Title : Preparation and oxygen evolution reaction on nanoporous semi-transparent La0.8Sr0.2CoO3 coatings: Stability and mechanism in neutral medium
Abstract:
For the prospective use in oxygen evolution reaction as an electrocatalyst, the semi-transparent thin film of La0.8Sr0.2CoO3 (LSCO), was deposited on FTO (Fluorine-doped tin oxide) coated glass substrate, by using a sol-gel method. This involves gelation of LSCO sol followed by spin coating. Detailed characterization explains the homogeneity and nanoporosity of the film (Figure 1). Films are conducting with low sheet resistance and high carrier concentration. Sheets are also semi-transparent and very homogeneous. Electrochemical measurements in 0.1 M phosphate buffer solution (pH 7.4) confirm evolution of oxygen which starts at 1.51 V vs RHE with an overpotential value of 280 mV and Tafel slope value of 104 mv dec-1 in a neutral medium (0.1 M phosphate buffer), which remain stable for a long time. The overvoltage is comparable to the other studies done in the basic medium. LSCO is a well-known material for OER reaction in basic medium, as demonstrated in many literature studies. However, this study demonstrates its electrocatalytic activity in neutral medium and how the surface of material changes after some time. Catalyst is subjected to the stability test for 1 and 2 hours and it is found that for one hour the stability is good and after that surface oxidation process is visible. Post electrochemical characterization with the aid of XRD and XPS indicates that the bulk lattice remains intact but breakdown of the surface lattice structure produces separate oxides. Briefly, reduced cobalt oxide and oxidised Sr species form on the surface after electrocatalysis. The reduction is well correlated with the depletion of lattice oxygen from the La0.8Sr0.2CoO3 compound depicting its role in the OER process. The assumption that cobalt ions play a decisive role in the electrochemical reaction is also established from XPS studies (Figure 2) and cobalt is indeed the active site during the OER process. As mentioned earlier, while several studies exist in literature which talks about the activity of LSCO in basic medium, this study is one of its kind where neutral medium is explored. Neutral medium studies are important and can serve a starting point in developing electrolysers based on sea water.
Audience Takeaway Notes:
- This work belongs to fundamental research on the area of electrochemistry. Thus, the audience belonging to this area will learn how experimental and analysis in the area of electrochemistry
- Probing the active site is difficult understand unless expensive techniques ate available. But here it is shown hoe just one XPS data can be used to probe the same
- This research can also be expanded in the sea water electrolysers technology because Sea water is pH neutral and the studies reported here have also been carried out in neutral medium.
