Methods and apparatus for improving mass transfer in microfluidic laminar stirring structures. The structures include a pair of opposite planar surfaces each configured with a series of dual-chevron grooves. Each series of grooves may include a preselected number of individual grooves that can be substantially identical to each other within each series. One or more series of such dual-chevron grooves may be consecutively formed along a planar surface which constitutes one cycle. Each planar surface may be an electrode layer within a fuel cell structure whereby laminar flows fuel or oxidant are directed past the grooved surfaces to induce stirring. In a preferable embodiment of the invention, a symmetrical stirred structure is provided wherein each of a pair of top and bottom layers are formed with dual-chevron grooves which are symmetrical and mirror images of each other. Increased rates of mass transfer at the boundary layers in proximity to the electrodes and other benefits over current membraneless mixing cell structures are provided.
 The invention was made at least in part with the support of a grant from the Government of the United States of America, Department of Energy (DE-FG02-05ER46250). The Government may have certain rights to the invention.