Modulating the Hydrothermal Synthesis of Co3O4 and CoOOH Nanoparticles by H2O2 Concentration

Real Active Site Identification of Co/Co3O4 Anchoring Ni-MOF Nanosheets with Fast OER Kinetics for Overall Water Splitting

Doping metals and constructing heterostructures are pivotal strategies to enhance the electrocatalytic activity of metal-organic frameworks (MOFs). Nevertheless, effectively designing MOF-based catalysts that incorporate both doping and multiphase interfaces poses a significant challenge. In this study, a one-step Co-doped and Co3O4-modified Ni-MOF catalyst (named Ni NDC-Co/CP) with a thickness of approximately 5.0 nm was synthesized by a solvothermal-assisted etching growth strategy. Studies indicate that the formation of the Co-O-Ni-O-Co bond in Ni NDC-Co/CP was found to facilitate charge density redistribution more effectively than the Co-O-Ni bimetallic synergistic effect in NiCo NDC/CP. The designating Ni NDC-Co/CP achieved superior oxygen evolution reaction (OER) activity (245 mV @ 10 mA cm-2) and robust long stability (100 h @ 100 mA cm-2) in 1.0 M KOH. Furthermore, the Ni NDC-Co/CP(+)||Pt/C/CP(-) displays pregnant overall water splitting performance, achieving a current density of 10 mA cm-2 at an ultralow voltage of 1.52 V, which is significantly lower than that of commercial electrolyzer using Pt/C and IrO2 electrode materials. In situ Raman spectroscopy elucidated the transformation of Ni NDC-Co to Ni(Co)OOH under an electric field. This study introduces a novel approach for the rational design of MOF-based OER electrocatalysts.

A simple microplasma reactor paired with indirect ultrasonication for aqueous phase synthesis of cobalt oxide nanoparticles

Cobalt oxide nanoparticles are widely used owing to their distinct properties such as their larger surface area, enhanced reactivity, and their superior optical, electronic, and magnetic properties when compared to their bulk counterpart. The nanoparticles are preferably synthesized using a bottom-up approach in liquid as it allows the particle size to be more precisely controlled. In this study, we employed microplasma to synthesize Co₃O₄ nanoparticles because it eliminates harmful reducing agents and is efficient and cost-effective. Microplasma reactors are equipped with copper wire electrodes to generate plasma and are simple to configure. The product was characterized using UV-Vis spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). The experimental parameters that were varied for the synthesis were: with or without stirring, with or without indirect ultrasonication, and with or without capping agents (urea and sucrose). The results showed that the microplasma enabled Co₃O₄ nanoparticles to be successfully synthesized, with particle sizes of 10.9-17.7 nm, depending on the synthesis conditions.

CoMo layered double hydroxide equipped with carbon nanotubes for electrocatalytic oxygen evolution reaction

To carry out effective resource reforming of sustainable electricity, hydrogen production by electrochemical water splitting provides an eco-friendly and economical way. Nevertheless, the oxygen evolution reaction (OER) at the anode is limited by the slow reaction process, which hinders the large-scale development and application of electrolysis technology. In this work, we present an electrocatalyst with superior OER performance, which attributed to the abundant active sites and good electronic conductivity. The two-dimensional CoMo Layered Double Hydroxide nanosheets are synthesized and deposited on conductive carbon nanotubes (CoMo LDH/CNTs), and then hybrid composites show better catalytic performance than their undecorated counterpart under identical conditions. Specifically, CoMo LDH/CNTs exhibit the low overpotential of 268 mV to obtain 10 mA cm^-2and satisfactory stability (more than 40 h). We emphasize that this hybridization strategy with a conductive supporting framework could design more abundant and low-cost OER electrocatalysts to minimize electrical energy consumption, thereby achieving efficient conversion between energy sources.

