Microwave-assisted synthesis of iridium oxide and palladium nanoparticles supported on a nitrogen-rich covalent triazine framework as superior electrocatalysts for the hydrogen evolution and oxygen reduction reaction

Microwave-Assisted Ultrafast Synthesis of Bimetallic Nickel-Cobalt Metal-Organic Frameworks for Application in the Oxygen Evolution Reaction

Herein, a series of monometallic Ni-, Co- and Zn-MOFs and bimetallic NiCo-, NiZn- and CoZn-MOFs of formula M2(BDC)2DABCO and (M,M')2(BDC)2DABCO, respectively, (M, M'=metal) with the same pillar and layer linkers 1,4-diazabicyclo[2.2.2]octane (DABCO) and benzene-1,4-dicarboxylate (BDC) were prepared through a fast microwave-assisted thermal conversion synthesis method (MW) within only 12 min. In the bimetallic MOFs the ratio M:M' was 4 : 1. The mono- and bimetallic MOFs were selected to systematically explore the catalytic-activity of their derived metal oxide/hydroxides for the oxygen evolution reaction (OER). Among all tested bimetallic MOF-derived catalysts, the NiCoMOF exhibits superior catalytic activity for the OER with the lowest overpotentials of 301 mV and Tafel slopes of 42 mV dec-1 on a rotating disk glassy carbon electrode (RD-GCE) in 1 mol L-1 KOH electrolyte at a current density of 10 mA cm-2. In addition, NiCoMOF was insitu grown in just 25 min by the MW synthesis on the surface of nickel foam (NF) with, for example, a mass loading of 16.6 mgMOF/gNF, where overpotentials of 313 and 328 mV at current densities of 50 and 300 mA cm-2, respectively, were delivered and superior long-term stability for practical OER application. The low Tafel slope of 27 mV dec-1, as well as a low reaction resistance from electrochemical impedance spectroscopy (EIS) measurement (Rfar=2 Ω), confirm the excellent OER performance of this NiCoMOF/NF composite. During the electrocatalytic processes or even before upon KOH pre-treatment, the MOFs are transformed to the mixed-metal hydroxide phase α-/β-M(OH)2 which presents the active species in the reactions (turnover frequency TOF=0.252 s-1 at an overpotential of 320 mV). Compared to the TOF from β-M(OH)2 (0.002 s-1), our study demonstrates that a bimetallic MOF improves the electrocatalytic performance of the derived catalyst by giving an intimate and uniform mixture of the involved metals at the nanoscale.

Boosting lithium storage in covalent triazine framework for symmetric all-organic lithium-ion batteries by regulating the degree of spatial distortion

Covalent triazine frameworks (CTFs) with tunable structure, fine molecular design and low cost have been regarded as a class of ideal electrode materials for lithium-ion batteries (LIBs). However, the tightly layered structure possessed by the CTFs leads to partial hiding of the redox active site, resulting in their unsatisfactory electrochemical performance. Herein, two CTFs (BDMI-CTF and TCNQ-CTF) with higher degree of structural distortion, more active sites exposed, and large lattice pores were prepared by dynamic trimerization reaction of cyano. As a result, BDMI-CTF as a cathode material for LIBs exhibits high initial capacity of 186.5 mAh/g at 50 mA g-1 and superior cycling stability without capacity loss after 2000 cycles at 1000 mA g-1 compared with TCNQ-CTF counterparts. Furthermore, based on their bipolar functionality, BDMI-CTF can be used as both cathode and anode materials for symmetric all-organic batteries (SAOBs), and this work will open a new window for the rational design of high performance CTF-based LIBs.

Microwave Encounters Ionic Liquid: Synergistic Mechanism, Synthesis and Emerging Applications

Progress in microwave (MW) energy application technology has stimulated remarkable advances in manufacturing and high-quality applications of ionic liquids (ILs) that are generally used as novel media in chemical engineering. This Review focuses on an emerging technology via the combination of MW energy and the usage of ILs, termed microwave-assisted ionic liquid (MAIL) technology. In comparison to conventional routes that rely on heat transfer through media, the contactless and unique MW heating exploits the electromagnetic wave-ions interactions to deliver energy to IL molecules, accelerating the process of material synthesis, catalytic reactions, and so on. In addition to the inherent advantages of ILs, including outstanding solubility, and well-tuned thermophysical properties, MAIL technology has exhibited great potential in process intensification to meet the requirement of efficient, economic chemical production. Here we start with an introduction to principles of MW heating, highlighting fundamental mechanisms of MW induced process intensification based on ILs. Next, the synergies of MW energy and ILs employed in materials synthesis, as well as their merits, are documented. The emerging applications of MAIL technologies are summarized in the next sections, involving tumor therapy, organic catalysis, separations, and bioconversions. Finally, the current challenges and future opportunities of this emerging technology are discussed.

Novel Microwave-Assisted Synthesis of COFs: 2020–2022

Covalent organic frameworks (COFs) have emerged as a new type of crystalline porous polymers of great interest. However, their preparation requires long reaction times. Microwave-assisted synthesis (MAS) offers an interesting approach to increasing the reaction rate of chemical processes. Thus, microwaves can be a key tool for the fast and scalable synthesis of COFs. Since our previous review on the topic, the preparation of COFs with microwaves has been evolving. Herein, we present a compilation of COFs studies and experiments published in the last three years on the synthesis of COFs using microwave-assisted synthesis as a source of energy. The articles include imine, triazine, and other 2D COFs synthesized using MAS. The 3D COFs have also been compiled. The chemical structure of the monomers and the COFs and their main parameters of synthesis and application are summarized for each article.

Tunable Aryl Alkyl Ionic Liquid Supported Synthesis of Platinum Nanoparticles and Their Catalytic Activity in the Hydrogen Evolution Reaction and in Hydrosilylation

Tunable aryl alkyl ionic liquids (TAAILs) are ionic liquids (ILs) with a 1-aryl-3-alkylimidazolium cation having differently substituted aryl groups. Herein, nine TAAILs with the bis(trifluoromethylsulfonyl)imide anion are utilized in combination with and without ethylene glycol (EG) as reaction media for the rapid microwave synthesis of platinum nanoparticles (Pt-NPs). TAAILs allow the synthesis of small NPs and are efficient solvents for microwave absorption. Transmission electron microscopy (TEM) shows that small primary NPs with sizes of 2 nm to 5 nm are obtained in TAAILs and EG/TAAIL mixtures. The Pt-NPs feature excellent activity as electrocatalysts in the hydrogen evolution reaction (HER) under acidic conditions, with an overpotential at a current density of 10 mA cm^-2 as low as 32 mV vs the reversible hydrogen electrode (RHE), which is significantly lower than the standard Pt/C 20% with 42 mV. Pt-NPs obtained in TAAILs also achieved quantitative conversion in the hydrosilylation reaction of phenylacetylene with triethylsilane after just 5 min at 200 °C.