Wide Range Of Current Densities Research Articles

Dynamically Reconstructed Triple-Copper-Vacancy Associates Confined in Cu Nanowires Enabling High-Rate and Selective CO2 Electroreduction to C2+ Products.

Electrochemically reconstructed Cu-based catalysts always exhibit enhanced CO2 electroreduction performance; however, it still remains ambiguous whether the reconstructed Cu vacancies have a substantial impact on CO2 -to-C2+ reactivity. Herein, Cu vacancies are first constructed through electrochemical reduction of Cu-based nanowires, in which high-angle annular dark-field scanning transmission electron microscopy image manifests the formation of triple-copper-vacancy associates with different concentrations, confirmed by positron annihilation lifetime spectroscopy. In situ attenuated total reflection-surface enhanced infrared absorption spectroscopy discloses the triple-copper-vacancy associates favor *CO adsorption and fast *CO dimerization. Moreover, density-functional-theory calculations unravel the triple-copper-vacancy associates endow the nearby Cu sites with enriched and disparate local charge density, which enhances the *CO adsorption and reduces the CO-CO coupling barrier, affirmed by the decreased *CO dimerization energy barrier by 0.4eV. As a result, the triple-copper-vacancy associates confined in Cu nanowires achieve a high Faradaic efficiency of over 80% for C2+ products in a wide current density range of 400-800mA cm-2 , outperforming most reported Cu-based electrocatalysts.

Pyrolysis-free synthesis of a high-loading single-atom Cu catalyst for efficient electrocatalytic CO2-to-CH4 conversion.

Electrocatalytic CO2-to-CH4 conversion provides a promising means of addressing current carbon resource recycling and intermittent energy storage. Cu-based single-atom catalysts have attracted extensive attention owing to their high intrinsic activity toward CH4 production; however, they suffer from uncontrollable metal loading and aggregation during the conventional pyrolysis process of carbon-based substrates. Herein, we developed a pyrolysis-free method to prepare a single-atom Cu catalyst anchored on a formamide polymer substrate with a high loading amount and well atomic dispersion through a mild polycondensation reaction. Owing to the isolation of copper active sites, efficient CO2-to-CH4 conversion is achieved over the single-atom Cu catalyst, along with the significant suppression of C-C coupling. As a result, the optimal single-atom catalyst with 5.87 wt% of Cu offers high CH4 faradaic efficiencies (FEs) of over 70% in a wide current density range from 100 to 600 mA cm-2 in the flow cell, together with a maximum CH4 partial current density of 415.8 mA cm-2. Moreover, the CH4 FE can reach 74.2% under optimized conditions in a membrane electrode assembly electrolyzer. This work provides new insights into the subtle design of highly efficient electrocatalyst for CO2 reduction.

Relationship between Bubble Generation Behavior and Hydrogen Evolution Performance at High Current Densities during Alkaline Water Electrolysis

