Competition between Lattice Oxygen and Adsorbate Evolving Mechanisms in Rutile Ru-Based Oxide for the Oxygen Evolution Reaction

The oxygen evolution reaction (OER) is the primary bottleneck for electrochemical splitting of water into H2. Developing robust and active OER electrocatalysts through understanding the OER mechanism is essential. However, the mechanism for OER is not yet well understood even for the most studied rutile Ru-based oxide, especially in a water-solvent environment. It is still disputed whether the adsorbate evolving mechanism (AEM) is competitive with the lattice oxygen mechanism (LOM). In this article, the AEM and LOM for OER in transition metal (TM)-doped rutile RuO2 with different ratios of TM and Ru are discussed through density functional theory + U calculation. In low TM doping concentration, the evolved O2 is generated through the AEM, and the OER activity is limited by the scaling relationship of OER intermediates. In higher TM doping concentration, the evolved O2 is generated through the LOM for Cu- or Ni-doped RuO2. We find that the distribution of Ru 4d and O 2p orbitals and the adsorption energy of H and O are the major factors that affect the conversion of AEM into LOM. By explicitly considering the water-solvent environment, the LOM can result in higher theoretical OER activity arising from the effects of hydrogen-bond networks.