Facile Synthesis of 3d Transition-Metal-Doped α-Co(OH)2 Nanomaterials in Water-Methanol Mediated with Ammonia for Oxygen Evolution Reaction

Support based metal incorporated layered nanomaterials for photocatalytic degradation of organic pollutants

An effective approach to producing sophisticated miniaturized and nanoscale materials involves arranging nanomaterials into layered hierarchical frameworks. Nanostructured layered materials are constructed to possess isolated propagation assets, massive surface areas, and envisioned amenities, making them suitable for a variety of established and novel applications. The utilization of various techniques to create nanostructures adorned with metal nanoparticles provides a secure alternative or reinforcement for the existing physicochemical methods. Supported metal nanoparticles are preferred due to their ease of recovery and usage. Researchers have extensively studied the catalytic properties of noble metal nanoparticles using various selective oxidation and hydrogenation procedures. Despite the numerous advantages of metal-based nanoparticles (NPs), their catalytic potential remains incompletely explored. This article examines metal-based nanomaterials that are supported by layers, and provides an analysis of their manufacturing, procedures, and synthesis. This study incorporates both 2D and 3D layered nanomaterials because of their distinctive layered architectures. This review focuses on the most common metal-supported nanocomposites and methodologies used for photocatalytic degradation of organic dyes employing layered nanomaterials. The comprehensive examination of biological and ecological cleaning and treatment techniques discussed in this article has paved the way for the exploration of cutting-edge technologies that can contribute to the establishment of a sustainable future.

Atomic-Level Observation of Potential-Dependent Variations at the Surface of an Oxide Catalyst during Oxygen Evolution Reaction

Understanding the intricate details of the surface atomic structure and composition of catalysts during the oxygen evolution reaction (OER) is crucial for developing catalysts with high stability in water electrolyzers. While many notable studies highlight surface amorphization and reconstruction, systematic analytical tracing of the catalyst surface as a function of overpotential remains elusive. Heteroepitaxial (001) films of chemically stable and lattice-oxygen-inactive LaCoO3 are thus utilized as a model catalyst to demonstrate a series of atomic-resolution observations of the film surface at different anodic potentials. The first key finding is that atoms at the surface are fairly dynamic even at lower overpotentials. Angstrom-scale atomic displacements within the perovskite framework are identified below a certain potential level. Another noteworthy feature is that amorphization (or paracrystallization) with no long-range order is finally induced at higher overpotentials. In particular, surface analyses consistently support that the oxidation of lattice oxygen is coupled with amorphous phase formation at the high potentials. Theoretical calculations also reveal an upward shift of oxygen 2p states toward the Fermi level, indicating enhanced lattice oxygen activation when atom displacement occurs more extensively. This study emphasizes that the degradation behavior of OER catalysts can distinctively vary depending on the overpotential level.

Investigating metal (M = Mn, Fe, and Ni)-doped Co(OH)2 nanofibers for electrocatalytic oxygen evolution and electrochemical biosensing performance

To achieve efficient and cost-effective electrochemical water splitting, highly active and affordable nanostructured catalysts are the key requirement. The current study presents the investigations of the efficacy of metal (Mn, Fe and Ni)-doped Co(OH)2 nanofibers towards oxygen evolution via water splitting. Notably, Ni-doped Co(OH)2 demonstrates superior OER performance in KOH electrolyte, surpassing standard IrO2 with a modest potential of 1.62 V at 10 mA cm-2. The remarkable activity is attributed to the nanofiber structure, facilitating faster conduction and offering readily available active sites. Ni-doped Co(OH)2 nanofibers displayed enduring stability even after 1000 cycles. This work underscores the importance of transition-metal based catalysts as effective electrocatalysts, providing the groundwork for the development of cutting-edge catalysts. Additionally, the electrochemical sensing capability towards ascorbic acid is evaluated, with Ni-doped Co(OH)2 showing the most promising response, characterized by the lowest LOD and LOQ values. These findings highlight the potential of Ni-doped Co(OH)2 nanofibers for upcoming diagnostic detection devices.

Enhancing the oxygen evolution reaction of cobalt hydroxide by fabricating nanocomposites with fluorine-doped graphene oxide

