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Recently, water oxidation or oxygen evolution reaction (OER) in electrocatalysis has attracted huge attention due to its prime role in water splitting, rechargeable metal–air batteries, and fuel cells. Here, we demonstrate a facile and scalable fabrication method of a rod-like structure composed of molybdenum disulfide and carbon (MoS2/C) from parent 2D MoS2. This novel composite, induced via the chemical vapor deposition (CVD) process, exhibits superior oxygen evolution performance (overpotential = 132 mV at 10 mA cm−2 and Tafel slope = 55.6 mV dec−1) in an alkaline medium. Additionally, stability tests of the obtained structures at 10 mA cm−2 during 10 h followed by 20 mA cm−2 during 5 h and 50 mA cm−2 during 2.5 h have been performed and clearly prove that MoS2/C can be successfully used as robust noble-metal-free electrocatalysts. The promoted activity of the rods is ascribed to the abundance of active surface (ECSA) of the catalyst induced due to the curvature effect during the reshaping of the composite from 2D precursor (MoS2) in the CVD process. Moreover, the presence of Fe species contributes to the observed excellent OER performance. FeOOH, Fe2O3, and Fe3O4 are known to possess favorable electrocatalytic properties, including high catalytic activity and stability, which facilitate the electrocatalytic reaction. Additionally, Fe-based species like Fe7C3 and FeMo2S5 offer synergistic effects with MoS2, leading to improved catalytic activity and durability due to their unique electronic structure and surface properties. Additionally, turnover frequency (TOF) (58 1/s at the current density of 10 mA cm−2), as a direct indicator of intrinsic activity, indicates the efficiency of this catalyst in OER. Based on ex situ analyzes (XPS, XRD, Raman) of the electrocatalyst the possible reaction mechanism is explored and discussed in great detail showing that MoS2, carbon, and iron oxide are the main active species of the reaction. [ABSTRACT FROM AUTHOR]

Developing a robust and highly efficient electrocatalyst for the oxygen evolution reaction (OER) is required, due to its sluggish mechanism and high overpotential. Here, we present the Ti 3 C 2 T x and ZIF-67 composites (MXene/ZIF-67) for an efficient OER. The MXene/ZIF-67_1:10 exhibits an overpotential of 366 mV, which is better than MXene (548 mV) and RuO 2 (395 mV). Moreover, it shows improved electrochemical stability at 20 mA·cm− 2 with only a 0.2% increase in potential after 5 h, while RuO 2 with an overpotential loss of 3.5%. After an increase in the current density of 10–20 mA cm−2 the potential increase by 7.4%, while in RuO 2 by 25.3%. To reveal the observed performance, the composite's robustness and explain each component's role. Moreover, a detailed OER mechanism is discussed. It was realized via in situ Raman microscopy and XRD which allowed the revealing of the active species responsible for boosting OER. • MXene/ZIF-67 composite was designed for OER. • MXene/ZIF-67 presented outstanding electrocatalytic activity in OER. • MXene/ZIF-67 structures exhibit robust stability at high current density for a long time. • In situ Raman and XRD were applied to revile the mechanism of OER. [ABSTRACT FROM AUTHOR]

