Jing Liu ^a, Jie Wang ^a, Yumeng Fo ^b, Boyang Zhang ^a, Costas Molochas ^d, Jie Gao ^a,

Wenzhen Li ^c, Xuejing Cui ^a, Xin Zhou*^b, Luhua Jiang*^a, Panagiotis Tsiakaras^*d

^a College of Materials Science and Engineering, Qingdao University of Science and Technology,

Qingdao, Shandong 266042, China.

^b College of Environment and Chemical Engineering, Dalian University, Dalian, 116622, China.

^c Department of Chemical & Biological Engineering, Iowa State University, Ames, IA 50011-1098, United States.

^d Laboratory of Alternative Energy Conversion Systems, Department of Mechanical Engineering,

School of Engineering, University of Thessaly, Pedion Areos 38834, Greece.

ABSTRACT: Herein, unique Ni-Ru nano-twins (Ni₁Ru₁/C) are reported for the first time as a superior bifunctional catalyst for hydrogen oxidation/hydrogen evolution reaction (HOR/HER). Compared to Pt/C, the Ni₁Ru₁/C nano-twins display a remarkable HOR activity with a comparable mass activity of 0.12Amg^-1_metal and superior HER activity, with an overpotential (դ) of only 16mV for achieving a cathodic HER current of 10mAcm^-2, together with a high turnover-frequency of 1.88s^-1 (@դ=30mV). Additionally, the HOR limiting current of the Ni₁Ru₁/C nano-twins can be maintained up to a break-down potential of 0.25V_RHE, demonstrating excellent electrochemical stability. Experimental and theoretical studies reveal that the electron re-distribution at the Ni/Ru interface of Ni-Ru nano-twins optimizes the binding energy of the adsorbed hydrogen (H_ad) and the adsorbed hydroxyl (OH_ad) intermediates, allowing the HOR/HER to proceed via a low energy barrier. This work provides a strategy to synthesize hetero-metal nano-twins as promising multi-functional catalysts and highlights the critical role of interfaces for heterostructured electrocatalysts.

Keywords: Ni-Ru nano-twins; hydrogen oxidation reaction; hydrogen evolution reaction; bifunctional catalyst; interface engineering.

*Corresponding authors: luhuajiang@qust.edu.cn (L. Jiang); zhouxin@dlu.edu.cn (X. Zhou); tsiak@uth.gr (P. Tsiakaras).

DOI：10.1016/j.cej.2022.139959