Scientific publications

Within the present work, a thermo-responsive ultrafiltration membrane is manufactured based on a polystyrene-block-poly(diethyl acrylamide) block copolymer (BCP). The poly(diethyl acrylamide) block segment features a lower critical solution temperature (LCST) in water, similar to the well-known poly(N-isopropylacrylamide), but having increased biocompatibility and without exhibiting a hysteresis of the thermally induced switching behavior. The BCP is synthesized via sequential “living” anionic polymerization protocols and analyzed by 1H-NMR spectroscopy, size exclusion chromatography, and differential scanning calorimetry. The resulting morphology in the bulk state is investigated by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) revealing the intended hexagonal cylindrical morphology. The BCPs form micelles in a binary mixture of tetrahydrofuran and dimethylformamide, where BCP composition and solvent affinities are discussed in light of the expected structure of these micelles and the resulting BCP membrane formation. The membranes are manufactured using the non-solvent induced phase separation (NIPS) process and are characterized via scanning electron microscopy (SEM) and water permeation measurements. The latter are carried out at room temperature and at 50 °C revealing up to a 23-fold increase of the permeance, when crossing the LCST of the poly(diethyl acrylamide) block segment in water.

It is commonly observed that voids can nucleate and grow in the lithium anode of a solid state Li-ion battery at a location adjacent to the solid electrolyte during the stripping (discharge) phase of the battery; a similar phenomenon is observed in sodium-based batteries. It is hypothesised in the current literature that the formation of these voids is due to the coalescence of vacancies that have been generated at the electrode/electrolyte interface when metal atoms are oxidized and transported into the electrolyte: the slow diffusion of the vacancies away from the electrolyte interface into the adjacent electrode results in their coalescence and the consequent growth of voids. These hypotheses are challenged in the current study by using the Onsager formalism to generate a variational principle for vacancy diffusion. Our analysis reveals that no driving force exists for the diffusion of vacancies into a homogeneous metal electrode that thins by stripping. This finding is contrary to models in the literature which have mistakenly assumed that the vanishing flux at the current collector prevents rigid body motion (drift) of the electrode which in turn prevents thinning of the electrode during stripping. Based on our analysis, we conclude that vacancy diffusion within a homogeneous electrode is not responsible for the nucleation and growth of voids at the interface between a stripping metal electrode and a solid electrolyte.

Recently, carbon spherogels have been introduced as a novel monolithic aerogel composed of hollow spheres. This material is conveniently obtained via polystyrene (PS) sphere templating. In the present study, we apply a water-soluble titania precursor (titanium(IV) bis(ammonium lactate) to the aqueous sol-gel synthesis based on resorcinol-formaldehyde (RF) to effectively encapsulate titania. In this way, a very high mass loading of up to 59 mass% of titania can be confined strictly to the inside of the hollow carbon spheres. In the final synthesis step, carbonization at 800 °C has three simultaneous effects: Transformation of the RF coating on PS into microporous carbon, PS template removal by decomposition, and formation of titania due to precursor dissociation. A deliberate tuning of the microporous carbon shell, accessibility of the titania, titania amount, and titania's polymorph is further demonstrated by thermal treatment under a carbon dioxide atmosphere. In contrast to non-tuned or TiC-containing carbon spherogels, CO2 activation of the composites results in a three orders of magnitude rise of their photocatalytic activity towards hydrogen evolution reaction, which we evaluate using flow and batch reactors. We further show that this effect is related to the partial etching of the carbon shell, which renders the TiO2 surface accessible to the reactants in the solution and allows for an efficient hole scavenging. Given the simplicity of the hybrid carbon spherogel (HCS) composite fabrication, the high degree of control of their morphological characteristics, and the striking effects of CO2-activation on performance, we believe that our results will contribute to the development of similar carbon-inorganic composites.

Herein, a rapid electrochemical approach for testing of yeast cells damage using hydrogen peroxide spiking and Pd-NPs-based electrodes was proposed. The approach is based on the analyzing of electrochemical interactions between the droplets of yeast suspension spiked with hydrogen peroxide solutions (H2O2) and the surface of screen printed electrode modified by palladium nanoparticles (Pd-NPs). For the intact cells the characteristic anodic electrochemical signal recorded at 0.28 – 0.3 V remains at a constant level due to self-regulation processes regardless the spiked amount of hydrogen peroxide. In contrast, the increase of the anodic current corresponding to the added H2O2 concentration reflects the damage of yeast cells. Significantly, by introduction of peroxide-sensitive oxidoreductase in the design of Pd-NPs, which led to the formation of hybrid oxidoreductase-Pd-NPs electrodes, it was possible to modify the electrochemical read-out of the proposed approach.

Lithium-ion batteries are constantly developing as the demands for power and energy storage increase. One promising approach to designing high-performance lithium-ion batteries is using conversion/alloying materials, such as SnO2. This class of materials does, in fact, present excellent performance and ease of preparation; however, it suffers from mechanical instabilities during cycling that impair its use. One way to overcome these problems is to prepare composites with bi-dimensional materials that stabilize them. Thus, over the past 10 years, two-dimensional materials with excellent transport properties (graphene, MXenes) have been developed that can be used synergistically with conversion materials to exploit both advantages. In this work, a 50/50 (by mass) SnO2/Ti3C2Tz nanocomposite is prepared and optimized as a negative electrode for lithium-ion batteries. The nanocomposite delivers over 500 mAh g−1 for 700 cycles at 0.1 A g−1 and demonstrates excellent rate capability, with 340 mAh g−1 at 8 A g−1. These results are due to the synergistic behavior of the two components of the nanocomposite, as demonstrated by ex situ chemical, structural, and morphological analyses. This knowledge allows, for the first time, to formulate a reaction mechanism with lithium-ions that provides partial reversibility of the conversion reaction with the formation of SnO.

