Prof. Dr. Volker Presser

This study reports on the low-pressure hydrogen (H2) and deuterium (D2) physisorption processes in nanoporous activated carbon cloth at supercritical temperatures. In-situ small-angle neutron scattering (SANS) is employed as a hydrogen-sensitive method to determine the pore-size-dependent and isotope-dependent adsorbate densification for different gas pressures up to 1 bar. The changes of the SANS signal resulting from the physisorption of adsorbate molecules in the pore space is described by analytical pore scattering functions resembling slit-like pores. Analysis based on a hierarchical pore model allows quantifying the pore-size-dependent physical density of the confined adsorbate for three pore classes, resembling roughly the IUPAC classes of ultramicropores, supermicropores, and mesopores. While the adsorbate density within the very smallest pores approaches the bulk solid density of H2 for pressures of about 1 bar at 77 K, it remains much lower for larger pores. A high density is also found for D2 within ultramicropores, but these results are hampered by a subtle effect of an exchange of chemically bound hydrogen by deuterium in the sample. These findings contribute to a fundamentally better understanding of confinement effects on hydrogen densification, and affect materials design for efficient hydrogen storage devices working at realistic cryogenic conditions and low pressures.

The development of flexible and wearable electronics has grown in recent years with applications in different fields of industry and science. Consequently, the necessity of functional, flexible, safe, and reliable energy storage devices to meet this demand has increased. Since the classical electrochemical systems face structuration and operational limitations to match the needs of flexible devices, novel approaches have been in the research spotlight: gel polymer electrolytes (GPEs). Combining comparable ionic conductivity with liquid electrolytes with desirable mechanical stability, GPEs have been investigated in various electrochemical applications in sensors, actuators, and energy storage. This versatile class of quasi-solid material finds applications in the different components of energy storage devices. They are being investigated as electrodes, binders, electrolytes, and stand-alone systems due to desirable physical-chemical characteristics such as a wider potential operational window and high adhesion to solid electrode materials. Coalescing a liquid phase occluded into an entangled 3D polymeric matrix, these materials withstand elevated mechanical stress such as strain and compression, and they are also interesting materials for various applications. Moreover, they allow further functionalization to match the specific requirements of various energy storage systems. In this review, we summarize different applications of GPEs in energy storage devices, highlighting many valuable properties and emphasizing their enhancements compared to classical liquid electrochemical energy storage systems.

Environmentally friendly polymers such as cellulose acetate (CA) and chitosan (CS) were used to obtain electrospun fibers for Cu2+, Pb2+, and Mo6+ capture. The solvents dichloromethane (DCM) and dimethylformamide (DMF) allowed the development of a surface area of 148 m2 g−1 for CA fibers and 113 m2 g−1 for cellulose acetate/chitosan (CA/CS) fibers. The fibers were characterized by IR-DRIFT, SEM, TEM, CO2 sorption isotherms at 273 K, Hg porosimetry, TGA, stress-strain tests, and XPS. The CA/CS fibers had a higher adsorption capacity than CA fibers without affecting their physicochemical properties. The capture capacity reached 102 mg g−1 for Cu2+, 49.3 mg g−1 for Pb2+, and 13.1 mg g−1 for Mo6+. Furthermore, optimal pH, adsorption times qt, and C0 were studied for the evaluation of kinetic models and adsorption isotherms. Finally, a proposal for adsorbate-adsorbent interactions is presented as a possible capture mechanism where, in the case of Mo6+, a computational study is presented. The results demonstrate the potential to evaluate the fibers in tailings wastewater from copper mining.

MXene is investigated as an electrode material for different energy storage systems due to layered structures and metal-like electrical conductivity. Experimental results show MXenes possess excellent cycling performance as anode materials, especially at large current densities. However, the reversible capacity is relatively low, which is a significant barrier to meeting the demands of industrial applications. This work synthesizes N-doped graphene-like carbon (NGC) intercalated Ti3C2Tx (NGC-Ti3C2Tx) van der Waals heterostructure by an in situ method. The as-prepared NGC-Ti3C2Tx van der Waals heterostructure is employed as sodium-ion and lithium-ion battery electrodes. For sodium-ion batteries, a reversible specific capacity of 305 mAh g−1 is achieved at a specific current of 20 mA g−1, 2.3 times higher than that of Ti3C2Tx. For lithium-ion batteries, a reversible capacity of 400 mAh g−1 at a specific current of 20 mA g−1 is 1.5 times higher than that of Ti3C2Tx. Both sodium-ion and lithium-ion batteries made from NGC-Ti3C2Tx shows high cycling stability. The theoretical calculations also verify the remarkable improvement in battery capacity within the NGC-Ti3C2O2 system, attributed to the additional adsorption of working ions at the edge states of NGC. This work offers an innovative way to synthesize a new van der Waals heterostructure and provides a new route to improve the electrochemical performance significantly.

The demand for electronic devices that utilize lithium is steadily increasing in this rapidly advancing technological world. Obtaining high-purity lithium in an environmentally friendly way is challenging by using commercialized methods. Herein, we propose the first fuel cell system for continuous lithium-ion extraction using a lithium superionic conductor membrane and advanced electrode. The fuel cell system for extracting lithium-ion has demonstrated a twofold increase in the selectivity of Li+/Na+ while producing electricity. Our data show that the fuel cell with a titania-coated electrode achieves 95% lithium-ion purity while generating 10.23 Wh of energy per gram of lithium. Our investigation revealed that using atomic layer deposition improved the electrode's uniformity, stability, and electrocatalytic activity. After 2000 cycles determined by cyclic voltammetry, the electrode preserved its stability.