Introduction Alkaline water electrolysis (AWE) has attracted considerable attention as a method to produce hydrogen. However, one of the problems with AWE is the increase in overpotential, which is attributed to bubbles covering the electrode surface at high current densities. Therefore, it is important to understand the bubble generation behavior to develop strategies for reducing the overpotential. In this study, we observed bubble generation behavior on Platinum (Pt) electrodes using a high-speed camera [1] and conducted electrochemical measurements to investigate the relationship between the current density/electrode potential and bubble generation behavior. Experiments Pt wires with diameters of 200 μm were used as the working electrodes. The reference and counter electrodes were a reversible hydrogen electrode (RHE) and Ni rods with a diameter of 3 mm, respectively. All measurements were conducted using a three-electrode electrochemical cell with a 2 M KOH aqueous solution as the electrolyte at 303±1K. To minimize the solution resistance, the working and reference electrodes were positioned as close as possible to each other, with a separation distance of approximately 2 mm. To ensure a uniform current-density distribution, a Ni-rod counter electrode was inserted on both sides of the cell. Observation windows were installed on the sides of the cells. Only a 3-mm parallel section of the working-electrode wire was exposed to the electrolyte to observe the electrolytic reaction, while the rest of the wire was covered with PTFE heat-shrink tube and epoxy resin. After appropriate pretreatment, cyclic voltammetry (CV) measurements were performed at a scan rate of 5 mV s-1 to obtain the polarization curves. Electrochemical impedance spectroscopy (EIS) measurements were conducted at −0.2 to −0.8 V vs. RHE with a potential amplitude of 10 mV, over a frequency range of 3×105 to 1 Hz, where 60 repeated measurements were performed for each frequency. The solution resistance was obtained from Cole–Cole plots and corrected for potential losses. The current density (i geo / A cm-2) was normalized by the geometric surface area of the cylindrically shaped working electrode. Constant current electrolysis was performed under twelve conditions of i geo = −0.05 to −1.5 A cm-2. Under each condition, the formation behavior of hydrogen bubbles was photographed using a high-speed video camera. Results and discussion Figures 1 and 2 show the polarization curves at the cathode and anode, respectively [2]. The overvoltage increased with i geo, as evidenced by the shift of the polarization curves from Tafel slope, in the range of −i geo ＜ 0.9 A cm−2 at the cathode and in the range of i geo > 0.6 A cm−2 at the anode. Figure 3 shows Cole–Cole plots obtained at i geo = −1.0 A cm−2 at the cathode and Figure 4 shows Cole–Cole plots obtained at i geo = 1.0 A cm−2 at the anode [2]. Figure 5 shows the hydrogen bubble generation behavior obtained at i geo = −1.0 A cm−2 at the cathode, and Figure 6 shows oxygen bubble generation behavior obtained at i geo = 1.0 A cm−2 at the anode [2]. The Cole–Cole plots indicate the resistance component on the low-frequency side at high current densities in addition to the charge transfer resistance. Moreover, the arc shapes of the resistance components differ between the anode and cathode, suggesting that different mechanisms are responsible for the increase in the overvoltage at high current densities. We believe that these resistances arise from reactant transfer limitations due to the hydrogen and oxygen bubble layers covering the electrode surfaces. Moreover, it was also confirmed that the charge-transfer resistance is inversely proportional to the current density, indicating that the effective electrode surface area does not change over a wide range of current densities. By comparing Figures 5 and 6, it was observed that oxygen bubbles at the anode where a larger overvoltage increase than cathode was measured had larger diameters and were less likely to detach from the electrode. Furthermore, the bubble layer formed on the electrode surface was thicker on the anode than on the cathode. Acknowledgements Part of this study was based on results obtained from the Development of Fundamental Technology for Advancement of Water Electrolysis Hydrogen Production in the Advancement of Hydrogen Technologies and Utilization Project (JPNP14021), commissioned by the New Energy and Industrial Technology Development Organization (NEDO).

Constructing molybdenum vacancy defect for MoP with optimized p-band center towards high-efficiency hydrogen evolution

Vacancy engineering has been widely used to enhance the hydrogen evolution reaction (HER) performance due to its effective electronic modulation effect. Herein, the molybdenum (Mo) vacancies were introduced into molybdenum phosphide (MoP) towards high-efficiency hydrogen evolution for the first time. Benefiting from the charge redistribution around the Mo vacancies, the exposed P sites can serve as ideal catalytic sites with a free energy of hydrogen adsorption close to zero. Meanwhile, an internal polarization field from terminal Mo atoms to exposed P atoms can offer a more efficient “H delivery” mechanism, achieving fast HER kinetics with a dominant Volmer-Heyrovsky mechanism at a wide range of current density and ultimately exceeding the commercial Pt/C catalyst for high-efficiency hydrogen evolution. More importantly, we first report that the P p-band center can be used as an alternative descriptor to evaluate the HER performance of the electrocatalysts which utilize P atoms as the main active sites. Furthermore, this work also demonstrates that metal vacancies provide an effective tactic to optimize catalytic activity for metal compound-based electrocatalysts.

Metallic Cu Surface Enables Reversible Na Metal Anodes and Stabilizes Anode-Free Sodium Metal Batteries

Anode free Na metal batteries are promising for future energy storage because they not only provide the highest energy densities but also eliminate the need of handling hazardous Na metals during battery manufacturing. However, they suffer from much faster degradation due to strong sensitivities even to trace levels of side reactions. In view of the crucial roles of surface chemistry on modulating electrochemical plating, this work systematically investigated a series of Cu surfaces for Na plating and stripping in the 1.0 M NaPF6 diglyme electrolyte. Our results suggest that Na plating and stripping on pure Cu surface without Cu oxide species exhibits much better reversibility and smaller overpotentials across a wide range of current densities, especially for the first plating/stripping cycle. The high performance includes consistently higher than 99.8% Faradaic efficiencies, much more stable interfacial resistance, and negligible formation of mossy Na after 500 cycles. This improved performance can be explained based on the stronger Na-Cu affinity compared with the Na-CuO affinity. Anode-free Na metal batteries equipped with high-capacity sodium vanadium phosphate cathodes and pure Cu current collector exhibited at least 70% capacity retention for 100 cycles.

