In this paper we synthesized a crystalline Ag-C-i oxygen-evolution catalyst with an entirely new composition and structure in situ in a carbonate solution (pH = 8.3) with Ag+ at 70 degrees C. We studied the factors that influenced the synthesis of the oxygen-evolution catalyst (electrolyte environment temperature, silver ion concentration, concentration of carbonates) under mild conditions. The structure, morphology, composition, and catalytic activity of Ag-C-i catalyst were analyzed using techniques such as X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and electrochemical measurements. Our results showed that the diffraction peaks of the Ag-C-i catalysts synthesized at 70 degrees C were consistent with the Ago phase and that the catalytic composition of the Ag-C-i catalyst was the (AgO)-O-I/(AgO)-O-II redox couple. The oxygen-evolution rate of the catalyst synthesized in a carbonate solution (pH = 8.3) at 70 degrees C was 50 times higher than that synthesized at 5 degrees C (18.3 mu mol h(-1)); additionally, its oxygen evolution overpotential decreased to 246.7 mV. The electrolyte solution and Ag+ ion concentration greatly impacted the catalytic activity of the Ag-C-i catalyst for water splitting. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.