Covalent organic framework assisted low-content ultrafine Ru on porous N-doped carbon for efficient hydrogen evolution reaction

Abstract

Pt-based materials are the benchmarked catalysts in the cathodic hydrogen evolution reaction (HER) of water splitting; the prohibitive cost and scarcity of Pt immensely impede the commercialization of hydrogen energy. Ru has aroused significant concern because of its Pt-like activity and much lower price. However, it’s still a top priority to minimize the Ru loading and pursue the most superior cost performance. Herein, N-rich covalent organic framework (COF) was employed to assist the preparation of ultrafine Ru, including nanoclusters and single atoms loaded onto porous N-doped carbon by a simple impregnation-pyrolysis process with a low Ru content of 6.60 wt%, exhibiting superior HER activity with mass activity of 21.86 and 11.52 A·mg⁻¹_Ru (@100 mV) in alkaline and acidic conditions, separately 14.7 and 2.12 times higher than that of commercial Pt/C. Both alkaline and acidic HERs proceed via the Volmer–Tafel route with the Tafel step as the rate-determining step (RDS), and the alkaline HER contains the water dissociation on Ru single atoms and H desorption on Ru nanoclusters accompanied by H transfer between the two. The simple synthesis, low-content Ru and exceptional activity render our catalyst greatly promising as an alternative to commercial Pt/C in the advancement of hydrogen economy.