Metallic Ru─Ru Interaction in Ruthenium Oxide Enabling Durable Proton Exchange Membrane Water Electrolysis.

Developing efficient and robust electrocatalysts toward the oxygen evolution reaction (OER) is critical for proton exchange membrane water electrolysis (PEMWE). RuO 2 possesses intrinsically high OER activity, but the concurrent electrochemical dissolution leads to rapid deactivation. Here a unique RuO 2 catalyst containing metallic Ru─Ru interactions (m-RuO 2 ) is reported, which maintains stability in practical PEMWE for 100 h at 60 °C and 1 A cm -2 . Experimental and theoretical investigations suggest that the presence of Ru─Ru interactions significantly increases the energy barrier for the formation of RuO 2 (OH) 2 , which is a key intermediate for Ru dissolution, and hence substantially mitigates the electrochemical corrosion of m-RuO 2 . Meanwhile, the Ru4d band center downshifts, accordingly, ensuring the high OER activity, and the participation of lattice oxygen in the OER is also suppressed at the Ru─Ru sites, further contributing to the enhanced durability. Interestingly, such enhanced stability is also dependent on the size of metallic Ru─Ru cluster, where the energy barrier is further increased for Ru 3 , but is decreased for Ru 5 . These results highlight the significance of local coordination structure modulation on the electrochemical stability of RuO 2 and open a feasible avenue toward the development of robust OER electrocatalysts for high-performance PEMWE.