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Addressing the low conductivity and porosity of ZIF-67-based oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalysts is a top priority. Noble metal-free highly active bifunctional catalysts F-N/FeCoNC 900 with three-dimensional interconnected porous structure and high electrical conductivity were successfully prepared by co-doping Fe, F, and N on the precursor ZIF-67. In terms of ORR performance, F-N/FeCoNC 900 has a high onset potential (E onset) of 0.97 V (vs. RHE), a half-wave potential (E 1/2) of 0.87 V (vs. RHE), and an ultimate current density (J L) of 5.7 mA cm−2, superior to commercially available Pt/C (0.95 V, 0.85 V, 5.3 mA cm−2). In addition, F-N/FeCoNC 900 provides high ORR activity with constant 4 electron transfer (n = 3.91–3.99) for methanol resistance and long-lasting stability (initial current retention of 96.32% after 21600 s). In terms of OER performance, F-N/FeCoNC 900 exhibits ultra-low overpotential (273 mV) and ultra-high Faraday efficiency (93%) at constant 4 (n = 3.91–3.99) electron transfer mode. This work provides a new pathway of doped ZIFs-derived composites as efficient bifunctional non-precious metal catalysts. [Display omitted] • Exquisite structure: The F-N/FeCoNC 900 catalyst has the following structural advantages:(a) A unique three-dimensional interconnected hierarchical porous structure is formed, which promotes the diffusion of oxygen and electrolytes and improves the utilization of internal active sites. (b) High specific surface area and high electrochemical active surface area enable highly exposed active centers, while abundant pyridinic nitrogen and graphitic nitrogen content overcome reaction barriers. • The highly efficient synergistic effect between composition and structure: The F-N/FeCoNC 900 catalyst has the following structure-activity relationship: (a) In view of the positive deep synergies among Co, Fe, F, N, and C atoms in the graphite lattice of F-N/FeCoNC 900 catalyst, reflecting F-N/FeCoNC 900 contains higher charge density to have smaller electrochemical impedance. (b) Abundant M-N x species serve as active sites with high structural stability and electrochemical activity. • This work not only delivers a low-cost and high-efficient ORR and OER catalyst, but also offers a new insight to develop a well-organized carbon hybrid electrocatalyst for various energy-related applications. [ABSTRACT FROM AUTHOR]

Development of low-cost and high-efficient oxygen reduction reaction (ORR) catalyst is a crucial challenge in fuel cell technology. Herein, we proposed a simple and scalable strategy to fabricate an interconnected 3D Fe 3 O 4 /rGO composite, in which Fe 3 O 4 nanoparticles mechanically anchor in reduced graphene oxide (rGO). Benefiting from its 3D layered structure with loose skeleton and rich porosity, and strong synergetic coupling between Fe 3 O 4 nanoparticles and rGO, the prepared composite, Fe 3 O 4 /rGO, provides better catalytic performance for ORR compared with commercial Pt/C catalyst, featuring high limiting current density (4.6 mA cm−2) close to that of Pt/C (4.7 mA cm−2), low H 2 O 2 yield (1%–6%), high electron transfer number (∼4), and outstanding long-term durability and methanol resistance in alkaline electrolytes. These encouraging results manifest that the Fe 3 O 4 /rGO composite holds great promise as a low-cost and high-performance alternative catalyst for ORR. • Simple and effective method to prepare 3D structured Fe 3 O 4 /rGO as ORR catalyst. • Fe 3 O 4 /rGO has a 3D layered structure with loose skeleton and rich porosity. • Fe 3 O 4 with an average particle size of about 20 nm uniformly anchored on graphene. • Fe 3 O 4 /rGO shows similar catalytic activity and better stability compared with Pt/C. [ABSTRACT FROM AUTHOR]

