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 Ba0.5Sr0.5Co0.8Fe0.2O3–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.