Cation Effects on the Acidic Oxygen Reduction Reaction at Carbon Surfaces

Hydrogen peroxide (H2O2) is a widely used green oxidant. Until now, research has focused on the development of efficient catalysts for the two-electron oxygen reduction reaction (2e- ORR). However, electrolyte effects on the 2e- ORR have remained little understood. We report a significant effect of alkali metal cations (AMCs) on carbons in acidic environments. The presence of AMCs at a glassy carbon electrode shifts the half wave potential from -0.48 to -0.22 VRHE. This cation-induced enhancement effect exhibits a uniquely sensitive on/off switching behavior depending on the voltammetric protocol. Voltammetric and in situ X-ray photoemission spectroscopic evidence is presented, supporting a controlling role of the potential of zero charge of the catalytic enhancement. Density functional theory calculations associate the enhancement with stabilization of the *OOH key intermediate as a result of locally induced field effects from the AMCs. Finally, we developed a refined reaction mechanism for the H2O2 production in the presence of AMCs.

Artificial Intelligence-Based, Wavelet-Aided Prediction of Long-Term Outdoor Performance of Perovskite Solar Cells

The commercial development of perovskite solar cells (PSCs) has been significantly delayed by the constraint of performing time-consuming degradation studies under real outdoor conditions. These are necessary steps to determine the device lifetime, an area where PSCs traditionally suffer. In this work, we demonstrate that the outdoor degradation behavior of PSCs can be predicted by employing accelerated indoor stability analyses. The prediction was possible using a swift and accurate pipeline of machine learning algorithms and mathematical decompositions. By training the algorithms with different indoor stability data sets, we can determine the most relevant stress factors, thereby shedding light on the outdoor degradation pathways. Our methodology is not specific to PSCs and can be extended to other PV technologies where degradation and its mechanisms are crucial elements of their widespread adoption.

Interface Modification for Energy Level Alignment and Charge Extraction in CsPbI3 Perovskite Solar Cells

In perovskite solar cells (PSCs) energy level alignment and charge extraction at the interfaces are the essential factors directly affecting the device performance. In this work, we present a modified interface between all-inorganic CsPbI3 perovskite and its hole-selective contact (spiro-OMeTAD), realized by the dipole molecule trioctylphosphine oxide (TOPO), to align the energy levels. On a passivated perovskite film, with n-octylammonium iodide (OAI), we created an upward surface band-bending at the interface by TOPO treatment. This improved interface by the dipole molecule induces a better energy level alignment and enhances the charge extraction of holes from the perovskite layer to the hole transport material. Consequently, a Voc of 1.2 V and a high-power conversion efficiency (PCE) of over 19% were achieved for inorganic CsPbI3 perovskite solar cells. Further, to demonstrate the effect of the TOPO dipole molecule, we present a layer-by-layer charge extraction study by a transient surface photovoltage (trSPV) technique accomplished by a charge transport simulation.

Expanding the Potential of Identical Location Scanning Transmission Electron Microscopy for Gas Evolving Reactions: Stability of Rhenium Molybdenum Disulfide Nanocatalysts for Hydrogen Evolution Reaction

Identical location (scanning) transmission electron microscopy provides valuable insights into the mechanisms of the activity and degradation of nanocatalysts during electrochemical reactions. However, the technique suffers from limitations that hinder its widespread use for nanocatalysts of gas evolving reactions, e.g., the hydrogen evolution reaction (HER). The main issue is the production of bubbles that cause the loss of electric contact in identical location measurements, which is critical for the correct cycling of the nanocatalysts and interpretation of the electron microscopy results. Herein, we systematically evaluate different set-ups, materials, and tools to allow the facile and reliable study of the stability of HER nanocatalysts. The optimized conditions are applied for the study of layered rhenium molybdenum disulfide (Re0.2Mo0.8S2) nanocatalysts, a relevant alternative to Pt catalysts for the HER. With our approach, we demonstrate that although the morphology of the Re0.2Mo0.8S2 catalyst is maintained during HER, chemical composition changes could be correlated to the electrochemical reaction. This study expands the potential of the IL(S)TEM technique for the construction of structure-property relationships of nanocatalysts of gas evolving reactions.

