The geometry of a membraneless micro fuel cell influences reactant mixing and depletion in the downstream section of the cell channel. A small passage restricts the mixing of the anode and cathode fluids in the channel. The optimal design for H-shaped membraneless micro fuel cells has previously been obtained numerically, and in this study is fabricated and tested. The H-shaped design increases the maximum current density, which means that the maximum power density increases. It is also found that high flow rates increase the maximum current density and decrease fuel utilization. The use of different fuels alters the open circuit voltage and thus changes the current density. The maximum current density increases with increases in the reactant concentrations. For visualization of the flow in the H-shaped channel, a polydimethylsiloxane (PDMS) cell is fabricated. The mixing region in the downstream section of the H-shaped channel is much smaller than that in the downstream section of a comparable rectangular channel. (C) 2012 Elsevier B.V. All rights reserved.