Prof. Dr. Volker Presser

Summary Electrochemical seawater desalination has drawn significant attention as an energy-efficient technique to address the global issue of water remediation. Microporous carbons, that is, carbons with pore sizes smaller than 2 nm, are commonly used for capacitive deionization. However, micropores are ineffective for capacitive deionization at high molar strength because of their inability to permselectively uptake ions. In our work, we combine experimental work with molecular dynamics simulation and reveal the ability of sub-nanometer pores (ultramicropores) to effectively desalinate aqueous media at seawater-like molar strength. This is done without any ion-exchange membrane. The desalination capacity in 600 mM reaches 12 mg/g, with a charge efficiency of 94% and high cycling stability over 200 cycles (97% of charge efficiency retention). Using molecular dynamic simulations and providing experimental data, our work makes it possible both to understand and to calculate desalination capacity and charge efficiency at high molar strength as a function of pore size.

As freshwater shortage has become a global issue, water desalination technique is of great importance to meet the increasing demand for freshwater resources of human beings. Capacitive deionization (CDI) has attracted significant attention in the current desalination technology portfolio. This is because of the use of low-cost electrode materials and the promise of high energy efficiency when including the energy recovery process. CDI, which has its advantage for applying low ionic strength by using various materials, has been explored to improve the system's performance. However, very few have addressed the importance of proper parameter designs, especially the electrodes. In our work, the same activated carbon of different average particle sizes has been studied by applying different desalination parameters (flow rate, holding time, salt concentrations). Our data show that larger particles limit intraparticle ion transportation because of the increased diffusion path length. We also see that a higher packing density, often favored by smaller particles or distribution of particle sizes, is detrimental to interparticle ion transportation. Our work addressed the importance of proper electrode and desalination parameter design for higher desalination performances.

Electrolyte confinement inside carbon nanopores strongly affects ion electrosorption in capacitive deionization. A thorough understanding of the intricate pore size influence enables enhanced charge storage performance and desalination in addition to ion separation. In subnanometer pores, where the pore size is smaller than hydrated ion size, a dehydration energy barrier must be overcome before the ions can be electrosorbed into the pores. Ion sieving is observed when the dehydration energy is larger than the applied energy. However, when a high electrochemical potential is used, the ions can desolvate and enter the pores. Capitalizing on the difference in size and dehydration energy barriers, this work applies the subnanometer porous carbon material, and a high electrochemical ion selectivity for Cs+ and K+ over Na+, Li+, Mg2+, and Ca2+ is observed. This establishes a possible way for selective heavy metal removal by varying pore and solvated ion sizes. Our work also shows the transition from double-layer capacitance to diffusion-limited electrochemical features in narrow ultramicropores.

A nanocomposite of graphene, cobalt hydroxide and nickel can conveniently be synthesized on gold-silver alloy lines. Using a two-step electrodeposition method, the scaly morphology is pre-deposited on a Ni film, followed by the interconnecting corrugated graphene/cobalt hydroxide composite nanomaterial. Due to the pre-deposited Ni film, the area capacity of the graphene/cobalt hydroxide/Ni electrode is 1.6-times of the graphene/cobalt hydroxide electrode. The kinetic analysis of the graphene/cobalt hydroxide/Ni electrode displays diffusion and non-diffusion contributions of 38% and 62% at 10 mV s−1, respectively. X-ray photoelectron spectroscopy exhibits the oxidation of Co2+ to Co3+ dedicated to the OH- ion insertion. Furthermore, graphene/cobalt hydroxide/Ni//activated carbon flexible micro-supercapacitor (MSC) was assembled by gel KOH-PVA electrolyte, graphene/cobalt hydroxide/Ni (positive electrode), and activated carbon (negative electrode), which manifests maximum volumetric energy of 18.6 mWh cm−3. Moreover, MSC retains over 94% capacitance after 10,000 cycles. After 1,000 continuous bending/unbending cycles at a 180° bending angle with the frequency of 100 mHz, the capacitance retention of MSC is still maintained at 97% of the initial value. The results show outstanding flexibility and mechanical stability of MSC based on graphene/cobalt hydroxide/Ni electrode and confirm that further chemical and physical optimization may lead to the development of quasi-solid-state hybrid MSCs.

Highly water-soluble, persistent, and mobile organic compounds (PMOCs) are more and more often detected in surface and groundwater, evoking potential threats to the environment and human health. Traditional water treatment strategies, including adsorption by activated carbon materials, fail to efficiently remove PMOCs due to their hydrophilic nature. Electro-assisted sorption processes offer a clean, facile, and promising solution to remove PMOCs on activated carbon-based electrodes and potentially allow an easy on-site sorbent regeneration (trap&release). In this work, the electrosorption of five selected PMOCs, that is, tetrapropylammonium (TPA+), benzyltrimethylammonium (BTMA+), p-tosylate (p-TsO-), p-toluenesulfonamide (p-TSA), and methyl-tert-butyl ether (MTBE), were investigated on two comprehensively characterized activated carbon felt (ACF) types carrying different surface functionalities. Significant enrichment factors in ranges of 102 to 103 for charged PMOCs were expected by our first estimation for electro-assisted trap&release on ACFs in flow systems applying potentials in the range of −0.1 V/+0.6 V vs. SHE for ad-/desorption, respectively. Defunctionalized ACF carrying larger density in surface π-systems and lower O-content promises a higher capability in electrosorption processes than the pristine material in terms of better material stability (tested for 5 cycles over 500 h) and better removal efficiency of ionic PMOCs. To improve ACFs adsorption performance for cationic and anionic PMOCs, permanent chemical surface modification and reversible electric polarization as alternative strategies are compared. Our findings explore future electrode and process design of electrosorption for applications to treat water contaminated by emerging PMOCs.