Electrochemical Stability of Rhodium-Platinum Core-Shell Nanoparticles: An Identical Location Scanning Transmission Electron Microscopy Study

Rhodium-platinum core-shell nanoparticles on a carbon support (Rh@Pt/C NPs) are promising candidates as anode catalysts for polymer electrolyte membrane fuel cells. However, their electrochemical stability needs to be further explored for successful application in commercial fuel cells. Here we employ identical location scanning transmission electron microscopy to track the morphological and compositional changes of Rh@Pt/C NPs during potential cycling (10 000 cycles, 0.06-0.8 VRHE, 0.5 H2SO4) down to the atomic level, which are then used for understanding the current evolution occurring during the potential cycles. Our results reveal a high stability of the Rh@Pt/C system and point toward particle detachment from the carbon support as the main degradation mechanism.

Relationship between the Annealing Temperature and the Presence of PbI2 Platelets at the Surfaces of Slot-Die-Coated Triple-Halide Perovskite Thin Films

We investigated triple-halide perovskite (THP) absorber layers with 5 mol % MAPbCl3 added to the double-halide perovskite (Cs0.22FA0.78)Pb(I0.85Br0.15)3. As a deposition method, a highly scalable printing technique, slot-die coating, with a subsequent annealing step was used. We found a strong power conversion efficiency (PCE) dependence of the corresponding solar cells on the annealing temperature. The device performance deteriorated when increasing the annealing temperature from 125 to 170 °C, mainly via losses in the open-circuit voltage (Voc) and in the fill factor (FF). To understand the mechanisms behind this performance loss, extensive characterizations were performed on both, the THP thin films and the completed solar-cell stacks, as a function of annealing temperature. Correlative scanning electron microscopy analyses, i.e., electron backscatter diffraction, energy-dispersive X-ray spectroscopy, and cathodoluminescence, in addition to X-ray diffraction and photoluminescence, confirmed the presence of PbI2 platelets on the surface of the THP thin films. Moreover, the area fraction of the PbI2 platelets on the film surface increased with increasing annealing temperature. The deteriorated device performance when the annealing temperature is increased from 125 to 170 °C is explained by the increased series resistance and increased interface recombination caused by the PbI2 platelets, leading to decreased Voc and FF values of the solar-cell devices. Thus, the correlative analyses provided insight into microscopic origins of the efficiency losses.

Ferroelectric Content-Addressable Memory Cells with IGZO Channel: Impact of Retention Degradation on the Multibit Operation

Indium gallium zinc oxide (IGZO)-based ferroelectric thin-film transistors (FeTFTs) are being vigorously investigated for being deployed in computing-in-memory (CIM) applications. Content-addressable memories (CAMs) are the quintessential example of CIM, which conduct a parallel search over a queue or stack to obtain the matched entries for a given input data. CAM cells offer the ability for massively parallel searches in a single clock cycle throughout an entire CAM array for the input query, thereby enabling pattern matching and searching functionality. Therefore, CAM cells are used extensively for pattern matching or search operations in data-centric computing. This paper investigates the impact of retention degradation on IGZO-based FeTFT on the multibit operation in content CAM cell applications. We propose a scalable multibit 1FeTFT-1T-based CAM cell composed of only one FeTFT and one transistor, thus significantly improving the density and energy efficiency compared with conventional complementary metal-oxide-semiconductor (CMOS)-based CAM. We successfully demonstrate the operations of our proposed CAM with storage and search by exploiting the multilevel states of the experimentally calibrated IGZO-based FeTFT devices. We also investigate the impact of retention degradation on the search operation. Our proposed IGZO-based 3-bit and 2-bit CAM cell shows 10⁴ s and 10⁶ s retention, respectively. The single-bit CAM cell shows lifelong (10 years) retention.

