Bond engineering: weakening Ru–O covalency for efficient and stable water oxidation in acidic solutions

Abstract

The persistent stability of ruthenium dioxide (RuO₂) in acidic oxygen evolution reactions (OER) is compromised by the involvement of lattice oxygen (LO) and metal dissolution during the OER process. Heteroatom doping has been recognized as a viable strategy to foster the stability of RuO₂ for acidic OER applications. This study presented an ion that does not readily gain or lose electrons, Ba²⁺, into RuO₂ (Ba–RuO₂) nanosheet (NS) catalyst that increased the number of exposed active sites, achieving a current density of 10 mA/cm² with an overpotential of only 229 mV and sustaining this output for over 250 h. According to density functional theory (DFT) and X-ray absorption spectroscopy, Ba doping resulted in a longer Ru–O bond length, which in turn diminished the covalency of the bond. This alteration curtailed the involvement of LO and the dissolution of ruthenium (Ru), thereby markedly improving the durability of the catalyst over extended periods. Additionally, attenuated total reflectance-surface enhanced infrared absorption spectroscopy analysis substantiated that the OER mechanism shifted from a LO-mediated pathway to an adsorbate evolution pathway due to Ba doping, thereby circumventing Ru over-oxidation and further enhancing the stability of RuO₂. Furthermore, DFT findings uncovered that Ba doping optimizes the adsorption energy of intermediates, thus enhancing the OER activity in acidic environments. This study offers a potent strategy to guide future developments on Ru-based oxide catalysts’ stability in an acidic environment.