Pneumococcal infections represent a global health threat, which requires novel vaccine developments. Extracellular vesicles are secreted from most cells, including prokaryotes, and harbor virulence factors and antigens. Hence, bacterial membrane vesicles (MVs) may induce a protective immune response. For the first time, we formulate spray-dried gram-positive pneumococcal MVs-loaded vaccine microparticles using lactose/leucine as inert carriers to enhance their stability and delivery for pulmonary immunization. The optimized vaccine microparticles showed a mean particle size of 1–2 µm, corrugated surface, and nanocrystalline nature. Their aerodynamic diameter of 2.34 µm, average percentage emitted dose of 88.8%, and fine powder fraction 79.7%, demonstrated optimal flow properties for deep alveolar delivery using a next-generation impactor. Furthermore, confocal microscopy confirmed the successful encapsulation of pneumococcal MVs within the prepared microparticles. Human macrophage-like THP-1 cells displayed excellent viability, negligible cytotoxicity, and a rapid uptake around 60% of fluorescently labeled MVs after incubation with vaccine microparticles. Moreover, vaccine microparticles increased the release of pro-inflammatory cytokines tumor necrosis factor and interleukin-6 from primary human peripheral blood mononuclear cells. Vaccine microparticles exhibited excellent properties as promising vaccine candidates for pulmonary immunization and are optimal for further animal testing, scale-up and clinical translation.

Abstract Electrochemical ion separation is a promising technology to recover valuable ionic species from water. Pseudocapacitive materials, especially 2D materials, are up-and-coming electrodes for electrochemical ion separation. For implementation, it is essential to understand the interplay of the intrinsic preference of a specific ion (by charge/size), kinetic ion preference (by mobility), and crystal structure changes. Ti3C2Tz MXene is chosen here to investigate its selective behavior toward alkali and alkaline earth cations. Utilizing an online inductively coupled plasma system, it is found that Ti3C2Tz shows a time-dependent selectivity feature. In the early stage of charging (up to about 50 min), K+ is preferred, while ultimately Ca2+ and Mg2+ uptake dominate; this unique phenomenon is related to dehydration energy barriers and the ion exchange effect between divalent and monovalent cations. Given the wide variety of MXenes, this work opens the door to a new avenue where selective ion-separation with MXene can be further engineered and optimized.

The considerable growth of the world population, concomitant with an increase in environmental pollution, aggravates the antinomy between supply and demand for drinking water. Various desalination technologies have been developed to address this issue, allowing for abundant saltwater as a source for drinking water. Electrochemical desalination attracts more and more attention due to its high energy efficiency, facile operation, and low cost. Especially within the last decade, tremendous scientific progress on electrochemical desalination technologies has been made. This paper reviews the development of electrochemical desalination technologies and introduces a facile classification into three generations according to the different working principles. The cell architecture, metrics, advantages, and disadvantages of other electrochemical desalination technologies are introduced and compared.

Capacitive deionization (CDI) is based on ion electrosorption and has emerged as a promising desalination technology, for example, to obtain drinking water from brackish water. As a next-generation technology, battery desalination uses faradaic processes and, thereby, enables higher desalination capacities and remediation of feed water with high molar strength such as seawater. However, the full use of a large capacity of charge transfer processes is limited by the voltage window of water and the need to use electrode materials non-reactive towards the water. Using our multi-channel bi-electrolyte cell, we now introduce for the first time an alloying electrode for sodium removal in the context of water desalination. Separated by a ceramic sodium superionic conductor (NASICON) membrane, the antimony/carbon composite electrode accomplished sodium removal while chlorine removal is enabled via ion electrosorption with nanoporous carbon (activated carbon cloth). In a sodium-ion battery half-cell setup, the antimony/carbon composite electrode reaches an initial capacity of 714 mA h g−1 at a specific current of 200 mA g−1, which shows a slow but continuous degrading over the course of 80 cycles (426 mA h g−1 in 80th cycle). Our hybrid CDI cell provides a desalination capacity of an average of 294 mgNa gSb−1 (748 mgNaCl gSb−1) with a charge efficiency of ca. 74% in a 600 mM NaCl at a specific current of 200 mA g−1 and a voltage range of −2.0 V to +2.0 V.

Due to their various applications, metal oxides are of high interest for fundamental research and commercial usage. Per applications as catalysts or electrochemical devices, the tailored design of metal oxides featuring a high specific surface area and additional functionalities is of the utmost importance for the performance of the resulting materials. We report a new method for preparing free-standing films consisting of hierarchically porous metal oxides (titanium and niobium based) by combining emulsion polymerization and shear-induced monodisperse particle self-assembly in the presence of sol–gel precursors. After thermal treatment, the resulting porous materials can be used as electrodes in Li-ion batteries. The titanium and niobium sol–gel precursors were partially immobilized to the surface of organic core–interlayer particles featuring hydroxyl groups to obtain hybrid organic–inorganic particles through the melt–shear organization process. Free-standing particle-based films, in analogy to elastomeric opal films and colloidal crystals, can be prepared in a convenient one-step preparation process. After thermal treatment, ordered pores are obtained, while the pristine metal oxide precursor shell can be converted to the (mixed) metal oxide matrix. Heat treatment under CO2 leads to mixed-TiNb oxide/carbon hybrid materials. The highly porous derivative structure enhances electrolyte permeation. When tested as Li-ion battery electrodes, it shows a specific capacity of 335 mAh·g–1 at a rate of 10 mA·g–1. After 1000 cycles at 250 mA·g–1, the electrodes still provided a specific capacity of 191 mAh·g–1.