Atomic interface regulation is thought to be an efficient method to adjust the performance of single atom catalysts. Herein, a practical strategy was reported to rationally design single copper atoms coordinated with both sulfur and nitrogen atoms in metal-organic framework derived hierarchically porous carbon (S-Cu-ISA/SNC). The atomic interface configuration of the copper site in S-Cu-ISA/SNC is detected to be an unsymmetrically arranged Cu-S 1 N 3 moiety. The catalyst exhibits excellent oxygen reduction reaction activity with a half-wave potential of 0.918 V vs. RHE. Additionally, through in situ X-ray absorption fine structure tests, we discover that the low-valent Cuprous-S 1 N 3 moiety acts as an active center during the oxygen reduction process. Our discovery provides a universal scheme for the controllable synthesis and performance regulation of single metal atom catalysts toward energy applications.

Single atomic Fe-N x moieties embedded on a high surface area carbon (Fe-N/C) represents one of the most promising nonprecious metal electrocatalysts for the oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cells. While significant progress has been made in the preparation of Fe-N/C catalysts with high-density Fe-N x sites, key structural descriptors determining the intrinsic activity of the Fe center remain elusive, and effective ways to enhance the intrinsic activity are still lacking. Moreover, most Fe-N/C catalysts developed to date are built on carbons with rather low graphitization degree, which suffer from relatively severe carbon corrosion and thereby poor stability. The direct growth of carbon nanotubes doped with high-density Fe-N x sites neighbored with graphitic-nitrogen-rich environment is reported here, which are successfully applied as a both active and stable ORR electrocatalyst in fuel cells. Combining both experiments and density functional theory calculations, it is revealed that the neighboring graphitic nitrogen can effectively induce higher filling degree of d-orbitals and simultaneously decrease on-site magnetic moment (namely, lowered spin) of the Fe center, which can optimize the binding energies of ORR intermediates and thereby substantially enhance intrinsic ORR activity.

due to their mechanical flexibility in volume and shape requirement, high power density, rapid charge/discharge rate, long cycle lifetimes, and remarkable stitchability. [1][2][3][4][5][6][7][8] However, one of the key challenges of the FSCs in the light of their practical applications is to increase their volumetric energy density to the value approaching to or even exceeding those of microbatteries without sacrificing the power density, cycle life, and other performance para meters. [9][10][11][12][13][14][15] Both the energy and power density of a SC is strongly dependent on the operating voltage, that is, V 2 (E = 1/2 CV 2 and P = V 2 /4R ESR , where C is the capacitance of the device, V is the operating voltage, and R ESR is the equivalent series resistance). [16][17][18][19][20][21][22][23][24][25] Therefore, increasing the voltage window would be an effective approach to achieve highefficiency FSCs.To this end, enormous efforts have been devoted to the fabrication of asymmetric FSCs (AFSCs) which make full utilization of the operational windows of both the positive and negative electrode materials. [25][26][27][28][29][30][31][32] Nevertheless, the intrinsic characteristic voltage of water splitting (1.23 V) means that an aqueous electrolyte is limited to a potential domain of around 1 V, thus constraining the operating voltage to a maxi mum of 1.8-2.0 V, [28][29][30][31][32][33] which is indeed lower than that of Fiber supercapacitors (FSCs) represent a promising class of energy storage devices that can complement or even replace microbatteries in miniaturized portable and wearable electronics. One of their main limitations, however, is the low volumetric energy density when compared with those of rechargeable batteries. Considering the energy density of FSC is proportional to CV 2 (E = 1/2 CV 2 , where C is the capacitance and V is the operating voltage), one would explore high operating voltage as an effective strategy to promote the volumetric energy density. In the present work, an all-solid-state asymmetric FSC (AFSC) with a maximum operating voltage of 3.5 V is successfully achieved, by employing an ionic liquid (IL) incorporated gel-polymer as the electrolyte (EMIMTFSI/PVDF-HFP). The optimized AFSC is based on MnO x @TiN nanowires@carbon nanotube (NWs@CNT) fiber as the positive electrode and C@TiN NWs@CNT fiber as the negative electrode, which gives rise to an ultrahigh stack volumetric energy density of 61.2 mW h cm −3 , being even comparable to those of commercially planar lead-acid batteries (50-90 mW h cm −3 ), and an excellent flexibility of 92.7% retention after 1000 blending cycles at 90°. The demonstration of employing the ILs-based electrolyte opens up new opportunities to fabricate high-performance flexible AFSC for future portable and wearable electronic devices.

