Ag2−xO with highly exposed {111} crystal facets for efficient electrochemical oxygen evolution: Activity and mechanism

Abstract

A series of Ag2–xO/FTO-i electrodes (where i denotes the current density during the electrodeposition, and i = 0.5, 1, 2, 3, 4, or 7) was fabricated in 0.1 M K2B4O7 electrolyte containing Ag+ ions by galvanostatic electrocrystallization. The electrode composition and morphology were characterized using X-ray powder diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy. The results reveal that the electrode films consist of Ag2O, but some of the Ag+ ions on the {111} crystal facets are oxidized into Ag2+ ions. Furthermore, the Ag2–xO/FTO-1 electrode shows a triangular slice shape of a parallel matrix with a larger exposed area of {111} crystal facets than other Ag2–xO/FTO-i (i = 0.5, 2, 3, 4, or 7) electrodes. Electrocatalytic experiments prove that the Ag2−xO/FTO-1 electrode produces the highest oxidative current density, has an overpotential of 417 mV at 10 mA cm−2, and has a Tafel slope of 47 mV dec−1 in 0.1 M K2B4O7. Electrochemical impedance spectra indicate that Ag2−xO/FTO-1 electrodes have the best ability for charge transfer. In addition, in the I-t test over 10 h, the current density decreased 4%. Fortunately, both O–O and Ag2+ species were detected after electrocatalysis and a possible mechanism for the oxygen evolution reaction is proposed in which the formation of Ag2+ and O–O species on {111} facets plays a critical role.