Capacitive deionization using biomass-based microporous salt-templated heteroatom-doped carbons

Microporous carbons are an interesting material for electrochemical applications. In this study, we evaluate several such carbons without/with N or S doping with regard to capacitive deionization. For this purpose, we extent the salt-templating synthesis towards biomass precursors and S-doped microporous carbons. The sample with the largest specific surface area (2830 m2 g−1) showed 1.0 wt % N and exhibited a high salt-sorption capacity of 15.0 mg g−1 at 1.2 V in 5 mM aqueous NaCl. While being a promising material from an equilibrium performance point of view, our study also gives first insights to practical limitations of heteroatom-doped carbon materials. We show that high heteroatom content may be associated with a low charge efficiency. The latter is a key parameter for capacitive deionization and is defined as the ratio between the amounts of removed salt molecules and electrical charge

The sustainable materials roadmap

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 'critical' by the European Union and Department of Energy. Except in sustainable energy, materials are also key components in packaging, construction, and textile industry along with many other industrial sectors. This roadmap authored by prominent researchers working across disciplines in the very important field of sustainable materials is intended to highlight the outstanding issues that must be addressed and provide an insight into the pathways towards solving them adopted by the sustainable materials community. In compiling this roadmap, we hope to aid the development of the wider sustainable materials research community, providing a guide for academia, industry, government, and funding agencies in this critically important and rapidly developing research space which is key to future sustainability.journal articl

Opening of bottleneck pores for the improvement of nitrogen doped carbon electrocatalysts

A facile synthesis strategy to control the porosity of ionothermal nitrogen doped carbons is demonstrated. Adenine is used as cheap and biomass based precursor and a mixture of NaCl/ZnCl2 as combined solvent-porogen. Variation of the ratio between the two salt influences the pore structure over a wide range. The eutectic mixture leads to micro- and mesoporous material with high total pore volume (TPV) of 3.0 cm3 g−1 and very high surface area of 2900 m2 g−1 essentially rendering the product an “all-surface-area” nitrogen doped carbon. Increasing NaCl contents cause a continuous increase of the mesopore size and the formation of additional macropores resulting in a very high maximal TPV of 5.2 cm3 g−1, showing 2540 m2 g−1 specific surface area using 60 mol% NaCl. Interestingly, the electrocatalytic activity of the samples toward oxygen reduction is strongly affected by the detailed pore structure. The different—however, chemically equivalent—catalysts vary up to 70 mV in their half wave potentials (E 1/2).The sample with optimized pore system shows a high selectivity toward the favored four electron process and an outstanding E 1/2 of ≈880 mV versus reversible hydrogen electrode (RHE), which is one of the best values reported for nitrogen doped carbons so far

Glucose derived ionothermal carbons with tailor-made porosity

An ionothermal synthesis strategy to obtain a set of glucose derived carbons with tailored pore system is demonstrated. The biomass derived materials possess high surface areas and large total pore volumes with values up to 2160 m2 g−1 and 1.74 cm3 g−1, respectively. The tailoring of the pore system is realized by simply changing the molar composition of the KCl/ZnCl2 mixture which serves as combined solvent-porogen. Increasing KCl contents result in a continuous pore opening and rising pore volume leading to enhanced mass transport porosity. Those effects are accompanied by a linear decrease of the specific surface area which allows for the preparation of porous carbons of high and predictable surface areas between 2160 and 960 m2 g−1. Experiments exemplarily shown for the application as supercapacitor electrodes, the different materials show a decreased gravimetric capacity, but enhanced capacity retention as well as improved areal capacity with increased KCl content nicely supporting the improved mass transport properties

Ionothermal template transformations for preparation of tubular porous nitrogen doped carbons

A facile approach for the Zn-free ionothermal synthesis of highly porous nitrogen doped carbons possessing tubular transport pores is demonstrated employing adenine as biomass derived precursor and surfactant together with calcium or magnesium chloride hydrates as combined solvent-porogens. The overall process can be regarded as a combination of liquid templating by means of sol–gel synthesis with hard templating via in situ transformation of the melt into solid fibrous salt crystals. The employment of MgCl2·6H2O results in tubular nitrogen doped carbons showing anisotropic porosity and very high specific surface areas up to 2780 m2 g−1 and total pore volumes up to 3.86 cm3 g−1. The formation of the tubular porosity can be connected to a cooperative effect between in situ formed, solid hydrate phases and their modulation with adenine and its polycondensation products. The combination of high SSA with the channel-like porosity generates a highly accessible structure making those carbon materials appealing for applications that demand good mass transport. The obtained materials were exemplarily employed as supercapacitor electrodes resulting in high specific capacitances up to 238 F g−1 at a low scan rate of 2 mV s−1 and up to 144 F g−1 at a high scan rate of 200 mV s−1

