More Like this

1. Understanding and Controlling the Performance-Limiting Steps of Catalyst-Modified Semiconductors

   https://doi.org/10.1021/acs.jpclett.0c02386  

   Nguyen, Nghi P.; Wadsworth, Brian L.; Nishiori, Daiki; Reyes Cruz, Edgar A.; Moore, Gary F. (January 2020, The Journal of Physical Chemistry Letters)

   null (Ed.)

   Understanding and controlling factors that restrict the rates of fuel-forming reactions are essential to designing effective catalyst-modified semiconductors for applications in solar-to-fuel technologies. Herein, we describe GaAs semiconductors featuring a polymeric coating that contains cobaloxime-type catalysts for photoelectrochemically powering hydrogen production. The activities of these electrodes (limiting current densities >20 mA cm–2 under 1-sun illumination) enable identification of fundamental performance-limiting bottlenecks encountered at relatively high rates of fuel formation. Experiments conducted under varying bias potential, pH, illumination intensity, and scan rate reveal two distinct mechanisms of photoelectrochemical hydrogen production. At relatively low polarization and pH, the limiting photoactivity is independent of illumination conditions and is attributed to a mechanism involving reduction of substrate protons. At relatively high polarization or pH, the limiting photoactivity shows a linear response to increasing photon flux and is attributed to a mechanism involving reduction of substrate water. This work illustrates the complex interplay between transport of photons, electrons, and chemical substrates in photoelectrosynthetic reactions and highlights diagnostic tools for better understanding these processes. 

   more » « less
2. Exploring Enhanced Oxygen Reduction Reactions: A Study on Nanocellulose, Dopamine, and Cobalt Complex-Derived Non-Precious Electrocatalyst

   https://doi.org/10.3390/catal14090613  

   Patwary, Md Mohsin; Haque, Shanzida; Szwedo, Peter; Hasan, Ghada; Kondrapolu, Raja Shekhar; Watanabe, Fumiya; KC, Krishna; Wang, Daoyuan; Ghosh, Anindya (September 2024, Catalysts)

   Cobalt-based catalysts are recognized as promising electrocatalysts for oxygen reduction reactions (ORRs) in fuel cells that operate within acidic electrolytes. A synthesis process involving a cobalt complex, nanocellulose, and dopamine, followed by pyrolysis at 500 °C under a nitrogen atmosphere, was used to create a cobalt and nitrogen-doped carbonaceous material. Additionally, urea was incorporated to enhance nitrogen doping in the carbonaceous material. The morphology and structure of the material were examined using Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD), where SEM unveiled dispersed metal oxides within the carbonaceous framework. Energy Dispersive X-ray Spectroscopy (EDS) analysis showed an even distribution of elements across the cobalt-doped carbonaceous material. X-ray Photoelectron Spectroscopy (XPS) analysis further highlighted significant alterations in the elemental composition due to pyrolysis. The electrochemical behavior of the cobalt-doped carbonaceous material, with respect to the oxygen reduction reaction (ORR) in an acidic medium, was investigated via cyclic voltammetry (CV), revealing an ORR peak at 0.30 V against a reversible hydrogen reference electrode, accompanied by a notably high current density. The catalyst’s performance was evaluated across different pH levels and with various layers deposited, showing enhanced effectiveness in acidic conditions and a more pronounced reduction peak with uniformly applied electrode layers. Rotating disk electrode (RDE) studies corroborated the mechanism of a four-electron reduction of oxygen to water, emphasizing the catalyst’s efficiency. 

   more » « less
3. Nickel nanoparticles supported on multi-walled carbon nanotubes; versatile catalyst for Suzuki cross-coupling reactions in batch and continuous flow

   Coker, Katherine A; Winkleman, Harlee; Siamaki, Ali R (October 2023, American Chemical Society (ACS))

   NA (Ed.)

