Metal-Organic Framework Supported Dual Functional Air Cathode Carbon Nanofiber as an Efficient Electrocatalyst for the Rechargeable Zinc-Air Batteries

Fabricating efficient bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) remains a major challenge in renewable energy technologies. To develop a high-performance bifunctional electrocatalyst, a strategy combining electrospinning, in-situ synthesis, and carbonization was employed to fabricate three-dimensional (3D) flexible porous carbon nanofiber electrocatalysts. A thermal treatment approach using in situ grown metal-organic frameworks (MOFs) is employed to synthesize highly porous, nitrogen-doped carbon nanotubes (N-CNTs) embedded with cobalt nanoparticles, along with hydroxy-functionalized boron nitride nanosheets (HO-BN) uniformly incorporated into electrospun carbon nanofibers (CNFs), forming a composite (N-CNT@MOF-Co/HO-BN/CNFs). Thus, the synthesized electrocatalyst reveals exceptional bifunctional catalytic performance for both the ORR and OER. This is indicated by a small potential gap of 0.70 V between the ORR half-wave potential and the OER potential at a current density of 10 mA cm-2, a value that is competitive with that of the mixed commercial noble catalyst made up of 30% Pt/C and IrO2. The rechargeable zinc-air battery is designed to exhibit a noteworthy open-circuit voltage of 1.448 V, impressive power density (142.9 mW cm-2), and energy density (700 Wh kg-1). This research introduces a methodology for the synthesis and construction of high-performance bifunctional electrocatalysts.

Achievements and Challenges in Surfactants-Assisted Synthesis of MOFs-Derived Transition Metal-Nitrogen-Carbon as a Highly Efficient Electrocatalyst for ORR, OER, and HER

Metal-organic frameworks (MOFs) are excellent precursors for preparing transition metal and nitrogen co-doped carbon catalysts, which have been widely utilized in the field of electrocatalysis since their initial development. However, the original MOFs derived catalysts have been greatly limited in their development and application due to their disadvantages such as metal atom aggregation, structural collapse, and narrow pore channels. Recently, surfactants-assisted MOFs derived catalysts have attracted much attention from researchers due to their advantages such as hierarchical porous structure, increased specific surface area, and many exposed active sites. This review mainly focuses on the synthesis methods of surfactants-assisted MOFs derived catalysts and comprehensively introduces the action of surfactants in MOFs derived materials and the structure-activity relationship between the catalysts and the oxygen reduction reaction, oxygen evolution reaction, and hydrogen evolution reaction performance. Apparently, the aims of this review not only introduce the status of surfactants-assisted MOFs derived catalysts in the field of electrocatalysis but also contribute to the rational design and synthesis of MOFs derived catalysts for fuel cells, metal-air cells, and electrolysis of water toward hydrogen production.

Metal-Organic Framework-Derived Atomically Dispersed Co-N-C Electrocatalyst for Efficient Oxygen Reduction Reaction

In this work, an atomically dispersed cobalt-nitrogen-carbon (Co-N-C) catalyst is prepared for the oxygen reduction reaction (ORR) by using a metal-organic framework (MOF) as a self-sacrifice template under high-temperature pyrolysis. Spherical aberration-corrected electron microscopy is employed to confirm the atomic dispersion of high-density Co atoms on the nitrogen-doped carbon scaffold. The X-ray photoelectron spectroscopy results verify the existence of Co-N-C active sites and their content changes with the Co content. The electrochemical results show that the electrocatalytic activity shows a volcano-shaped relationship, which increases with the Co content from 0 to 0.99 wt.% and then decreases when the presence of Co nanoparticles at 1.61 wt.%. The atomically dispersed Co-N-C catalyst with Co content of 0.99 wt.% shows an onset potential of 0.96 V vs. reversible hydrogen electrode (RHE) and a half-wave potential of 0.89 V vs. RHE toward ORR. The excellent ORR activity is attributed to the high density of the Co-N-C sites with high intrinsic activity and high specific surface area to expose more active sites.