Interfacial Engineering of RuO_x on Rutile TiO₂ Supports to Boost the Acidic Oxygen Evolution Reaction

As global concerns about crises such as climate change and fossil fuel depletion increase, the importance of hydrogen energy is being further emphasized. In particular, there is growing interest in the commercial feasibility of using polymer electrolyte membrane water electrolysis (PEMWE) for large-scale production of green hydrogen. However, there are significant obstacles to overcome, mainly related to the slow kinetics of the acidic oxygen evolution reaction (OER) that occurs at the anode. Ruthenium (Ru)-based materials (e.g. RuO₂), which are much more abundant and have relatively high OER activity, are very attractive alternatives to rare iridium (Ir)-based materials such as IrO₂, the most commercialized acidic OER catalyst. Nonetheless, Ru has a critical drawback in that it is easily over-oxidized and dissolved as a soluble species (Ru^&gt;4) under acidic OER operating conditions. Therefore, additional research is required to find solutions to this issue. In this study, we tried to develop a highly efficient and durable Ru-based acidic OER electrocatalyst, employing interfacial engineering. Ruthenium oxide (RuO_x) nanoparticles were coated on the surface of one-dimensional (1D) rutile TiO₂ nanofibers using a facile hydrothermal method. Introducing rutile TiO₂ as a support is advantageous in enhancing the OER stability and promoting an interfacial affinity with the catalyst due to its excellent corrosion resistance and the common crystal structure sharing with RuO_x. Notably, the size, morphology, and crystallinity of Ru species crystal grains on the TiO₂ surface changed depending on the pH conditions during the reaction process. When RuO₂ was grown in the form of a large nanosheet with high crystallinity through alkaline pretreatment (RT-NSs), it was less affected by strain effect and showed OER performance with no significant difference from general RuO₂. On the other hand, in the case of a sample composed of a small nanoparticle film on a TiO₂ support synthesized in an acidic solution (RT-NPs), the interfacial synergy with TiO₂ was maximized, showing excellent OER activity. Finally, we achieved enhanced acidic OER performance by improving stability through a low-temperature post-annealing process.<br/> <br/><b>Acknowledgement:</b><br/>This work is supported by the National Research Foundation of Korea (NRF) Grant funded by the Ministry of Science and ICT [NRF-2020R1A6A1A03045059].