Publikationen

Soft robots consisting of stimuli-responsive soft materials are expected to achieve tasks otherwise impossible by robots with conventional rigid counterparts. In spite of good progress made over the past several years, robot mobility on various surfaces remains challenging. Here, we report a footed soft robot with good terrain adaptability and large load carrying capability by mimicking the anisotropic friction of gecko setae and the gait of caterpillars. The robot, termed as Geca-Robot, is composed of gecko-inspired triangular micropillars as the feet and alternating cuboids of polydimethylsiloxane (PDMS) and graphene–PDMS as the muscle. Geca-Robot is remotely powered by light with wavelengths ranging from ultraviolet to infrared, and moves with a caterpillar-like gait. The gecko-inspired feet allows Geca-Robot to unidirectionally travel on terrains of varying roughness, slope, and dryness with a wide working temperature range, and to carry loads weighing approximately 50 times its own mass. Geca-Robot will inspire the creation of further soft robot designs for various natural terrains.

In this paper we explore the printability of reversible networks formed by catechol functionalized PEG solutions and metal cations (Al3+, Fe3+ or V3+). The printability and shape fidelity were dependent on the ink composition (metal ion type, pH, PEG molecular weight) and printing parameters (extrusion pressure and printing speed). The relaxation time, recovery rate and viscosity of the inks were analyzed in rheology studies and correlated with thermodynamic and ligand exchange kinetic constants of the dynamic bonds and the printing performance (i.e. shape fidelity of the printed structures). The relevance of the relaxation time and ligand exchange kinetics for printability was demonstrated. Cells seeded on the materials crosslinked with Al3+, Fe3+ ions were viable and revealed well-spread morphologies during 7 day culture, indicating the potential of the formulations to be used as inks for cell encapsulation. The proposed dynamic ink design offers significant flexibility for 3D bioprinting, and enables straightforward adjustment of the printable formulation to meet application-specific needs.

Light-responsive hydrogels are useful platforms to study cellular responses. Current photosensitive motifs need UV light to be activated, which is intrinsically cytotoxic and has a low penetration depth in tissues. Herein we describe a strategy for near-infrared (NIR) controlled activation of cellular processes (3D cell spreading and angiogenesis) by embedding upconverting nanoparticles (UCNPs) in a hydrogel modified with light-activatable cell adhesive motifs. The UCNPs can convert NIR light (974 nm) into local UV emission and activate photochemical reactions on-demand. Such optoregulation is spatially controllable, dose-dependent and can be performed at different timepoints of the cell culture without appreciable photodamage of the cells. HUVEC cells embedded in this hydrogel can form vascular networks at predefined geometries determined by the irradiation pattern. The penetration depth of NIR light enabled activation of the angiogenesis response through skin tissue with a thickness of 2.5 mm. Our strategy opens a new avenue for 4D cell cultures, with the potential to be extended to dynamically manipulate cell–matrix interactions and derived cellular processes in vivo.

Capacitive deionization with porous carbon electrodes is an energy-efficient water treatment technique limited to the remediation of only brackish water due to the severe efficiency drop at high molar strength. Combining experiment and simulation, our work demonstrates the ability of subnanometer pores for permselective ion electrosorption, which enables capacitive deionization for saline media with high concentrations. Molecular dynamics simulations reveal the origin of permselective ion electrosorption in subnanometer pores at high molar strength. Within the subnanometer range, carbon pores with smaller size become more ionophobic and then express a higher ability of permselective ion electrosorption. This can be understood by the effects of the pore size on the microstructure of in-pore water and ions and the nanoconfinement effects on the ion hydration. These findings provide a new avenue for capacitive deionization of saline water (seawater-like ionic strength) to enable the application of highly concentrated saline media by direct use of porous carbons.

Electrolyte-filled subnanometre pores exhibit exciting physics and play an increasingly important role in science and technology. In supercapacitors, for instance, ultranarrow pores provide excellent capacitive characteristics. However, ions experience difficulties in entering and leaving such pores, which slows down charging and discharging processes. In an earlier work we showed for a simple model that a slow voltage sweep charges ultranarrow pores quicker than an abrupt voltage step. A slowly applied voltage avoids ionic clogging and co-ion trapping—a problem known to occur when the applied potential is varied too quickly—causing sluggish dynamics. Herein, we verify this finding experimentally. Guided by theoretical considerations, we also develop a non-linear voltage sweep and demonstrate, with molecular dynamics simulations, that it can charge a nanopore even faster than the corresponding optimized linear sweep. For discharging we find, with simulations and in experiments, that if we reverse the applied potential and then sweep it to zero, the pores lose their charge much quicker than they do for a short-circuited discharge over their internal resistance. Our findings open up opportunities to greatly accelerate charging and discharging of subnanometre pores without compromising the capacitive characteristics, improving their importance for energy storage, capacitive deionization, and electrochemical heat harvesting.

