High Surface Area IrOx Synthesis By Glycine-Assisted Adams Fusion Method for Improved Electrocatalysis of Oxygen Evolution Reaction

Abstract

As renewable energy generation increases, the storage of intermittently excess electricity is becoming an important challenge due to the instability of photovoltaic and wind generation. Among many approaches, hydrogen production through water electrolysis features the advantages of long-term large-scale storability [1]. Especially, proton exchange membrane water electrolysis (PEMWE) has benefits at high current operation and gas purity compared to the alkaline water electrolysis. Iridium oxide (IrO2), which is the most widely using catalysts for PEMWE at present, were developed intensely to overcome the sluggish oxygen evolution reaction (OER) kinetics and unsatisfied stability under acidic conditions [2-3]. Recent studies demonstrated amorphous IrOx have higher OER activity than rutile IrO2 owing to IrIIIOOH species. Despite the high OER activity, amorphous IrOx has issues in high Ir dissolution rate during OER which is critical for OER stability. In this study, high surface area IrOx was synthesized by Adams fusion method with glycine as an additive (denoted by IrOx (G)) to enhance OER activity and stability. From the XRD analysis, IrOx was observed with crystallite of 2.4 nm calculated from (101) by Scherrer equation. XPS results show positive peak shifts at Ir 4f and higher Oads/Olatt ratio of O 1s peak compared to rutile IrO2 which is well-known features of hydrated amorphous IrOx [4]. The specific surface areas of IrOx (G) obtained by BET equation were 385 m2 g-1 which is 170 % larger than IrO2 prepared by the common Adams fusion method (225 m2 g-1, denoted by Adams-IrO2). The result shows that glycine acts as a pore-forming agent and also prevent the development of rutile IrO2 during thermal treatment. The amorphous structure and high specific surface area of IrOx (G) are the main reasons which increase OER activity and stability. IrOx (G) exhibited 305 mV overpotential at 10 mA cm-2 which is a significantly lower overpotential than Adams-IrO2 (340 mV). Also, no significant change occurred during 6 hours of chronopotentiometry at 10 mA cm-2 which implies excellent stability at OER. References E. Hosseini, M.A. Wahid, Renew. Sust. Energy Rev., 57, 850 (2016).Faustini, M. Giraud, D. Jones, J. Rozière, M. Dupont, T.R. Porter, S. Nowak, M. Bahri, O. Ersen, C. Sanchez., Adv. Energy Mater., 9, 1802136, (2019).Li, S. Li, M. Xiao, J. Ge, C. Liu, W. Xing, Nanoscale, 9, 9291, (2017).F., Abbott, D., Lebedev, K., Waltar, M., Povia, M., Nachtegaal, E., Fabbri, C., Copéret, T. J., Schmidt, Chem. Mater., 28, 6591, (2016).