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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] • 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]

Disposable aluminum cans and plastic bottles are common wastes found in modern societies. This article shows that they can be upcycled into functional materials, such as metal-organic frameworks and hierarchical porous carbon nanomaterials for high-value applications. Through a solvothermal method, used poly(ethylene terephthalate) bottles and aluminum cans are converted into MIL-53(Al). Subsequently, the as-prepared MIL-53(Al) can be further carbonized into a nitrogen-doped (4.52 at%) hierarchical porous carbon framework. With an optical amount of urea present during the carbonization process, the carbon nanomaterial of a high specific surface area of 1324 m2 g−1 with well-defined porosity can be achieved. These features allow the nitrogen-doped hierarchical porous carbon to perform impressively as the working electrode of supercapacitors, delivering a high specific capacitance of 355 F g−1 at 0.5 A g−1 in a three-electrode cell and exhibiting a high energy density of 20.1 Wh kg−1 at a power density of 225 W kg−1, while simultaneously maintaining 88.2% capacitance retention over 10,000 cycles in two-electrode system. This work demonstrates the possibility of upcycling wastes to obtain carbon-based high-performance supercapacitors. [Display omitted] • Upcycle used PET bottles and aluminum cans into the nitrogen-doped hierarchical porous carbons. • Prepared carbon as supercapacitor electrode delivers a high energy density of 20.1 Wh/kg. • Well-defined porous carbon framework is vital to the excellent supercapacitive performance. • This work paves an effective environmental-friendly way to prepare carbon-based supercapacitor. [ABSTRACT FROM AUTHOR]