Nb2O5 has been explored as a promising anode material for use as lithium-ion batteries (LIBs), but depending on the crystal structure, the specific capacity was always reported to be usually around or below 200 mAh/g. For the first time, we present coarse-grained Nb2O5 materials that significantly overcome this capacity limitation with the promise of enabling high power applications. Our work introduces coarse-grained carbide-derived Nb2O5 phases obtained either by a one-step or a two-step bulk conversion process. By in situ production of chlorine gas from metal chloride salt at ambient pressure, we obtain in just one step directly orthorhombic Nb2O5 alongside carbide-derived carbon (o-Nb2O5/CDC). In situ formation of chlorine gas from metal chloride salt under vacuum conditions yields CDC covering the remaining carbide core, which can be transformed into metal oxides covered by a carbon shell upon thermal treatment in CO2 gas. The two-step process yielded a mixed-phase tetragonal and monoclinic Nb2O5 with CDC (m-Nb2O5/CDC). Our combined diffraction and spectroscopic data confirm that carbide-derived Nb2O5 materials show disordering of the crystallographic planes caused by oxygen deficiency in the structural units and, in the case of m-Nb2O5/CDC, severe stacking faults. This defect engineering allows access to a very high specific capacity exceeding the two-electron transfer process of conventional Nb2O5. The charge storage capacities of the resulting m-Nb2O5/CDC and o-Nb2O5/CDC are, in both cases, around 300 mAh/g at a specific current of 10 mA/g, thereby, the values are significantly higher than that of the state-of-the-art for Nb2O5 as a LIB anode. Carbide-derived Nb2O5 materials also show robust cycling stability over 500 cycles with capacity fading only 24% for the sample m-Nb2O5/CDC and 28% for o-Nb2O5/CDC, suggesting low degree of expansion/compaction during lithiation and delithiation.

Abstract Continuous and low-energy desalination technologies are in high demand to enable sustainable water remediation. Our work introduces a continuous desalination process based on the redox reaction of a dual-zinc electrode. The system consists of two zinc foils as redox electrodes with flowing ZnCl2 electrolyte, concentrated and diluted salt streams with three anion- and cation-exchange membranes (AEM and CEM) separated configuration (AEM|CEM|AEM). If a constant current is applied, the negative zinc electrode is oxidized, and electrons are released to the external circuit, whereas the positive zinc electrode is reduced, causing salt removal in the dilution stream. The results showed that brackish water can be directly desalted to 380.6 ppm during a continuous batch-mode process. The energy consumption can be as low as 35.30 kJ mol−1 at a current density of 0.25 mA cm−2, which is comparable to reverse osmosis. In addition, the dual-zinc electrode electrochemical desalination demonstrates excellent rate performance, reversibility, and batch cyclability through electrode exchange regeneration. Our research provides a route for continuous low-energy desalination based on metal redox mediators.

There is an urgent global need for electrochemical energy storage that includes materials that can provide simultaneous high power and high energy density. One strategy to achieve this goal is with pseudocapacitive materials that take advantage of reversible surface or near-surface Faradaic reactions to store charge. This allows them to surpass the capacity limitations of electrical double-layer capacitors and the mass transfer limitations of batteries. The past decade has seen tremendous growth in the understanding of pseudocapacitance as well as materials that exhibit this phenomenon. The purpose of this Review is to examine the fundamental development of the concept of pseudocapacitance and how it came to prominence in electrochemical energy storage as well as to describe new classes of materials whose electrochemical energy storage behavior can be described as pseudocapacitive.

Many metal sulfides present a layered structure with large interlayer space and a high theoretical capacity for lithium-ion battery applications. Compared to other transition metal dichalcogenides, vanadium sulfides remain little explored. Vanadium sulfides are commonly obtained by hydrothermal synthesis, which requires further post-processing and coating with binder and carbon additives. Here, we introduce a route to obtain free-standing vanadium sulfide fiber mats with in-built carbon. The combination of electrospinning and thermal sulfidation with H2S produces homogeneous vanadium sulfide particles embedded in carbon fibers that provide electrical conductivity and mechanical resistance for the electrode. The fibers were tested as a binder-free lithium-ion battery cathode within different potential ranges to evaluate insertion and conversion mechanisms and contributions to the overall capacity. Between 1.2 V and 3.5 V vs. Li/Li+, lithium intercalation provides a specific capacity up to 138 mAh∙g−1 at 0.01 A g−1 with good rate handling. When operating in a larger potential range between 0.1 V and 3.0 V vs. Li/Li+, the contribution by conversion reactions increases the capacity to 790 mAh∙g−1, but there is a fast capacity fading.

MAX phases are etched using an ionic liquid–water mixture to produce titanium carbide MXenes. The process avoids the use of any acid. Hydrolysis of the fluorine-containing ionic liquid leads to the selective removal of Al, while the ionic liquid is intercalated in-between the transition metal carbide layers.