Influence of ferric oxides with varying crystallinity on the enrichment of halophilic exoelectrogens: An application for power generation in microbial fuel cells

Pre-enriching electroactive microbes (EAM) capable of respiration using solid terminal electron acceptors (TEA) is a prospective strategy that promotes faster start-up of bioanodes in microbial fuel cells (MFC) for energy-efficient treatment of saline wastewater. Previous studies demonstrated a reduction in the start-up times of bioanodes with ferric oxides as TEA, though the enriched EAM generated a wide range of current densities as opposed to those using graphene oxide (GO) as TEA. Additionally, the influence of ferric oxides with varying crystallinity on the anode-respiring activity of halophilic EAM is understudied. This study elaborates a systematic investigation into the influence of inoculum sources, different crystallinity of ferric oxides and their redox potentials on the selective enrichment of GO-respiring EAM for developing bioanodes with high current-generating capacity at shorter start-up times. A holistic assessment of the bioanodes, including analysis of their electrochemical performance and generated power densities, revealed that enrichment of GO-respiring EAM with amorphous ferrihydrite as TEA fostered the growth of high-performing biofilms at shorter start-up times (48–72 h) compared to crystalline goethite used as TEA (∼96 h). These biofilms produced power densities ranging from 142 ± 10 mW/m2 to 276 ± 76 mW/m2 with corresponding Coulombic efficiencies of 16 ± 6 % to 30 ± 6 %. Finally, the implications of promising halophilic EAM consortia were explored for saline MFC as a prospective energy-neutral wastewater treatment technology.

Commercially Accessible High-Performance Aluminum-Air Battery Cathodes through Electrodeposition of Mn and Ni Species on Fuel Cell Cathodes.

This study presents a cost-effective method for producing high-performance cathodes for aluminum-air batteries. Commercial fuel cell cathodes are modified through electrodeposition of nickel and manganese species. The optimal conditions for electrodeposition are determined using a combination of structural (Raman, SEM, TEM) and electrochemical (LSV, EI, discharge curves) characterization techniques. The structural analysis confirms successful incorporation of nickel and manganese species onto the cathode surface. Electrochemical tests demonstrate enhanced electrochemical activity compared to unmodified cathodes. By combining the favorable properties of electrodeposited manganese species with nickel species, a high-performance cathode is obtained. The developed cathode exhibits capacities of 50 mA h cm-2 in aluminum-air batteries across a wide range of current densities. The electrodeposition method proves effective in improving electrochemical performance. A key advantage of this method is its simplicity and cost-effectiveness. The use of commercially available materials and well-established electrodeposition techniques allows for easy scalability and commercialization. This makes it a viable option for large-scale production of high-performance cathodes for the next-generation energy storage devices.

Ultra-elevated power density and high energy efficiency of protonic ceramic fuel cells: Numerical and experimental results

The fabrication of high-performance protonic ceramic fuel cells (PCFCs) and the accurate evaluation of their energy efficiency remain challenging because of electron–hole leakage. By combining an established numerical method with experiments, we developed high-performance chemically stable Ce-free PCFCs with a BaZr0.8Yb0.2O3−δ electrolyte that perform comparably to first-tier PCFCs, which typically employ Ce-containing electrolytes. To the best of our knowledge, this study is the first to numerically reproduce experimental performance over a wide range of temperatures, electrolyte thicknesses, and current densities. Importantly, our study can accurately predict the ultra-elevated performance of cells under different conditions without the need for conducting additional experiments (e.g., > 3.0 W·cm−2 power density or > 70% lower heating value energy efficiency)

Artificial neural network-enabled approaches toward mass balancing and cell optimization of lithium dual ion batteries

