The improvement of total nitrogen content and nitrogen-doping efficiency in carbon-based electrocatalysts is greatly significant to boost the electrocatalytic activity for the oxygen reduction reaction (ORR). Here, we report a new strategy for the synthesis of a highly mesoporous cobalt and nitrogen co-doped carbon electrocatalyst (3D-Co–N–C) with a three-dimensional network structure and a high BET surface area (∼638 m2 g−1) via using a novel cobalt-2,4,6-tri(2-pyridyl)-1,3,5-triazine complex with a strong molecular-level coordination effect as a single-source precursor and self-assembled sodium chloride aggregates as a space-confined nanoreactor for effective control of a high-temperature calcination process to reduce the thermal loss of nitrogen atoms and promote the nitrogen-doping efficiency, facilitating boosting of the ORR electrocatalytic activity in alkaline medium. The prepared 3D-Co–N–C catalyst exhibits unexpectedly excellent ORR activity with an onset potential of ∼1.0 V and a half-wave potential of ∼0.83 V, which is comparable to that of the commercial 20 wt% Pt/C catalyst. Additionally, the H2O2 yield (<17.0%) and the average electron transfer number of ∼3.8 for 3D-Co–N–C indicate a quasi four-electron pathway for ORR catalysis, suggesting that 3D-Co–N–C is a promising carbon-based electrocatalyst. It is proposed that the formation of the Co–Nx active structure can effectively enhance the electrocatalytic activity, but high contents of pyridinic- and graphitic-N can be mainly responsible for the ORR activity, which may be the electrocatalytically active site centers for the ORR. Besides, high BET surface area, highly mesoporous characteristics and outstanding electronic conductivity are also significant for the improvement of ORR activity. This study can provide a new, facile and green method for building high-performance carbon-based ORR electrocatalysts derived from easily available and innoxious transition metal–organic complexes, which can also help us to better understand the origin of the activity, active sites and their catalysis mechanism.
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.
危险品化学品经营许可证（带存储）