Uphill and downhill charge generation from charge transfer to charge separated states in organic solar cells. - In: Journal of materials chemistry, ISSN 2050-7534, Bd. 9 (2021), 40, S. 14463-14489
It is common knowledge that molecular energy level offsets of a type II heterojunction formed at the donor-acceptor interface are considered to be the driving force for photoinduced charge transfer in organic solar cells. Usually, these offsets - present between molecular energy levels of the donor and acceptor - are obtained via cyclic voltammetry (CV) measurements of organic semiconductors cast in a film or dissolved in solution. Simply transferring such determined energy levels from solution or film of single materials to blend films may be obviously limited and not be possible in full generality. Herein, we report various cases of material combinations in which novel non-fullerene acceptors did not yield successful charge transfer, although energy levels obtained by CV on constituting single materials indicate a type II heterojunction. Whilst the integer charge transfer (ICT) model provides one explanation for a relative rise of molecular energy levels of acceptors, further details and other cases have not been studied so far in great detail. By applying energy-resolved electrochemical impedance spectroscopy (ER-EIS) on several donor-acceptor combinations, a Fano-like resonance feature associated with a distinctive molecular energy level of the acceptor as well as various relative molecular energy level shifts of different kinds could be observed. By analyzing ER-EIS and absorption spectra, not only the exciton binding energy within single materials could be determined, but also the commonly unknown binding energy of the CT state with regard to the joint density of states (jDOS) of the effective semiconductor. The latter is defined by transitions between the highest occupied molecular orbitals (HOMO) of the donor and the lowest unoccupied molecular orbitals (LUMO) of the acceptor. Using this technique among others, we identified cases in which charge generation may occur either via uphill or by downhill processes between the charge transfer exciton and the electronic gap of the effective semiconductor. Exceptionally high CT-exciton binding energies and thus low charge generation yields were obtained for a case in which the donor and acceptor yielded a too intimate blend morphology, indicating π-π stacking as a potential cause for unfavorable molecular energy level alignment.
https://doi.org/10.1039/D1TC02351A
Corrosion of aluminium current collector in lithium-ion batteries: a review. - In: Journal of energy storage, ISSN 2352-152X, Bd. 43 (2021), 103226
Calendar and cycle ageing affects the performance of the lithium-ion batteries from the moment they are manufactured. An important process that occurs as a part of the ageing is corrosion of the current collectors, especially prominent in the case of the aluminium substrate for the positive electrode. Generally, aluminium resists corrosion due to the formation of a non-permeable film of native aluminium oxide. Nevertheless, at certain electrochemical conditions corrosion affects the interface of the current collector. As a consequence of corrosion, the cathode materials lose electrical and mechanical contact with the current collector, leading to capacity and power fading. Therefore, a deeper understanding of this process and effective corrosion inhibition are necessary to prevent the deterioration of the battery performance. This review provides an updated critical overview of the mechanisms of aluminium corrosion, methodologies for analysing this phenomenon, and approaches for its effective mitigation. As the influence of multiple factors on the corrosion process has a central impact, the review discusses how they specifically affect the undergoing processes. Therefore, appropriate examples of important factors like electrolyte composition, thermal conditions and electrochemical parameters are presented to explain the specific mechanism of aluminium corrosion. Since corrosion inhibition is an important technological issue with a tremendous economic impact the review summarises how to achieve this by adjusting the electrochemical system and enhancing the knowledge on the safe operation of the positive electrode.
