RESUMO
Rational design of highly efficient catalyst for ORR is critical for development of advanced air cathode in Zn-air cells and fuel cells. To optimize the ORR performance of Co based cathode, the structure of carbon nanotube from DCI-Co precursor could be controlled through modulate synthetic parameters. The optimized ORR catalyst Co@NCNT-700 exhibit larger BET area, higher content of Co-N x and graphitic N, which performance could be improved in further through Cu doping. The experiment data approved that the activity of Co-N x was enhanced by the synergistic effect with introduced Cu. Furthermore, the high-performance zinc-air batteries was fabricated with the bimetal catalyst CuCo@NCNT-700 as an air electrode. The high open-cycle potential (1.54 V) and peak power density (0.275 W.cm-2 at 0.474 A.cm-2) were achieved, which would be potentially used to develop next generation energy conversion devices.
RESUMO
A covalent organic framework that is composed of hexachlorocyclotriphosphazene and dicyanamide has been coated on CNT to prepare metal-free oxygen reduction reaction catalyst through thermal polymerization of the Zn-air battery cathode. The N,P-codoped nanohybrids have highly porous structure and active synergistic effect between graphitic-N and -P, which promoted the electrocatalytic performance. The electrocatalysts exhibits remarkable half-wave potential (-0.162 V), high current density (6.1 mA/cm-2), good stability (83%), and excellent methanol tolerance for ORR in alkaline solution. Furthermore, the N,P-codoped nanohybrids were used as an air electrode for fabrication of a high performance Zn-air battery. The battery achieves a high open-circuit potential (1.53 V) and peak power density (0.255 W cm-2). Moreover, the effect of N,P codoping on the conjugate carbon system and the synergistic effect between graphitic-N and P have been calculated through density functional theory calculations, which are essentially in agreement with experimental data.
RESUMO
Developing highly efficient and stable non-Pt electrocatalysts for the oxygen reduction reaction (ORR) to replace the state-of-the-art noble metal is essential for commercialization of fuel cells. Fe-N-C-based electrocatalysts are considered as a promising alternative to commercial Pt/C. An efficient electrocatalyst commonly requires large density of active site, high surface area, and desirable porosity, especially multimodal porosity with both large pores for efficient mass transfer and small pores for exposing as many active sites as possible. Herein, a lamellar metal organic framework (MOF) was developed as a precursor to directly achieve such a highly active Fe-N-C electrocatalyst with high surface area and desirable bimodal porosity. The mesopores arising from the special lamellar morphology of MOF benefits efficient mass transfer, and the nanopores resulting from pyrolysis of the MOF makes the majority of active sites accessible to electrolyte and thus effective for ORR. Uniform distribution of active elements N, C, and Fe at the molecular level in MOF precursor ensures abundant well-dispersed highly active sites in the catalyst. As a result, the catalyst exhibited superior ORR electrocatalytic activity and stability to commercial Pt/C. This strategy, using rarely reported lamellar MOF to prepare ORR catalysts with the merits mentioned, could inspire the exploration of a wide range of electrocatalysts from lamellar MOF precursors for various applications.