FeNC materials have shown a promising nonprecious oxygen reduction reaction (ORR) electrocatalyst yet their active site structure remains elusive. Several previous works suggest the existence of a mysterious axial ligand on the Fe center, which, however, is still unclarified. In this study, the mysterious axial ligand is identified as a hydroxyl ligand on the Fe centers and selectively promotes the ORR activities depending on different FeN4C configurations, on which the adsorption free energy of the hydroxyl ligand also differs greatly. The selective formation of hydroxyl ligand on specific FeNC configurations can resolve contradictories between previous theoretical and experimental results regarding the ORR activities and associated active configurations of FeNC catalysts. It also explains the pH‐dependent ORR activities and, moreover, a previously unreported pH‐dependent poisoning kinetics of the FeNC catalysts.

increasing by the abundant WN bond. To the best of our knowledge, the experimental synthesis of 2D nitrogen-rich tungsten nitrides is not reported in literature because of the harsh synthesis condition, stemming from the sluggish reaction thermodynamics of penetrating nitrogen into tungsten lattice. [9] Overall, high pressure and temperature (P-T) synthetic method (5 GPa and 880-2570 K) was adopted to prepare various nitrogen-rich tungsten nitrides such as W 2 N 3 , W 3 N 4 . [10] However, this harsh synthesis condition is laborious to control the morphology of tungsten nitrides, especially for the 2D structure. [11][12][13][14] As an alternative strategy, ammoniating tungsten metals or compounds are extensively studied to produce tungsten nitrides. [9,15] Yet, the reaction is always incomplete, leading to low nitrogen ratio in final products with unreacted tungsten precursor (tungsten, tungsten oxides, etc.). [16] Consequently, developing a facile and real-world synthetic strategy, with favorable reaction thermodynamics and facile morphology control for 2D nitrogen-rich tungsten nitrides, is highly desired but still thought provoking.Herein, we synthesize atomically thin 2D nitrogen-rich hexagonal W 2 N 3 (h-W 2 N 3 ) nanosheets via salt-templated method at atmospheric pressure for the first time. In this strategy, h-W 2 N 3 2D transition metal nitrides, especially nitrogen-rich tungsten nitrides (W x N y , y > x), such as W 3 N 4 and W 2 N 3 , have a great potential for the hydrogen evolution reaction (HER) since the catalytic activity is largely enhanced by the abundant WN bonding. However, the rational synthesis of 2D nitrogen-rich tungsten nitrides is challenging due to the large formation energy of WN bonding. Herein, ultrathin 2D hexagonal-W 2 N 3 (h-W 2 N 3 ) flakes are synthesized at atmospheric pressure via a salt-templated method. The formation energy of h-W 2 N 3 can be dramatically decreased owing to the strong interaction and domain matching epitaxy between KCl and h-W 2 N 3 . 2D h-W 2 N 3 demonstrates an excellent catalytic activity for cathodic HER with an onset potential of −30.8 mV as well as an overpotential of −98.2 mV for 10 mA cm −2 . ElectrocatalysisThe ORCID identification number(s) for the author(s) of this article can be found under https://doi.

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Utilizing both cationic and anionic oxygen redox reactions is regarded as an important approach to exploit high‐capacity layered cathode materials with earth abundant elements. It has been popular strategies to effectively elevate the oxygen redox activities by Li‐doping to introduce unhybridized O 2p orbitals in NaxMnO2‐based chemistries or enabling high covalency transition metals in P2‐Na0.66MnxTM1−xO2 (TM = Fe, Cu, Ni) materials. Here, the effect of Li doping on regulating the oxygen redox activities P2‐structured Na0.66Ni0.25Mn0.75O2 materials is investigated. Systematic X‐ray characterizations and ab initio simulations have shown that the doped Li has uncommon behavior in modulating the density of states of the neighboring Ni, Mn, and O, leading to the suppression of the existing oxygen and Mn redox reactivities and the promotion of the Ni redox. The findings provide a complementary scenario to current oxygen redox mechanisms and shed lights on developing new routes for high‐performance cathodes.

Solid oxide fuel cells (SOFCs) can directly operate on hydrocarbon fuels such as natural gas; however, the widely used nickel-based anodes face grand challenges such as coking, sulfur poisoning, and redox instability. We report a novel double perovskite oxide Sr2Co0.4Fe1.2Mo0.4O6−δ (SCFM) that possesses excellent redox reversibility and can be used as both the cathode and the anode. When heat-treated at 900 °C in a reducing environment, double perovskite phase SCFM transforms into a composite of the Ruddlesden–Popper structured oxide Sr3Co0.1Fe1.3Mo0.6O7−δ (RP-SCFM) with the Co–Fe alloy nanoparticles homogeneously distributed on the surface of RP-SCFM. At 900 °C in an oxidizing atmosphere, the composite transforms back into the double perovskite phase SCFM. The excellent oxygen reduction reaction catalytic activity and mixed ionic–electronic conductivity make SCFM an excellent cathode material for SOFCs. When SCFM is used as the anode, excellent performance and stability are achieved upon either direct oxidation of methane as a fuel or operation with sulfur-containing fuels. The excellent redox reversibility coupled with outstanding electrical and catalytic properties manifested by SCFM will enable a broad application in energy conversion applications.