RESUMEN
Interface engineering is a promising strategy to enhance the catalytic performance of electrocatalysts for the oxygen reduction reaction (ORR). However, it is still a challenge to modulate the size into a suitable range (e.g., nanocluster-scale) to make the most of the interface. Moreover, the explicit mechanism of the interface for enhancing catalytic performance is still elusive. Herein, a model catalyst (FeCu@NC) loaded with nanocluster-scaled Fe2O3/Cu interfaces was prepared by modulating the metal components of the precursor to explore the enhancement of interface engineering for the ORR. Benefiting from the synergistic effect of the strong interfacial coupling effects of Fe2O3/Cu and optimized microstructure, FeCu@NC exhibited superior ORR activity and zinc-air battery performance. Experimental and theoretical calculations revealed that the presence of the Fe2O3/Cu interface breaks the traditional cognition to endow the Cu atoms (intrinsically inferior for the ORR) with a slight positive charge, which serves as the active sites for the ORR. This study provides a novel insight into the design of advanced electrocatalysts for the ORR by interface engineering.
RESUMEN
Metal-organic frameworks (MOFs) have been widely used as precursors to derive carbon-based electrocatalysts for the oxygen reduction reaction (ORR) due to their high porosity and tunable chemical composition/structure. However, the influence of MOF type on the structure and further ORR activity of derived metal-free carbon catalysts is still elusive. In the present work, a series of different Zn-based MOFs were employed as precursors to explore this issue. Meanwhile, prepare N-doped metal-free carbon catalysts were prepared for the ORR under the activation of sacrificial urea (which is effective to enhance the ORR activity of carbon-based catalysts). By analyzing the intermediates during pyrolysis, it is found that the decisive role of MOF types on the doped N and the morphology of derived carbon catalysts was played by the Zn coordination environment of MOFs and its reactivity with the decomposition intermediate of urea. Although the structure and porosity of derived carbon catalysts from different MOFs are very different, they all showed superior ORR activity and Zn-air battery performance up to 20 wt% Pt/C benchmark catalysts. From the above analyses, the combination of urea and compounded Zn is also a promising activation method for the preparation of highly-efficient metal-free carbon electrocatalysts.
RESUMEN
Zinc-air batteries (ZAB), especially those assembled on flexible substrates, have attracted great research attention in electronics and wearable electronics. However, the air-cathode reaction-oxygen reduction reaction (ORR) has limited the development of ZAB technology. In this study, a hollow carbon catalyst, NOC-1000-1, was prepared by pyrolysis of a mixture of a N-enriched Zn/bispyrozolate-based metal-organic framework and urea to replace the labile Pt-based catalysts for ORR. The employment of sacrifical urea eliminated the requirement for complicated post-treatment compared to the template method. Combined with self-activation (Zn evaporation), the obtained carbon showed a micro- and mesopore-dominant hierarchical structure coexisting with some macropores. Moreover, the doped N and O species were also tailored in a preferable configuration for ORR by simply screening the pyrolysis conditions. Under the synergistic effect of the preferable N and O configurations and pore structure, the derived carbon catalyst displayed superior ORR activity of 0.977 V onset potential and 0.867 V half-wave potential; these values are slightly better than those of the 20% Pt/C benchmark catalyst (0.985 and 0.861 V, respectively). Flexible solid-state ZABs were further assembled by employing the derived carbon catalyst as an air-cathode, and they exhibited a higher peak power density of 100.92 mW cm-2 than a 20% Pt/C-RuO2 battery as well as previously reported similar batteries and very high stability for up to 30 h. The flexible solid-state ZABs could drive a red light-emitting diode and run a 130-type motor for hours, which indicates their promising applications in real-world technologies.
