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The problems of underdeveloped pores and high electrochemical impedance of oxygen reduction reaction (ORR) catalysts need to be urgently addressed. Heteroatoms F and N are doped on precursor Fe‐zeolitic imidazolate framework (ZIF)‐8 to increase the activity of Fe‐ZIF‐8‐derived porous carbon materials and a noble metal‐free high‐activity ORR catalyst F–N/FeNC with 3D interconnected porous structure and high conductivity is successfully prepared. Experiments show that the synergistic effect of CF ionic bonds, pyridinic‐N, pyrrolic‐N, graphitic‐N, FeNx sites, and CF semi‐ionic bonds in F–N/FeNC can improve the ORR activity of the F–N/FeNC. The developed F–N/FeNC is advantageous with excellent specific surface area, ultra‐high electrical conductivity, and extremely high ORR mass transfer efficiency. As such, the F–N/FeNC has a high onset potential of 0.95 V (vs RHE) and a half‐wave potential of 0.84 V (vs RHE), implying excellent ORR performance even better than commercially available Pt/C catalyst. In addition, the carefully prepared F–N/FeNC demonstrated higher long‐term durability and excellent resistance to methanol influence compared with commercially available Pt/C catalyst. The developed strategy provides new insights into heteroatom‐doped metal–organic frameworks as a precursor of ORR catalysts. [ABSTRACT FROM AUTHOR]

A kind of Co-N-C catalysts with hollow core-shell structures with large amount of carbon nano tubes (CNTs) growing on the surface were prepared, using polystyrene (PS) spheres as sacrificial templates, ZIF-8 @ZIF-67 as Co-N-C source and PVP as binder, and their performances in oxygen reduction reaction (ORR) were further explored. The electrochemical test results show that the prepared electrocatalyst Co/NHCNT-160 has good catalytic activity for ORR process and a nearly four-electron reaction path. Co/NHCNT-160 has long-term stability at high onset potential (0.955 V), half-wave potential (0.88 V) and limiting current density (6.3 mA cm−2), with a current retention rate of 99.7 % after 7 h. The ORR performance of Co/NHCNT-160 has surpassed that of commercially available Pt/C catalyst and most of the non-precious metal catalysts reported to date. Its excellent ORR catalytic performance is mainly due to its unique hollow core-shell structure and the abundance of CNTs spawned, the high degree of graphitization facilitating electron migration, the graded pores facilitating mass migration, and the functionalization of the Co-Nx active site with a highly dispersed carbon backbone. This catalyst preparation strategy will provide some ideas for the development of other ZIF-based ORR catalysts for energy storage and electrochemical devices. [Display omitted] [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]