Single atomic dispersed M-N-C (M = Fe, Co, Ni, Cu, etc.) composites display excellent performance for catalytic reactions. However, the analysis and understanding of neighboring M-N-C centers at the atomic level are still insufficient. Here, FeCo-N-doped hollow carbon nanocages (FeCo-N-HCN) with neighboring Fe-N 4 -C and Co-N 4 -C dual active centers as efficient catalysts are reported. Spherical aberration-corrected high angle annular darkfield scanning transmission electron microscopy, small area (1 nm 2 ) electron energy loss spectroscopy, and X-ray absorption spectroscopy data analysis and fitting prove the neighboring Fe-N 4 -C and Co-N 4 -C dual active structure in FeCo-N-HCN. Experimental tests and density functional theory calculation results reveal that the FeCo-N-HCN catalyst displays better catalytic activity than Fe single-metal catalyst for oxygen reduction reaction (ORR), which is attributed to the synergistic effect of Fe-N 4 -C and Co-N 4 -C dual active centers reducing the reaction energy barriers for ORR. Although the catalytic performance of the FeCo-N-HCN catalyst is not comparable to the-state-of-art catalysts reported due to the low metal contents (Fe: 1.96 wt% and Co: 1.31 wt%), these results can refresh the understanding of neighboring M-N-C centers at the atomic level and provide guidance for the design of catalysts in the future.

Nanoporous anodic aluminum oxide (AAO) tubular membranes were fabricated from aluminum alloy tubes in sulfuric and oxalic acid electrolytes using a two-step anodization process. The membranes were investigated for characteristics such as pore size, interpore distance and thickness by varying applied voltage and electrolyte concentration. Morphology of the membranes was examined using light optical and scanning electron microscopy and characterized using ImageJ software. Results showed that membranes having narrow pore size and uniform pore distribution with parallel channel arrays were obtained. The pore sizes were ranging from 14 to 24 nm and the wall thicknesses as high as 76 µm. It was found that the pore size increased in direct proportion with the applied voltage and inversely with the electrolyte concentration while the interpore distance increased linearly with the applied voltage. It was also observed that increase in acid concentration increased tubular membrane wall thickness that improved mechanical handling. By using anodic alumina technology, robust ceramic tubes with uniformly distributed pore-structure and parallel nano-channels of lengths and sizes practical for industrial applications were reliably produced in quantity.

Herein, we have developed a rather simple composite fabrication approach to achieving molecular-level dispersion and planar orientation of chemically modified graphene (CMG) in the thermosetting polyimide (PI) matrix as well as realizing strong adhesion at the interfacial regions between reinforcing filler and matrix. The covalent adhesion of CMG to PI matrix and oriented distribution of CMG were carefully confirmed and analyzed by detailed investigations. Combination of covalent bonding and oriented distribution could enlarge the effectiveness of CMG in the matrix. Efficient stress transfer was found at the CMG/PI interfaces. Significant improvements in the mechanical performances, thermal stability, electrical conductivity, and hydrophobic behavior were achieved by addition of only a small amount of CMG. Furthermore, it is noteworthy that the hydrophilic-to-hydrophobic transition and the electrical percolation were observed at only 0.2 wt % CMG in this composite system. This facile methodology is believed to afford broad application potential in graphene-based polymer nanocomposites, especially other types of high-performance thermosetting systems.

Y. (2018). Ultra-thin Fe 3 C nanosheets promote the adsorption and conversion of polysulfides in lithium-sulfur batteries. Energy Storage Materials.

and cycle life. However, LIBs suffer from issues including flammability, toxicity, cost, and scarcity of Li metal. [4,5] Rechargeable batteries based on an aqueous electrolyte and earth-abundant elements are regarded as a more sustainable alternative to the current LIBs. Aqueous metal-ion batteries are inherently safe, eco-friendly, cheap, and capable of operating at large currents. [6][7][8] Aqueous zinc-ion battery (ZIB) is one of the types and offers a high theoretical capacity (820 mAh g −1 ) and a low electrochemical potential of metallic Zinc (−0.76 V vs standard hydrogen electrode), [9][10][11][12][13] but the development of highly stable cathode for ZIBs is still challenging.Prussian blue analogues (PBAs) with a formula of A x M[Fe(CN) 6 ] y •nH 2 O (0 < x < 2, 0 < y ≤ 1, A = alkaline metal, M = transition metal) have been considered as promising cathode materials for aqueous alkali metalion batteries. The capacity of PBAs can reach more than 120 mAh g −1 [14][15][16][17] and the stability is excellent, due to the presence of two redox couples and robust 3D open-framework structures allowing the insertion of a variety of alkaline ions without distortion. [18][19][20] However, PBAs only provide a relatively low specific capacity for Zn 2+ cations (typically less than 80 mAh g −1 ), and intercalation of Zn 2+ can lead to uncontrolled phase transition and consequent performance degrading. [9,21,22] Liu et al. first proposed a ZIB using a rhombohedral Zn 3 [Fe(CN) 6 ] 2 (ZnHCF) cathode, which exhibited a low capacity of 65.4 mAh g −1 with 76% capacity retention after 100 cycles. [23] A cubic structure PBA (CuHCF) was synthesized for Zn 2+ storage, and this cathode completed 100 cycles with a capacity of 56 mAh g −1 . [24] Mantia et al. suggested that the capacity decay in CuHCF can be attributed to a phase transition to a second phase which is electrochemically less active. [25,26] To reduce the influence of phase transition resulted from Zn 2+ insertion, researchers employed electrolytes with a low or even zero Zn 2+ concentration to make NiHCF//Zn, [27] CuHCF//Zn, [28] and NaFe-PB//Zn [29] hybrid-ion batteries. Nonetheless, the storage capacities of Zn 2+ in these cathodes were still low despite that the cycle life was improved by increasing the scanning voltage. [30] In this work, we introduce a high voltage aqueous PBA-Zn hybrid-ion battery with KMnHCF (K 1.6 Mn[Fe(CN) 6 ] 0.94 •0.63H 2 O) cathode, zinc foil anode, and 30 m KFSI + 1 m Zn(CF 3 SO 3 ) 2 Prussian blue analogues (PBAs), featuring an open framework for accommodating large ions and tunable valence states, have garnered wide interest in the context of aqueous zinc-ion batteries (ZIBs). However, PBAs in ZIBs currently still suffer from low capacity and poor cycling stability due to structural instability. Here a K 2 MnFe(CN) 6 cathode achieving a very stable capacity of 100 mAh g −1 is reported in a ZIB charged/discharged to 400 cycles. Interestingly, such a stable capacity is attributed to the fact that the K 2 MnFe(CN) 6 cathode is gradually t...