N doped reduced graphene oxide nanosheets (N-GNSs) with controllable N-doping and integrated with stainless steel are explored as an efficient metal-free catalyst for the I-3(-) reduction reaction, revealing evident correlations between the electrocatalytic activity and the N-doping content of graphene. In addition, it is found that V-OC is enhanced by about 60 mV for the cells constructed with N-GNSs and the increment of VOC increases with a decreasing amount of N-doping, as expected from the trend in the flat-band potential (E-fb).