Dual ion batteries (DIBs) are gaining prominence as alternate energy storage devices in recent years due to their high operating potential and low cost. For an all-carbon based DIB, owing to the low cathode capacity, the anode:cathode mass ratio has a much more significant effect on the overall cell performance. Achieving a generalized model towards optimization of active mass balancing in these devices still remains a challenge. With an aim to accelerate the development of dual ion batteries, herein, we attempt to make an experimental data-driven deep neural network model towards mass balancing and cell optimization of a graphite-graphite lithium dual ion battery. We designed appropriate experimental conditions with maximum ranges of control variables and performed detailed electrochemical studies. The data generated through such a minimum number of experiments are used to predict the performance characteristics of the graphite/graphite-based lithium dual ion full cell under a wide range of active electrode mass ratios and current densities, through a machine learning approach. We demonstrate that our model can predict the charge-discharge profiles of the full cell at any given current density in the range 50 mA g−1 and 1 A g−1. Further, using these charge-discharge profiles, we find the discharge capacities of the cell for varying mass ratios and different mass loading. Though we address here the case of graphite/graphite lithium dual ion battery cells, the approach can easily be extended to other battery chemistries to achieve accelerated development of advanced energy storage devices.

(Invited) Dendrite Formation in Lithium Electrodeposition – Insights from Experiments and Modeling

High-energy density batteries are essential for powering future electric vehicles and electric aircrafts. The Li-metal anode offers the highest theoretical specific energy among practically available anode materials; however, a major hurdle in the progress towards rechargeable Li-metal batteries is the dendritic electrodeposition of Li metal during the battery charging process. The physicochemical mechanisms behind Li dendrite formation have been a topic of rich and fervent research, but many questions remain presently unanswered. Among these, a key question of significance to battery charging is: at what time instant is Li dendritic growth initiated? In the present talk, this question will be addressed through a combination of experiments and modeling. Chronopotentiometry during galvanostatic Li electrodeposition coupled with in situ optical microscopy reveals that the first emergence of Li dendrites corresponds to the time instant when the surface overpotential reaches a maximum.1 Electrochemical impedance spectroscopy shows that the increase in the surface overpotential preceding this maximum is due to gradual growth of the solid electrolyte interphase (SEI). This SEI layer growth induces Li+ concentration depletion at the electrode-SEI interface, promoting amplification of surface asperities and thus dendrites that rupture the SEI. A transport model incorporating Li+ diffusion across a growing SEI layer is developed, and shown to predict Li dendrite onset times that are in good agreement with experimental observations over a wide range of current densities, temperature, and initial SEI thicknesses.2 A key conclusion of our work is that liquid-phase mass transport limitations, often characterized by the Sand’s equation, do not reliably predict the onset of Li dendrites.3 Rather, transport characteristics and associated instabilities within solid-phase surface films on Li are predominantly responsible for dendrite formation. Our work provides clues for how dendrite formation could be arrested for enabling rechargeable Li-metal anodes for use in next-generation batteries.

AgZn-BDC-derived catalyst for CO2 electroreduction to syngas with fixed ratio over wide current density

Electrochemical CO2 reduction (CO2RR) to produce syngas (CO and H2) is an attractive method for achieving carbon neutrality. However, it remains a challenge to simultaneously control the CO/H2 ratio of the syngas produced over a wide range of current densities. Here, we report a bimetallic Ag and Zn MOF-derived catalyst that achieves a stable CO/H2 ratio of around 1:1 over a wide current density range of 50–200 mA cm−2. In situ Raman measurements, XRD pattern and FTIR images demonstrate that the MOF-derived catalyst transforms into Ag2O and ZnO surrounded by amorphous carbon during CO2RR. In-situ ATR-SEIRAS measurements and CO-TPD reason that the Ag and Zn MOF-derived catalyst strengthens the binding strength of *CO, which ends up with the CO to H2 ratio in the syngas approaches 1:1.

