Co3O4@carbon with high Co2+/Co3+ ratios derived from ZIF-67 supported on N-doped carbon nanospheres as stable bifunctional oxygen catalysts. (September 2021)

• Record Type: Journal Article
• Authors: Li, Y.; Li, J.; Dai, Y.; Li, X.; Shao, C.; Sun, Y.; Wang, R.; Zou, J.
• Is Part Of: Materials today energy. Volume 21(2021)
• Publication Date: 2021-09
• Subjects: Bifunctional oxygen electrocatalyst -- Methanol resistance -- Corrosion inhibition -- Structure-activity relationship -- Zeolitic-imidazolate-framework-67; Energy development -- Periodicals; Energy industries -- Periodicals; Power resources -- Periodicals; Energy policy -- Periodicals; Energy development; Energy industries; Energy policy; Power resources; Electronic journals; Periodicals; 621.042
• DOI: 10.1016/j.mtener.2021.100737
• Languages: English
• ISSNs: 2468-6069

Abstract

Abstract: Zeolite imidazole framework-67 (ZIF-67) derivatives are increasingly used for oxygen reduction and evolution reactions (ORR/OER). Many fundamental issues concerning their structure-bifunctional activity relationships still remain unknown. Here, we use nitrogen-doped carbon nanospheres (NCS) to support ZIF-67-derived Co3 O4 @carbon to obtain Co3 O4 @Z67/NCS catalysts with the assistance of polyvinylpyrrolidone. Carbonization temperatures have great effects on the structure and active-component changes of Co3 O4 @Z67/NCS. Co3 O4 @Z67/NCS-850 (850 °C) with the Co 2+ /Co 3+ ratio of 1.58 shows the promising bifunctional (ORR/OER) activity (ΔE = Ej=10 (1.55 V)-E1/2 (0.812 V) = 0.738 V) and long-term stability via the 4e − process in alkaline electrolytes. Co3 O4 @Z67/NCS-850 exhibits a comparable half wave potential of 0.812 V with a better ORR durability (an activity decline of 16.3% after 30, 000 s) and methanol resistance, by comparing with commercial Pt/C (0.817 V and 29.1%). For OER, Co3 O4 @Z67/NCS-850 obtains a low overpotential of 0.32 V at 10 mA/cm 2 and a low charge transfer resistance of 9.69 Ω. The active-sites (Co 2+ (ORR) and Co 3+ -CoOOH (OER)) on Co3 O4 are well protected by carbon shell (Z67), which can hinder the fast deactivation (corrosion and agglomeration) of Co3 O4 during electrocatalysis. The high porosity (387.88 m 2 /g) of Z67/NCS-850 should facilitate the mass transfer through the pores to promote the in situ electrochemical O2 reduction/evolution on the Co and/or N active sites. These results not only find the relationships between structure/components and ORR/OER activities but also indicate a direction on promoting ZIF-derived catalysts. Graphical abstract: Image 1 Highlights: N-doped carbon nanospheres (NCS) are used to support ZIF-67-derived Co3 O4 @carbon. Co3 O4 @Z67/NCS (850 °C) obtains promising ORR/OER activity (ΔE = 0.738 V) and stability. Co 2+ (ORR) and Co 3+ (OER) on Co3 O4 are protected by carbon shell from fast corrosion. High porosity boosts the mass transfer to promote the in situ O2 reduction/evolution. Synergy between surface Co 2+ /CoOOH and oxygen vacancies enhances ORR/OER activity.