Abstract:

In this study, we used electrochemical impedance spectroscopy (EIS) to monitor the behavior of a series of BaMxIr1-xO3 perovskite catalysts for oxygen evolution reactions (OER). The catalysts were compared with IrO2. We used EIS and TPD-O2 techniques to characterize the oxygen mobility of the samples and their activity toward OER. Using EIS, the contributions of the cell components and the electrodes/electrolytes interface to the cell behaviour were studied. In the Nyquist plots, the high-frequency semicircle is assigned to the impedance at the interface, involving adsorption/desorption of oxygen ion on the surface of the catalytic sites coupled with electron transfer to the surface of the perovskite electrode. The low-frequency semicircle, corresponding to the charge transfer resistance, is associated with exchanging of oxygen ions and intercalation/deintercalation of mainly Ba and some M elements into/from BaMxIr1-xO3. The impedance at low-frequency semicircle was varied at different applied DC voltages, suggesting the formation of a passive layer on Ti substrate and the formation of sulfate phases. The EIS test results uggest that some perovskites are under complete mass transport limitation control at low frequencies, which may be due to the formation of sulfate phases blocking the catalytic sites. The formation of the sulfate phase was confirmed by EIS and corresponding XRD analysis on the used samples at a 1.55 V applied voltage versus SHE. Compared to the benchmark IrO2 catalyst, most perovskite compounds exhibited lower impedance and better capacitive behavior, demonstrating better catalytic activity for Ir sites in the perovskites structure, whuch contains substantially lower Ir content.

Keywords: Perovskite structure, oxygen mobility, barium sulfate, catalytic activity, benchmark IrO2

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Hossein Fadaei