Structurally and Magnetically Frustrated Co–Ru Double Perovskite for Bifunctional Electrocatalysis

Abstract

Developing structural and magnetic frustration in complex oxides offers a powerful frontier for tuning surface electronic states, which eventually drives the frustrated lattice to exhibit an efficient electrocatalytic effect. In this work, we report the synthesis of a structurally and magnetically frustrated Co–Ru-based double perovskite oxide (CCR) and demonstrate its performance as a bifunctional electrocatalyst for alkaline water splitting. Rietveld refinements of synchrotron X-ray and neutron diffraction data reveal a multiphase coexistence predominantly featuring the Ca2CoRuO6 (Pnma) phase and a metastable rhombohedral Ca3CoRuO6 (R3̅c) intermediate phase. The observed Curie–Weiss temperature θp = −239 K indicates antiferromagnetic interactions with frustration parameter f = |θp|/TN ≈ 7.96, showing a magnetically frustrated ground state. XPS analysis suggests that this magnetic frustration might be induced by mixed-valent Co3+/Co4+ and Ru4+/Ru5+ redox couples. Consequently, CCR shows bifunctional performance in alkaline media, achieving low overpotentials of 248 mV for the hydrogen evolution reaction (HER) and 384 mV for the oxygen evolution reaction (OER) at a current density of 10 mA cm–2, alongside operational stability of 100 h. In-situ Raman and ex-situ XPS studies establish the OER mechanism, evidencing the adsorbate evolution mechanism (AEM), preferably along with the partially lattice oxygen mechanism (LOM). Structure–property relationships are validated through DFT studies and formulate the suitable pathway for electrocatalytic activity in a frustrated magnetic system. These findings establish that a coupled redox system with competitive structural phase with induced magnetic frustration is a viable materials design strategy to unlock active sites in polycrystalline double perovskite for sustainable energy applications.