Ligand-Controlled Electroreduction of CO2 to Formate over Facet-Defined Bimetallic Sulfide Nanoplates

CO2 reduction (CO2R) catalyzed by an efficient, stable, and earth-abundant electrocatalyst offers an attractive means to store energy derived from renewable sources. Here, we describe the synthesis of facet-defined Cu2SnS3 nanoplates and the ligand-controlled CO2R property. We show that thiocyanate-capped Cu2SnS3 nanoplates possess excellent selectivity toward formate over a wide range of potentials and current densities, attaining a maximum formate Faradaic efficiency of 92% and partial current densities as high as 181 mA cm–2 when tested using a flow cell with gas-diffusion electrode. In situ spectroscopic measurements and theoretical calculations reveal that the high formate selectivity originates from favorable adsorption of HCOO* intermediates on cationic Sn sites that are electronically modulated by thiocyanates bound to adjacent Cu sites. Our work illustrates that well-defined multimetallic sulfide nanocrystals with tailored surface chemistries could provide a new avenue for future CO2R electrocatalyst design.

Sn-based redox cycle mediated microenvironment regulation of Cu sites on poly(ionic liquid) enhance electrocatalytic CO-to-C2+ conversion

Electrocatalytic CO reduction provides a sustainable route for high-value CO utilization. To promote the selectivity of C2+ products (FEC2+) at high reaction rates, the electronic structure and the microenvironment of Cu sites in Cu@PIL were regulated by introducing a Sn-mediated redox cycle. The obtained Cu@PIL@Sn-x hybrids provided high FEC2+ (> 70%) within a wide current density (j) range from –100 to −700 mA cm–2. Particularly, an excellent FEC2+ of 96.8 % with a high jC2+ of −484.2 mA cm–2 was obtained on Cu@PIL@Sn-1.0. Besides, it exhibited high tolerance of diluted CO gas at −250.0 mA cm–2. Mechanistic studies demonstrated the rich high-valence Cu species and the adjacent Sn-Cl species at the Cu@PIL@Sn-x hybrids jointly account for the local enrichment of oxygen-containing species on Cu surface during the electrolysis of CO, even at high overpotentials, which enables the C–C coupling at high reaction rates.

Defect-engineered carbon-confined silver for enhanced CO2 electrocatalytic reduction to CO in acidic media

Electrocatalytic CO2 reduction (CO2RR) to carbon monoxide (CO) holds great promise for carbon capture and utilization. Despite the proposal of electrocatalytic CO2RR in acidic media for high-efficiency CO2 conversion, the challenges of low CO selectivity caused by the highly competitive hydrogen evolution reaction and catalyst corrosion have not been adequately addressed. Here, we present a strategy that restricts proton migration and stabilizes key intermediates over a defective carbon layers confined Ag catalyst (Ag@C-d) to enhance the catalytic selectivity and stability for CO2RR in acidic media. Density functional theory simulations first discovered that electron polarization from Ag to vacancy-defective carbon creates the desired electric field at the interface between Ag and defective carbon layers, enabling efficient acidic CO2RR to CO. We synthesized Ag@C-d catalyst and that exhibits exceptional CO Faraday efficiency (FE, >98 %) and activity across a wide range of current densities (50–500 mA cm−2) in an acidic flow cell. At a current density of 500 mA cm−2, the single-pass conversion efficiency of CO2RR to CO can reached 71.5 %, surpassing that of alkaline systems. An excellent operational stability, operating continuously for over 100 h at industrial-scale current density, was also achieved. In a membrane electrode assembly electrolyzer incorporating the Ag@C-d catalyst at the cathode, a 91.6 % CO FE at 200 mA cm−2 can be achieved, accompanied by an energy conversion efficiency of nearly 40 %. These findings highlight the promising performance and potential applications of the developed catalyst for acidic CO2RR.

High-rate and selective conversion of CO2 from aqueous solutions to hydrocarbons

Electrochemical carbon dioxide (CO2) conversion to hydrocarbon fuels, such as methane (CH4), offers a promising solution for the long-term and large-scale storage of renewable electricity. To enable this technology, CO2-to-CH4 conversion must achieve high selectivity and energy efficiency at high currents. Here, we report an electrochemical conversion system that features proton-bicarbonate-CO2 mass transport management coupled with an in-situ copper (Cu) activation strategy to achieve high CH4 selectivity at high currents. We find that open matrix Cu electrodes sustain sufficient local CO2 concentration by combining both dissolved CO2 and in-situ generated CO2 from the bicarbonate. In-situ Cu activation through alternating current operation renders and maintains the catalyst highly selective towards CH4. The combination of these strategies leads to CH4 Faradaic efficiencies of over 70% in a wide current density range (100 – 750 mA cm-2) that is stable for at least 12 h at a current density of 500 mA cm-2. The system also delivers a CH4 concentration of 23.5% in the gas product stream.

