Despite extensive research in photocatalytic water splitting, electrolyte usage varies greatly across different photocells. Photocatalytic water splitting continues to be performed in a wide range of electrolytes, from very acidic to very basic, with incomplete understanding of how the electrolyte composition affects performance. This study provides guidelines for electrolyte selection in water splitting applications. To determine properties that comprise an ideal electrolyte for photocatalytic electrolysis, the effects of several parameters were studied: pH, dissolved oxygen, conductivity, and composition. The photoactive anode was a nanostructured thin TiO2 film synthesized by a flame aerosol process. The photocatalytic conversion efficiency increased with both pH and conductivity, but changes in dissolved oxygen levels had no discernible effect. The electrolyte composition was adjusted using selected salts and bases. Although the effect of the cation was negligible, anions were found to reduce efficiencies if their oxidation potential makes them thermodynamically favored over water molecules for oxidation. The results of these studies were applied in an analysis of the prospects for splitting seawater to produce hydrogen. c 2009 The Electrochemical Society. [DOI: 10.1149/1.3090177] All rights reserved.