Developing thin, freestanding electrodes that work simultaneously as a current collector and electroactive material is pivotal to integrating portable and wearable chemical sensors. Herein, we have synthesized graphene/Prussian blue (PB) electrodes for hydrogen peroxide detection (H2O2) using a two-step method. First, an reduced graphene oxide/PAni/Fe2O3 freestanding film is prepared using a doctor blade technique, followed by the electrochemical deposition of PB nanoparticles over the films. The iron oxide nanoparticles work as the iron source for the heterogeneous electrochemical deposition of the nanoparticles in a ferricyanide solution. The size of the PB cubes electrodeposited over the graphene-based electrodes was controlled by the number of voltammetric cycles. For H2O2 sensing, the PB10 electrode achieved the lowest detection and quantification limits, 2.00 and 7.00 μM, respectively. The findings herein evidence the balance between the structure of the graphene/PB-based electrodes with the electrochemical performance for H2O2 detection and pave the path for developing new freestanding electrodes for chemical sensors.

The unsustainable dependence of nitrogen fertilizers (NFs) production on energy-intensive processes and its association with nitrate-laden wastewater that fuels harmful algal blooms (HABs) necessitate innovative solutions. Here, we propose a paradigm shift: repurposing HABs biomass as carbon-based catalysts (Cu1Mo1/NC) for the ambient-condition electrosynthesis of NFs from NO3− and CO2. Remarkably, Cu1Mo1/NC delivers a high NFs yield rate of 2303 μg h−1 mgcat−1 (772 μg h−1mgcat−1 for urea and 1531 μg h−1 mgcat−1 for ammonia) with a Faradaic efficiency (FE) of 68.4% (15.2% for urea and 53.2% for ammonia) at −1.05 V vs. RHE. Experimental and theoretical evidence reveal that Cu doping tunes the d-band center of Cu1Mo1/NC, bringing it closer to the Fermi level. This enhances the intermediate adsorption, thereby propelling the C-N coupling reaction. Carbon reduction potential analysis underscores the promising feasibility and sustainable value of the presented method.

Herein, we report polyphosphonate covalent organic frameworks (COFs) constructed via P-O-P linkages. The materials are synthesized via a single-step condensation reaction of the charge-assisted hydrogen-bonded organic framework, which is constructed from phenylphosphonic acid and 5,10,15,20‐tetrakis[p‐phenylphosphonic acid]porphyrin and is formed by simply heating its hydrogen-bonded precursor without using chemical reagents. Above 210 °C, it becomes an amorphous microporous polymeric structure due to the oligomerization of P-O-P bonds, which could be shown by constant-time solid-state double-quantum 31P nuclear magnetic resonance experiments. The polyphosphonate COF exhibits good water and water vapor stability during the gas sorption measurements, and electrochemical stability in 0.5 M Na2SO4 electrolyte in water. The reported family of COFs fills a significant gap in the literature by providing stable microporous COFs suitable for use in water and electrolytes. Additionally, we provide a sustainable synthesis route for the COF synthesis. The narrow pores of the COF effectively capture CO2.

Efficient separation of specific ions from aqueous media is crucial for advanced water treatment and resource recovery. Flow electrode capacitive deionization (FCDI) offers potential for selective ion removal through continuous operation. This study evaluates the performance of selective cation separation using a commercial activated carbon slurry in a multi-ion solution of monovalent (Li+, Na+, K+) and bivalent (Ca2+, Mg2+) cations. We assess ion removal and cation selectivity under different operational parameters, such as applied potential, slurry flow rate, and feed water flow rate. Our data show that bivalent cations, namely Ca2+ and Mg2+, are preferentially removal due to their higher charge-to-size ratio, aligning with hydrated ion sizes. The highest separation rate was observed for Ca2+ (5.7 μg cm−2 min−1), and the lowest for Li+ (0.2 μg cm−2 min−1). At the highest applied voltage (1.2 V), charge efficiencies reached 70 %, with an energy consumption of 41 Wh mol−1 for nearly complete cation removal. Optimal conditions were identified with a slurry flow rate of 6 mL min−1, feed water flow rate of 2 mL min−1, activated carbon content of 10 mass%, 1 mass% carbon black, and a cell voltage of 1.2 V. These findings highlight the importance of optimizing operational parameters to enhance ion removal.

This study explores the potential of re-purposing end-of-life commercial supercapacitors as electrochemical desalination cells, aligning with circular economy principles. A commercial 500-Farad supercapacitor was disassembled, and its carbon electrodes underwent various degrees of modification. The most straightforward modification involved NaOH-etching of the aluminum current collector to produce free-standing carbon films. More advanced modifications included CO2 activation and binder-added wet processing of the electrodes. When evaluated as electrodes for electrochemical desalination via capacitive deionization of low-salinity (20 mM) NaCl solutions, the minimally modified NaOH-etched carbon electrodes achieved an average desalination capacity of 5.8 mg g−1 and a charge efficiency of 80 %. In contrast, the CO2-activated, wet-processed electrodes demonstrated an improved desalination capacity of 7.9 mg g−1 and a charge efficiency above 90 % with stable performance over 20 cycles. These findings highlight the feasibility and effectiveness of recycling supercapacitors for sustainable water desalination applications, offering a promising avenue for resource recovery and re-purposing in pursuing environmental sustainability.