Understanding the strain effect in alkaline hydrogen oxidation reaction over well-defined Ru surfaces: insights into catalyst design

Surface strain has general impacts on the electronic structure and catalytic properties of catalyst surfaces. However, accurately deciphering the strain effect in many catalytic processes, such as the alkaline hydrogen oxidation reaction (HOR), remains a long-standing challenge due to the difficulty in isolating the strain and ligand effects in most catalytic systems. Here the Ru(111) surfaces are designed and constructed via epitaxially growing five atomic layers of Ru onto Pd octahedra and Pd icosahedra, respectively, providing the model surfaces to explore the strain effect. Atomic-level structural characterization studies reveal that the average surface strain on a Pd icosahedron is 2.5%, while the Ru surface on Pd octahedron is almost unstrained. We demonstrate that the strained Ru surface exhibits a 2.8-fold enhancement in mass activity at 50 mV for the HOR compared to the unstrained Ru surface. Combining in situ vibrational spectroscopy studies and theoretical calculations, we find that the tensile strain upshifts the d-band center of the Ru surface, thereby strengthening OH* adsorption and promoting HOR activity. This work provides general guidance for the design of remarkable electrocatalysts.