Confinement of ionomer for electrocatalytic CO2 reduction reaction via efficient mass transfer pathways.

Gas diffusion electrodes (GDEs) mediate the transport of reactants, products and electrons for the electrocatalytic CO2 reduction reaction (CO2RR) in membrane electrode assemblies. The random distribution of ionomer, added by the traditional physical mixing method, in the catalyst layer of GDEs affects the transport of ions and CO2. Such a phenomenon results in elevated cell voltage and decaying selectivity at high current densities. This paper describes a pre-confinement method to construct GDEs with homogeneously distributed ionomer, which enhances mass transfer locally at the active centers. The optimized GDE exhibited comparatively low cell voltages and high CO Faradaic efficiencies (FE>90%) at a wide range of current densities. It can also operate stably for over 220h with the cell voltage staying almost unchanged. This good performance can be preserved even with diluted CO2 feeds, which is essential for pursuing a high single-pass conversion rate. This study provides a new approach to building efficient mass transfer pathways for ions and reactants in GDEs to promote the electrocatalytic CO2RR for practical applications.

TECHNOLOGICAL INDICATORS OF THE CATHODIC PROCESS IN THE REGENERATION OF USED SULFO-ACID SOLUTIONS FOR ETCHING STEEL

The current state of regeneration of sulfate solutions was analyzed, it was established that the existing physico-chemical methods do not solve the problem of regeneration of sulfuric acid, but only neutralize it, for transfer according to the standards of the MPC to neutralization and into the sewage system with subsequent disposal. It has been confirmed that it is advisable to carry out the regeneration by an electrochemical method using a three-chamber electrolyzer, when the solution is fed into the middle chamber, the concentration of regenerated sulfuric acid increases to 180-200 g/l, with simultaneous iron deposition, with a current yield of 65-70%. This method reduces waste and allows switching to a closed cycle on sulfuric acid. It was found that in the process of digestion, the concentration of sulfuric acid decreases from 2.0 to 0.5 mol·dm-3, and the concentration of iron (II) sulfate increases accordingly. Under the conditions of a decrease in the concentration of sulfuric acid, its chemical activity also decreases when interacting with iron oxides and hydroxides. To increase the reactivity of pickling solutions, an increase in the temperature of the entire process is used. The kinetic regularity of combined cathodic processes in model solutions of iron (II) sulfate with sulfuric acid was established. Platinum, copper and carbon steel were used as cathode material. The choice of the cathode material was based on the different electrochemical properties of these selected metals with respect to the hydrogen reaction. The main process at the platinum cathode is hydrogen release in a wide range of current densities. At current densities greater than 0.1 A/cm2, a sharp increase in potential was observed due to the incorporation of Fe2+ into the composition of the cathode-electrolyte interface, but Fe2+ reduction potentials were not reached. When replacing the cathode material from platinum to carbon steel, a significant inhibition of hydrogen release was observed, which made it possible to reach the potentials for the simultaneous reduction of hydrogen and iron, however, the maximum current of the rectilinear section of the electrochemical process with electrochemical control was reduced from 10 at 20 0C to 3 times at 80 0C. The use of a copper cathode made it possible to reveal the influence of the hydrogen reaction on the course of Fe2+ reduction. The release of hydrogen at the copper cathode was accompanied by a significant inhibition of the hydrogen ion discharge. When using an iron cathode, electrochemical desorption is the limiting stage, which leads to the existence of layers of adsorbed hydrogen firmly attached to the surface of the iron cathode. A comparative analysis of the voltage-current dependences for the final investigated temperatures indicates a significant effect of an increase in temperature from 20 0C to 80 0C by approximately 120-150 mV. The cathodic process at 20 0C takes place in the mode of increased kinetics for both combined processes. At 80 0С, rectilinear sections of electrochemical control of the cathodic process appear on the voltage–voltage dependences, at Fe2+ concentrations of 1.0 and 1.5 mol/dm3. These areas range from 20 to 60 mA/cm2. The concentration of iron ions and the temperature of electrolysis have a significant effect on the process of electrochemical reduction of Fe2+, which was confirmed experimentally. Since the target process in the electrochemical regeneration of spent pickling solutions is the regeneration of sulfuric acid itself, and not the removal of Fe2+ from this solution, the cathodic mode of operation of the electrode unit was determined according to the technological indicators of the anodic process.

