A Bifunctional RuO x Film‐Coated Electrode for Efficient Water Splitting as Prepared by a Mixed Metal‐Imidazole Casting (MiMIC) Method

Development of highly active and durable bifunctional electrodes working for both oxygen and hydrogen evolving reactions (OER and HER) is productive for improving the performance and scalability of a water‐splitting electrolyzer. Toward such bifunctional electrodes, a rigidly‐adhered RuO x (RuO x ( w )) film was formed on a fluorine‐doped tin oxide conducting glass (FTO) or glassy carbon (GC) substrate by a facile and scalable technique of a mixed metal‐imidazole casting (MiMIC) method with 1‐methylimidazole (MeIm). The RuO x ( w ) film demonstrated superior OER and HER performances in a 1.0 M KOH solution compared with the RuO x ( w/o ) film prepared without MeIm due to the uniformly dense RuO x ( w ) film composed of well‐interconnected RuO x nanoparticles. The mass activities ( j m ) of the RuO x ( w ) / GC electrode for OER and HER were 309.6 and 1027.2 mA cm −2 mg Ru −1 at overpotential ( η ) of 400 and 100 mV, respectively, both of which are the highest or favorably comparable among the RuO x ‐based catalysts as the state‐of‐the‐art OER anodes and HER cathodes. The high OER and HER performances of the RuO x ( w ) film are attributed to the high‐rate constants of OER and HER at the surface, although charge transport in the RuO x ( w ) film is not appreciably different from that in the RuO x ( w/o ) film.