• A core-shell ZIF-8@ZIF-67 derived route was synthesized by CoNHPC ORR electrocatalysts. • The carbonation temperature affected the performance of CoNHPC-920. • The CoNHPC-920 could catalyze ORR via a direct 4e- pathway. • Unique hollow polyhedral structure gives CoNHPC-920 excellent ORR activity. [Display omitted] The rational design and construction of non-precious metal-based electrocatalysts with high activity and stability toward oxygen reduction reactions (ORR) are essential but challenging. In this work, a novel hybrid nanoporous structure of Co nanoparticles uniformly embedded in hollow porous carbon doped with nitrogen (CoNHPC) was constructed by a melt-evaporation-pyrolysis method, in which NaCl is utilized as an auxiliary template. The introduction to NaCl in this process served as the confining template to prevent nitrogen loss and promote graphitization, and the intercalating agent to form a mesoporous product. Due to the composite hierarchical porous structure, higher graphitization degree, and desirable nitrogen bonding type, the as-prepared CoNHPC-920 presents outstanding ORR electrocatalytic activity in terms of a half-wave potential of 0.87 V (vs. RHE) and onset potential of 0.97 V (vs. RHE). The composite material also shows higher selectivity and outstanding durability with most transition metal porous carbon materials reported. The strategy proposed in this study may provide ideas about metal nitrogen-carbon type catalysts enriched with carbon nanotubes and bare leaky hollow structures of the construction of advanced ORR electrocatalysts, opening up a new pathway. [ABSTRACT FROM AUTHOR]

• A facile epitaxial growth-pyrolysis tactic is proposed. • Highly porous and hollow non-noble metal carbon nanoarchitecture has been constructed. • The N-rich carbon protective layers embedded with cobalt nanoparticles boost the stability of the catalyst. • The Co@N-CNT-HC shows superior electrocatalytic activity for ORR. Fuel cells have emerged as a charming candidate for next-generation energy conversion devices. However, it is highly desired but challenging to engineer advanced non-precious oxygen reduction catalysts with highly actives and stability due to the sluggish kinetics of oxygen reduction reaction (ORR) on fuel cell cathode. Herein, a novel hybrid architecture with Co nanoparticles embedded in N-doped carbon nanotubes and hollow nanocarbon polyhedron (Co@N-CNT-HC) was constructed from core-shell ZIF-67@ZIF-8 via a facile epitaxial growth-pyrolysis process. With the Co@N-CNT-HC as the catalyst, a remarkable ORR performance is achieved in terms of a high half-wave potential of 0.84 V, a large limiting current density of 4.70 mA/cm2, and excellent long-term durability (97.8% current retention after 8 h) in alkaline medium, which outperform commercial Pt/C catalyst. Further dynamic calculations indicated that ORR follows a four-electron reaction mechanism. The enhancement activity of Co@N-CNT-HC is mainly due to the effective integration of 0D Co nanoparticles, 1D carbon nanotubes and 3D hollow nanocarbon, which synergistically strengthen the interfacial reaction kinetics of oxygen and accelerate mass/charge transfer. The strategy reported in this work provides a new insight to synthesis of low-cost and well-designed carbon hybrid electrocatalyst for ORR. [ABSTRACT FROM AUTHOR]

• Ti-V-Cr-Al light-weight medium entropy alloys are developed with outstanding tensile properties at the as-cast state. • The tensile ductility is much improved when Cr and Al are added equiatomically in the Ti 44 V 44 Cr x Al (12−x) alloys. • As-cast (TiV) 91 Cr 4.5 Al 4.5 alloy has a specific tensile yield stress of 160 MPa/(g/cm3) and a fracture elongation of 32%. [Display omitted] Light-weight (LW) high/medium entropy alloys have gained much attention due to the high specific strength, but they usually suffer from poor ductility, especially in the tensile tests at the as-cast state. In this study, the mechanical properties of a series of Ti-V-Cr-Al medium entropy alloys, with Ti and V maintaining equiatomic ratio, are investigated. An outstanding strength-ductility relationship is achieved in a (TiV) 91 Cr 4.5 Al 4.5 alloy, with a relatively low density of 5.1 g/cm3, a high specific yield strength of 160 MPa/(g/cm3), and a high tensile fracture elongation over 30%, even at its as-cast state. The tensile deformation is dominantly through the typical nucleation, planar migration, and entanglement of dislocations. Secondary phase formation and chemical inhomogeneity in this alloy are both insignificant. The frustration of dislocation motions are mainly attributed to the solid solution strengthening, which also enhances the work-hardening, delays the occurrence of necking, and benefits the overall ductility. The outstanding specific strength-ductility combination of this LW-alloy at the as-cast state makes it promising for potential engineering applications. [ABSTRACT FROM AUTHOR]