Nitro lignin-derived nitrogen-doped carbon as an efficient and sustainable electrocatalyst for oxygen reduction

The use of lignin as a precursor for the synthesis of materials is nowadays considered very interesting from a sustainability standpoint. Here we illustrate the synthesis of a micro-, meso-, and macroporous nitrogen-doped carbon (NDC) using lignin extracted from beech wood via alkaline hydrothermal treatment and successively functionalized via aromatic nitration. The so obtained material is thus carbonized in the eutectic salt melt KCl/ZnCl2. The final NDC shows an excellent activity as electrocatalyst for the oxygen reduction reaction

Template-Free One-Pot Synthesis of Porous Binary and Ternary Metal Nitride@N-Doped Carbon Composites from Ionic Liquids

Herein we present a straightforward synthesis approach toward composites of titanium, vanadium, and titanium–vanadium nitride nanoparticles embedded in nitrogen-doped carbon. These materials can be easily prepared via the heat treatment of mixtures of the corresponding metal precursors TiCl₄ or VOCl₃ dissolved in the ionic liquid 1-butyl-3-methyl-pyridinium dicyanamide (Bmp-dca) as the nitrogen/carbon source. WAXS diffractograms and TEM pictures of the resulting materials reveal the presence of highly crystalline metal nitride nanoparticles with an average diameter of 5 nm embedded in a graphitic carbon matrix. XPS measurements show that the carbon network is heavily doped with nitrogen; that is, it can be described as a nitrogen-doped carbon. Nitrogen sorption measurements show type I isotherms indicative of mainly microporous composites. The specific BET surface area increases with increasing amount of the metal precursor, and it is also dependent on the respective metal ion used. Under similar synthetic conditions, the specific surface areas for VN composites are higher than those of TiN materials, reaching values up to 550 m² g^–1 for VN. It is worth mentioning that these high surface areas can be reached without a template or etching; thus, it is an inherent structural feature of the composite. Furthermore, the use of ionic liquids as precursors offers the possibility for facile processing before material generation; that is, shaping, printing, or casting can be easily performed

Vertically Aligned Two-Dimensional Graphene-Metal Hydroxide Hybrid Arrays for Li–O₂ Batteries

Lithium oxygen batteries (LOBs) are a very promising upcoming technology which, however, still suffers from low lifespan and dramatic capacities fading. Solid discharge products increase the contact resistance and block the electrochemically active electrodes. The resulting high oxidative potentials and formation of Li₂CO₃ due to electrolyte and carbon electrode decomposition at the positive electrode lead to irreversible deactivation of oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) sites. Here we demonstrate a facile strategy for the scalable production of a new electrode structure constituted of vertically aligned carbon nanosheets and metal hydroxide (M­(OH)_<i>x</i>@CNS) hybrid arrays, integrating both favorable ORR and OER active materials to construct bifunctional catalysts for LOBs. Excellent lithium–oxygen battery properties with high specific capacity of 5403 mAh g^–1 and 12123 mAh g^–1 referenced to the carbon and M­(OH)_<i>x</i> weight, respectively, long cyclability, and low charge potentials are achieved in the resulting M­(OH)_<i>x</i>@CNS cathode architecture. The properties are explained by improved O₂/ion transport properties and spatially limited precipitation of Li₂O₂ nanoparticles inside interstitial cavities resulting in high reversibility. The strategy of creating ORR and OER bifunctional catalysts in a single conductive hybrid component may pave the way to new cathode architectures for metal air batteries

Mesoporous Nitrogen-Doped Carbon for the Electrocatalytic Synthesis of Hydrogen Peroxide

Mesoporous nitrogen-doped carbon derived from the ionic liquid <i>N</i>-butyl-3-methylpyridinium dicyanamide is a highly active, cheap, and selective metal-free catalyst for the electrochemical synthesis of hydrogen peroxide that has the potential for use in a safe, sustainable, and cheap flow-reactor-based method for H₂O₂ production