The electrochemical performance of an unsupported PtIr electrocatalyst was evaluated as a bifunctional oxygen electrode in a unitized regenerative fuel cell (URFC). The catalyst was a mixture of unsupported Pt black and Ir black catalysts in varying proportions. The performance of the unsupported PtIr catalyst was studied by using a rotating ring disc electrode (RRDE) and linear sweet) voltammetry (LSV). In addition, a unit cell lest was performed simultaneously in the electrolyzer and in the fuel cell mode to evaluate the performance and durability of PtIr catalysts. The catalyst composition consisting of 85 wt.% Pt and 15 wt.% Ir showed high oxygen evolution reactivity and comparable electrochemical activity compared to the unsupported Pt black catalyst. The URFC using Pt85Ir15 catalyst showed the highest round-trip efficiency when estimated at different current densities. The cycle performance of URFC Pt85Ir15 catalyst was stable for 120 h at an applied cut rent density of 0.5 A cm(-2). (C) 2009 Elsevier B.V. All rights reserved.