Deep-Breathing Honeycomb-like Co-Nx-C Nanopolyhedron Bifunctional Oxygen Electrocatalysts for Rechargeable Zn-Air Batteries

Abstract

Summary Metal organic framework (MOF) derivatives have been extensively used as bifunctional oxygen electrocatalysts. However, the utilization of active sites is still not satisfactory owing to the sluggish mass transport within their narrow pore channels. Herein, interconnected macroporous channels were constructed inside MOFs-derived Co-N x -C electrocatalyst to unblock the mass transfer barrier. The as-synthesized electrocatalyst exhibits a honeycomb-like morphology with highly exposed Co-N x -C active sites on carbon frame. Owing to the interconnected ordered macropores throughout the electrocatalyst, these active sites can smoothly “exhale/inhale” reactants and products, enhancing the accessibility of active sites and the reaction kinetics. As a result, the honeycomb-like Co-N x -C displayed a potential difference of 0.773 V between the oxygen evolution reaction potential at 10 mA cm −2 and the oxygen reduction reaction half-wave potential, much lower than that of bulk-Co-N x -C (0.842 V). The rational modification on porosity makes such honeycomb-like MOF derivative an excellent bifunctional oxygen electrocatalyst in rechargeable Zn-air batteries.

Metal–Organic Framework-Derived Nitrogen-Doped Cobalt Nanocluster Inlaid Porous Carbon as High-Efficiency Catalyst for Advanced Potassium–Sulfur Batteries

“…X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) measurements were carried out to identify the chemical state and coordination environment of Co atoms in the N–Co l –C sample . As shown in the Co K-edge XANES spectra of N–Co l –C and the referenced Co foil and CoO (Figure a), the position of the absorption edge for N–Co l –C is located in the middle of the referenced Co foil and CoO, suggesting that the valence state of Co is situated between Co 0 and Co 2+ . , The Fourier transformed k 3 -weighted EXAFS profile for N–Co l –C is shown in Figure b ( R space).…”

Air Electrodes for Flexible and Rechargeable Zn−Air Batteries

“…[ 179 ] Silica or polystyrene templates were adopted to achieve structure controlling and obtain pertinent porosity during pyrolysis. [ 180 ] The surface area and total pore volume were improved with a remarkable macropore distribution, as reported by several studies. [ 152,181 ] However, the balance between porous structures and high graphitization is a challenging problem that has to be solved to improve the performance of bifunctional catalysts.…”

Hollow Spherical Superstructure of Carbon Nanosheets for Bifunctional Oxygen Reduction and Evolution Electrocatalysis

“…Therefore, the nanosheet-assembled superstructure of FeCoNi/HCS is crucial for providing mesopores. In the electrocatalytic process, a mesoporous structure can facilitate the diffusion of gas and electrolyte, create more triphase reaction regions, and also make the active material well exposed to the reactants. , …”