of new and sustainable energy technologies, key to our transition to net zero. Currently ‘critical materials’ are central components of sustainable energy systems because they are the best performing. A few examples include the permanent magnets based on rare earth metals (Dy, Nd, Pr) used in wind turbines, Li and Co in Li-ion batteries, Pt and Ir in fuel cells and electrolysers, Si in solar cells just to mention a few. These materials are classified as

For Li‐ion and Na‐ion batteries, the intercalation behavior of graphite anodes is quite different. While Li‐ions intercalate, Na‐ions only co‐intercalate with solvent molecules from the electrolyte solution leading to ternary graphite intercalation compound (t‐GIC) formation along with an expansion of the graphite interlayer spacing to 1.2 nm. This large interlayer spacing represents a micropore with parallel slit geometry. Little is known about t‐GIC formation, but it is commonly believed that throughout the reaction the ion is accompanied by either a full or partial solvation shell. Here, it is elucidated for the first time, using two independent methods – mass measurements and electrochemical impedance spectroscopy – supplemented by operando microscopy, entropymetry and simulations, that the storage mechanism is far more complex. A new model for the electrochemical solvent co‐intercalation process is proposed: As soon as solvated ions enter, the graphite structure is flooded with free solvents, which are subsequently replaced by solvated ions. Close to full sodiation, few free solvents remain and structural rearrangement take place to reach the full storage capacity. Thus, t‐GICs represent a unique case of switchable microporous systems and hence appear as a bridge between ion storage in the bulk phase and in micropores, i.e., between batteries and supercapacitors., Peer Reviewed

Over the past 150 years, our ability to produce and transform engineered materials has been responsible for our current high standards of living, especially in developed economies. However, we must carefully think of the effects our addiction to creating and using materials at this fast rate will have on the future generations. The way we currently make and use materials detrimentally affects the planet Earth, creating many severe environmental problems. It affects the next generations by putting in danger the future of the economy, energy, and climate. We are at the point where something must drastically change, and it must change now. We must create more sustainable materials alternatives using natural raw materials and inspiration from nature while making sure not to deplete important resources, i.e. in competition with the food chain supply. We must use less materials, eliminate the use of toxic materials and create a circular materials economy where reuse and recycle are priorities. We must develop sustainable methods for materials recycling and encourage design for disassembly. We must look across the whole materials life cycle from raw resources till end of life and apply thorough life cycle assessments (LCAs) based on reliable and relevant data to quantify sustainability. We need to seriously start thinking of where our future materials will come from and how could we track them, given that we are confronted with resource scarcity and geographical constrains. This is particularly important for the development of new and sustainable energy technologies, key to our transition to net zero. Currently 'critical materials' are central components of sustainable energy systems because they are the best performing. A few examples include the permanent magnets based on rare earth metals (Dy, Nd, Pr) used in wind turbines, Li and Co in Li-ion batteries, Pt and Ir in fuel cells and electrolysers, Si in solar cells just to mention a few. These materials are classified as

The co-intercalation of solvent molecules along with Na+ into the crystal lattice of electrode materials is an undesired process in sodium batteries. An exception is the intercalation of ether solvated alkali ions into graphite, a fast and highly reversible process. Here, reversible co-intercalation is shown to also be possible for other layered materials, namely titanium disulfide. Operando X-ray diffraction and dilatometry are used to demonstrate different storage mechanisms for different electrolyte solvents. Diglyme is found to co-intercalate into the TiS2 leading to a change in the voltage profile and an increase in the interlayer spacing (≈150%). This behavior is different compared to other solvents, which expand much less during Na storage (24% for tetrahydrofuran [THF] and for a carbonate mixture). For all solvents, specific capacities (2nd cycle) exceed 250 mAh g−1 whereas THF exhibited the best stability after 100 cycles. The solvent co-intercalation is rationalized by density functional theory and linked to the stability of the solvation shells, which is largest for diglyme. Finally, the TiS2 electrode with diglyme electrolyte is paired with a graphite electrode to realize the first proof-of-concept solvent co-intercalation battery, that is, a battery with two electrodes that both rely on reversible co-intercalation of solvent molecules., European Research Council http://dx.doi.org/10.13039/501100000781, Peer Reviewed

