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AbstractCarbon and transition metals have emerged as promising candidates for many energy storage and conversion devices. They facilitate charge transfer reactions whilst showing a good stability. These materials, fabricated as freestanding electrodes pose the potential of simplified electrode manufacturing procedures whilst demonstrating excellent electrocatalytic, mechanical, and structural properties, resulting from interconnected (via chemical or van der Waals force bonded) network structures. In such freestanding configuration, the lack of a binder leads to a better conductivity, ease in the manufacturing processing, and allows a lower catalyst mass loading, all of which lead to obvious benefits. This Minireview summarizes different fabrication techniques of freestanding non‐precious‐metal oxygen electrocatalysts along with their performance towards the oxygen evolution reaction (OER) and/or oxygen reduction reaction (ORR). Here, we discuss electrocatalysts produced by using freestanding substrates and those obtained through the self‐assembly of different precursors. The advantages of using freestanding versus non‐freestanding configurations are also pondered. Challenges and perspectives for freestanding electrocatalysts are presented at the end of the Minireview as a guideline for future studies in the field. This work is expected to serve as inspiration for science colleagues to develop further studies into design, processing and testing strategies of freestanding low‐cost oxygen electrocatalysts.

Abstract The effects of plasma injection upon MILD combustion of a mixture of methane and hydrogen are investigated numerically. The injected plasma includes the flow of a highly air-diluted methane including C2H2, C2H4, C2H6, CH, CH2, CH3, CO, and CO2. The results show that among all the constitutes of plasma, CH3 is the most effective in improving the characteristics of MILD combustion. Injection of this radical leads to the occurrence of reactions at a closer distance to the burner inlet and thus provides longer time for completion of combustion. Further, mass fractions of OH, CH2O, and HCO are considerably affected by the injections of CH3, indicating structural modifications of the reacting flow. Importantly, as Reynolds number of the plasma flow increases, the volume and width of the flame decrease, while the formations of prompt and thermal NOx are intensified. However, injection of CH3, as plasma, reduces the emission of thermal NOx.

The interfacial reactions in Sn-0.7wt%Cu/ENIG SUS304 couples at 240, 255, and 270 °C are examined in this study. The Ni-containing ternary Cu6Sn5 phase is formed at the Ni/liquid interface in the early reaction stage then it detaches massively from the SUS304 substrate and splits into two layers in the molten solder as the reaction time increases. This phase finally disintegrates and disappears. The square pillar-shaped FeSn2 phase is found on top of the SUS304 substrate when the Cu6Sn5 layer detaches. The reaction phase formation, detachment, and split mechanisms are proposed. The spalling phenomenon is reviewed and discussed. The growth mechanism of the FeSn2 phase obeys the parabolic law, and the activation energy is determined to be 112.5 KJ/mol.

AbstractPyridinium electrolytes are promising candidates for flow-battery-based energy storage1–4. However, the mechanisms underlying both their charge–discharge processes and overall cycling stability remain poorly understood. Here we probe the redox behaviour of pyridinium electrolytes under representative flow battery conditions, offering insights into air tolerance of batteries containing these electrolytes while providing a universal physico-chemical descriptor of their reversibility. Leveraging a synthetic library of extended bispyridinium compounds, we track their performance over a wide range of potentials and identify the singlet–triplet free energy gap as a descriptor that successfully predicts the onset of previously unidentified capacity fade mechanisms. Using coupled operando nuclear magnetic resonance and electron paramagnetic resonance spectroscopies5,6, we explain the redox behaviour of these electrolytes and determine the presence of two distinct regimes (narrow and wide energy gaps) of electrochemical performance. In both regimes, we tie capacity fade to the formation of free radical species, and further show that π-dimerization plays a decisive role in suppressing reactivity between these radicals and trace impurities such as dissolved oxygen. Our findings stand in direct contrast to prevailing views surrounding the role of π-dimers in redox flow batteries1,4,7–11 and enable us to efficiently mitigate capacity fade from oxygen even on prolonged (days) exposure to air. These insights pave the way to new electrolyte systems, in which reactivity of reduced species is controlled by their propensity for intra- and intermolecular pairing of free radicals, enabling operation in air.

Highly efficient bifunctional P,N co-doped graphene framework (PNGF) with both ORR and OER activities that are superior to noble metal catalysts.

Abstract We present a facile methodology for the synthesis of a novel 2D-MoS2, graphene and CuNi2S4 (MoS2-g-CuNi2S4) nanocomposite that displays highly efficient electrocatalytic activity towards the production of hydrogen. The intrinsic hydrogen evolution reaction (HER) activity of MoS2 nanosheets was significantly enhanced by increasing the affinity of the active edge sites towards H+ adsorption using transition metal (Cu and Ni2) dopants, whilst also increasing the edge sites exposure by anchoring them to a graphene framework. Detailed XPS analysis reveals a higher percentage of surface exposed S at 17.04%, of which 48.83% is metal bonded S (sulfide). The resultant MoS2-g-CuNi2S4 nanocomposites are immobilized upon screen-printed electrodes (SPEs) and exhibit a HER onset potential and Tafel slope value of – 0.05 V (vs. RHE) and 29.3 mV dec−1, respectively. These values are close to that of the polycrystalline Pt electrode (near zero potential (vs. RHE) and 21.0 mV dec−1, respectively) and enhanced over a bare/unmodified SPE (– 0.43 V (vs. RHE) and 149.1 mV dec−1, respectively). Given the efficient, HER activity displayed by the novel MoS2-g-CuNi2S4/SPE electrochemical platform and the comparatively low associated cost of production for this nanocomposite, it has potential to be a cost-effective alternative to Pt within electrolyser technologies.

AbstractThe paper discusses the challenges associated with the performance of zinc‐ion batteries (ZIBs), such as side reactions that lead to reduced capacity and lifespan. The strategies for mitigating side reactions in ZIBs, including additives, electrolyte‐electrode interface modification, and electrolyte composition optimization, are explored. Combinations of these approaches may be necessary to achieve the best performance for ZIBs. However, continued research is needed to improve the commercial viability of ZIBs. Areas of research requiring attention include the understanding of the mechanisms behind side reactions in ZIBs and the development of cost‐effective and scalable manufacturing processes for ZIBs with available electrolyte. By developing effective strategies for mitigating side reactions, researchers can improve the efficiency and lifespan of ZIBs, making them more competitive with lithium‐ion batteries in various applications, including grid energy storage.