A unique sandwich-structured Ru-TiO/TiO2@NC as an efficient bi-functional catalyst for hydrogen oxidation and hydrogen evolution reactions
Jing Liu, Gao Jie, Wanqing Yu, Huanwei Ren, Xuejing Cui, Xin Chen, Luhua Jiang
Abstract
Developing active and stable non-Pt electrocatalysts for hydrogen oxidation (HOR) and evolution reactions (HER) are critical for anion exchange membrane fuel cells and water electrolyzers. Herein, we report a highly active and robust electrocatalyst Ru-TiO/TiO 2 @NC, in which Ru nanoclusters are sandwiched between TiO/TiO 2 nanosheets and nitrogen-doped carbon layers. Taking advantage of both the optimized Ru-TiO/TiO 2 interaction and the conductive carbon coating layers, the Ru-TiO/TiO 2 @NC exhibits both exceptional HOR/HER activity and superior stability, outperforming Pt/C in the alkaline solution. The HOR mass activity reaches up to 107.2 A g Ru -1 at an overpotential of 50 mV, and the specific exchange current density is 0.271 mA cm −2 . The HER overpotential at 10 mA cm −2 is only 39 mV, 34 mV lower than required by Pt/C. More importantly, the Ru-based catalyst exhibits excellent anti-oxidation ability by virtue of the unique sandwich structure. Density functional theory calculations discover that the d-band center of Ru in Ru-TiO/TiO 2 is downshifted by 0.29 eV compared to Ru-TiO 2 , decoupling and optimizing the H ad /OH ad adsorption on Ru, i.e., H ad is promoted, while OH ad is inhibited and transferred to TiO/TiO 2 . As a result, (i) the energy required by the potential determining step of HOR/HER is lowered, and (ii) the anti-oxidation ability of the Ru-TiO/TiO 2 is enhanced. This work not only addresses the issue of Ru passivation at high anode potentials but also provides an innovative and versatile approach to designing advanced electrocatalysts.