Abstract: A series of Ag_2-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 Ag_2-xO/FTO-1 electrode shows a triangular slice shape of a parallel matrix with a larger exposed area of {111} crystal facets than other Ag_2-xO/FTO-i (i=0.5, 2, 3, 4, or 7) electrodes. Electrocatalytic experiments prove that the Ag_2-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 Ag_2-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.

Key words: Ag₂O, Crystal facet, Ag²⁺ ions, Electrocatalysis, Water oxidation, Oxygen evolution reaction