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Descriptive Role of Pt/PtO Ratio on the Selective Chlorine Evolution Reaction under Polarity Reversal as Studied by
Woonghee Lee1, Teayoung Lee2, Seok Kim1
1Division of Environmental Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang 37673, Republic of Korea.
Abstract:
This study investigated competing chlorine evolution reaction (ClER) and oxygen evolution reaction (OER) on Pt electrodes under variable polarity reversal intervals (±16.7 mA cm-2, 30-600 s) in the context of distinctive roles of Pt(0) and PtO on the surface in dilute (0.1 M) NaCl solutions. The substrate generation/tip collection mode of scanning electrochemical microscopy (SECM) quantified the current efficiency (CE) of ClER with a large tip-to-substrate distance (>500 μm) to avoid intervention of bubbles and spatial variations. Surface interrogation SECM using [Ru(NH3)6]2+/3+ coupled with X-ray photoelectron spectroscopy (XPS) identified the Pt4+-enriched surface of PtO with a bilayer structure to give more efficient regeneration of Pt(0) under the shorter reversal interval. The in situ SECM complemented bulk electrolysis and XPS to demonstrate that ClER on Pt(0) and OER on PtO primarily determine the CE of ClER, in agreement with a kinetic model. The descriptive role of surface Pt/PtO ratio rationalized the enhanced selectivity for ClER upon the polarity switching, being independent on a scaling relationship. The current reversal (not allowed to IrO2 electrodes) also alleviated calcareous scale deposit in the electrolyte with hardness.
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