Branched Copper Oxide Nanoparticles Induce Highly Selective Ethylene Production by Electrochemical Carbon Dioxide Reduction

© 2019 American Chemical Society. For long-term storage of renewable energy, the electrochemical carbon dioxide reduction reaction (CO 2 RR) offers a promising option for converting electricity to permanent forms of chemical energy. In this work, we present highly selective ethylene production dependent upon the catalyst morphology using copper oxide nanoparticles. The branched CuO nanoparticles were synthesized and then deposited on conductive carbon materials. After activation, the major copper species changed to Cu + , and the resulting electrocatalyst exhibited a high Faradaic efficiency (FE) of ethylene reaching over 70% and a hydrogen FE of 30% without any byproducts in a neutral aqueous solution. The catalyst also showed high durability (up to 12 h) with the ethylene FE over 65%. Compared to cubic morphology, the initial branched copper oxide structure formed highly active domains with interfaces and junctions in-between during activation, which caused large surface area with high local pH leading to high selectivity and activity for ethylene productio

Gold Nanoparticles-Based Colorimetric Assay for Cathepsin B Activity and the Efficiency of Its Inhibitors

Cathepsin B has been suggested to be a prognostic marker of melanoma, glioma, and a variety of cancers such as brain, breast, colon, esophageal, gastric, lung, ovarian, and thyroid cancers. Cathepsin B inhibitors have also been considered as anticancer drug candidates; hence, there has been a growing need for a probe which enables the selective and simple detection of cathepsin B and its inhibitors. For the purpose of selective assay, a cathepsin B-specific substrate, <i>N,N</i>′-diBoc-dityrosine-glycine-phenylalanine-3-(methylthio)­propylamine (DBDY-Gly-Phe-MTPA) was synthesized in this study. Phe-MTPA, which was produced via cathepsin B-catalyzed hydrolysis of DBDY-Gly-Phe-MTPA, allowed aggregation of gold nanoparticles (AuNPs) leading to a color change from red to blue. When tested for cathepsins B, L, and S, this assay method exhibited AuNPs color change only in reaction to cathepsin B. The limits of detection for cathepsin B was 10 and 5 nM in the 1 and 2 h hydrolysis reactions, respectively. The efficiency of cathepsin B inhibitors such as leupeptin, antipain, and chymostatin was easily compared by the degree of color change. Moreover, IC₅₀ values of leupeptin, antipain, and chymostatin were found to be 0.11, 0.48, and 1.78 μM, respectively, which were similar to the results of previous studies. Therefore the colorimetric assay of cathepsin B and cathepsin B inhibitors using DBDY-Gly-Phe-MTPA and AuNPs allowed not only the selective but also the simple assay of cathepsin B and its inhibitors, which was possible with the naked eye

Insight into Electrochemical CO₂ Reduction on Surface-Molecule-Mediated Ag Nanoparticles

The electrochemical CO₂ reduction reaction to form valued hydrocarbon molecules is an attractive process, because it can be coupled with renewable energy resources for carbon recycling. For an efficient CO₂ conversion, designing a catalyst with high activity and selectivity is crucial, because the CO₂ reduction reaction in aqueous media competes with the hydrogen evolution reaction (HER) intensely. We have developed a strategy to tune CO₂ reduction activity by modulating the binding energies of the intermediates on the electrocatalyst surfaces with the assistance of molecules that contain the functional group. We discovered that the amine functional group on Ag nanoparticle is highly effective in improving selective CO production (Faradaic efficiency to 94.2%) by selectively suppressing HER, while the thiol group rather increases HER activity. A density functional theory (DFT) calculation supports the theory that attaching amine molecules to Ag nanoparticles destabilizes the hydrogen binding, which effectively suppresses HER selectively, while an opposite tendency is found with thiol molecules. In addition, changes in the product selectivity, depending on the functional group, are also observed when the organic molecules are added after nanoparticle synthesis or nanoparticles are immobilized with an amine (or thiol)-containing anchoring agent. CO Faradaic efficiencies were consistently improved when the Ag nanoparticle was modified with amine groups, compared with that of its thiol counterpart

Achieving Selective and Efficient Electrocatalytic Activity for CO₂ Reduction Using Immobilized Silver Nanoparticles

Selective electrochemical reduction of CO₂ is one of the most sought-after processes because of the potential to convert a harmful greenhouse gas to a useful chemical. We have discovered that immobilized Ag nanoparticles supported on carbon exhibit enhanced Faradaic efficiency and a lower overpotential for selective reduction of CO₂ to CO. These electrocatalysts were synthesized directly on the carbon support by a facile one-pot method using a cysteamine anchoring agent resulting in controlled monodispersed particle sizes. These synthesized Ag/C electrodes showed improved activities, specifically decrease of the overpotential by 300 mV at 1 mA/cm², and 4-fold enhanced CO Faradaic efficiency at −0.75 V vs RHE with the optimal particle size of 5 nm compared to polycrystalline Ag foil. DFT calculations enlightened that the specific interaction between Ag nanoparticle and the anchoring agents modified the catalyst surface to have a selectively higher affinity to the intermediate COOH over CO, which effectively lowers the overpotential

Designing Atomically Dispersed Au on Tensile-Strained Pd for Efficient CO2 Electroreduction to Formate

Pd is one of the most effective catalysts for the electrochemical reduction of CO2 to formate, a valuable liquid product, at low overpotential. However, the intrinsically high CO affinity of Pd makes the surface vulnerable to CO poisoning, resulting in rapid catalyst deactivation during CO2 electroreduction. Herein, we utilize the interaction between metals and metal-organic frameworks to synthesize atomically dispersed Au on tensile-strained Pd nanoparticles showing significantly improved formate production activity, selectivity, and stability with high CO tolerance. We found that the tensile strain stabilizes all reaction intermediates on the Pd surface, whereas the atomically dispersed Au selectively destabilizes CO* without affecting other adsorbates. As a result, the conventional COOH* versus CO* scaling relation is broken, and our catalyst exhibits 26- and 31-fold enhancement in partial current density and mass activity toward electrocatalytic formate production with over 99% faradaic efficiency, compared to Pd/C at -0.25 V versus RHE.