Enhancing the activity and stability of RuO₂-based catalyst via nano-confinement effect for O₂ evolution reaction in acid electrolyte

The oxygen evolution reaction (OER), as a pivotal process in electrochemical water splitting, directly determines energy conversion efficiency. Ruthenium (Ru)-based catalysts have gained considerable attention in recent years due to their decent intrinsic activity in acidic media. Previous studies have demonstrated that while Ru exhibits superior OER activity compared to RuO₂ in acidic environments, its operational stability remains markedly inferior. This performance dichotomy, coupled with the persistent challenges of active species dissolution and catalyst particle aggregation during prolonged operation, significantly hinders their practical implementation in electrochemical systems. To address these challenges, this study develops a CNT/Fe-Ni@RuO₂@PANI-350 composite catalyst composed of RuO₂ nanoparticles supported on bimetallic Fe-Ni modified carbon nanotubes (CNT/Fe-Ni) and encapsulated with polyaniline (PANI). This catalyst utilizes the anchoring effect of bimetallic Fe-Ni sites and the spatial confinement effect of PANI coating layer, effectively inhibiting the dissolution and agglomeration of RuO₂ during both high-temperature processing and electrochemical operation, thereby significantly enhancing electrochemical stability. The anchoring strength of RuO₂ nanoparticles on CNT/Fe-Ni support via the nano-confinement effect, as well as the microscopic mechanisms underlying the performance enhancement, are revealed by density functional theory (DFT) calculations and experimental characterizations. The composite catalyst demonstrates fascinating OER performance in 0.5 M H₂SO₄, exhibiting a low Tafel slope of 39.1 mV dec^-1 as well as low overpotentials of 188 mV and 225 mV at current densities of 10 mA cm^-2 and 100 mA cm^-2, respectively. Remarkably, the composite catalyst demonstrates significantly enhanced stability, exhibiting only ~30 mV overpotential increase during 150 h continuous operation at 10 mA cm^-2. This study highlights a simple yet effective nano-confinement strategy to address the challenges of Ru-based catalysts, and provides a practical paradigm for designing and preparing highly efficient OER electrocatalysts with enhanced stability.