Rationalizing Synergic Role of Ti─O─Ru Distortion and Ferromagnetic Superexchange Coupling for Envisaging Electrocatalytic Oxygen Evolution Activity in Double Perovskite

A clear understanding of the activity descriptors governing the oxygen evolution reaction (OER) mechanism in 3d-4d transition metal-based complex oxide system is essential for the rational design of advanced OER electrocatalysts toward green energy and sustainability. To address this uncover goal, herein, we have synthesized a new double perovskite (DP) oxide i.e., Ca₂TiRuO₆ (CTRO) which can offer the choice of specific active metal sites to perform and enhance the electrocatalytic OER activity in the variable pH conditions. When this low-Ru-content CTRO DP oxide is employed as an active electrocatalyst for the OER, it exhibits an overpotential of 273 mV, which further decreased to 245 mV upon incorporation with a small amount of conducting Vulcan carbon (15 wt.%) at pH 13.8, maintaining excellent durability over 100 h with a remarkable Faradic efficency of 92.4%. The formation of high-valent Ru-oxo-hydroxy species, which facilitate the OER through the adsorbate evolution mechanism (AEM), is corroborated by in situ Raman spectroscopic and ex situ ATR-FTIR studies for the title catalyst. Notably, the higher octahedral distortion of Ti─O─Ru linkage and subtle role of Ru-sites over the Ti-sites arising from the ferromagnetic superexchange coupling of Ru (IV)-ions in the present disordered DP structure contribute to the superior OER activity over other state-of-the-art oxide electrocatalysts. Moreover, in-depth DFT studies was performed to elucidate ferromagnetic superexchange interactions and to explore the active OER sites along with the energetically favorable H₂O adsorption mechanism across various surface terminations in the CTRO catalyst.