Modeling and Simulation of Reaction Environment in Photoredox Catalysis: A Critical Review

From the pharmaceutical industry’s point of view, photoredox catalysis has emerged as a powerful tool in the field of the synthesis of added-value compounds. With this method, it is possible to excite the catalyst by the action of light, allowing electron transfer processes to occur and, consequently, oxidation and reduction reactions. Thus, in association with photoredox catalysis, microreactor technology and continuous flow chemistry also play an important role in the development of organic synthesis processes, as this technology offers high yields, high selectivity and reduced side reactions. However, there is a lack of a more detailed understanding of the photoredox catalysis process, and computational tools based on computational fluid dynamics (CFD) can be used to deal with this and boost to reach higher levels of accuracy to continue innovating in this area. In this review, a comprehensive overview of the fundamentals of photoredox catalysis is provided, including the application of this technology for the synthesis of added-value chemicals in microreactors. Moreover, the advantages of the continuous flow system in comparison with batch systems are pointed out. It was also demonstrated how modeling and simulation using computational fluid dynamics (CFD) can be critical for the design and optimization of microreactors applied to photoredox catalysis, so as to better understand the reagent interactions and the influence of light in the reaction medium. Finally, a discussion about the future prospects of photoredox reactions considering the complexity of the process is presented.

Exploring the Limits of the Rapid-Charging Performance of Graphite as the Anode in Lithium-Ion Batteries

Graphite is, in principle, applicable as a high-power anode in lithium-ion batteries (LIBs) given its high intralayer lithium diffusivity at room temperature. However, such cells are known to exhibit poor capacity retention and/or undergo irreversible side reactions including lithium plating when charged at current rates above ~2C (~740 mA g-1). To explore the inherent materials properties that limit graphite anodes in rapid-charge applications, a series of full-cells consisting of graphite as the anode and a standard Li[Ni0.8Mn0.1Co0.1]O2 (NMC811) cathode was investigated. Instead of a conventional cathode-limited cell design, an anode-limited approach was used in this work to ensure that the overall cell capacity is only determined by the graphite electrode of interest. The optimized N:P capacity ratio was determined as N/P = 0.67, enabling stable cycling across a wide range of charging rates (4-20C) without inhibition by the NMC811 cathode. The results show that unmodified, highly crystalline graphite can be an excellent anode for rapid-charge applications at up to 8C, even with a standard electrolyte and NMC811 cathode and in cells with 1.0 mAh cm-2 loadings. As a rule, capacity and specific energy are inversely proportional to crystallite size at high rates; performance can likely be improved by electrolyte/cathode tuning.

Charge Utilization Efficiency and Side Reactions in the Electrochemical Mechanical Polishing of 4H-SiC (0001)

Slurryless electrochemical mechanical polishing (ECMP) is very effective in the polishing of silicon carbide (SiC) wafers. To achieve a high material removal rate (MRR) of SiC wafer using ECMP with low electrical energy loss, charge utilization efficiency in the anodic oxidation of the SiC surface was investigated and the underlying mechanism was clarified by modeling the anodic oxidation system of SiC in 1 wt% NaCl aqueous solution. The charge utilization efficiency in the anodic oxidation of SiC was found to be constant when the current density was less than 20 mA/cm2 and significantly decreased when the current density was greater than 30 mA/cm2, resulting in a significant reduction in the MRR. Modeling of the anodic oxidation system indicates that the charge utilization efficiency depended on the potential applied on the SiC surface: the oxidation of SiC occupied the dominant position in the anodizing system when the potential is lower than 25 V vs Ag|AgCl, charge utilization efficiency greatly decreased when the applied potential was greater than 25 V owing to the occurrence of oxidations of the H2O and Cl-. This research provides both a theoretical and practical foundation for using ECMP to polish SiC wafers.

