Web‐Like Interconnected Carbon Networks from NaCl‐Assisted Pyrolysis of ZIF‐8 for Highly Efficient Oxygen Reduction Catalysis

Abstract

The oxygen reduction reaction (ORR) is under intense research due to its significance in energy storage and conversion processes. Recent studies show that interconnected and hierarchically porous structures can further enhance ORR kinetics as well as catalyst durability, but their preparation can be quite time and/or chemical consuming. Here, a simple approach is reported to prepare such complex structures by pyrolyzing composites containing NaCl and ZIF-8. The templating effect of molten NaCl connects ZIF-8 particles into web-like carbon networks. During ORR activity measurements, it achieves a 0.964 V onset potential and a 38 mV dec Tafel slope, which are comparable to those of the benchmark Pt/C (0.979 V and 40 mV dec ). Due to the metal-free feature, this catalyst exhibits a 16 mV shift in half-wave potential after a 10 000-cycle durability test, which is only 60% of that of Pt/C. The catalyst is also tested in Zn-air batteries and the assemblies are able to work at above 1.2 V for 140 h, which triples the life held by those with Pt/C. This study demonstrates a facile strategy to prepare metal-free ORR catalysts with interconnectivity and hierarchical porosity, and proves their great potentials in ORR catalysis and Zn-air batteries.

Recent Advances in Materials and Design of Electrochemically Rechargeable Zinc–Air Batteries

“…[205] The same research group further used an inorganic salt (NaCl) to create web-like structures in carbon materials, leading to increased surface area and improved mass transfer. [211] Li et al coated a covalent organic framework comprised of hexachlorocyclotriphosphazene and dicyanamide on CNTs, which yielded an N, P-codoped nanohybrid. [206] Luo et al used potassium phytate as a carbonaceous precursor to synthesize porous carbon materials codoped with N and P. It was proposed that the formation of K 4 P 2 O 7 help to self-terminate the carbon activation, resulting in a low material weight loss less than 17%.…”

Recent Advances in Metal‐Organic Framework Derivatives as Oxygen Catalysts for Zinc‐Air Batteries

“…While more investigations on their application in Zn–air batteries are still required, some pioneering works on this topic are valuable for guiding the further development. ZIF‐8 with Zn metal node is the most studied precursor for synthesizing metal‐free carbon materials, since the Zn intermediates produced are likely to evaporate during the high‐temperature calcination process, thus leaving highly porous carbon frameworks with rich N dopants and ultrahigh specific surface areas …”

“…This feature provides excellent ORR performance for primary Zn–air batteries. Molten salt‐assisted calcination has been shown to further optimize the morphology and porous structure ,,. For example, Xuan et al.…”

“…In this regard, hollow and core/shell structures,,,, 1D thin rods/bars,,,,,,,,,, 2D thin sheets,,,,,,, are shown to be favorable. In addition, highly interconnected 3D structures,,,, are also beneficial to improving the long‐range electronic conductivity of the cathode.…”

Fabrication of a Spherical Superstructure of Carbon Nanorods

“…[13][14][15] Low-dimensional carbon nanomaterials have been widely used in energy storage and conversion owing to their distinct electrochemical properties and mechanical and thermal stability. Although various synthetic approches have been developed for the synthesis of lowdimensional carbon nanostructures with well-defined size and controllable composition, [21][22][23] no techniques have been applied for controlling the assembly of 1D carbon nanomaterials into 3D spherical superstructure with uniform morphology.Metal-organic frameworks (MOF) are a class of porous crystalline materials that are constructed by metal ions/clusters and organic linkers. [19,20] However, the self-assemblies of 1D carbon nanomaterials into 3D ordered spherical superstructures are considerably challenging owing to the reduced accessible contact areas between the building blocks and core templates.…”