A membrane-free direct borohydride fuel cell that is operated with a borohydride containing electrolyte is designed and constructed. Main focus of this study is the cathode catalyst that has to show high tolerance against borohydride. Both catalysts, Ag-Mn3O4/C as cathode catalyst and commercial Pt/C as anode catalyst, are characterized electrochemically using a rotating disk electrode. The number of exchanged electrons is calculated employing Levich and Koutecky-Levich analysis. Cathodes are fabricated using a cross rolling method with an in-house made gas diffusion layer. A cell with an implemented Luggin capillary is designed in order to follow the electrode potentials. The BH4-/O-2 fuel cell shows a power density of 17 mW cm(-2) using a 1 M NaBH4/1 M NaOH/5 mM thiourea electrolyte. (C) 2016 The Electrochemical Society. All rights reserved.