(Tetrafluorovinylphenyl)carbazole as a Multifunctional Material for OLED Applications

The multifunctional materials for application in organic light-emitting devices (OLEDs) based on a single structural motif are very desired but quite rare species. Such structures allow simplifying the chemical variety within OLED heterostructures and thus reducing their cost, manufacturing time, and logistic efforts. In this paper, we report the 9-(2,3,5,6-tetrafluoro-4-vinylphenyl)carbazole molecule (Cz4FS) utilized as a fluorescent emitter, host material for quantum dot based OLEDs (QLEDs), acceptor part of the exciplex active layer, and monomer that can be used for the preparation of emissive polymers and copolymers. The external quantum efficiency (EQE) of the corresponding fluorescent OLED based on a Cz4FS single emitter doped into a 1,3-bis(carbazol-9-yl)benzene matrix is 4.2%, which is close to the theoretical limit and maximum brightness at the level of 3600 cd/m2. An OLED based on exciplex emission obtained utilizing Cz4FS as an acceptor demonstrates higher efficiency (5.3%) and much higher brightness near 25 000 cd/m2. A QLED based on Cz4FS as a host for CdSeS/ZnS core–shell quantum dots demonstrates excellent energy transfer from the Cz4FS matrix that results in a clear spectrum of quantum dots with an EQE of 2.3%, maximum of 19 000 cd/m2, and narrow spectral distribution. An OLED based on a Cz4FS-based polymer and copolymer demonstrates not extraordinary efficiency but low-efficiency roll-off in a wide range of current densities.

Pre‐Activation of CO2 at Cobalt Phthalocyanine‐Mg(OH)2 Interface for Enhanced Turnover Rate

AbstractCobalt phthalocyanine (CoPc) anchored on heterogeneous scaffold has drawn great attention as promising electrocatalyst for carbon dioxide reduction reaction (CO2RR), but the molecule/substrate interaction is still pending for clarification and optimization to maximize the reaction kinetics. Herein, a CO2RR catalyst is fabricated by affixing CoPc onto the Mg(OH)2 substrate primed with conductive carbon, demonstrating an ultra‐low overpotential of 0.31 ± 0.03 V at 100 mA cm−2 and high faradaic efficiency of >95% at a wide current density range for CO production, as well as a heavy‐duty operation at 100 mA cm−2 for more than 50 h in a membrane electrode assembly. Mechanistic investigations employing in situ Raman and attenuated total reflection surface‐enhanced infrared absorption spectroscopy unravel that Mg(OH)2 plays a pivotal role to enhance the CO2RR kinetics by facilitating the first‐step electron transfer to form anionic *CO2− intermediates. DFT calculations further elucidate that introducing Lewis acid sites help to polarize CO2 molecules absorbed at the metal centers of CoPc and consequently lower the activation barrier. This work signifies the tailoring of catalyst‐support interface at molecular level for enhancing the turnover rate of CO2RR.

Multiphysics modeling of flow-through advanced oxidation photoreactors with in-situ hydrogen peroxide electrogeneration

Advanced oxidation processes (AOPs) commonly use chemicals such as hydrogen peroxide (H2O2) in combination with ultraviolet (UV) radiation to produce hydroxyl radicals (·OH). As supply chain management and storage of concentrated H2O2 is challenging, in recent years, in situ H2O2 generation systems are gaining attention. These systems are in early stages of research and development, and a numerical model can help accelerate the development of highly efficient systems. In this work, for the first time, we describe a mechanistic multiphysics model to simulate a flow-through electrochemical AOP photoreactor with in situ H2O2 electrogeneration and UV radiation. The electrochemical, hydrodynamic, radiation, and kinetic phenomena were incorporated into the model. The model showed good agreement with the experimental results over a wide range of flow rates (5% average difference in 35–95 mL min–1) and current densities (9% average difference 7–34 mA cm–2). The computational model was verified with the experimental data obtained for the degradation of 2,4-dichlorophenoxyacetic acid (2,4-D), and it was applied to study the performance of some design variations in terms of hydrodynamics and radiation. The results showed that implementing reflective walls will increase the UV fluence, which ultimately led to a 45% improvement in the contaminant removal.