A bifunctional electrode structure for a unitized proton exchange membrane regenerative fuel cell has been developed. The electrode has only a thin catalyst layer; it reduces the loading of the catalyst to 0.4 mg cm(-2), and minimizes mass transport and ohmic limitations. A satisfactory performance of a unitized proton exchange membrane fuel cell is achieved with this electrode structure. 50 wt.% Pt + 50 wt.% IrO2 is a good bifunctional catalyst for the oxygen electrode. Examination of this catalyst by transmission electron microscopy and of the electrode by scanning electron microscopy is reported.