The role of graphitic and amorphous nitrogen-doped carbon dots (N-CDs) as additives for perovskite solar cells (PSCs) is investigated. A detailed study of N-CDs: perovskite (PVSK) blends through X-ray diffraction, nuclear magnetic resonance, field emission scanning electron microscopy, UV-vis, and photoluminescence spectroscopy reveals the existence of interactions between N-CDs and PVSK. The amorphous or graphitic nature of these carbon nanoforms, as well as the interactions between CDs and PVSK, clearly determines the photovoltaic outcome of the PSCs. Thus, a small amount of graphitic carbon dots (g-N-CDs) leads to more-stable PSCs, while maintaining and even improving the power conversion efficiency (PCE). In addition, the long-term evaluation of the g-N-CDs-containing cells shows improvement of the PCE over time, up to 109% of the initial efficiency after 40 days while the reference performance is dropped to 86%.

Lithium-ion batteries and related battery concepts show an expansion and shrinkage ("breathing") of the electrodes during cell cycling. The dimensional changes of an individual electrode or a complete cell can be continuously measured by electrochemical dilatometry (ECD). The obtained data provides information on the electrode/cell reaction itself but can be also used to study side reactions or other relevant aspects, e.g., how the breathing is influenced by the electrode binder and porosity. The method spans over a wide measurement range and allows the determination of macroscopic as well as nanoscopic changes. It has also been applied to supercapacitors. The method has been developed already in the 1970s but recent advancements and the availability of commercial setups have led to an increasing interest in ECD. At the same time, there is no "best practice" on how to evaluate the data and several pitfalls exist that can complicate the comparison of literature data. This review highlights the recent development and future trends of ECD and its use in battery and supercapacitor research. A practical guide on how to evaluate the data is provided along with a discussion on various factors that influence the measurement results.

Reverse electrowetting-on-dielectric (REWOD)-based energy harvesting has been studied over the last decade as a novel technique of harvesting energy by actuating liquid droplet(s) utilizing applied mechanical modulation. Much prior research in REWOD has relied on planar electrodes, which by its geometry possess a limited surface area. In addition, most of the prior REWOD works have applied a high bias voltage to enhance the output power that compromises the concept of self-powering wearable motion sensors in human health monitoring applications. In order to enhance the REWOD power density resulting from an increased electrode-electrolyte interfacial area, high surface area electrodes are required. Herein, electrical and multiphysics-based modeling approaches of REWOD energy harvester using structured rough surface electrodes are presented. By enhancing the overall available surface area, an increase in the overall capacitance is achieved. COMSOL and MATLAB-based models are also developed, and the empirical results are compared with the models to validate the performance. Root mean square (RMS) power density is calculated using the RMS voltage across an optimal load impedance. For the proposed rough electrode REWOD energy harvester, maximum power density of 3.18 μW cm is achieved at 5 Hz frequency, which is ≈4 times higher than that of the planar electrodes.

The electrochemical intercalation/deintercalation of solvated sodium ions into graphite is a highly reversible process, but leads to large, undesired electrode expansion/shrinkage ("breathing"). Herein, two strategies to mitigate the electrode expansion are studied. Starting with the standard configuration (-) sodium | diglyme (2G) electrolyte | graphite (poly(vinylidene difluoride) (PVDF) binder) (+), the PVDF binder is first replaced with a binder made of the sodium salt of carboxymethyl cellulose (CMC). Second, ethylenediamine (EN) is added to the electrolyte solution as a co-solvent. The electrode breathing is followed in situ (operando) through electrochemical dilatometry (ECD). It is found that replacing PVDF with CMC is only effective in reducing the electrode expansion during initial sodiation. During cycling, the electrode breathing for both binders is comparable. Much more effective is the addition of EN. The addition of 10 v/v EN to the diglyme electrolyte strongly reduces the electrode expansion during the initial sodiation (+100% with EN versus +175% without EN) as well as the breathing during cycling. A more detailed analysis of the ECD signals reveals that solvent co-intercalation temporarily leads to pillaring of the graphite lattice and that the addition of EN to 2G leads to a change in the sodium storage mechanism.