https://doi.org/10.1016/j.est.2021.103226
Efficient preparation of Ni-M (M = Fe, Co, Mo) bimetallic oxides layer on Ni nanorod arrays for electrocatalytic oxygen evolution. - In: Applied materials today, ISSN 2352-9407, Bd. 25 (2021), 101185
Fabrication of economic and high-performance electrodes for electrocatalytic oxygen evolution reaction (OER) accounts for a crucial issue associated with developing powerful and practical water splitting systems. In this work, free-standing Ni/Ni-M (M = Fe, Co, Mo) bimetallic oxides core/shell nanorod arrays (Ni/Ni-M NRAs) were prepared through electroless deposition of transition metal species on black nickel sheet (nickel nanorod arrays (Ni NRAs)) followed by electrochemical oxidation. All three types of Ni/Ni-M NRAs demonstrated enhanced electrocatalytic activity toward oxygen evolution reactions (OER). Especially, Ni/Ni-Fe NRAs electrode exhibit small onset potential of 1.535 V at current density of 10 mA&hahog;cm^-2. In contrast, the OER durability of these three samples was distinct. At 500 mV constant overpotential, the current density loss in OER of Ni/Ni-Fe NRAs was merely 13.5% for a period of 20000 s; but Ni/Ni-Mo and Ni/Ni-Co NRAs had almost disappeared catalytic activity under the identical conditions. According to many reports, the results were different for the superior OER stability of Ni-based bimetallic catalysts. Electrochemical analysis revealed that the NRAs structure dramatically improves charge transfer efficiency and electrochemically active surface area (ECSA). The present study might provide a new insight to design and fabricate more practical and high-performance Ni-based electrodes for OER.
https://doi.org/10.1016/j.apmt.2021.101185
Rapid fabrication and interface structure of highly faceted epitaxial Ni-Au solid solution nanoparticles on sapphire. - In: Acta materialia, ISSN 1873-2453, Bd. 220 (2021), 117318, insges. 12 S.
Supersaturated Ni-Au solid solution particles were synthesized by rapid solid-state dewetting of bilayer thin films deposited onto c-plane sapphire single-crystals. Rapid thermal annealing above the miscibility gap of the Ni-Au system followed by quenching to room temperature resulted in textured and faceted submicron-sized particles as a function of alloying content in the range of 0-28 at% Au. Morphologically, the observed kinetic crystal shapes are confined by close-packed planes; in addition, high-index facets are identified as a function of alloying content by TEM cross-sectioning and equilibrium crystal shape simulations. All samples exhibit a distinct <111> out-of-plane as well as in-plane texture along densely packed directions. Lattice parameters extracted from independent orthogonal X-ray and electron diffraction techniques prove the formation of a solid solution without tetragonal distortion imposed by the sapphire substrate. At the particle-substrate interface of highly alloyed particles segregation of Au atoms as well as dislocations in stand-off position are found. These observations are in-line with a semi-coherent interface, where Au segregation is triggered by the reduction of the overall strain energy due to: (i) a lower shear modulus on the particle side of the interface, (ii) the shifting of misfit dislocations in stand-off position further away from the stiffer substrate and (iii) a reduction of intrinsic misfit dislocation strain energy on the tensile side. In addition, the mechanical properties of pure and alloyed particles were characterized by in situ compression experiments in the SEM. Typical force-displacement data of defect-free single-crystals were obtained, reaching the theoretical strength of Ni for particles smaller than 400 nm. Alloying changes the mechanical response from an intermittent and discrete plastic flow behavior into a homogeneous deformation regime at large compressive strain.
https://doi.org/10.1016/j.actamat.2021.117318
The Arch electrode: a novel dry electrode concept for improved wearing comfort. - In: Frontiers in neuroscience, ISSN 1662-453X, Bd. 15 (2021), 748100, S. 1-14
https://doi.org/10.3389/fnins.2021.748100
Specific electrical contact resistance of copper in resistance welding. - In: Physica status solidi, ISSN 1862-6319, Bd. 218 (2021), 19, 2100224, insges. 11 S.
