Controlled Assembly of Cu/Co-Oxide Beaded Nanoclusters on Thiolated Graphene Oxide Nanosheets for High-Performance Oxygen Evolution Catalysts

Electronic and Structural Modification of Mn3O4 Nanosheets for Selective and Sustained Seawater Oxidation

The accomplishment of seawater electrolysis to produce green hydrogen energy needs an efficient and durable electrocatalyst with high selectivity and corrosion resistance. Here we report a free-standing amorphous nanostructured oxygen evolution reaction (OER) electrocatalyst with microvoids developed by embedding Gd-doped Mn₃O₄ nanosheets in a CuO-Cu(OH)₂ nanostructure array (Gd-Mn₃O₄@ CuO-Cu(OH)₂. The surface oxygen vacancies modulated the electronic structure of the catalyst and offered active sites with optimal chemisorption energy to OER intermediates. The hierarchical surface structure provides a large specific surface area, high electrical conductivity, ionic mobility, intrinsic activity for each active site, and efficient charge transfer, leading to an outstanding catalytic performance. The enhanced structural, chemical, and corrosion resistance ensures effectiveness as an anode in direct seawater electrolysis. Specifically, it needs an input voltage of 1.63 V to deliver a current density of 500 mA cm^-2 in alkaline seawater, with the stability of more than 75 h of continuous electrolysis without hypochlorite formation. The high Faradaic efficiency demonstrates its potential for hydrogen fuel production from seawater.

Highly-stable cobalt metal organic framework with sheet-like structure for ultra-efficient water oxidation at high current density

The development of efficient and robust non-precious electrocatalysts for water oxidation at a mild condition is extremely desirable for industrial water splitting. Herein we developed a facile solvothermal strategy to synthesize cobalt metal organic frameworks (Co-MOFs) with sheet-like structure, which showed highly promising performance for electrocatalytic oxygen evolution. The best Co-MOF sample afforded an ultra-high oxygen evolution current density of 63.4 mA cm^-2 at 1.75 V in 1 M KOH with a catalyst loading of only 0.21 mg cm^-2. Notably, its electrochemical performance remained unchanged after 10,000 cyclic voltammograms indicating very promising long-term stability. Detailed study of the mechanism of the oxygen evolution by density functional theory (DFT) indicated that the strong π-conjugation formed between the central cobalt ion and adjacent aromatic rings favored the high electrocatalytic performance. The solvothermally synthesized MOFs proposed in this paper are expected to inspire the rational design of high-performance electrocatalysts for water oxidation with atomic and molecular level structural control and the exploration of structure-performance relationships to understand the electrocatalytic origin.

Improved Interface Charge Transfer and Redistribution in CuO-CoOOH p-n Heterojunction Nanoarray Electrocatalyst for Enhanced Oxygen Evolution Reaction

Electron density modulation is of great importance in an attempt to achieve highly active electrocatalysts for the oxygen evolution reaction (OER). Here, the successful construction of CuO@CoOOH p-n heterojunction (i.e., p-type CuO and n-type CoOOH) nanoarray electrocatalyst through an in situ anodic oxidation of CuO@CoSx on copper foam is reported. The p-n heterojunction can remarkably modify the electronic properties of the space-charge region and facilitate the electron transfer. Moreover, in situ Raman study reveals the generation of SO4 2- from CoSx oxidation, and electron cloud density distribution and density functional theory calculation suggest that surface-adsorbed SO4 2- can facilitate the OER process by enhancing the adsorption of OH- . The positively charged CoOOH in the space-charge region can significantly enhance the OER activity. As a result, the CuO@CoOOH p-n heterojunction shows significantly enhanced OER performance with a low overpotential of 186 mV to afford a current density of 10 mA cm-2 . The successful preparation of a large scale (14 × 25 cm2 ) sample demonstrates the possibility of promoting the catalyst to industrial-scale production. This study offers new insights into the design and fabrication of non-noble metal-based p-n heterojunction electrocatalysts as effective catalytic materials for energy storage and conversion.

Green synthesis of zinc oxide nanoparticles using Elaeagnus angustifolia L. leaf extracts and their multiple in vitro biological applications

Due to their versatile applications, ZnONPs have been formulated by several approaches, including green chemistry methods. In the current study, convenient and economically viable ZnONPs were produced using Elaeagnus angustifolia (EA) leaf extracts. The phytochemicals from E. angustifolia L. are believed to serve as a non-toxic source of reducing and stabilizing agents. The physical and chemical properties of ZnONPs were investigated employing varying analytical techniques (UV, XRD, FT-IR, EDX, SEM, TEM, DLS and Raman). Strong UV–Vis absorption at 399 nm was observed for green ZnONPs. TEM, SEM and XRD analyses determined the nanoscale size, morphology and crystalline structure of ZnONPs, respectively. The ZnONPs were substantiated by evaluation using HepG2 (IC₅₀: 21.7 µg mL⁻¹) and HUH7 (IC₅₀: 29.8 µg mL⁻¹) cancer cell lines and displayed potential anticancer activities. The MTT cytotoxicity assay was conducted using Leishmania tropica “KWH23” (promastigotes: IC₅₀, 24.9 µg mL⁻¹; and amastigotes: IC₅₀, 32.83 µg mL⁻¹). ZnONPs exhibited excellent antimicrobial potencies against five different bacterial and fungal species via the disc-diffusion method, and their MIC values were calculated. ZnONPs were found to be biocompatible using human erythrocytes and macrophages. Free radical scavenging tests revealed excellent antioxidant activities. Enzyme inhibition assays were performed and revealed excellent potential. These findings suggested that EA@ZnONPs have potential applications and could be used as a promising candidate for clinical development.