• Low-temperature (250 °C), Environmentally Friendly Methodology addresses the challenges of low catalytic activity and stability associated with Oxygen Evolution Reaction (OER) catalysts. • Synergistic Interplay of three different Fe-based heterojunctions (Fe 3 O 4 , Fe 3 C, and FeNi 3), enhancing the stability of the catalyst and facilitating efficient charge transfer in OER. • Optimized Catalyst Performance of Fe/Ni_3.0h with an overpotential of 310 mV at 10 mA/cm2, Tafel slope of 37 mV/dec, and stability retaining ∼98.8 %. • Comprehensive Mechanism Revealed through Advanced Analyses through Ex-Situ XRD and Mössbauer spectroscopy analyses. This research addresses the inherent challenges of low catalytic activity and stability often associated with Oxygen Evolution Reaction (OER) catalysts. We designed composites with outstanding electrocatalytic performance. The methodology is characterized by low-temperature operation and environmentally friendly substrates. We have successfully fostered a synergistic interplay between Fe and oxygen, carbon and nickel, respectively. Fabricated material composed of three different heterojunctions triggered the stability of the catalyst and facilitated efficient charge transfer in OER. Our optimized catalyst (Fe/Ni_3.0h), emerges as a promising candidate for practical applications, exhibiting an overpotential of 310 mV, a Tafel slope of 37 mV/dec, and a potential retention of 98.8 % which is a 50 % lower drop in respect to commercial RuO 2. Therefore, our approach underlines the substantial influence of conductive Fe-based materials: FeNi 3 , Fe 3 C, and Fe 3 O 4 on OER performance with revealed comprehensive mechanism via ex-situ XRD and Mössbauer spectroscopy analyses. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Novel 2D borophene-NiO composite electrocatalyst. • Composite exhibits low overpotential, high stability, and enhanced kinetics. • Borophene-NiO composite with exceptional Tafel slope and active sites. • Spectroscopic and microscopic analyses reveal facilitated electron transfer and new reaction intermediates. • Borophene functionalized by NiO opens new avenues in catalytic research. Electrochemical water splitting has great potential for converting electricity into clean energy through electrode reactions. However, the anodic oxygen evolution reaction (OER) exhibits serious drawbacks such as: (i) high overpotential, slow reaction dynamics, limited robustness at high current density, and (ii) high cost of standard catalysts in OER (IrO 2 or RuO 2). Therefore, in our study, we address those issues and present a new composite based on 2D borophene functionalized with nickel oxide nanoparticles with highly active electrocatalytic properties in OER, with a low overpotential of 191 mV reaching j = 10 mA/cm2 and Tafel slope of 44 mV/dec. Additionally, the structure showed electrochemical and physical stability during long-term measurements, with excellent potential retention of 99.9 % at 50 mA/cm2. The electrochemical surface area (ECSA) revealed an increase in the number of active sites available for the reaction to occur, with respect to individual components of composites. Detailed spectroscopic and microscopic analyses of the electrocatalyst conducted before and after OER allowed us to propose insight into the reaction mechanism indicating the synergy between borophene and NiO nanoparticles (facilitated electron charge transfer and additional reaction intermediate such as NiB 12 O 14 (OH) 10). The proposed fabrication process of borophene functionalized by NiO is facile, low-cost, and scalable. Moreover, this strategy offers an additional avenue to explore a 2D family of electrocatalysts in OER enriching the current state of the art in the field. [ABSTRACT FROM AUTHOR]

[Display omitted] • Overpotential of ZIF-67 calcinated at 200 °C (ZIF-67 200) is 317.8 mV, lower than for RuO 2 (411.5 mV). • The robustness of ZIF-67 200 was proved in the stability test (potential retention of 99.6% at 20 mA·cm−2). • Optimal low-temperature calcination exposes coordinatively unsaturated Co sites and accelerates electrochemical activity. • Low-temperature calcination is a general approach to boost the electroactivity of metal-organic frameworks. An efficient electrocatalyst is crucial for sustainable hydrogen-fuel production, where cobalt oxyhydroxide is one of the most active catalysts for alkaline water splitting. Here, we designed a series of Co-based catalysts fabricated by direct low-temperature calcination of ZIF-67 for electrocatalytic oxygen evolution reaction (OER). Interestingly, the treatment of the pristine ZIF-67 by the temperature of only 200 °C was found to induce the most electroactive composition with a high electrochemically active surface of 373.5 cm2 and turnover frequency of 129.7 s−1, while a high specific surface area (1745 m2·g−1) is preserved. It resulted in a robust catalyst with a low overpotential of 317.8 mV at 10 mA·cm−2 and accelerated charge transfer, leading to improved performances in electrochemical energy conversion from water. Moreover, using in situ spectroscopy, XRD and microscopic techniques the active intermediates, for example, M-O, M-OH, and M-OOH were revealed and thus the exact mechanism of the reaction was proposed. Due to the formation of active species a lattice oxygen mechanism (LOM) was revealed. [ABSTRACT FROM AUTHOR]

The renewable energy technologies require electrocatalysts for reactions, such as the oxygen and/or hydrogen evolution reaction (OER/HER). They are complex electrochemical reactions that take place through the direct transfer of electrons. However, mostly they have high over-potentials and slow kinetics, that is why they require electrocatalysts to lower the over-potential of the reactions and enhance the reaction rate. The commercially used catalysts (e.g., ruthenium nanoparticles—Ru, iridium nanoparticles—Ir, and their oxides: RuO2, IrO2, platinum—Pt) contain metals that have poor stability, and are not economically worthwhile for widespread application. Here, we propose the spinel structure of nickel-cobalt oxide (NiCo2O4) fabricated to serve as electrocatalyst for OER. These structures were obtained by a facile two-step method: (1) One-pot solvothermal reaction and subsequently (2) pyrolysis or carbonization, respectively. This material exhibits novel rod-like morphology formed by tiny spheres. The presence of transition metal particles such as Co and Ni due to their conductivity and electron configurations provides a great number of active sites, which brings superior electrochemical performance in oxygen evolution and good stability in long-term tests. Therefore, it is believed that we propose interesting low-cost material that can act as a super stable catalyst in OER. [ABSTRACT FROM AUTHOR]