High-performance electrochemical applications have expedited the research in high-power devices. As such, supercapacitors, including electrical double-layer capacitors (EDLCs) and pseudocapacitors, have gained significant attention due to their high power density, long cycle life, and fast charging capabilities. Yet, no device lasts forever. It is essential to understand the mechanisms behind performance degradation and aging so that these bottlenecks can be addressed and tailored solutions can be developed. Herein, the factors contributing to the aging and degradation of supercapacitors, including electrode materials, electrolytes, and other aspects of the system, such as pore blocking, electrode compositions, functional groups, and corrosion of current collectors are examined. The monitoring and characterizing of the performance degradation of supercapacitors, including electrochemical methods, in situ, and ex situ techniques are explored. In addition, the degradation mechanisms of different types of electrolytes and electrode materials and the effects of aging from an industrial application standpoint are analyzed. Next, how electrode degradations and electrolyte decompositions can lead to failure, and pore blocking, electrode composition, and other factors that affect the device's lifespan are examined. Finally, the future directions and challenges for reducing supercapacitors' performance degradation, including developing new materials and methods for characterizing and monitoring the devices are summarized.

Solvent engineering is a powerful and versatile method to tune colloidal stability. Here, we link the molecular structure of apolar ligand shells on gold nanoparticles with their colloidal stability in solvent mixtures. The agglomeration temperature of the particles was measured with small-angle X-ray scattering. It depended on solvent composition and changed linearly for hexane–hexadecane mixtures, but nonlinearly for cyclohexane–hexadecane and hexanol–hexadecane mixtures. Molecular dynamics (MD) simulations indicate that agglomeration is dominated by temperature-dependent ligand order in the alkane mixtures and that the temperature at which the ligand shell orders depends on the solvent composition near the ligands, which can differ substantially from the bulk composition. Small-angle neutron scattering confirmed that, at intermediate solvent compositions above the agglomeration temperature, the fraction of cyclohexane near the ligands was larger than in the bulk. The enrichment of cyclohexane near the ligands stabilized their disordered state, which, consequently, led to the experimentally observed nonlinear trend of the agglomeration temperature. In contrast, hexanol was depleted from the ligand shell at all temperatures. This again stabilized the disordered state. Furthermore, we found that agglomeration at high hexanol fractions was driven by a solvophobic effect that exceeded the influence of ligand order. The results show that strong nonlinearities in the colloidal stability of nanoparticle dispersions in solvent mixtures are directly linked to the molecular details of ligand–solvent and solvent–solvent interactions, which can be used to precisely tune stability.

Supercapacitors are highly valued energy storage devices with high power density, fast charging ability, and exceptional cycling stability. A profound understanding of their charging mechanisms is crucial for continuous performance enhancement. Electrochemical quartz crystal microbalance (EQCM), a detection means that provides in situ mass change information during charging–discharging processes at the nanogram level, has received greatly significant attention during the past decade due to its high sensitivity, non-destructiveness and low cost. Since being used to track ionic fluxes in porous carbons in 2009, EQCM has played a pivotal role in understanding the charging mechanisms of supercapacitors. Herein, we review the critical progress of EQCM hitherto, including theory fundamentals and applications in supercapacitors. Finally, we discuss the fundamental effects of ion desolvation and transport on the performance of supercapacitors. The advantages and defects of applying EQCM in supercapacitors are thoroughly examined, and future directions are proposed.

Additive manufacturing enables the fabrication of bio-inspired materials possessing intricate architectures across broad length scales leading to systems that are simultaneously stiff, tough, and lightweight. A digital light processing (DLP) strategy was used to additively manufacture polymer foams with controlled porosity through the incorporation of thermally expandable microspheres. Following initial photopolymerization, a subsequent thermal processing step reproducibly allows access to a broad range of foam densities. Using uniaxial compression, we investigated how foaming impacts the mechanics of the composite material, including modulus, Poisson’s ratio, and energy dissipation. It was observed that the 3D-printed foams are remarkably resilient under cyclic loading, with sustained values of both modulus and energy dissipation under repeated loading at large deformations.

Actin-based motility is a complex process in which the actin-polymerization is the primary force-generating motor machinery. It can produce protrusive forces through actin filaments polymerization and cross-link during lamellipodia protrusion in migrating cells and it is responsible for the intracellular motion of certain pathogens in infected host cells. We propose a multi-physics model for actin-based motility, stemming from continuity equations that account for the actin chemical kinetics. Thermodynamic restrictions are identified, moving from the multiplicative decomposition of the deformation gradient into chemical and elastic parts. Constitutive theory and chemical kinetics are prescribed to finally write governing equations for the multi-physics problem. The field equations are solved numerically with the finite element method. As a proof of concept, a one-dimensional model for actin-based motility of bacteria pathogens is studied.