Three-phase composites of NiFe2O4/Ni@C nanoparticles derived from metal-organic frameworks as electrocatalysts for the oxygen evolution reaction

An oxycarbide-derived-carbon supported nickel ferrite/copper tungstate ternary composite for enhanced electrocatalytic activity towards the oxygen evolution reaction

This work integrates a unique porous carbon with a binary heterostructured NiFe2O4/CuWO4 composite to enhance electrocatalytic activity towards the oxygen evolution reaction. The NiFe2O4/CuWO4 binary heterostructure was prepared through the conventional co-precipitation method. The porous carbon with turbostratic order was obtained by the selective etching of SiO2 nanodomains from preceramic polymer-derived SiOC. Finally, an optimum ternary NiFe2O4/CuWO4/C composite was prepared through hydrothermal treatment. Microstructural findings reveal that NiFe2O4/CuWO4 nanocomposite particulates are distributed homogeneously within the porous carbon matrix. Electrochemical findings reveal that the optimum composite with uniform carbon distribution requires an overpotential of 360 mV to attain a current density of 10 mA cm-2 with the lowest Tafel slope of 43 mV dec-1 as opposed to 450 mV and 55 mV dec-1, respectively, for the composites without carbon. The ternary composite demonstrated a stable potential over a prolonged period of 24 hours with enhanced mass activity. The improved electrocatalytic efficiency of the material is attributed to the presence of graphitic carbon and ample porosity within the additive carbon phase, which enhances the catalyst-electrolyte interaction interface area and electronic conductivity.

Not Only Graphene Two-Dimensional Nanomaterials: Recent Trends in Electrochemical (Bio)sensing Area for Biomedical and Healthcare Applications

Two-dimensional (2D) nanomaterials (e.g., graphene) have attracted growing attention in the (bio)sensing area and, in particular, for biomedical applications because of their unique mechanical and physicochemical properties, such as their high thermal and electrical conductivity, biocompatibility, and large surface area. Graphene (G) and its derivatives represent the most common 2D nanomaterials applied to electrochemical (bio)sensors for healthcare applications. This review will pay particular attention to other 2D nanomaterials, such as transition metal dichalcogenides (TMDs), metal-organic frameworks (MOFs), covalent organic frameworks (COFs), and MXenes, applied to the electrochemical biomedical (bio)sensing area, considering the literature of the last five years (2018-2022). An overview of 2D nanostructures focusing on the synthetic approach, the integration with electrodic materials, including other nanomaterials, and with different biorecognition elements such as antibodies, nucleic acids, enzymes, and aptamers, will be provided. Next, significant examples of applications in the clinical field will be reported and discussed together with the role of nanomaterials, the type of (bio)sensor, and the adopted electrochemical technique. Finally, challenges related to future developments of these nanomaterials to design portable sensing systems will be shortly discussed.

Sodium Tartrate-Assisted Synthesis of High-Purity NiFe2O4 Nano-Microrods Supported by Porous Ketjenblack Carbon for Efficient Alkaline Oxygen Evolution

Herein, a simple two-step synthetic method was developed for the synthesis of NiFe₂O₄ nano-microrods supported on Ketjenblack carbon (NiFe₂O₄/KB). A sodium tartrate-assisted hydrothermal method was employed for the synthesis of a NiFe-MOF/KB precursor, which was then pyrolyzed under N₂ at 500 °C to yield NiFe₂O₄/KB. Benefiting from the presence of high-valence Ni³⁺ and Fe³⁺, high conductivity, and a large electrochemically active surface area, NiFe₂O₄/KB delivered outstanding OER electrocatalytic performance under alkaline conditions, including a very low overpotential of 258 mV (vs RHE) at 10 mA cm^-2, a small Tafel slope of 43.01 mV dec^-1, and excellent durability in 1.0 M KOH. Density functional theory calculations verified the superior alkaline OER electrocatalytic activity of NiFe₂O₄ to IrO₂. While both catalysts possessed a similar metallic ground state, NiFe₂O₄ offered a lower energy barrier in the rate-determining OER step (*OOH → O₂) compared to IrO₂, resulting in faster OER kinetics.