An iridium-free and low-ruthenium-content oxide (Cr_0.6Ru_0.4O₂) derived from a metal-organic framework was prepared recently by Prof. CHEN Liang’s research group at the Institute of New Energy Technology, Ningbo Institute of Materials Technology and Engineering of Chinese Academy of Sciences.

This substance is quite active and low-cost, featuring excellent oxygen evolution reaction performance in acidic conditions with a record low overpotential of 178 mV at 10 mA cm^-2. This study was published in Nature Communications.

Renewable energy sources will be of great significance in the near future. However, they are usually intermittent. It is necessary to explore the technology for converting the surplus power obtained from renewable energy sources to storable energy carriers such as hydrogen.

Members of Prof. CHEN's group have committed themselves to developing efficient electrocatalysts for the oxygen evolution reaction (OER). Recently Dr. LIN Yichao from this group prepared a new CrO₂-RuO₂ solid solution by using a Cr-based metal-organic framework (MOF) and determined the structure of the solid solution via PXRD characterizations and refinement.

Through the atomic-solution high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), scientists observed that in this structure, Cr and Ru atoms are evenly distributed in the same nano-monocrystal.

They found that the solid solution exhibited an overpotential of merely 178 mV at the current density of 10 mA cm^-2, and the overpotential only increased by 11 mV after 10,000 times of circulation, much more superior to the commercial RuO₂.

"Such excellent performance is due to the shortening of Ru-O bond length and the valence of Ru atoms, which is slightly higher than +4, in the crystal structure caused by the strong electron withdrawing of Cr with a valence of +4," said Dr. LIN.

The reason for the superb performance was also verified theoretically. Through density functional theory (DFT) calculations, scientists found that the catalytic activity of Ru is increased because of the electron withdrawing of Cr with a valence of +4 in the lattice, thus reducing the reaction energy barrier.

Ru accounts for only 40% of the solid solution and the cost of this electrocatalyst was significantly reduced, making it ideal for commercialization and industrial application.