The electrical contact resistance (ECR) of copper (Cu-ETP R200, soft) contacts for resistance welding (RW) is characterized. ECR plays a major role in the RW process and provides local heat generation between the parts. A special determination method is used on different testing variants to observe the influence of contact pressure (two levels: 68, 155 MPa), contact temperature (20-550 ˚C), and surface parameters, like roughness or oxide layer thickness, on the specific electrical contact resistance (SECR). For each surface parameter, three different levels are investigated. The study shows decreasing SECR with higher mechanical load on the contact and a more complex behavior for increase in contact temperature. SECR shows a characteristic behavior for contact states near the temperature-dependent tensile strength of the base material for rough and clean surfaces, where SECR approaches toward zero. The variation of oxide layer thickness and surface roughness has a strong influence on the resulting SECR and both surface parameters show a strong coupling regarding their effects.
https://doi.org/10.1002/pssa.202100224
Ordered nanostructures arrays fabricated by anodic aluminum oxide (AAO) template-directed methods for energy conversion. - In: Nanotechnology, ISSN 1361-6528, Bd. 32 (2021), 50, 502006, S. 1-27
Clean and efficient energy conversion systems can overcome the depletion of the fossil fuel and meet the increasing demand of the energy. Ordered nanostructures arrays convert energy more efficiently than their disordered counterparts, by virtue of their structural merits. Among various fabrication methods of these ordered nanostructures arrays, anodic aluminum oxide (AAO) template-directed fabrication have drawn increasing attention due to its low cost, high throughput, flexibility and high structural controllability. This article reviews the application of ordered nanostructures arrays fabricated by AAO template-directed methods in mechanical energy, solar energy, electrical energy and chemical energy conversions in four sections. In each section, the corresponding advantages of these ordered nanostructures arrays in the energy conversion system are analysed, and the limitation of the to-date research is evaluated. Finally, the future directions of the ordered nanostructures arrays fabricated by AAO template-directed methods (the promising method to explore new growth mechanisms of AAO, green fabrication based on reusable AAO templates, new potential energy conversion application) are discussed.
https://doi.org/10.1088/1361-6528/ac268b
Probing transient localized electromagnetic fields using low-energy point-projection electron microscopy. - In: ACS photonics, ISSN 2330-4022, Bd. 8 (2021), 9, S. 2573-2580
Low kinetic energy electrons are of interest for probing nanoscale dynamic processes using ultrafast electron microscopy techniques. Their low velocities reduce radiation doses and enhance the interaction with confined electromagnetic fields and, thus, may enable ultrafast spectroscopy of single nanostructures. Recent improvements in the spatial and temporal resolution of ultrafast, low-energy electron microscopy have been achieved by combining nanotip photoemitters and point-projection imaging schemes. Here, we use such an ultrafast point-projection electron microscope (UPEM) to analyze the interaction of low-energy electrons with transient electric fields created by photoemission from a nanogap antenna. By analyzing their kinetic energy distribution, we separate angular deflection due to radial field components from electron energy gain and loss due to their axial acceleration. Our measurements open up a route toward the spatial and temporal characterization of vectorial near-fields by low-energy electron streaking spectroscopy.
https://doi.org/10.1021/acsphotonics.1c00775
Cost-effective sensor for flow monitoring in biologic microreactors. - In: IEEE sensors journal, ISSN 1558-1748, Bd. 21 (2021), 19, S. 21314-21321
https://doi.org/10.1109/JSEN.2021.3102262
Antitumor efficiency of the natural alkaloid berberine complexed with C60 fullerene in Lewis lung carcinoma in vitro and in vivo. - In: Cancer nanotechnology, ISSN 1868-6966, Bd. 12 (2021), 24, insges. 18 S.
Berberine (Ber) is a herbal alkaloid with pharmacological activity in general and a high anticancer potency in particular. However, due to its low bioavailability, the difficulty in reaching a target and choosing the right dose, there is a need to improve approaches of Ber use in anticancer therapy. In this study, Ber, noncovalently bound to a carbon nanostructure C60 fullerene (C60) at various molar ratios of the components, was explored against Lewis lung carcinoma (LLC).
https://doi.org/10.1186/s12645-021-00096-6