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Single-atom catalysts (SACs) based on metal–nitrogen–carbon (M–N–C) compounds have been identified as a potential substitute for Pt-based oxygen reduction reaction (ORR) catalysts due to their facile availability and low cost. M1M2–N–C based dual-atom catalysts (DACs) may be utilised to regulate the active site and optimise their ORR activity. Accordingly, M1M2–N6–C14 (M1 = Mn, Fe, Co; M2 = late transition metals) DACs were constructed within a graphene slab. M1M2–N–C is more stable than the corresponding M1–N–C and M2–N–C due to the affinity between M1 and M2. Furthermore, the ORR activity of FeM–N–C (M = late transition metals), MnM–N–C (Co, Ru, Rh, Os, Ir, and Re) and CoM–N–C (M = Cu, Zn, Pd, and Pt) is enhanced in comparison to that of Fe–N–C, due to the modified electronic properties. In comparison to other active ORR electrocatalysts, FeCu–N–C is positioned at a relatively high level on the volcano plot. To gain further insight into the dynamic stability of FeCu–N–C under working conditions (*OOH, 80 °C), an ab initio molecular dynamics simulation was employed. The accelerated structural evolution of the FeCu–N–C electrocatalyst resulted in the Cu atom being pulled out of the N–C substrate plane. Nevertheless, the resulting Fe(vacancy)–N–C and Fe(vacancy)–NH–C electrocatalysts have been observed to retain high ORR activity and stability. The findings of this study have significant implications for the design of DACs. [ABSTRACT FROM AUTHOR]

Novel exohedral metalloborospherenes Al12Li20&B60 and Al20Li12&B60 with the classical fullerene-like borospherene B60 were theoretically predicted and their structures and properties were studied. Incredibly, the B60 cage (pull electron oxidizer) pulls 50 and 60e− from exohedral metal atoms, forming two super-reduced polyanionic states B6050− and B6060−, respectively. Next, the two super-reduced polyanionic states (push electron oxidizers) owing to their negative electric fields push out the remaining valence electrons of exohedral metal atoms. Accordingly, the metalloborospherenes convert to electride salt molecules 6e−&[(Al3+)12(Li+)20]&B6050− and 12e−&[(Al3+)20(Li+)12]&B6060− due to the pull–push electron oxidation relay. It is known that the loss of electrons by the reducing agent results in an oxidation effect. The mechanism of losing electrons involves not only the pull electron but also the push electron, which results in push electron oxidation. As long as there is enough reducing agents in oxidation–reduction electride systems, the unusual pull–push electron oxidation relay will occur, showing new physical insights. More interestingly, the B60x− (x = 50 or 60) polyanions can also display push electron oxidation for embedded calcium atoms, forming endohedral spherical electride molecules 14e−&[(Al3+)12(Li+)20]&[(Ca6)8+@B6050−] and 22e−&[(Al3+)20(Li+)12]&[(Ca6)10+@B6060−], in which the supernormal pull–push–push electron oxidizing ability of the B60 cage is reflected in the total number of pull–push electrons up to 64 and 82, respectively. Remarkably, these spherical electride molecules have extraordinarily small multiple ionization potential (VIPn, n = 1–22) values, demonstrating a nuclear large-scale effect of the superatomic model on VIPn. [ABSTRACT FROM AUTHOR]

Triggering rapid reconstruction reactions holds the potential to approach the theoretical limits of the oxygen evolution reaction (OER), and spin state manipulation has shown great promise in this regard. In this study, the transition of Fe spin states from low to high was successfully achieved by adjusting the surface electronic structure of pentlandite. In situ characterization and kinetic simulations confirmed that the high‐spin state of Fe promoted the accumulation of OH− on the surface and accelerated electron transfer, thereby enhancing the kinetics of the reconstruction reaction. Furthermore, theoretical calculations revealed that the lower d‐band center of high‐spin Fe optimized the adsorption of active intermediates, thereby enhancing the reconstruction kinetics. Remarkably, pentlandites with high‐spin Fe exhibited ultra‐low overpotential (245 mV @ 10 mA cm−2) and excellent stability. These findings provided new insights for the design and fabrication of highly active OER electrocatalysts. [ABSTRACT FROM AUTHOR]

Aqueous zinc-ion hybrid supercapacitors (ZHSs) are promising energy storage devices owing to their high energy and power density. However, the selection of the voltage window to achieve the balance between energy density and cycling stability is still difficult. Herein, the protective effect of by-products deposited on the surface structure of the cathode material was studied based on the differences in the cycling stability of ultrathin carbon materials (UTCs) at different voltage windows. Through the calculation of the Gibbs free energy of the hydrogen evolution reaction (HER) process, the association of cathode by-products with voltage windows was described and confirmed for the first time: whether the by-product layer on the surface of the cathode material is broken or not can be considered a criterion for selecting the voltage window. Based on this, a flat pouch cell was fabricated in a wide voltage window of 0–1.9 V and exhibited an extremely high energy density of 267.9 W h kg−1 coupled with good flexibility and long cycle life with a capacity retention of 90.0% after 3000 cycles. Overall, this work introduces the relationship between cathode by-products and voltage windows for the first time, useful for providing more specific criteria for the selection of voltage windows. [ABSTRACT FROM AUTHOR]

