Unraveling Thermodynamics, Stability, and Oxygen Evolution Activity of Strontium Ruthenium Perovskite Oxide

Extensive investigations in understanding the functional mechanisms of metal oxides behind oxygen evolution have been carried out since an electrolyzer has demonstrated promising possibilities as a device to produce hydrogen for electrochemical energy conversion systems. In particular, perovskite oxides are reputable for high activity toward the oxygen evolution reaction (OER). Here, we revisited the list of active perovskite oxides constructed based on theoretical oxygen binding energies of reaction intermediates to the catalyst surface. From this list, Ru-based perovskites, i.e. SrRuO3 and LaRuO3, have been predicted as active perovskites to exhibit a particularly high OER activity. We report on the stability of nanoscaled SrRuO3 perovskite prepared by a simple and scalable flame synthesis method. Attempts to obtain LaRuO3 were made; however, its DFT calculated phase diagram suggests that its perovskite phase is not thermodynamically stable, which supports our experimental results such that only a mixture of different La Ru O phases has been obtained. Nanoscaled SrRuO3 is evaluated for its electrochemical activity with a particular emphasis pointed toward stability in both alkaline and acidic media. Through conjoining electrochemical methods, operando X-ray absorption spectroscopy (XAS), and theoretical calculations, we show that SrRuO3 exhibits trivial activity toward OER that decreases promptly. The loss in activity is rationalized through DFT based computations, which corroboratively suggest the poor chemical stability of both selected perovskites. Regardless of the predicted theoretical OER activity, the intrinsic instability strongly suggests that Sr- and La-based ruthenium oxides are not viable catalysts for OER in aqueous media. This further suggests that their activities are independent of their binding energies between intermediates and catalyst surface but rather closely associated with material dissolution. We highlight that understanding the origin of stability under a real operating environment is absolutely essential for the design of a sustainable electrocatalyst with optimal balance between activity and stability.