Flame synthesis of Fe₃O₄/Fe₂O₃ on stainless steel grid surfaces to improve anodic electrochemical properties

Stainless steel (SS) is attractive, easy to handle, cost-effective and offers several advantages (i.e., conductivity, durability, commercial availability) to make anodes. However, the presence of some iron oxides (mainly Fe₂O₃) on the SS surface improves electron transfer for potential use as an anode in sediment microbial fuel cells. Although several procedures are available to synthesize Fe₂O₃ on SS surfaces, most of them involve several careful steps, taking time (several hours or days) from start to finish. Fortunately, iron oxides can be synthesized on the SS surface quickly and very easily. Flame synthesis of iron oxides is a straightforward process, and it can be scalable. Using this procedure, two types of SS-grids 304 (wire diameters of 100 μm and 230 μm) material acquired from a common hardware store were flamed, forming Fe₂O₃ on their surface. Under different conditions (polished, polished then flamed, flamed) SS-grid (SSg) specimens were studied. All specimen surfaces were characterized by field emission scanning electron microscopy combined with X-rays chemical analysis. The chemical information of the iron oxides formed on the surface was obtained by X-ray diffractometer. The electrochemical responses of modified SSg pieces were assessed by cyclic voltammetry, and finally, their resistances were assessed by electrochemical impedance spectroscopy. An equivalent circuit was included to describe the electrode-electrolyte interface. The best electroactive area with small resistance in the electrode-electrolyte interface corresponds to the flamed SS grid (wire diameters of 100 mm). (author)