This work reports the evolution of design, fabrication and testing of direct formic acid microfluidic fuel cells (DFA mu FFC), the architecture and channel dimensions are miniaturized from a thousand to few cents of micrometers. Three generations of DFA mu FFCs are presented, from the initial Y-shape configuration made by a hot pressing technique; evolving into a novel miniaturized fuel cell based on microfabrication technology using SU-8 photoresist as core material; to the last air-breathing mu FFC with enhanced performance and built with low cost materials and processes. The three devices were evaluated in acidic media in the presence of formic acid as fuel and oxygen/air as oxidant. Commercial Pt/C (30 wt. % E-TEK) and Pd/C XC-72 (20 wt. %, E-TEK) were used as cathode and anode electrodes respectively. The air-breathing mu FFC generation, delivered up to 27.3 mW cm(-2) for at least 30 min, which is a competitive power density value at the lowest fuel flow of 200 mu L min(-1) reported to date. (C) 2014 Elsevier B.V. All rights reserved.