Electrification is progressing significantly within the present and future vehicle sectors such as large commercial vehicles (e.g., trucks and buses), high-altitude long endurance (HALE), high-altitude pseudosatellites (HAPS), and electric vertical take-off and landing (eVTOL). The battery systems' performance requirements differ across these applications in terms of power, cycle life, system cost, etc. However, the need for high gravimetric energy density, 400 Wh kg and beyond, is common across them all, as it enables vehicles to achieve extended range, a longer mission duration, lighter weight, or increased payload. The system-level requirements of these emerging applications are broken down into the component-level developments required to integrate Li-S technology as the power system of choice. To adapt batteries' properties, such as energy and power density, to the respective application, the academic research community has a key role to play in component-level development. However, materials and component research must be conducted within the context of a viable Li-S cell system. Herein, the key performance benefits, limitations, modeling, and recent progress of the Li-S battery technology and its adaption toward real-world application are discussed.

Grid applications require high power density (for frequency regulation, load leveling, and renewable energy integration), achievable by combining multiple batteries in a system without strict high capacity requirements. For these applications however, safety, cost efficiency, and the lifespan of electrode materials are crucial. Titanates, safe and longevous anode materials providing much lower energy density than graphite, are excellent candidates for this application. The innovative molten salt synthesis approach proposed in this work provides exceptionally pure NaTiO nanorods generated at 900-1100 °C in a yield ≥80 wt%. It is fast, cost-efficient, and suitable for industrial upscaling. Electrochemical tests reveal stable performance providing capacities of ≈100 mA h g (Li) and 40 mA h g (Na). Increasing the synthesis temperature to 1100 °C leads to a capacity decrease, most likely resulting from 1) the morphology/volume change with the synthesis temperature and 2) distortion of the NaTiO tunnel structure indicated by electron energy-loss and Raman spectroscopy. The suitability of pristine NaTiO as the anode for grid-level energy storage systems has been proven a priori, without any performance-boosting treatment, indicating considerable application potential especially due to the high yield and low cost of the synthesis route.

Magnetic refrigeration is an upcoming technology that could be an alternative to the more than 100-year-old conventional gas-vapor compression cooling. Magnetic refrigeration might answer some of the global challenges linked with the increasing demands for readily available cooling in almost every region of the world and the global-warming potential of conventional refrigerants. Important issues to be solved are, for example, the required mass and the ecological footprint of the rare-earth permanent magnets and the magnetocaloric material, which are key parts of the magnetic cooling device. The majority of existing demonstrators use Nd-Fe-B permanent magnets, which account for more than 50% of the ecological footprint, and Gd, which is a critical raw material. This work shows a solution to these problems by demonstrating the world's first magnetocaloric demonstrator that uses recycled Nd-Fe-B magnets as the magnetic field source, and, as a Gd replacement material, La-Fe-Mn-Si for the magnetocaloric heat exchanger. These solutions show that it is possible to reduce the ecological footprint of magnetic cooling devices and provides magnetic cooling as a green solid-state technology that has the potential to satisfy the rapidly growing global demands.

The wide-bandgap methylammonium lead bromide perovskite is promising for applications in tandem solar cells and light-emitting diodes. Despite its utility, there is a limited understanding of its reproducibility and stability. Herein, the dependence of the properties, performance, and shelf storage of thin films and devices on minute changes to the precursor solution stoichiometry is examined in detail. Although photovoltaic cells based on these solution changes exhibit similar initial performance, shelf storage depends strongly on precursor solution stoichiometry. While all devices exhibit some degree of healing, bromide-deficient films show a remarkable improvement, more than doubling in their photoconversion efficiency. Photoluminescence spectroscopy experiments performed under different atmospheres suggest that this increase is due, in part, to a trap-healing mechanism that occurs upon exposure to the environment. The results highlight the importance of understanding and manipulating defects in lead halide perovskites to produce long-lasting, stable devices.

Thanks to their broadly tunable bandgap and strong absorption, colloidal lead chalcogenide quantum dots (QDs) are highly appealing as solution-processable active layers for third-generation solar cells. However, the modest reproducibility of this kind of solar cell is a pertinent issue, which inhibits the exploitation of this material class in optoelectronics. This issue is not necessarily imputable to the active layer but may originate from different constituents of the device structure. Herein, the deposition of TiO electron transport layer is focused on. Atomic layer deposition (ALD) greatly improves the reproducibility of PbS QD solar cells compared with the previously optimized sol-gel (SG) approach. Power conversion efficiency (PCE) of the solar cells using atomic layer-deposited TiO lies in the range between 5.5% and 7.2%, whereas solar cells with SG TiO have PCE ranging from 0.5% to 6.9% with a large portion of short-circuited devices. Investigations of TiO layers by atomic force microscopy and scanning electron microscopy reveal that these films have very different surface morphologies. Whereas the TiO films prepared by SG synthesis and deposited by spin coating are very smooth, TiO films made by ALD repeat the surface texture of the fluorine-doped tin oxide (FTO) substrate underneath.