Over the past 150 years, our ability to produce and transform engineered materials has been responsible for our current high standards of living, especially in developed economies. However, we must carefully think of the effects our addiction to creating and using materials at this fast rate will have on the future generations. The way we currently make and use materials detrimentally affects the planet Earth, creating many severe environmental problems. It affects the next generations by putting in danger the future of the economy, energy, and climate. We are at the point where something must drastically change, and it must change now. We must create more sustainable materials alternatives using natural raw materials and inspiration from nature while making sure not to deplete important resources, i.e. in competition with the food chain supply. We must use less materials, eliminate the use of toxic materials and create a circular materials economy where reuse and recycle are priorities. We must develop sustainable methods for materials recycling and encourage design for disassembly. We must look across the whole materials life cycle from raw resources till end of life and apply thorough life cycle assessments (LCAs) based on reliable and relevant data to quantify sustainability. We need to seriously start thinking of where our future materials will come from and how could we track them, given that we are confronted with resource scarcity and geographical constrains. This is particularly important for the development of new and sustainable energy technologies, key to our transition to net zero. Currently ‘critical materials’ are central components of sustainable energy systems because they are the best performing. A few examples include the permanent magnets based on rare earth metals (Dy, Nd, Pr) used in wind turbines, Li and Co in Li-ion batteries, Pt and Ir in fuel cells and electrolysers, Si in solar cells just to mention a few. These materials are classified as, Peer Reviewed

Lithium-ion batteries and related battery concepts show an expansion and shrinkage (“breathing”) of the electrodes during cell cycling. The dimensional changes of an individual electrode or a complete cell can be continuously measured by electrochemical dilatometry (ECD). The obtained data provides information on the electrode/cell reaction itself but can be also used to study side reactions or other relevant aspects, e.g., how the breathing is influenced by the electrode binder and porosity. The method spans over a wide measurement range and allows the determination of macroscopic as well as nanoscopic changes. It has also been applied to supercapacitors. The method has been developed already in the 1970s but recent advancements and the availability of commercial setups have led to an increasing interest in ECD. At the same time, there is no “best practice” on how to evaluate the data and several pitfalls exist that can complicate the comparison of literature data. This review highlights the recent development and future trends of ECD and its use in battery and supercapacitor research. A practical guide on how to evaluate the data is provided along with a discussion on various factors that influence the measurement results., Peer Reviewed

orous carbon materials constitute an excellent conductive matrix for the immobilization of sulfur in the cathode of lithium–sulfur batteries. Herein, we provide a novel, easy, sustainable, general and scalable procedure for the preparation of such cathodes, which combines in the same process both the generation of a S-doped porous carbon and the incorporation of elemental sulfur within the pores. To achieve this, a biomass-based substance (i.e., tannic acid) is activated with sodium thiosulfate, yielding a carbonized solid that includes a high-surface area carbon (up to 2550 m2 g−1) and sodium polysulfides. Once this solid is immersed in an acid medium, the polysulfides generated as activation by-products are oxidized in situ to elemental sulfur that spontaneously diffuses into the pores of the carbon, which gives rise to the hybrid sulfur–carbon composite. When tested as cathodes in lithium–sulfur batteries, these hybrid materials exhibit high sulfur utilization (∼80%) even for the composites with a sulfur content as high as 82%, as well as an excellent rate performance (590 mA h g−1 S at 5C). The cycling stability of the batteries was confirmed by their low capacity fading (0.049% of capacity decay per cycle), maintaining 85% of their initial capacity after 300 charge–discharge cycles at 1C. Cathodes with a high sulfur loading (7.1 mg S per cm2) were steady cycled providing reversible areal capacities of 4.4 mA h cm−2 at 0.2C after 100 charge–discharge cycles.

Highly porous materials with a 3D framework have been produced by a sustainable salt template‐assisted chemical activation approach based on the use of KCl particles as template, K2CO3 particles as both template and activating agent, and biomass‐derivatives as carbon precursor (i. e., glucose and soybean meal). The self‐assembly of all the constituents into a 3D structure is achieved by a freeze‐drying process. After carbonization and a simple washing step with water, a 3D hierarchical porous carbon is obtained. The sustainability of the process is ensured by using chemicals of low or null toxicity and renewable carbon precursors. The materials produced are characterized by a 3D framework composed of thin walls rich in micropores, with BET surface areas in excess of 2000 m2 g−1 and pore volumes of up to 1.4 cm3 g−1. These materials show an improved rate capability in supercapacitors based on aqueous (H2SO4 and Li2SO4) and ionic liquid electrolytes (EMImTFSI/AN) with carbon electrode loadings well within the range of commercial values.