Longitudinal Relaxation (T 1) of Methane/Hydrogen Mixtures for Operando Characterization of Gas-Phase Reactions

Catalytic hydrogenation reactions are important in a modern hydrogen-based society. To optimize these gas-phase reactions, a deep understanding of heat, mass, and momentum transfer inside chemical reactors is required. Nuclear magnetic resonance (NMR) measurements can be used to obtain spatially resolved values of temperature, gas composition, and velocity in the usually opaque catalytic macrostructures. For this, the desired values are calculated from measured NMR parameters like signal amplitude, T ₁, or T ₂. However, information on how to calculate target values from these NMR parameters in gases is scarce, especially for mixtures of gases. To enable detailed NMR studies of hydrogenation reactions, we investigated the T ₁ relaxation of methane and hydrogen, which are two gases commonly present in hydrogenation reactions. To achieve industrially relevant conditions, the temperatures are varied from 290 to 600 K and the pressure from 1 bara to 5 bara, using different mixtures of methane and hydrogen. The results show that hydrogen, which is usually considered to be nondetectable in standard MRI sequences, can be measured at high concentrations, starting at a pressure of 3 bara even at temperatures above 400 K. In the investigated parameter range, the absolute T ₁ values of hydrogen show only small dependence on temperature, pressure, and composition, while T ₁ of methane is highly dependent on all three parameters. At a pressure of 5 bara, the measured values of T ₁ for methane agree very well with theoretical predictions, so that they can also be used for temperature calculations. Further, it can be shown that the same measurement technique can be used to accurately calculate gas ratios inside each voxel. In conclusion, this study covers important aspects of spatially resolved operando NMR measurements of gas-phase properties during hydrogenation reactions at industrially relevant conditions to help improve chemical processes in the gas phase.

Slot-Die Coated Triple-Halide Perovskites for Efficient and Scalable Perovskite/Silicon Tandem Solar Cells

Wide bandgap halide perovskite materials show promising potential to pair with silicon bottom cells. To date, most efficient wide bandgap perovskites layers are fabricated by spin-coating, which is difficult to scale up. Here, we report on slot-die coating for an efficient, 1.68 eV wide bandgap triple-halide (3halide) perovskite absorber, (Cs_0.22FA_0.78)Pb(I_0.85Br_0.15)₃ + 5 mol % MAPbCl₃. A suitable solvent system is designed specifically for the slot-die coating technique. We demonstrate that our fabrication route is suitable for tandem solar cells without phase segregation. The slot-die coated wet halide perovskite is dried by a "nitrogen (N₂)-knife" with high reproducibility and avoiding antisolvents. We explore varying annealing conditions and identify parameters allowing crystallization of the perovskite film into large grains reducing charge collection losses and enabling higher current density. At 150 °C, an optimized trade-off between crystallization and the PbI₂ aggregates on the film's top surface is found. Thus, we improve the cell stability and performance of both single-junction cells and tandems. Combining the 3halide top cells with a 120 μm thin saw damage etched commercial Czochralski industrial wafer, a 2-terminal monolithic tandem solar cell with a PCE of 25.2% on a 1 cm² active area is demonstrated with fully scalable processes.

Single-Color Barcoding for Multiplexed Hydrogel Bead-Based Immunoassays

Current developments in precision medicine require the simultaneous detection of an increasing number of biomarkers in heterogeneous, complex solutions, such as blood samples. To meet this need, immunoassays on barcoded hydrogel beads have been proposed, although the encoding and decoding of these barcodes is usually complex and/or resource-intensive. Herein, an efficient method for the fabrication of barcoded, functionalized hydrogel beads is presented. The hydrogel beads are generated using droplet-based microfluidics in combination with photochemically induced C-H insertion reactions, allowing photo-crosslinking, (bio-) functionalization, and barcode integration to be performed in a single step. The generated functionalized beads carry single-color barcodes consisting of green-fluorescent particles of different sizes and concentrations, allowing simple and simultaneous readout with a standard plate reader. As a test example, the performance of barcoded hydrogel beads (3 × 3 matrix) functionalized with capture molecules of interest (e.g., antigens) is investigated for the detection of Lyme-disease-specific antibodies in patient sera. The described barcoding strategy for hydrogel beads does not interfere with the bioanalytical process and captivates by its simplicity and versatility, making it an attractive candidate for multiplex bioanalytical processes.

