Regulating Hollow Carbon Cage Supported NiCo Alloy Nanoparticles for Efficient Electrocatalytic Hydrogen Evolution Reaction

Design and fabrication of intermetallic NiCo electrocatalysts for the alkaline HER

The design and fabrication of highly efficient electrocatalysts are crucial for reducing energy consumption, improving hydrogen production rates, and prolonging the service life of alkaline electrolyzers. In this study, intermetallic L10-NiCo electrocatalysts were designed using DFT calculations and fabricated through a one-step solid-state reaction method. The DFT calculations indicated that L10-NiCo presented a lower H adsorption Gibbs free energy and a moderate H2O dissociation barrier compared to the commonly used Ni catalyst and disordered NiCo alloy. Increasing the solid-state reaction temperature facilitated the formation of intermetallic L10-NiCo. Electrocatalytic tests for the alkaline HER demonstrated that the ECSA of L10-NiCo nanoparticles increased to 2.3 times, the overpotential decreased by 19%, the electrocatalytic activity increased to 1.5 times, and the stability improved to 2.2 times compared to those of the Ni nanoparticles. This research provides insights into the design and fabrication of highly efficient catalytic electrodes for alkaline electrolyzers.

Cu Regulating the Bifunctional Activity of Co-O Sites for the High-Performance Rechargeable Zinc-Air Battery

The rational design of cost-effective and highly active electrocatalysts becomes the crucial energy storage technology to boost the kinetics of the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER), which hinders the large-scale application of metal-air batteries under the situation of increasingly pressing energy anxiety. Herein, the Co-based ZIF introduced the moderate amount of Cu2+-derived Cu/Co metal nanoparticles (NPs) embedded in carbon frameworks after high-temperature calcination. The Co-O bond on the surface of Co nanoparticles is modulated by adjacent Cu nanoparticles with the surface Cu-O bonds. The resulted increase of the Co2+/Co3+ ratio in 0.1CuCo-NC enhances the ORR/OER bifunctional catalytic kinetics along with the ΔE of 0.639 V. In situ Raman spectra of the catalyst on the three-electrode system as well as in the driven zinc-air battery (ZAB) show that the Co-O active sites regulated by Cu nanoparticles with Cu-O bonds maintain a periodic lattice expansion and compression during discharging and charging. The zinc-air battery based on 0.1CuCo-NC has a peak power density of up to 198.3 mW cm-2, a mass-specific capacity of 798.2 mAh g-1, and a cycling stability of 923 h at room temperature. This work makes up the research gap of a Co-based metal-organic framework (MOF)-derived catalyst regulated by a transition metal.

Integrating Sulfur Doping with a Multi-Heterointerface Fe7S8/NiS@C Composite for Wideband Microwave Absorption

Heterointerface engineering is presently considered a valuable strategy for enhancing the microwave absorption (MA) properties of materials via compositional modification and structural design. In this study, a sulfur-doped multi-interfacial composite (Fe7S8/NiS@C) coated with NiFe-layered double hydroxides (LDHs) is successfully prepared using a hydrothermal method and post-high-temperature vulcanization. When assembled into twisted surfaces, the NiFe-LDH nanosheets exhibit porous morphologies, improving impedance matching, and microwave scattering. Sulfur doping in composites generates heterointerfaces, numerous sulfur vacancies, and lattice defects, which facilitate the polarization process to enhance MA. Owing to the controllable heterointerface design, the unique porous structure induced multiple heterointerfaces, numerous vacancies, and defects, endowing the Fe7S8/NiS@C composite with an enhanced MA capability. In particular, the minimum reflection loss (RLmin) value reached -58.1 dB at 15.8 GHz at a thickness of 2.1 mm, and a broad effective absorption bandwidth (EAB) value of 7.3 GHz is achieved at 2.5 mm. Therefore, the Fe7S8/NiS@C composite exhibits remarkable potential as a high-efficiency MA material owing to the synergistic effects of the polarization processes, multiple scatterings, porous structures, and impedance matching.

Electronic Structure Regulated Nickel-Cobalt Bimetal Phosphide Nanoneedles for Efficient Overall Water Splitting

Transition metal phosphides (TMPs) have been widely studied for water decomposition for their monocatalytic property for anodic or cathodic reactions. However, their bifunctional catalytic activity still remains a major challenge. Herein, hexagonal nickel-cobalt bimetallic phosphide nanoneedles with 1-3 μm length and 15-30 nm diameter supported on NF (NixCo2-xP NDs/NF) with adjusted electron structure have been successfully prepared. The overall alkaline water electrolyzer composed of the optimal anode (Ni0.67Co1.33P NDs/NF) and cathode (Ni1.01Co0.99P NDs/NF) provide 100 mA cm-2 at 1.62 V. Gibbs Free Energy for reaction paths proves that the active site in the hydrogen evolution reaction (HER) is Ni and the oxygen evolution reaction (OER) is Co in NixCo2-xP, respectively. In the HER process, Co-doping can result in an apparent accumulation of charge around Ni active sites in favor of promoting HER activity of Ni sites, and ΔGH* of 0.19 eV is achieved. In the OER process, the abundant electron transfer around Co-active sites results in the excellent ability to adsorb and desorb *O and *OOH intermediates and an effectively reduced ∆GRDS of 0.37 eV. This research explains the regulation of electronic structure change on the active sites of bimetallic materials and provides an effective way to design a stable and effective electrocatalytic decomposition of alkaline water.

First Reusable Catalyst for the Reductive Coupling Reaction of Organohalides with Aldehydes

In this study, we simulate the reductive coupling (Barbier-Grignard-type) reaction of organohalides with aldehydes using a new reusable catalyst. In this regard, bimetallic alloys of NiCo encapsulated in melamine-based dendrimers (MBD) immobilized on magnetic nanoparticles symbolized as γ-Fe2O3-MBD/NiCo were designed and synthesized. The structure and properties of the catalyst were studied by a variety of techniques such as Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), vibrating sample magnetometry (VSM), energy-dispersive spectrometry (EDS) mapping, and inductively coupled plasma (ICP). The presence of NiCo nanoalloys was confirmed by XRD and XPS analysis, TEM images, and EDS mapping. Various secondary alcohols were produced in good to high yields by reductive coupling of different types of aldehydes and organohalides in the presence of HCO2K as a nonmetallic reducing agent in aqueous media catalyzed by γ-Fe2O3-MBD/NiCo. In these reactions, the high catalytic performance of γ-Fe2O3-MBD/NiCo was achieved in comparison to monometallic counterparts due to the synergistic cooperative effect of Co and Ni in the NiCo nanoalloys. Magnetic and hydrophilic properties of the catalyst facilitate the catalyst recyclability for seven runs. The reusability of γ-Fe2O3-MBD/NiCo, use of water as an environmentally friendly solvent, ease of processing, and absence of metal additives make this process an excellent choice for the reductive coupling reaction to produce secondary alcohols from aldehydes. This is the first report on these kinds of reactions using a reusable catalyst.