A Facile Reaction Strategy for the Synthesis of MOF-Based Pine-Needle-Like Nanocluster Hierarchical Structure for Efficient Overall Water Splitting.

Abstract

Solvothermal reactions of Co(NO3)2·6H2O, 3-amino-1,2,4-triazole, and 1,2,4,5-benzenetetracarboxylic acid afforded a Co-MOF: {[Co2(Hatz)(bta)]·H2O}n. Furthermore, a unique metal-organic-framework-based pine-needle-like nanocluster hierarchical architecture has been rationally designed and prepared on a nickel foam skeleton via a simple solvothermal method based on the Co(OH)F intermediate and directly adopted as an optimum bifunctional electrocatalyst for overall water splitting. The Co-MOF/NF exhibited enhanced catalytic performance for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). The optimized catalyst reveals the highest electrocatalytic characteristics, affording current densities of 50 mA cm-2 at an overpotential of 266 mV for the OER and 10 mA cm-2 at an overpotential of 115 mV forthe HER in 1 M KOH. Meanwhile, the catalyst exhibits an ultrastability in the OER process and long-term test at 20 mA cm-2 for 100 h led to only a 9.4% increase in overpotential. Furthermore, an electrolytic cell assembled from the bifunctional Co-MOF/NF delivers a current density of 10 mA cm-2 at a cell voltage of 1.548 V. This excellent performance is believed to be the result of the exotic pine-needle-like nanocluster structure with effective accessibility of dense catalytically active sites, as well as the high specific surface area and the promotion of reversible chemisorption for oxygen species due to the linkers interacting with Co ions. Further SEM, TEM, and XPS analyses of the catalyst after OER stability tests reveal that the formation of Co3O4 on the surface and unconsolidated architecture withinthe electrode materials are responsible for the high catalytic activity. This work extends the applications of MOFs in the field of electrocatalysis.