Robust crystalline aromatic imide-linked two-dimensional covalent organic frameworks confining ruthenium nanoparticles as efficient hydrogen evolution electrocatalyst

Abstract

The hydrogen evolution reaction (HER) is the crucial step in electrochemical water splitting. To succeed in real applications, one of the major challenges faced by HER is the development of robust and efficiency electrocatalysts. Herein, robust highly crystalline aromatic imide-based two-dimensional covalent organic frameworks (COFs) were prepared through a high temperature solvothermal process, taking advantage of the uniform pore size and specialized pore environment, efficient HER catalyst Cryst-2D-PMPI-Ru were synthesized in which ruthenium (Ru) nanoclusters are uniform dispersed with small particle size (less than 2 nm). In alkaline media, Cryst-2D-PMPI-Ru requires overpotential of only 35.1 mV to afford a current density of 10 mA/cm2, which outperforms the benchmark 20% Pt/C catalyst (37.3 mV). The excellent performance of was presumably attributed to the uniform and ultrasmall Ru nanoclusters with a satisfied dispersion, which provides the massive active sites for HER. In acid solution, the overpotential of Cryst-2D-PMPI-Ru (55.3 mV) is close to Pt/C (40.3 mV). The Tafel slope of PMDA/MA-Ru-180-800 is 36.5 mV/dec and the mechanism of the reaction is of the Volmer-Heyrovsky type. Besides, compared with their counterpart with low degree of crystllinity, the Cryst-2D-PMPI-Ru electrocatalyst also exhibits superior performance stability due to the stability of COF. The results provide important evidence that high crystallinity and robust aromatic structure of the polymeric frameworks precursors can substantially enhance their electrocatalytic performance and stability.