Hierarchically porous carbons with a high surface area have been synthesized by a salt template-assisted chemical activation approach using a biomass-derivative, tannic acid, as the carbon precursor. Tannic acid is pyrolyzed in the presence of KCl, acting as the template and reaction medium, and K2CO3, serving as both the template and activating agent. An important characteristic of our synthesis strategy is that the carbonaceous matter is immersed in a melted mixture constituted by the activating agent and KCl. This reaction medium greatly favours reactivity between the carbon and K2CO3, and yet enhances the carbon yields, which are in the 32–38% range. The porous carbons have large specific surface areas, in the 2250–2750 m2 g−1 range, and their microporosity can be fine-tuned by adjusting the carbonization temperature. When these carbons are tested as the electrode active material for supercapacitors, they exhibit a high capacitance in aqueous and organic electrolytes. The short diffusion pathways provided by their hierarchical architecture allow an excellent electrochemical response in situations of high power demand.

High-surface area carbons are produced from biomass-based products (wood sawdust and tannic acid) by means of an environmentally friendly process based on the use of sodium thiosulfate as activating agent and an inert salt (KCl) that serves as a confinement medium for the activation reaction. These porous carbons have high BET surface areas of up to 2650 m2 g-1, large pore volumes of up to 2.3 cm3 g-1 and a porosity that combines micro- and mesopores in different amounts depending on the quantity of activating agent employed. Such carbons have two additional remarkable properties: a) they are S-doped (2–6 wt% S) and b) they have good electrical conductivities in the 2.5–4.5 S cm-1 range. The above properties make these carbon materials highly attractive as supercapacitor electrodes. Indeed, when tested in a variety of electrolytes (H2SO4, TEABF4/AN and EMImTFSI) using commercial-level mass loadings, they show high specific capacitances (up to 200 F g-1, 140 F g-1 and 160 F g-1 in aqueous, organic and ionic liquid electrolytes, respectively) and high capacitance retention at high rates in all the electrolytes in combination with a good stability under cycling and floating modes.

In situ (operando) electrochemical dilatometry (ECD) provides information on the expansion/shrinkage of an electrode during cell cycling. It is shown that the ECD signal can be used as descriptor to characterize the charge storage behavior of lithium and sodium ions in hard carbon electrodes. It is found that sodium storage in hard carbons occurs by a three-step mechanism, namely I) insertion, II) pore filling, and III) plating. Step III can be seen from a sudden increase in electrode thickness for potentials below around 36 mV versus Na+/Na and is assigned to plating on the hard carbon surface. Interestingly, this last step is absent in the case of lithium which demonstrates that the storage behavior between both alkali metals is different. The plating mechanism is also supported by reference experiments in which bulk plating is enforced. Bulk plating on hard carbon electrodes can be detected more easily for sodium compared to lithium. It is also found that the type of binder strongly influences the dilatometry results. A comparison between the binders sodium salt of carboxymethyl cellulose and poly(vinylidene difluoride) shows that the use of the former leads to notably smaller first electrode expansion as well as a higher initial Coulomb efficiency., Peer Reviewed

A simple, sustainable, and affordable approach for the synthesis of highly porous carbons is presented. The procedure is based on the use of sodium thiosulfate as an activating agent and a variety of biomass-based products (glucose, sucrose, and gelatine) as carbon precursors. The synthesis scheme involves three steps: (a) mixing the reactants by grinding, (b) heat treatment at temperatures in the 800–900 °C range, and (c) extracting the carbon material from the carbonized solid by simple washing with water. The generation of the pore structure is based on the redox reaction between the carbonaceous matter and sodium thiosulfate acting as an oxidant. In this way, porous carbons with high BET surface areas in the ∼2000–2700 m2 g–1 range and large pore volumes of up to 2.4 cm3 g–1 are obtained. The porosity of these carbons consists of two pore systems made up of narrow micropores of 0.8 nm and larger pores of up to 5 nm. These porous carbons have a certain amount of sulfur (∼2–3%) that is incorporated into the carbon framework as thiophene-like and oxidized sulfur groups. Additionally, in the case of gelatine, N content up to 2–3% is preserved.

