(126b) Exploring Stability and Activity Trends in Transition Metal Doped Strontium Iridate for the Oxygen Evolution Reaction in Acid

The world’s energy and material demands are rapidly growing; developing carbon-free pathways to produce globally important fuels and chemicals is necessary to reduce our ecologically harmful carbon dioxide emissions. Electrochemical water splitting, when coupled with renewably produced electricity, is a carbon-free process for globally critical hydrogen gas production. The oxygen evolution reaction (OER) plays a crucial role in water electrolysis by supplying necessary protons and electrons to drive the complementary reductive hydrogen evolution reaction but suffers from inherently sluggish kinetics. This work aims to improve the activity, stability, and affordability of iridium-based electrocatalysts for the OER in acidic conditions. By doping strontium iridate (SrIr_1-xM_xO₃) with various inexpensive, non-precious transition metals, M, we tune the oxidation state and coordination environment of iridium atoms in the catalyst. Such tuning results in major changes to intrinsic activity and stability depending on the metal dopant. SrIr_1-xM_xO₃ experiences an initial increase in intrinsic activity with electrochemical OER performance before reaching a steady state activity. We observe this phenomenon to be caused by both surface dissolution of non-precious metals and rearrangement of the remaining iridium-rich surface at oxidizing potentials, forming highly active surface motifs with varying stability depending on the dopant metal, M. Additionally, we observe differences in Tafel slope with various dopants, indicating dopant-dependent differences in OER mechanisms. When doped with zinc, we show SrIr_0.8Zn_0.2O₃ outperforms benchmark iridium-based catalysts at significantly lower material costs and electrical potential inputs with excellent catalyst stability. While benchmark iridium oxide has a specific activity of 0.6 mA per cm² catalyst at 1.55 V vs RHE, SrIr_0.8Zn_0.2O₃ attains a specific activity of 2.6 mA per cm² catalyst after initial electrochemical cycling. Using a variety of ex situ and in situ characterization techniques, we aim to offer a fundamental understanding of the relationships between dopant and catalyst activity and stability.