Evaluating the impact of iron impurities in KOH on OER performance of BaNiO₃ single crystals using scanning electrochemical cell microscopy

Understanding the oxygen evolution reaction (OER) electrocatalysis requires a careful understanding of the surface and activity evolution of well-defined materials. An especially promising candidate is the BaNiO₃ hexagonal perovskite, matching strides with benchmark catalysts such as Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3–δ. Here, we conducted a structural and electrochemical analysis of BaNiO₃ single crystals to assess the influence of iron impurities in KOH electrolyte on their OER performance. We used scanning electrochemical cell microscopy (SECCM) for precise measurements on BaNiO₃ single crystals in the absence of carbon additives. Cyclic voltammetry (CV) revealed that the presence of iron consistently enhanced the OER current with subsequent cycles, indicating a dynamic improvement in BaNiO₃'s electrochemical activity. Conversely, in iron-free KOH electrolyte, performance diminished with cycling. These findings not only underscore the critical necessity of KOH purification for BaNiO₃ electrochemical studies but also showcase SECCM's unparalleled ability to offer insights into the electrochemical evolution of individual entities such as single crystals. This makes it a powerful operando tool for evaluating forthcoming single crystals, thereby aiding in the design of superior catalysts for OER reactions.