Abstract
The mixed coupled xPtOy-(100-x)IrO2 electrodes (x = 0, 10, 20, 30, 40, 50, 60, 70, 80, 90 and 100) were thermally prepared at 450 °C on titanium supports. The prepared electrodes were firstly physically characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Afterwards, electrochemical characterizations were performed by voltammetric (cyclic and linear) methods in different electrolyte media (KOH and HClO4). It is shown that the prepared electrodes are composed by both PtOy (platinum and platinum oxide) and IrO2 (iridium dioxide). For xPtOy-(100-x)IrO2 electrodes having higher content of IrO2, more surface cracks and pores are formed, defining a higher surface area with more active sites. Higher surface area due to presence of both PtOy and IrO2, is for xPtOy-(100-x)IrO2 electrodes in 1 M KOH solution confirmed by cyclic voltammetry at potentials of the oxide layer region. For all prepared electrodes, voltammetric charges were found higher than for PtOy, while the highest voltammetric charge is observed for the mixed 40PtOy-60IrO2 (x = 40) electrode. The Tafel slopes for oxygen evolution reaction (OER) in either basic (0.1 M KOH) or acid (0.1 M HClO4) media were determined from measured linear voltammograms corrected for the ohmic drop. The values of Tafel slopes for OER at PtOy, 90PtOy-10IrO2 and IrO2 in basic medium are 122, 55 and 40 mV dec-1, respectively. For other mixed electrodes, Tafel slopes of 40 mV dec-1 were obtained. Although proceeding by different OER mechanism, similar values of Tafel slopes were obtained in acid medium, i.e., Tafel slopes of 120, 60 and 39 mV dec-1 were obtained for PtOy, 90PtOy-10IrO2 and IrO2, and 40 mV dec-1 for other mixed electrodes. The analysis of Tafel slope values showed that OER is more rapid on coupled mixed electrodes than on pure PtOy. For mixed xPtOy-(100-x)IrO2 electrodes, OER is more rapid when the molar percent of PtOy meets the following condition: 0 ˂ x ≤ 80. This study also showed that the mixed coupled electrodes are more electrocatalytically active for OER than either PtOy or IrO2 in these two media.
Highlights
Climate changes and energy shortage are some of the greatest challenges for humanity [1,2,3]
This study showed that the mixed coupled electrodes are more electrocatalytically active for oxygen evolution reaction (OER) than either PtOy or IrO2 in these two media
The prepared electrodes were analyzed by scanning electron microscopy
Summary
Climate changes and energy shortage are some of the greatest challenges for humanity [1,2,3]. Increasing carbon dioxide (CO2) levels in the atmosphere cause severe issues such as global warming, energy security, and sustainability. These issues stimulated researchers to find new clean technologies that are high in efficiency and low in cost [4]. To fulfill this goal without destroying the environment, alternative methods of energy generation, conversion, and storage need to be employed [5,6,7,8]. Renewable energy from water splitting by the electrochemical route is considered as one of the important techniques to provide a solution for climate change and energy shortage. To realize the practical and sustainable application of electrocatalytic hydrogen/oxygen evolution reactions (HER/OER), an efficient, durable, and economical electrocatalyst is demanded triggering the reaction with minimal overpotential and fast kinetics [9,10,11]
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