Local current density distribution of a PEMFC was experimentally studied under different operating conditions by a local current density measurement device designed by the authors of this paper. This device is actually the flow field plate of the fuel cell with separated thin copper strips on the surfaces of ribs. The operating parameters contain gas flow rate and the temperature of gas humidifier. It is found that the performance of PEMFC can be improved more efficiently by increasing the flux of hydrogen than increasing the flux of oxygen and that the magnitude of local current density decreases along the flow...