Flux Synthesis of Lattice-Engineered Rutile Solid Solutions for Acidic Oxygen Evolution

Developing efficient and stable electrocatalysts for the acidic oxygen evolution reaction (OER) is vital for advancing proton exchange membrane water electrolysis (PEMWE) technologies. Here, we report a flux synthesis of nitrogen-doped Ti-Ru rutile-type solid-solution oxides (M-TiRu4) using molten NaNO₃ as the flux medium. The flux medium promotes the low-temperature conversion of TiN to rutile TiO₂, while in situ-formed RuO₂ nanoparticles facilitate lattice templating and couple with interfacial ion migration, enabling the formation of homogeneous solid solutions with abundant lattice heterogeneity. Simultaneously, nitrogen atoms are stably incorporated into the lattice of solid solutions, inducing bandgap narrowing, which enhances electronic conductivity. The developed M-TiRu4 catalyst exhibits exceptional acidic OER performance, delivering a low overpotential of 194 mV at 10 mA cm^-2, superior durability over 600 h, and a Ru mass activity 7.8 times that of commercial RuO₂. At the device level, M-TiRu4 enables PEMWE operation at 1.64 V @ 2 A cm^-2 and maintains stable performance at 500 mA cm^-2 for 200 h with a minimal degradation rate of 20 µV h^-1. This work demonstrates a robust approach for designing high-performance, durable acidic OER catalysts via synergistic lattice and electronic structure engineering, paving the way for next-generation water-splitting technologies.