The Faradaic processes related to electrochemical water reduction at the nanoporous carbon electrode under negative polarization are reduced when the concentration of aqueous sodium nitrate (NaNO) is increased or the temperature is decreased. This effect enhances the relative contribution of ion electrosorption to the total charge storage process. Hydrogen chemisorption is reduced in aqueous 8.0 m NaNO due to the low degree of hydration of the Na cation; consequently, less free water is available for redox contributions, driving the system to exhibit electrical double-layer capacitive characteristics. Hydrogen adsorption/desorption is facilitated in 1.0 m NaNO due to the high molar ratio. The excess of water shifts the local pH in carbon nanopores to neutral values, giving rise to a high overpotential for dihydrogen evolution in the latter. The dilution effect on local pH shift in 1.0 m NaNO can be reduced by decreasing the temperature. A symmetric activated carbon cell assembled with 8.0 m NaNO exhibits a high capacitance and coulombic efficiency, a larger contribution of ion electrosorption to the overall charge storage process, and a stable capacitance performance at 1.6 V.

1--Butyl-3-methylimidazolium methyl sulfate is incorporated into MIL-53(Al). Detailed characterization is done by X-ray fluorescence, Brunauer-Emmett-Teller surface area, scanning electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, and thermogravimetric analysis. Results show that ionic liquid (IL) interacts directly with the framework, significantly modifying the electronic environment of MIL-53(Al). Based on the volumetric gas adsorption measurements, CO, CH, and N adsorption capacities decreased from 112.0, 46.4, and 19.6 cc (STP) g to 42.2, 13.0, and 4.3 cc (STP) g at 5 bar, respectively, upon IL incorporation. Data show that this postsynthesis modification leads to more than two and threefold increase in the ideal selectivity for CO over CH and N separations, respectively, as compared with pristine MIL-53(Al). The isosteric heat of adsorption (Qst) values show that IL incorporation increases CO affinity and decreases CH and N affinities. Cycling adsorption-desorption measurements show that the composite could be regenerated with almost no decrease in the CO adsorption capacity for six cycles and confirm the lack of any significant IL leaching. The results offer MIL-53(Al) as an excellent platform for the development of a new class of IL/MOF composites with exceptional performance for CO separation.

Two perovskite type oxygen carriers, for the application in chemical looping combustion, called C14 and C28 are investigated. The composition of C14 is CaMnMgO and CaMnMgTiO for C28, respectively. Both oxygen carriers allow chemical looping with oxygen uncoupling (CLOU), they release oxygen under conditions with low oxygen partial pressure. The materials are tested in a 120 kWth pilot plant at TU Wien. Operating temperatures from 800 °C to 960 °C are investigated, further the influence of active inventory and air equivalence number is reviewed. In addition to the experiments in the pilot plant, particle analysis is performed. In total, the CLC operation for C14 was 29.5 h and 22.7 h for C28, resulting in 75 different operating points. Both oxygen carrier materials are able to fully convert the natural gas, used as fuel. A temperature dependency is noticeable for both, the best results are achieved at 960 °C, the highest investigated temperature. Both, C14 and C28 are able to release about 10 % of the total available oxygen via oxygen uncoupling. The performance of both oxygen carriers is strongly linked to the air equivalence number and the resulting amount of excess oxygen in the air reactor. Low oxygen partial pressures lead to incomplete fuel conversion.

