As the global demand for energy has increased in the past few decades, the search for new sources of green energy has become an important topic. Among the substantiable energy sources, a good way to address this problem is storing energy in the form of chemical bonds, such as H₂, which can react with oxygen, producing only water vapor. Hydrogen can be obtained from different sources, thus, one interesting way to obtain this product is from the water splitting reaction, however the bottleneck reaction in water splitting is the water oxidation, therefore, cost-effective catalysts have been researched in the past years, and among them, Prussian blue analogues (PBA) had stood out due to its great performance and stability in pH 7. Nevertheless, understanding the mechanism in a full way, still remains a challenge. Scanning electrochemical microscopy (SECM) is an electrochemical tool that is wildly used to probe surface reactions, working for both quantitative and qualitative analysis. SECM has been used to study water oxidation reaction (WOR) on the substrate generation-tip collection (SG-TG) mode, where the tip is a probe that reduces the O₂ produced by the catalyst, being able to identify spots and catalysts that have a higher production of oxygen.

In this work, we developed a 3D printed scanning electrochemical microscope and used it to monitor the WOR for different PBA supported on glassy carbon electrode (GCE), comparing their performances during this reaction. The platinum tip electrode was calibrated with a dissolved oxygen (DO) sensor (Hanna inst.) so the real concentration of evolved O₂ could be obtained, and therefore, turnover frequencies (TOFs) could be calculated to have real insights on their performances.