Constructing double-shell structured N-C-in-Co/N-C electrocatalysts with nanorod- and rhombic dodecahedron-shaped hollow morphologies to boost electrocatalytic activity for hydrogen evolution and triiodide reduction reaction

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 re-action (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.