Oxy-Combustion of Solid Recovered Fuel in a Semi-Industrial CFB Reactor: On the Implications of Gas Atmosphere and Combustion Temperature

Oxy-fuel combustion of refuse waste is gaining considerable attention as a viable CO₂ negative technology that can enable the continued use of stationary combustion plants during the transition to renewable energy sources. Compared to fossil fuels, waste-derived fuels tend to be highly heterogeneous and to contain a greater amount of alkaline metals and chlorine. Therefore, experimental studies are mandatory to thoroughly elucidate refuse materials' combustion and pollutant formation behavior. This paper presents an experimental investigation on the air and oxy-fuel combustion of solid recovered fuel at a 200 kW_th circulating fluidized bed facility. In the course of two experimental campaigns, the effects of combustion atmosphere and temperature on pollutant formation (i.e., NO _x , SO₂, and HCl) and reactor hydrodynamics were systematically studied. In contrast to air-firing conditions, the experimental results showed that oxy-fuel combustion enhanced the volume concentration of NO _x by about 50% while simultaneously decreasing the fuel-specific NO _x emissions (by about 33%). The volume concentrations of SO₂ and HCl were significantly influenced by the absorption capacity of calcium-containing ash particles, yielding corresponding values close to 10 and 200 ppmv at 871-880 °C under oxy-fuel combustion conditions. In addition, the analysis of hydrodynamic data revealed that smooth temperature profiles are indispensable to mitigate bed sintering and agglomeration risks during oxy-fuel operation. The results included in this study provide a valuable contribution to the database of experimental information on the oxy-fuel combustion of alternative fuels, which can be applied in future process model validations and scale-up studies.

The Gas Diffusion Electrode Setup as Straightforward Testing Device for Proton Exchange Membrane Water Electrolyzer Catalysts

Hydrogen production from renewable resources and its reconversion into electricity are two important pillars toward a more sustainable energy use. The efficiency and viability of these technologies heavily rely on active and stable electrocatalysts. Basic research to develop superior electrocatalysts is commonly performed in conventional electrochemical setups such as a rotating disk electrode (RDE) configuration or H-type electrochemical cells. These experiments are easy to set up; however, there is a large gap to real electrochemical conversion devices such as fuel cells or electrolyzers. To close this gap, gas diffusion electrode (GDE) setups were recently presented as a straightforward technique for testing fuel cell catalysts under more realistic conditions. Here, we demonstrate for the first time a GDE setup for measuring the oxygen evolution reaction (OER) of catalysts for proton exchange membrane water electrolyzers (PEMWEs). Using a commercially available benchmark IrO₂ catalyst deposited on a carbon gas diffusion layer (GDL), it is shown that key parameters such as the OER mass activity, the activation energy, and even reasonable estimates of the exchange current density can be extracted in a realistic range of catalyst loadings for PEMWEs. It is furthermore shown that the carbon-based GDL is not only suitable for activity determination but also short-term stability testing. Alternatively, the GDL can be replaced by Ti-based porous transport layers (PTLs) typically used in commercial PEMWEs. Here a simple preparation is shown involving the hot-pressing of a Nafion membrane onto a drop-cast glycerol-based ink on a Ti-PTL.

Role of Substrate Surface Morphology on the Performance of Graphene Inks for Flexible Electronics

Two-dimensional (2D) materials, such as graphene, are seen as potential candidates for fabricating electronic devices and circuits on flexible substrates. Inks or dispersions of 2D materials can be deposited on flexible substrates by large-scale coating techniques, such as inkjet printing and spray coating. One of the main issues in coating processes is nonuniform deposition of inks, which may lead to large variations of properties across the substrates. Here, we investigate the role of surface morphology on the performance of graphene ink deposited on different paper substrates with specific top coatings. Substrates with good wetting properties result in reproducible thin films and electrical properties with low sheet resistance. The correct choice of surface morphology enables high-performance films without postdeposition annealing or treatment. Scanning terahertz time-domain spectroscopy (THz-TDS) is introduced to evaluate both the uniformity and the local conductivity of graphene inks on paper. A paper-based strain gauge is demonstrated and a variable resistor acts as an on-off switch for operating an LED. Customized surfaces can thus help in unleashing the full potential of ink-based 2D materials.