Hydrothermal Synthesis and Formation Mechanism of Self-Assembled Strings of CoOOH Nanodiscs

The formation and self-assembly mechanisms of nanomaterials are of great significance for the preparation and application of materials. In this study, the orientationally aggregated CoOOH nanosheets and the self-assembled strings of CoOOH nanodiscs were prepared by hydrothermal method. The formation and self-assembly mechanisms of CoOOH nanodiscs were investigated by XRD, XPS, DLS, TEM, and SEM techniques, as well as DFT calculations. The results show that the formation process of the stacked CoOOH nanodiscs was driven by surface energy and can be divided into four steps: nucleation and growth of CoOOH primary nanosheets; oriented attachment of CoOOH nanosheets; self-assembly of CoOOH nanodiscs; and aggregation of strings of CoOOH nanodiscs. This study contributes meaningfully to the controllable preparation of CoOOH nanomaterials.

Porous N-doped carbon with confined Fe-doped CoP grown on CNTs for superefficient oxygen evolution electrocatalysis

Herein, Fe-doped CoP nanoparticles (Fe-CoP NPs) encapsulated in porous N-doped carbon (PNC)/carbon nanotubes (CNTs) have been successfully synthesized. The Fe doping and confined structures resulted in enhanced charge transfer and improved active sites for intermediates adsorption. The obtained Fe-CoP@PNC/CNTs materials exhibited superefficient OER performance.

Cobalt phosphide nanorings towards efficient electrocatalytic nitrate reduction to ammonia

High-quality CoP nanorings (CoP NRs) are easily achieved using a phosphorating treatment of CoOOH nanorings, and reveal high activity towards the hydrogen evolution reaction and the nitrate electrocatalytic reduction reaction due to substantial coordinately unsaturated active sites, a high surface area, and available mass transfer pathways. Consequently, the CoP NRs can achieve a faradaic efficiency of 97.1% towards NO₃^--to-NH₃ conversion and provide an NH₃ yield of 30.1 mg h^-1 mg^-1_cat at a -0.5 V potential.

Tuning Co2+ Coordination in Cobalt Layered Double Hydroxide Nanosheets via Fe3+ Doping for Efficient Oxygen Evolution

Inexpensive and efficient electrocatalysts are crucial for the development and practical application of energy conversion and storage technologies. Layered-double-hydroxide (LDH) materials have attracted much attention due to the special layered structure, but their electrocatalytic activity and stability are still limited. Herein, we propose to tune Co²⁺ occupancy and coordination in cobalt-based LDH nanosheets via Fe³⁺ doping for efficient and stable electrocatalysis for oxygen evolution reaction (OER). It is found that Fe doping regulates the occupancy and coordination of Co²⁺ in CoO₄ tetrahedrons and CoO₆ octahedrons of Co-LDHs. Through density functional theory calculation, we also clarified that Fe³⁺ not only modulated the Co²⁺ coordination but also functioned as an added catalytic active site. LDH nanosheets with a Co/Fe ratio of 5:1 show a low OER overpotential, much better than the commercial IrO₂, owing to the modulation of Fe³⁺ doping on the crystal and electronic structures. After appropriate incorporation of Fe³⁺, the almost inactive octahedral coordinated Co²⁺ is significantly activated with a partial deletion of tetrahedral coordinated Co²⁺, which greatly boosts the overall electrocatalytic activity. This study offers some new insights into tuning the crystal and electronic structures of LDHs by lattice doping to achieve high-efficiency electrocatalysis for OER.

One-Pot Efficient Catalytic Oxidation for Bio-Vanillin Preparation and Carbon Isotope Analysis

Vanillin (4-hydroxy-3-methoxybenzaldehyde) is one of the most widely used food spices. Aimed at bio-vanillin green production, the natural materials were directly catalytically oxidized efficiently in one pot under low O₂ pressure (0.035 MPa) in the presence of a non-noble metal oxidation combined catalyst (NiCo₂O₄/SiO₂ nanoparticles), which showed remarkable advantages of a short synthetic route and less industrial waste. The catalytic system showed good universality to many natural substrates with nearly 100% conversion and 86.3% bio-vanillin yield. More importantly, carbon isotope ratio investigations were employed to verify the origin of the organic matter. One hundred percent ¹⁴C content of the obtained vanillin was detected, which indicated that it was an efficient method to distinguish the vanillin from biomass or fossil materials. Furthermore, the ¹³C isotope examination showed effective distinguishing ability for the vanillin from a particular biomass source. The C isotope detection provides an effective method for commercial vanillin identification.