In Situ Design of a Nanostructured Interface between NiMo and CuO Derived from Metal-Organic Framework for Enhanced Hydrogen Evolution in Alkaline Solutions

Hydrogen shows great promise as a carbon-neutral energy carrier that can significantly mitigate global energy challenges, offering a sustainable solution. Exploring catalysts that are highly efficient, cost-effective, and stable for the hydrogen evolution reaction (HER) holds crucial importance. For this, metal-organic framework (MOF) materials have demonstrated extensive applicability as either a heterogeneous catalyst or catalyst precursor. Herein, a nanostructured interface between NiMo/CuO@C derived from Cu-MOF was designed and developed on nickel foam (NF) as a competent HER electrocatalyst in alkaline media. The catalyst exhibited a low overpotential of 85 mV at 10 mA cm-2 that rivals that of Pt/C (83 mV @ 10 mA cm-2). Moreover, the catalyst's durability was measured through chronopotentiometry at a constant current density of -30, -100, and -200 mA cm-2 for 50 h each in 1.0 M KOH. Such enhanced electrocatalytic performance could be ascribed to the presence of highly conductive C and Cu species, the facilitated electron transfer between the components because of the nanostructured interface, and abundant active sites as a result of multiple oxidation states. The existence of an ionized oxygen vacancy (Ov) signal was confirmed in all heat-treated samples through electron paramagnetic resonance (EPR) analysis. This revelation sheds light on the entrapment of electrons in various environments, primarily associated with the underlying defect structures, particularly vacancies. These trapped electrons play a crucial role in augmenting electron conductivity, thereby contributing to an elevated HER performance.

Stabilization of transition metal heterojunctions inside porous materials for high-performance catalysis

Transition metal-based heterostructural materials are a class of very promising substitutes for noble metal-based catalysts for high-performance catalysis, due to their inherent internal electric field at the interface in the heterojunctions, which could induce electron relocalization and facilitate charge carrier migration between different metal sites at heterostructural boundaries. However, redox-active metal species suffer from reduction, oxidation, migration, aggregation, leaching and poisoning in catalysis, which results in heavy deterioration of the catalytic properties of transition metal-based heterojunctions and frustrates their practical applications. To improve the stability of transition metal-based heterojunctions and sufficiently expose redox-active sites at the heterosurfaces, many kinds of porous materials have been used as porous hosts for the stabilization of non-precious metal heterojunctions. This review article will discuss recently developed strategies for encapsulation and stabilization of transition metal heterojunctions inside porous materials, and highlight their improved stability and catalytic performance through the spatial confinement effect and synergistic interaction between the heterojunctions and the host matrices.

Role of polymer template in crystal structure and photoactivity of Cu-TiO2 heterojunction nanostructures towards environmental remediation

Exploring porous heterojunction nanomaterials as a photocatalyst for water depollution strategies towards environmental restoration is exceedingly difficult in the perspective of sustainable chemistry. Herein, we first report a porous Cu-TiO₂ (TC40) heterojunction by using microphase separation of a novel penta-block copolymer (PLGA-PEO-PPO-PEO-PLGA) as a template through an evaporation induced self-assembly (EISA) method having nanorod-like particle shape. Furthermore, three types of photocatalysts were made with or without template polymer to clarify the function of that template precursor on the surface and morphology, as well as which variables are the most critical for a photocatalyst. TC40 heterojunction nanomaterial displayed high BET surface area along with lower band gap value viz.2.98 eV compare the other and all of these features make it a robust photocatalyst for wastewater treatment. In order to improve water quality, we have carried out experiments on the photodegradation of methyl Orange (MO), highly toxic pollutants that cause health hazards and bioaccumulate in the environment. Our catalyst, TC40 exhibits the 100% photocatalytic efficiency towards MO dye degradation in 40 and 360 min at a rate constant of 0.104 ± 0.007 min^-1 and 0.440 ± 0.03 h^-1 under UV + Vis and visible light irradiation respectively.

Heterostructured ZnCo2O4-CoOOH nanosheets on Ni foam for a high performance bifunctional alkaline water splitting catalyst

It is of utmost importance to explore bifunctional electrocatalysts for water splitting. Herein, unique ZnCo₂O₄-CoOOH heterostructured ultrathin nanosheets on Ni foam are reported that combines a two-step hydrothermal method. This catalyst exhibits excellent catalytic performances to achieve a current density of 10 mA cm^-2 with an ultralow overpotential of 115 mV for HER, attaining an overpotential of 238 mV at 20 mA cm^-2 for OER. Remarkably, ZnCo₂O₄-CoOOH/Ni shows a voltage of 1.494 V to drive a current density of 10 mA cm^-2. Such performances are due to the inter-penetrative pores present in the ultrathin nanosheets that provide large surface areas and expose massive active sites to enhance activities. In addition, the unique nanosheet structure and the 3D Ni foam substrate possess large specific surface areas, which can facilitate mass diffusion. This excellent performance is ascribed to the ZnCo₂O₄-CoOOH heterostructure that manipulates strong synergy to improve the electrochemical activity. This study offers new insight on an innovative approach for the exploitation of effective bifunctional electrocatalysts with a heterostructure.