High-entropy perovskite fluorides are very promising for the electrocatalytic oxygen evolution reaction (OER). However, the low kinetics of reconstruction reactions restrict their high catalytic activity. Herein, a novel strategy was developed for the modification of the surface K(CoMnFeNiCr)F3 (HEPF) using the electron-donating group pyrrolidone, for the first time, to promote the rate of reconstruction reactions. The experimental results and theoretical calculations demonstrated that after HEPF modification, the energy barrier for OH− adsorption was reduced to −5.37 eV. The surface modification with HEPF also enhanced the intrinsic conductivity owing to the improved band structure. This resulted in the formation of highly active catalytic species at lower potentials, leading to superior intrinsic catalytic activity. The optimized electrocatalyst exhibited an overpotential of only 242 mV at 10 mA cm−2, representing the best-reported value among similar materials. Overall, the proposed strategy looks promising for unlocking the excellent catalytic activity of high-entropy perovskite fluorides, useful for future syntheses of OER catalysts. [ABSTRACT FROM AUTHOR]

Phosphoric acid-doped polybenzimidazole (PA-doped PBI) membranes enable high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) to operate at elevated temperature (140–180 °C), with the advantages of simplified water/heat management. However, the relatively long start-up time and insufficient performance due to the introduction of the liquid phosphoric acid electrolyte are still major barriers to the application of HT-PEMFCs. Herein, a series of alkyl-substituted poly(arylene piperidinium) membranes are designed to modulate the content and distribution of phosphoric acid, which significantly reduces the ohmic and mass transfer resistance and boosts the performance of HT-PEMFCs in a wide operational temperature range. By tailoring the pendant alkyl groups of the piperidinium cations, the steric hindrance around the piperidinium cations and the free volume of poly(arylene piperidinium) can be well regulated. The optimized isobutyl-substituted poly(arylene piperidinium) membrane shows a high acid doping level (10.05) and a relatively high proton conductivity. As a result, a PEMFC based on this membrane shows significantly low ohmic and mass transfer resistances, consequently enhancing the peak power density of the HT-PEMFC to >1.5 W cm−2 at a moderate temperature of 120 °C under H2/O2 conditions. [ABSTRACT FROM AUTHOR]

The electrochemical decomposition of water plays a critical role in green and sustainable energy. However, the development of efficient and low-cost non-noble metal catalysts to overcome the high potential of the anodic oxygen evolution reaction (OER) is still challenging. In this work, electrocatalysts with high OER activity were obtained by doping Co/Fe bimetals into Ni3S2 (CF-NS) via a simple single-step hydrothermal method by adjusting the doping ratio of bimetals. A series of characterization studies revealed that the introduction of a Co/Fe co-dopant increased the number of active sites and improved the electroconductibility, while optimizing the electronic structure of Ni3S2. Meanwhile, Fe-induced high valence Ni contributed to the production of an OER active phase NiOOH. The unique dendritic crystal morphology facilitated the disclosure of the active sites and the expansion of mass transfer channels. The optimized sample required a low overpotential of 146 mV to obtain a current density of 10 mA cm−2 in 1.0 M KOH solution. The optimized sample also operated stably for at least 86 h. In sum, the proposed method looks very promising for designing efficient, stable, and low-cost non-precious metal catalysts with high conductivity and multiple active sites, useful for future synthesis of transition metal sulfide catalysts. [ABSTRACT FROM AUTHOR]

Vacancy engineering plays a significant role in the rational design of electrochemical energy conversion and storage. However, limited by traditional strategies, controllably introducing abundant vacancies remains challenging. Herein, a new strategy for controllable modulation of vacancy content by regulating the number of hydrogen bonds based on nickel fluoride alkoxide precursors (denoted as F–Ni–Ox–Ry) is proposed. The hydrogen bonds are formed by micro-design of the carbon chain structure to stabilize F ions on the surface during the synthesis process. Afterward, their breakage during electrochemical reconstruction processes leads to the overall release of F ions to generate vacancies. The adjustment of the carbon chain length can effectively control the number of hydrogen bonds, further microregulating the number of vacancies. The unique microstructural design yields a reconstructed nickel fluoride alkoxide (F–Ni–O2–R2) electrode with an ultra-high specific capacitance of 2975 F g−1 at a current density of 1 A g−1. This work not only provides a new strategy for the controllable modulation of vacancy engineering, but also a new perspective for the construction of novel energy storage electrodes by incorporating organic ligands into inorganic systems. [ABSTRACT FROM AUTHOR]

For a new challenge of stabilizing a classical fullerene-like borospherene composed of five- and six-membered rings, we take the lead to theoretically present a novel exohedral metalloborospherene Mg12Li8&B36 molecule (D6h). It features 12 η5(pentahapto)-Mg atoms and 8 η6-Li atoms capping 12 pentagonal faces and 8 hexagonal faces of classical fullerene-like borospherene D6h B36, respectively. Due to the pull-push electron transfer relay, the molecule is converted to an electride molecule (Mg2+)12(Li+)8&B3630− + 2e− with two excess electrons and an extraordinary high-valent B3630− polyanion with a full-shell electronic configuration, performing the stabilization of the classical fullerene-like B36 cage. As further findings emerge from this study, both the (Mg12Li8&B36)2+ cation (D6h) and the Mg12Li6&B36 salt (D6h) have higher stability than electride Mg12Li8&B36. Furthermore, embedding a metal atom pair in the boron cage of Mg12Li8&B36 leads to new endohedral electride molecules (Mg2+)12(Li+)8&(Mn+2@B3630−) + (2 + 2n) e− (M = Li, n = 1 and Be, n = 2). The embedded metal atom pair plays a prominent role in adding excess electrons. Notably, the Mg12Li8&B36 electride molecule can serve as both electron donor and electron acceptor and consequently acts as an electron reservoir. Encouragingly, Mg12Li8&B36 and its endohedral derivatives can be used as efficient external electric field manipulated second-order nonlinear optical (NLO) switches with high sensitivity and reversibility. In this sense, embedding a metal atom pair in the B36 cage provides a new strategy to manipulate NLO switching. [ABSTRACT FROM AUTHOR]