In this study Si-alloy/graphite composite electrodes are manufactured using water-soluble poly-acrylic acid (PAA) binder of different molecular weights (250, 450 and 1250 kg mol). The study aims to assess the behavior of the different binders across all the steps needed for electrodes preparation and on their influence on the electrodes electrochemical behavior. At first, rheological properties of the water-based slurries containing Si-alloy, graphite, conductive carbon and PAA are studied. After coating, the adhesion strength and electronic conductivity of the manufactured electrodes are evaluated and compared. Finally, the electrochemical behavior of the composite anodes is evaluated. The electrodes show high gravimetric as well as high areal capacity (∼750 mAh/g; ∼3 mAh/cm). The influence of the binder on the first cycle irreversible loss is considered as well as its effectiveness in minimizing the electrode volume variation upon lithiation/de-lithiation. It is finally demonstrated that the use of 8 wt.% of PAA-250k in the electrode formulation leads to the best performance in terms of high rate performance and long term stability.

The occurrence of the inverse (or negative) electrocaloric effect, where the isothermal application of an electric field leads to an increase in entropy and the removal of the field decreases the entropy of the system under consideration, is discussed and analyzed. Inverse electrocaloric effects have been reported to occur in several cases, for example, at transitions between ferroelectric phases with different polarization directions, in materials with certain polar defect configurations, and in antiferroelectrics. This counterintuitive relationship between entropy and applied field is intriguing and thus of general scientific interest. The combined application of normal and inverse effects has also been suggested as a means to achieve larger temperature differences between hot and cold reservoirs in future cooling devices. A good general understanding and the possibility to engineer inverse caloric effects in terms of temperature spans, required fields, and operating temperatures are thus of fundamental as well as technological importance. Here, the known cases of inverse electrocaloric effects are reviewed, their physical origins are discussed, and the different cases are compared to identify common aspects as well as potential differences. In all cases the inverse electrocaloric effect is related to the presence of competing phases or states that are close in energy and can easily be transformed with the applied field.

Nanowires of the ferroelectric co-polymer poly(vinylidenefluoride--triufloroethylene) [P(VDF-TrFE)] are fabricated from solution within nanoporous templates of both "hard" anodic aluminium oxide (AAO) and "soft" polyimide (PI) through a facile and scalable template-wetting process. The confined geometry afforded by the pores of the templates leads directly to highly crystalline P(VDF-TrFE) nanowires in a macroscopic "poled" state that precludes the need for external electrical poling procedure typically required for piezoelectric performance. The energy-harvesting performance of nanogenerators based on these template-grown nanowires are extensively studied and analyzed in combination with finite element modelling. Both experimental results and computational models probing the role of the templates in determining overall nanogenerator performance, including both materials and device efficiencies, are presented. It is found that although P(VDF-TrFE) nanowires grown in PI templates exhibit a lower material efficiency due to lower crystallinity as compared to nanowires grown in AAO templates, the overall device efficiency was higher for the PI-template-based nanogenerator because of the lower stiffness of the PI template as compared to the AAO template. This work provides a clear framework to assess the energy conversion efficiency of template-grown piezoelectric nanowires and paves the way towards optimization of template-based nanogenerator devices.

In the recent decade, CO has increasingly been regarded not only as a greenhouse gas but even more as a chemical feedstock for carbon-based materials. Different strategies have evolved to realize CO utilization and conversion into fuels and chemicals. In particular, biological approaches have drawn attention, as natural CO conversion serves as a model for many processes. Microorganisms and enzymes have been studied extensively for redox reactions involving CO. In this review, we focus on monitoring nonliving biocatalyzed reactions for the reduction of CO by using enzymes. We depict the opportunities but also challenges associated with utilizing such biocatalysts. Besides the application of enzymes with co-factors, resembling natural processes, and co-factor recovery, we also discuss implementation into photochemical and electrochemical techniques.

The continuous production of carbon monoxide (CO) and hydrogen (H) by dry reforming of methane (CH) is demonstrated isothermally using a ceramic redox membrane in absence of additional catalysts. The reactor technology realizes the continuous splitting of CO to CO on the inner side of a tubular membrane and the partial oxidation of CH with the lattice oxygen to form syngas on the outer side. LaSrCoFeO (LSCF) membranes evaluated at 840-1030 °C yielded up to 1.27 μmol    s from CO, 3.77 μmol g s from CH , and CO from CH at approximately the same rate as CO from CO. We compute the free energy of the oxygen vacancy formation for LaSrBB'O (B, B'=Mn, Fe, Co, Cu) using electronic structure theory to understand how CO reduction limits dry reforming of methane using LSCF and to show how the CO conversion can be increased by using advanced redox materials such as LaSrMnO and LaSrMnCoO .