Interfacial reactions in lithia-based cathodes depending on the binder in the electrode and salt in the electrolyte

Lithia (Li2O)-based cathodes, utilizing oxygen redox reactions for obtaining capacity, exhibit higher capacity than commercial cathodes. However, they are highly reactive owing to superoxides formed during charging, and they enable more active parasitic (side) reactions at the cathode/electrolyte and cathode/binder interfaces than conventional cathodes. This causes deterioration of the electrochemical performance limiting commercialization. To address these issues, the binder and salt for electrolyte were replaced in this study to reduce the side reaction of the cells containing lithia-based cathodes. The commercially used polyvinylidene fluoride (PVDF) binder and LiPF6 salt in the electrolyte easily generate such reactions, and the subsequent reaction between PVDF and LiOH (from decomposition of lithia) causes slurry gelation and agglomeration of particles in the electrode. Moreover, the fluoride ions from PVDF promote side reactions, and LiPF6 salt forms POF3 and HF, which cause side reactions owing to hydrolysis in organic solvents containing water. However, the polyacrylonitrile (PAN) binder and LiTFSI salt decrease these side reactions owing to their high stability with lithia-based cathode. Further, thickness of the interfacial layer was reduced, resulting in decreased impedance value of cells containing lithia-based cathodes. Consequently, for the same lithia-based cathodes, available capacity and cyclic performance were increased owing to the effects of PAN binder and LiTFSI salt in the electrolyte.

Single Particle Hopping as an Indicator for Evaluating Electrocatalysts

Design and screening electrocatalysts for gas evolution reactions suffer from scanty understanding of multi-phase processes at the electrode-electrolyte interface. Due to the complexity of multi-phase interface, it is still a great challenge to capture gas evolution dynamics under operando condition to precisely portray the intrinsic catalytic performance of interface. Here, we establish a single particle imaging method to real time monitor a potential-dependent vertical motion or hopping of electrocatalysts induced by electrogenerated gas nanobubbles. The hopping feature of single particle is closely correlated with intrinsic activities of electrocatalysts, thus is developed to be an indicator to evaluate gas evolution performance of various electrocatalysts. This optical indicator diminishes interferences from heterogeneous morphologies, non-Faradaic processes and parasitic side reactions that are unavoidable in conventional electrochemical measurements, therefore enables precise evaluation and high-throughput screening of catalysts for gas evolution systems.

Tertiary Alkylative Suzuki-Miyaura couplings

The Suzuki-Miyaura coupling is extremely useful to construct Csp2-Csp2 carbon bonds. On the other hand, Csp2-Csp3 coupling reactions are do not work well, and tert-alkylative Suzuki-Miyaura coupling is particularly challenging due to problematic oxidative addition and beta-hydride elimination side reactions. In this short review, we will introduce recent examples of tert-alkylative Suzuki-Miyaura couplings with tert-alkyl electrophiles or -boron reagents. The review will mainly focus on catalyst and product structures and the proposed mechanisms .

Strategies on regulating Zn2+ solvation structure for dendrites-free and side reactions-suppressed zinc-ion batteries

High‐safety and low‐cost aqueous zinc‐ion batteries (ZIBs) are an exceptionally compelling technology for grid‐scale energy storage, whereas the corrosion, hydrogen evolution reaction and dendrites growth of Zn anodes plague their...

Design of an Automated Assembly Station for Process Development of All-Solid-State Battery Cell Assembly

Today, lithium-ion batteries are a promising technology in the evolution of electro mobility, but still have potential for improvement in terms of performance, safety and cost. In order to exploit this potential, one promising approach is the replacement of liquid electrolyte with solid-state electrolyte and the use of lithium metal electrode as an anode instead of graphite based anodes. Solid-state electrolytes and the lithium metal anode have favorable electrochemical properties and therefore enable significantly increased energy densities with inherent safety. However, these materials are both, mechanically and chemically sensitive. Therefore, material-adapted processes are essential to ensure quality-assured manufacturing of all-solid-state lithium-ion battery cells. This paper presents the development of a scaled and flexible automated assembly station adapted to the challenging properties of the new all-solid-state battery materials. In the station various handling and gripping techniques are evaluated and qualified for assembly of all-solid-state battery cells. To qualify the techniques, image processing is set up as a quality measurement technology. The paper also discusses the challenges of enclosing the entire assembly station in inert gas atmosphere to avoid side reactions and contamination of the chemically reactive materials.