Fe-N-C electrocatalyst for enhancing iron (II/III) redox reaction kinetics in thermo-electrochemical cells

Abstract

In this paper, I have investigated that Fe2/3+ redox couple which is widely used as an n-type electrolyte, is defined as an inner-sphere electrode reaction. Therefore, there is the importance of an electrode material selection. In addition, we find that kinetics and thermopower is affected by the chaotropic of the counter-anion conjugated on active redox couple (Fe2+/3+). As a result, it was confirmed that thermopower and redox reaction kinetics of the Fe-ClO4 electrolyte were the best among various counter-anions of Fe2+/3+ redox couple. And considering the pH and operating voltage of the Fe-ClO4 electrolyte, he Fe-N-C electrode material was selected as an electrode that could replace Pt. The Pmax of the pellet-type Fe-N-C TEC was measured at 503 mW m-2, which was corresponding to the Pmax of the Pt. On the basis of the cost for Fe-N-C ($ 3,400 kg-1), just 1/750 than of Pt. Furthermore, the CV, LSV, and EIS results show that fast electron transfer of Fe-N-C like noble metal Pt. Also, the activity of the Fe-N-C electrode demonstrated in the pellet-type model test, extended surface electrodes are successfully transferred into cylindrical type TEC. The Fe-N-C coated CC electrode exhibited Pmax of 1.73 W m-2, demonstrating enhanced TEC performance using non-precious active material, Fe-N-C. Also, the power conversion efficiency relative to the Carnot cycle (ηr) of Fe-N-C based cylindrical cell can be calculated to be 1.242 %, which is the highest value in Fe2+/3+ redox couple, n-type electrolyte. Taken all together, Fe-N-C electrode for the TEC in Fe-ClO4 electrolyte can be potential for thermo-electrochemical cells.