   Metal catalyzed carbon-carbon bond forming reactions have rapidly become one of the most effective tools in organic synthesis for the assembly of highly functionalized molecules. These reactions have typically been carried out under homogeneous reaction conditions, which require the use of ligands to solubilize the catalyst and broaden its window of reactivity. However, the use of these catalysts under homogeneous conditions has limited their commercial viability due to product contamination as a direct result of inability to effectively separate the catalyst from the reaction product. Ligand-free heterogeneous catalysis presents a promising option to address this problem as evidenced by the significant increase in research activity in this area. We have recently developed a simple, one-step method for the preparation nickel nanoparticles supported on multi-walled carbon nanotubes (Ni/MWCNTs) under mechanical shaking in a ball-mill. The preparation method is very fast and straightforward which does not require any chemicals, solvents, or additional ligands. The as-prepared nanoparticles demonstrated remarkable catalytic activities in Suzuki cross-coupling reactions of the functionalized aryl halides and phenylboronic acids in batch with high turnover number in a single catalytic reaction. Batch operations have several inherent limitations that include reproducibility, scalability, and reactor productivity. Continuous flow chemistry has been considered as an alternative approach in academic and industrial processes due to its efficient and innovative synthetic design. Due to the low level of leaching observed in batch reactions as well as remarkable recyclability, the Ni/MWCNTs nanoparticles demonstrated remarkable catalytic activity in Suzuki coupling reactions with a diverse range of functionalized aryl halides and phenyl boronic acids under continuous flow conditions. Further optimization of the method including the reaction time, temperature, required solvents, flow rate, and minimum residence time will be discussed in this presentation. 

   more » « less
4. A model for the electric field-driven flow and deformation of a drop or vesicle in strong electrolyte solutions

   https://doi.org/10.1017/jfm.2022.469  

   Ma, Manman; Booty, Michael R.; Siegel, Michael (July 2022, Journal of Fluid Mechanics)

   A model is constructed to describe the flow field and arbitrary deformation of a drop or vesicle that contains and is embedded in an electrolyte solution, where the flow and deformation are caused by an applied electric field. The applied field produces an electrokinetic flow, which is set up on the charge-up time scale $$\tau _{*c}=\lambda _{*} a_{*}/D_{*}$$ , where $$\lambda _{*}$$ is the Debye screening length, $$a_{*}$$ is the inclusion length scale and $$D_{*}$$ is an ion diffusion constant. The model is based on the Poisson–Nernst–Planck and Stokes equations. These are reduced or simplified by forming the limit of strong electrolytes, for which dissolved salts are completely ionised in solution, together with the limit of thin Debye layers. Debye layers of opposite polarity form on either side of the drop interface or vesicle membrane, together forming an electrical double layer. Two formulations of the model are given. One utilises an integral equation for the velocity field on the interface or membrane surface together with a pair of integral equations for the electrostatic potential on the outer faces of the double layer. The other utilises a form of the stress-balance boundary condition that incorporates the double layer structure into relations between the dependent variables on the layers’ outer faces. This constitutes an interfacial boundary condition that drives an otherwise unforced Stokes flow outside the double layer. For both formulations relations derived from the transport of ions in each Debye layer give additional boundary conditions for the potential and ion concentrations outside the double layer. 

   more » « less
5. Bimetallic nickel-palladium nanoparticles supported on multi-walled carbon nanotubes for Suzuki and Sonogashira cross-coupling reactions in continuous flow

   Coker, Katherine A; Winkleman, Harlee B; Siamaki, Ali R (March 2024, ACS; American Chemical Society (CAS))

   NA (Ed.)

   The advancement of metal-catalyzed carbon-carbon bond forming reactions represents one of the most significant contributions to contemporary organic synthesis. Innovations in the area of palladium catalyzed homogeneous cross-coupling catalysis have dominated this area of chem. and are playing an increasingly important role in the area of pharmaceutical drug discovery and development. However, the use of these catalysts under homogeneous conditions has limited their com. viability due to product contamination as a direct result of inability to effectively sep. the catalyst from the reaction product. Ligand-free heterogeneous catalysis presents a promising option to address this problem as evidenced by the significant increase in research activity in this area. We have recently developed a simple, one-step method for the preparation of bimetallic nickel-palladium nanoparticles supported on multi-walled carbon nanotubes (Ni-Pd/MWCNTs) under mech. shaking in a ball- mill. The preparation method is very fast and straightforward which does not require any chems., solvents, or addnl. ligands. Notably, the concentration of palladium can be lowered to a min. amount of 1% and replaced by more abundant and less expensive nickel nanoparticles while effectively catalyzing the reaction. The as-prepared nanoparticles demonstrated remarkable catalytic activities in cross-coupling catalysis such as Suzuki and Sonoga shira reactions with functionalized substrates in batch with high turnover number in a single catalytic reaction. Batch operations have several inherent limitations that include reproducibility, scalability, and reactor productivity. Continuous flow chem. has been considered as an alternative approach in academic and industrial processes due to its efficient and innovative synthetic design. The low palladium loading and excellent recyclability of the catalyst make this an affordable and clean option for cross-coupling catalysis under continuous flow conditions, a feature that enables the large-scale industrial and pharmaceutical applications of this method in the future. 

   more » « less