The complex tris(4,4'-di-t-butyl-2,2'-bipyridine)cobalt(II/III) ([Co(DTB)(3)](2+/3+)) was one of the first systems other than I-/I-3(-) to be demonstrated to function as a competent electron transport mediator in dye-sensitized solar cells. As a consequence, understanding its heterogeneous electron-transfer chemistry on semiconductor oxide surfaces is important. Herein we report a combination of voltammetry and dye-cell studies on this complex that focus on the effects of added electrolyte cations, specifically Li+ and several tetraalkyl ammonium cations. (C) 2013 The Electrochemical Society. All rights reserved.