A novel Fe–N-doped carbon with a dendritic structure is analyzed as an electrocatalyst for the oxygen reduction reaction. The synthesis of the material was accomplished through a nanocasting approach using pyrrole as the nitrogen and carbon source, and iron chloride as the iron dopant. The Fe–N–C thus-synthesized consists of small nanoparticles with a diameter of ∼240 nm and a pompom-like morphology. They exhibit a relatively high specific surface area combined with a very accessible porosity and a high nitrogen (∼11 wt %) and iron (∼5 wt %) content. With respect to electrocatalytic activity, in basic electrolyte the Fe–N-doped carbon nanopompoms exhibited high onset (0.94 V) and half-wave potentials (0.82 V), and a large kinetic current density (19 mA cm–2), higher than commercial platinum catalysts. The electrocatalysts were also tested in acid electrolyte, giving an onset potential of 0.75 V and a peroxide yield lower than 10% over a wide range of potentials. Furthermore, the newly developed carbon nanostructures exhibit excellent durability, better than commercially available platinum in both media. The excellent electrocatalytic activity is attributed to a combination of a high specific surface area with very accessible porosity and the presence of numerous active centers (i.e., iron coordinated to nitrogen and nitrogen functional groups).

A simple one-pot route for the synthesis of highly porous N-doped carbons with an excellent performance as supercapacitor electrodes is presented. The synthesis scheme is based on the carbonization of an organic salt, potassium citrate, at a temperature in the 700-900 ºC range, in the presence of urea. Such porous carbons combine ultra-high BET surface areas of up to 3350 m2·g-1, a large pore volume of up to 2.65 cm3·g-1, a porosity which can be regulated to have a micropore or micro-mesopore network and a notable nitrogen content in the 0.5-4.5 wt % range, two essential properties for their use in electrochemical devices. The presence of urea in the synthesis mixture is the key to pore development in these synthesized carbons. The applicability of this type of carbon as supercapacitor electrode material with an ionic liquid as electrolyte has also been demonstrated in this study.

Polysulfide shuttle effects, active material losses, formation of resistive surface layers, and continuous electrolyte consumption create a major barrier for the lightweight and low-cost lithium-sulfur (Li-S) battery adoption. Tuning electrolyte composition by using additives and most importantly by substantially increasing electrolyte molarity was previously shown to be one of the most effective strategies. Contrarily, little attention has been paid to dilute and super-diluted LiTFSI/DME/DOL/LiNO3 based-electrolytes, which have been thought to aggravate the polysulfide dissolution and shuttle effects. Here we challenge this conventional wisdom and demonstrate outstanding capabilities of a dilute (0.1 mol L-1 of LiTFSI in DME/DOL with 1 wt. % LiNO3) electrolyte to enable better electrode wetting, greatly improved high-rate capability, and stable cycle performance for high sulfur loading cathodes and low electrolyte/sulfur ratio in Li-S cells. Overall, the presented study shines light on the extraordinary ability of such electrolyte systems to suppress short-chain polysulfide dissolution and polysulfide shuttle effects.

The electrochemical intercalation/deintercalation of solvated sodium ions into graphite is a highly reversible process, but leads to large, undesired electrode expansion/shrinkage (“breathing”). Herein, two strategies to mitigate the electrode expansion are studied. Starting with the standard configuration (−) sodium | diglyme (2G) electrolyte | graphite (poly(vinylidene difluoride) (PVDF) binder) (+), the PVDF binder is first replaced with a binder made of the sodium salt of carboxymethyl cellulose (CMC). Second, ethylenediamine (EN) is added to the electrolyte solution as a co‐solvent. The electrode breathing is followed in situ (operando) through electrochemical dilatometry (ECD). It is found that replacing PVDF with CMC is only effective in reducing the electrode expansion during initial sodiation. During cycling, the electrode breathing for both binders is comparable. Much more effective is the addition of EN. The addition of 10 v/v EN to the diglyme electrolyte strongly reduces the electrode expansion during the initial sodiation (+100% with EN versus +175% without EN) as well as the breathing during cycling. A more detailed analysis of the ECD signals reveals that solvent co‐intercalation temporarily leads to pillaring of the graphite lattice and that the addition of EN to 2G leads to a change in the sodium storage mechanism., Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659, European Research Council http://dx.doi.org/10.13039/100010663, Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347, Peer Reviewed

