Rare earth metal (Sm)-doped NiMnO3 nanostructures for highly competent alkaline oxygen evolution reaction

Hydrothermally grown Cu doped NiMnO3 perovskite nanostructures suitable for optoelectronic, photoluminescent and electrochemical properties

Transition metal-based perovskites have emerged as highly promising and economically advantageous semiconductor materials due to their exceptional performance in optoelectronics, photovoltaic, photocatalysis, and photoluminescence. In this study, we employed a microwave-assisted hydrothermal process to produce a Cu-doped NiMnO3 nanocomposite electrode material. The appearance of a peak corresponding to the (110) plane with a 2θ value of 36.6° confirmed the growth of the rhombohedral NiMnO3 crystal structure. The presence of metal-oxygen bonds in NiMnO3 was confirmed through FTIR spectra. XPS validates the chemical composition, providing additional support for the results obtained from XRD and FT-IR analyses. FE-SEM affirmed the anisotropic growth of small sphere-like structures that agglomerated to form broccoli-like shapes. Cu doping modified the band gap, reducing it from 2.2 to 1.7 eV and enhancing its photoluminescent (PL) activity by introducing defects. The increase in PL intensity (visible light luminescent intensity) can be attributed to a concurrent rise in complex defects and the rate of recombination of electron-hole pairs. Finally, the electrochemical activity demonstrated the pseudo-capacitor behavior of the synthesized material, with capacitance values increasing as the copper (Cu) content in the parent lattice increased.

Structural Engineering of Co-Metal-Organic Frameworks via Ce Incorporation for Improved Oxygen Evolution

The rational design of metal-organic framework (MOF)-based electrocatalysts plays a key role in achieving high-efficiency oxygen evolution reaction (OER). Herein, a synergetic morphology and electronic structure engineering strategy are proposed to design a Co-MOF nanoflower grown on carbon paper via rare-earth cerium doping (CoCe-MOF/CP). Compared with Co-MOF/CP, the developed CoCe-MOF/CP exhibited superior OER performance with a low overpotential of 267 mV at 10 mA cm-2 and outstanding long-term stability over 100 h. Theoretical calculations show that the unique 4f valence electron structure of Ce induced charge redistribution of the Co-MOF surface through the strong Co 3d-O 2p-Ce 4f orbital electronic coupling below the Fermi level. Ce-doped plays a key role in the engineering of the electronic states of the Co sites to endow them with the optimal free energy landscape for enhanced OER catalytic activity. This work provides new insights into comprehending the RE-enhanced mechanism of electrocatalysis and provides an effective strategy for the design of MOF-based electrocatalysts.

Metal-Oxides- and Metal-Oxyhydroxides-Based Nanocomposites for Water Splitting: An Overview

Water electrolysis is an important alternative technology for large-scale hydrogen production to facilitate the development of green energy technology. As such, many efforts have been devoted over the past three decades to producing novel electrocatalysis with strong electrochemical (EC) performance using inexpensive electrocatalysts. Transition metal oxyhydroxide (OxH)-based electrocatalysts have received substantial interest, and prominent results have been achieved for the hydrogen evolution reaction (HER) under alkaline conditions. Herein, the extensive research focusing on the discussion of OxH-based electrocatalysts is comprehensively highlighted. The general forms of the water-splitting mechanism are described to provide a profound understanding of the mechanism, and their scaling relation activities for OxH electrode materials are given. This paper summarizes the current developments on the EC performance of transition metal OxHs, rare metal OxHs, polymers, and MXene-supported OxH-based electrocatalysts. Additionally, an outline of the suggested HER, OER, and water-splitting processes on transition metal OxH-based electrocatalysts, their primary applications, existing problems, and their EC performance prospects are discussed. Furthermore, this review article discusses the production of energy sources from the proton and electron transfer processes. The highlighted electrocatalysts have received substantial interest to boost the synergetic electrochemical effects to improve the economy of the use of hydrogen, which is one of best ways to fulfill the global energy requirements and address environmental crises. This article also provides useful information regarding the development of OxH electrodes with a hierarchical nanostructure for the water-splitting reaction. Finally, the challenges with the reaction and perspectives for the future development of OxH are elaborated.

Interface Synergistic Effect from Hierarchically Porous Cu(OH)2@FCN MOF/CF Nanosheet Arrays Boosting Electrocatalytic Oxygen Evolution

The electrolysis of water is an efficient and environmentally friendly technology for large-scale hydrogen production. However, the oxygen evolution reaction (OER) involves a multi-electron–proton coupling transfer step that limits the efficiency of water splitting. Therefore, there is an urgent need to develop electrocatalysts with expected activity and stability to accelerate the kinetics of the oxygen evolution reaction. In this paper, hierarchically porous Cu(OH)2@(Fe, Co, Ni)MOF/CF nanosheet (denoted as Cu(OH)2@FCN MOF/CF) arrays were successfully prepared by the hydrothermally induced in situ growth of FCN MOF nanosheets using modified Cu(OH)2 nanowires as carriers; herein, the tuned active species of metal ligands in the FCN MOF composition structure are used as the main catalytic reaction size in the OER. The synergistic effect of a unique porous structure and the active metal-ligand species in the MOF render the catalyst a large electrochemically active surface area and more active species. Then, the active material is fully contacted with the electrolyte to expose more electrochemically active sites, thus greatly improving the electrocatalytic activity and durability of the OER. Specifically, the Cu(OH)2@FCN MOF/CF delivers a minimum overpotential of 290 mV and low Tafel slope of 96.15 mV·dec−1 at 10 mA·cm−2 as well as ultra-long cycling stability. The resulted OER performance is superior to most reported MOF-based electrocatalysts. This novel structural design not only provides a new strategy for the facile preparation of low-cost and high-efficiency OER electrocatalysts but also paves an avenue for the development of other MOF-based composite electrocatalysts with excellent electrocatalytic performances.