Fluorine and nitrogen codoped cobalt hydroxide-graphene oxide nanocomposites (N,F-Co(OH)₂/GO) were synthesized by a simple hydrothermal method and demonstrated highly enhanced oxygen evolution activity in an alkaline medium. N,F-Co(OH)₂/GO synthesized under optimized reaction conditions required an overpotential of 228 mV to produce the benchmark current density of 10 mA cm^-2 (scan rate 1 mV s^-1). In contrast, N,F-Co(OH)₂ without GO and Co(OH)₂/GO without fluorine required higher overpotentials (370 (N,F-Co(OH)₂) and 325 mV (Co(OH)₂/GO)) for producing the current density of 10 mA cm^-2. The low Tafel slope (52.6 mV dec^-1) and charge transfer resistance, and high electrochemical double layer capacitance of N,F-Co(OH)₂/GO compared to N,F-Co(OH)₂ indicate faster kinetics at the electrode-catalyst interface. The N,F-Co(OH)₂/GO catalyst showed good stability over 30 h. High-resolution transmission electron microscope (HR-TEM) images showed good dispersion of polycrystalline Co(OH)₂ nanoparticles in the GO matrix. X-ray photoelectron spectroscopic (XPS) analysis revealed the coexistence of Co²⁺/Co³⁺ and the doping of nitrogen and fluorine in N,F-Co(OH)₂/GO. XPS further revealed the presence of F in its ionic state and being covalently attached to GO. The integration of highly electronegative F with GO stabilizes the Co²⁺ active centre along with improving the charge transfer and adsorption process that contributes to improved OER. Thus, the present work reports a facile method for preparing F-doped GO-Co(OH)₂ electrocatalysts with enhanced OER activity under alkaline conditions.

Anchoring γ-MnO2 within β-NiCo(OH)2 as an Interfacial Electrode Material for Boosting Power Density in an Asymmetric Supercapacitor Device and for Oxygen Evolution Catalysis

The great challenge is to improve the high-competence electrochemical supercapacitor (ES) and oxygen evolution reaction (OER) electrocatalyst with earth-abundant transition metals rather than using limited noble metals. Herein, we developed a facile strategy to introduce two different phases such as α-MnO₂ or γ-MnO₂ on porous hexagonal bimetallic β-NiCo(OH)₂-layered double hydroxide (LDH) nanosheets for an enhanced bifunctionality and to ease out interfacial redox reaction kinetics. Due to the rational intend of LDH morphology and well-retained starlike γ-MnO₂ nanostructures, the bifunctional LDHs exhibit commendable activities toward ESs and in the OER study. Importantly, the γ-MnO₂ phase loaded at β-NiCo(OH)₂ LDHs shows superior ESs or electrocatalytic OER performance in comparison with the α-MnO₂ phase on LDHs. Besides, the assembled fabricated asymmetric supercapacitor (FASC) device possesses convincing energy (24.43 W h/kg) and power densities (5312 W/kg) and enabled us to glow a 1.4 V light-emitting diode for 45 s. Accordingly, three-/two-electrode systems or the solid-state FASC device has exhibited high efficiency in ESs. Also, the optimized γ-MnO₂ phase on β-NiCo(OH)₂ LDHs with the detailed mass ratio of Ni and Co has displayed the OER performance comparable to commercial RuO₂. The electrochemical studies and structural classifications offer in-depth analysis on the electrochemical behaviors, especially the stability in both ES and OER studies, signifying a promising aspirant in the alternative energy field.

NixCu1−x/CuO/Ni(OH)2 as highly active and stable electrocatalysts for oxygen evolution reaction

Ni–Cu alloy-based nanomaterials are representative cost-effective materials that have been widely used as highly active and stable electrocatalysts for electrochemical energy applications, such as the water oxidation reaction, the methanol/ethanol reaction and many other small molecule oxidation reactions.

Enhanced Electrochemical Properties and OER Performances by Cu Substitution in NiCo2O4 Spinel Structure

In order to improve the electrochemical performance of the NiCo2O4 material, Ni ions were partially substituted with Cu2+ ions having excellent reducing ability. All of the electrodes were fabricated by growing the Ni1-xCuxCo2O4 electrode spinel-structural active materials onto the graphite felt (GF). Five types of electrodes, NiCo2O4/GF, Ni0.875Cu0.125Co2O4/GF, Ni0.75Cu0.25Co2O4/GF, Ni0.625Cu0.375Co2O4/GF, and Ni0.5Cu0.5Co2O4/GF, were prepared for application to the oxygen evolution reaction (OER). As Cu2+ ions were substituted, the electrochemical performances of the NiCo2O4-based structures were improved, and eventually the OER activities were also greatly increased. In particular, the Ni0.75Cu0.25Co2O4/GF electrode exhibited the best OER activity in a 1.0 M KOH alkaline electrolyte: the cell voltage required to reach a current density of 10 mA cm-2 was only 1.74 V (η = 509 mV), and a low Tafel slope of 119 mV dec-1 was obtained. X-ray photoelectron spectroscopy (XPS) analysis of Ni1-xCuxCo2O4/GF before and after OER revealed that oxygen vacancies are formed around active metals by the insertion of Cu ions, which act as OH-adsorption sites, resulting in high OER activity. Additionally, the stability of the Ni0.75Cu0.25Co2O4/GF electrode was demonstrated through 1000th repeated OER acceleration stability tests with a high faradaic efficiency of 94.3%.