Dendrimer-Ni-Based Material: Toward an Efficient Ni-Fe Layered Double Hydroxide for Oxygen-Evolution Reaction

Iron Integration in Nickel Hydroxide Matrix vs Surface for Oxygen-Evolution Reaction: Where the Nernst Equation Does Not Work

This study focuses on the oxygen-evolution reaction (OER) activity comparison between two forms of NiFe (hydr)oxides: compound 1, where Fe ions are applied on the surface of nickel (hydr)oxide, and compound 2, with Fe ions incorporated into the structural matrix of nickel (hydr)oxide. The observed exponential link between Coulombic energy and the total charge of the system points to a direct proportionality between the potential and the concentration of oxidized nickel ions (e.g., V ∝ [oxidized Ni]), diverging from the logarithmic relationship outlined in the Nernst equation or its modifications, which is not evident in this case. Initial visible spectroscopy indicates a notable trend toward oxidation. As, during the oxidation, more Ni is oxidized, a repulsion effect develops, diminishing the likelihood of further oxidation, and a distinct linear correlation emerges between the quantity of oxidized Ni(II) and the applied potentials.

Ce-Modified Flowerlike NiFe-MOF Nanostructure Based on Ion Competitive Coordination for Enhancing the Oxygen Evolution Reaction

Metal-organic framework (MOF) has become a popular electrocatalyst for the oxygen evolution reaction (OER) because of its large specific surface area and adjustable porosity. Nevertheless, the electrochemical performance of MOFs has been greatly limited by poor intrinsic conductivity and catalytic activity. Herein, we report a Ce-doped nanoflower-like MOF material Ce@NiFe-MOF-5 via a facile ion competitive coordination effect and doping method. Benefiting from the nanoflower structure formed by the stacking of nanosheets, a large number of active sites can be exposed, which favors electron/mass transfer during water oxidation. The coordination substitution of Ce ions not only promoted an increase in the number of active sites on the surface of the nanosheets but also optimized the electronic structure of pristine NiFe-MOF. The well-designed Ce@NiFe-MOF-5 catalysts exhibited superior OER performance under basic conditions, which only required an overpotential of 258 mV at a current density of 10 mA cm^-2 and a Tafel slope of 54.44 mV dec^-1. Moreover, when Ce@NiFe-MOF-5 served as an anode and Pt/C as a cathode, the two-electrode system only needed 1.56 V to drive overall water splitting at 10 mA cm^-2.

Rapid “self-healing” behavior induced by chloride anions to renew Fe-Ni(oxy)hydroxide surface for long-term alkaline seawater electrolysis

Due to the surface adsorption and interlayer insertion behavior of chloride anions, Fe-Ni(oxy)hydroxide catalytic surface is easily destroyed, making it difficult to be used for long-term seawater electrolysis. Here, we...

Sodium Cobalticarborane: A Promising Precatalyst for Oxygen Evolution Reaction

Water splitting is a helpful way of converting renewable electricity into fuel. The oxygen evolution reaction (OER) is a slow reaction that provides low-cost electrons for water reduction reactions. Thus, finding an efficient, low-cost, stable, and environmentally friendly OER catalyst is critical for water splitting. Here, sodium cobalticarborane (1) is introduced as a promising precatalyst for forming an OER cobalt-based catalyst. The cobalt-based catalyst was characterized by several methods and is suggested to be Co(III) (hydr)oxide. Using fluorine-doped tin oxide, glassy carbon, platinum, and gold electrodes, the OER activity of the cobalt-based precatalyst was investigated. The overpotential for the onset of OER in the presence of 1 is 315 mV using fluorine-doped tin oxide electrodes. The onsets of OERs in the presence of 1 using gold, platinum, and glassy carbon electrodes in KOH solutions (1.0 M) turned out to be 275, 284, and 330 mV, respectively. The nanoparticles on the gold electrodes exhibit significant OER activity with a Tafel slope of 63.8 mV/decade and an overpotential at 541 mV for 50 mA/cm². In the case of the glassy carbon electrodes, a Tafel slope of 109.9 mV/decade and an overpotential of 548 mV for 10 mA/cm² is recorded for the catalyst. This paper outlines an interesting approach to synthesize cobalt oxide for OER through a slow decomposition of a precatalyst.

Magnetically Recoverable Nanoparticulate Catalysts for Cross-Coupling Reactions: The Dendritic Support Influences the Catalytic Performance

Carbon-carbon cross-coupling reactions are among the most important synthetic tools for the preparation of pharmaceuticals and bioactive compounds. However, these reactions are normally carried out using copper, phosphines, and/or amines, which are poisonous for pharmaceuticals. The use of nanocomposite catalysts holds promise for facilitating these reactions and making them more environmentally friendly. In the present work, the PEGylated (PEG stands for poly(ethylene glycol) pyridylphenylene dendrons immobilized on silica loaded with magnetic nanoparticles have been successfully employed for the stabilization of Pd2+ complexes and Pd nanoparticles. The catalyst developed showed excellent catalytic activity in copper-free Sonogashira and Heck cross-coupling reactions. The reactions proceeded smoothly in green solvents at low palladium loading, resulting in high yields of cross-coupling products (from 80% to 97%) within short reaction times. The presence of magnetic nanoparticles allows easy magnetic separation for repeated use without a noticeable decrease of catalytic activity due to the strong stabilization of Pd species by rigid and bulky dendritic ligands. The PEG dendron periphery makes the catalyst hydrophilic and better suited for green solvents. The minor drop in activity upon the catalyst reuse is explained by the formation of Pd nanoparticles from the Pd2+ species during the catalytic reaction. The magnetic separation and reuse of the nanocomposite catalyst reduces the cost of target products as well as energy and material consumption and diminishes residual contamination by the catalyst. These factors as well as the absence of copper in the catalyst makeup pave the way for future applications of such catalysts in cross-coupling reactions.