Rechargeable Zn–air batteries (ZABs) have received extensive attention, while their real applications are highly restricted by the slow kinetics of the oxygen reduction and oxygen evolution reactions (ORR/OER). Herein, we report a “bridge” structured flexible self-supporting bifunctional oxygen electrode (CNT@Co-CNF F50-900 ) with strong active and stable Co-N/C@pyridine N/C@CNTs reaction centers. Benefiting from the electron distribution optimization and the advantages of hierarchical catalytic design, the CNT@Co-CNF F50-900 electrode had superior ORR/OER activity with a small potential gap (ΔE) of 0.74 V. Reinforced by highly graphitized carbon and the “π–π” bond, the free-standing CNT@Co-CNF F50-900 electrode exhibited outstanding catalytic stability with only 36 mV attenuation. Impressively, the CNT@Co-CNF F50-900 -based liquid ZAB showed a high power density of 371 mW cm −2 , a high energy density of 894 Wh kg −1 , and a long cycling life of over 130 h. The assembled quasi-solid-state ZAB also demonstrated a high power density, attaining 81 mW cm −2 , with excellent charge–discharge durability beyond 100 h and extremely high flexibility under the multi-angle application. This study provides an effective electrospinning solution for integrating high-efficiency electrocatalysts and electrodes for energy storage and conversion devices. Graphical Abstract
Jiaoe Dang,Sining Yun,Yongwei Zhang,Jingjing Yang,Zhuolei Liu,Changwei Dang,Yinhao Wang,Yingying Deng
With the increasing energy demands and impending climate change, significant concerns have been raised over the metal–organic frameworks (MOFs)-derived porous carbons and their utilization for hydrogen evolution reaction (HER) and triiodide reduction reaction (IRR). However, the provision of high intrinsic activity, active-site accessibility, and structural stability of MOF-derived Co-embedded N-doped carbon (Co/N-C) for HER and IRR is challenging. In this work, core-shell MOF-in-MOF precursors are designed to construct novel double-shell N-C-in-Co/N-C electrocatalysts with nanorod- and rhombic dodecahedron-shaped hollow morphologies (NR-H-C and RD-H-C). The double-shell structured NR-H-C and RD-H-C significantly enhance the HER and IRR activity of Co-MOF-derived Co/N-C. Specifically, NR-H-C achieves a high N-content (10.35 at.%), large specific surface area (590.87 m 2 g −1 ), and hierarchical porous configuration (micropores and mesopores). When NR-H-C is applied as the HER catalyst in alkaline electrolyte, it exhibits an admired overpotential of 123 mV at 10 mA cm −2 and a Tafel slope of 51 mV dec −1 . The solar cell adopting NR-H-C as counter electrode for IRR achieves a high short circuit current density of 16.77 mA cm −2 , an open-circuit voltage of 0.745 V, a fill factor of 0.682, and a power conversion efficiency of 8.51%, higher than that of Pt-based solar cell (16.26 mA cm −2 , 0.744 V, 0.602, and 7.28%). The elucidatory Volmer-Heyrovsky HER mechanism and reversed Volmer-Heyrovsky IRR mechanism give a better understanding of the enhanced dual-functional activity of NR-H-C. This work provides an essential information for the rational design of high-performance dual-functional HER and IRR catalysts and further open up a new avenue for the construction of multicomponent MOFs in the energy conversion field.
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