A novel Fe/N-doped carbon with a pompom-like morphology has been synthesized by a nanocasting approach. Its nanosized dendritic structure (~ 240 nm) has a relatively high specific surface area (~ 500 m2/g) and a N content of ~11 wt.%, since a N-rich molecule as polypyrrole was used as the carbon source. A ~5 wt.% of Fe was also introduced by using FeCl3 as the iron dopant. Due to the combination of its readily accessible porosity and the presence of numerous active centers, the nanopompoms showed an excellent electrochemical activity as electrocatalyst for the oxygen reduction reaction in both acid and basic electrolytes, exhibiting high onset potentials (0.94 and 0.75 V in basic and acid electrolyte, respectively) and selectivity toward the preferential 4-electron process. In addition, the nanopompoms showed a better durability than commercially available platinum in both media.

Porous carbons with large specific surface areas (2250-2750 m2 g-1) and hierarchical micro-macro porosity have been synthesized by a salt template-assisted chemical activation route using tannic acid, a biomass-derived compound, as the carbon source. The proposed synthetic route involves the use of K2CO3 and KCl particles, both playing relevant roles, and a single thermal treatment. At low temperatures (~220 ºC), the tannic acid melts and occupies the interstices between the K2CO3 and KCl particles. As the temperature increases, the tannic acid pyrolyzes leaving a carbon framework with a sponge-like structure due to the templating effect of the inorganic particles. Then, the carbon reacts with K2CO3 through redox reactions that generate pores within the carbon framework. Noteworthy, at the temperatures at which activation reactions occur, KCl and K2CO3 form a eutectic liquid mixture in close contact with the carbonaceous matter, which boosts the activation reactions and also provides a confined medium advantageous for achieving high product yields (in the 32–38 % range). All of the inorganic matter can be removed from the carbonization product simply by washing with hot water, avoiding the use of toxic acids. The carbons were tested as electrode active material in symmetric supercapacitors, showing a high capacitance in both aqueous (260 F g-1 in 1M H2SO4) and organic (160 F g-1 in 1M TEABF4 and EMIMTFSI/AN) electrolytes. Moreover, an excellent electrochemical response in situations of high power demand was achieved by virtue of the short diffusional pathways provided by their hierarchical architecture.

A novel, green and sustainable approach for the synthesis of highly porous carbons (surface area ~2000¿2700 m2 g¿1 and pore volume of up to 2.4 cm3 g¿1) is presented. The procedure is based on the use of sodium thiosulfate as activating agent, an inert salt (KCl) as confinement medium for the activation reaction, and a variety of biomass-based products (from simple monosaccharides like glucose to more complex products such as sawdust) as carbon precursors. The porosity of these carbons consists of two pore systems made up of narrow micropores of 0.8 nm and larger pores tunable from 1.5 to 3 nm. An important feature of the developed synthesis strategy is its high yield, up to 20 %, which is similar to the value obtained by the carbonization of the different precursors. Besides, the porous carbons are S-doped (2-6 wt%) and dual N,S-doping can be achieved by using N-rich carbon precursors.

The oxygen reduction reaction (ORR) in aqueous media plays a critical role in sustainable and clean energy technologies such as polymer electrolyte membrane and alkaline fuel cells. In this work, we present a new concept to improve the ORR performance by engineering the interface reaction at the electrocatalyst/electrolyte/oxygen triple-phase boundary using a protic and hydrophobic ionic liquid and demonstrate the wide and general applicability of this concept to several Pt-free catalysts. Two catalysts, Fe–N codoped and metal-free N-doped carbon electrocatalysts, are used as a proof of concept. The ionic liquid layer grafted at the nanocarbon surface creates a water-equilibrated secondary reaction medium with a higher O2 affinity toward oxygen adsorption, promoting the diffusion toward the catalytic active site, while its protic character provides sufficient H+/H3O+ conductivity, and the hydrophobic nature prevents the resulting reaction product water from accumulating and blocking the interface. Our strategy brings obvious improvements in the ORR performance in both acid and alkaline electrolytes, while the catalytic activity of FeNC-nanocarbon outperforms commercial Pt–C in alkaline electrolytes. We believe that this research will pave new routes toward the development of high-performance ORR catalysts free of noble metals via careful interface engineering at the triple point.