Graphitic carbon nitride-carbon nanofiber (g-CN-CNF) was synthesized as a bifunctional catalyst in an anion exchange membrane water electrolyzer (AEMWE), and primary and rechargeable Zn-air cells. The g-CN-CNF catalyst shows high catalytic activity for oxygen reduction reaction and oxygen evolution reaction in half-cell, with low overpotentials and low Tafel slopes. The high activity is attributed to the synergistic effect of abundant active sites and the electrical conductivity following the pyrolysis of g-CN and CNF. As a result, AEMWE with the g-CN-CNF anode, the first application of a carbon-based catalyst, exhibits outstanding performance that is the highest record in the literature for AEMWE using a non-noble metal catalyst. In addition, the performance and durability of Zn-air cells with g-CN-CNF cathode outperform those fabricated with commercial platinum.