Layered spongy-like O-doped g-C₃N₄: An efficient non-metal oxygen reduction catalyst for alkaline fuel cells

Here we report a polycondensation reaction combined with a solution mixing pathway to synthesize an O-doped graphitic carbon nitride (g-C3N4) by using melamine and cyanuric acid. Structural and morphological characterizations revealed the successful preparation of O-doped g-C3N4with a layered spongy-like micro-nanostructure, which favored the enhancement of O2 adsorption and active sites. The UV-vis spectra and Mott-Schottky analysis indicated that the introduction of oxygen leaded to a narrow bandgap, a negative shift of valance band maximum and an increased electrical conductivity. As a result, the O-doped g-C3N4exhibited a higher mass activity (14.9 mA/mgcatalyst at -0.60 V and 1800 rpm) and 60 mV positive shift of half-wave potential toward oxygen reduction reaction (ORR) as well as a better electron transfer efficiency than did the g-C3N4without oxygen doping. In order to further increase the ORR activity, Ketjen black carbon was incorporated into the O-doped g-C3N4catalyst to promote the electron transfer. The resulting catalyst showed a comparable ORR activity (a kinetic-limiting current density of 21.5 mA cm-2at -0.6 V), excellent stability and remarkable tolerance to methanol as compared with the Pt/C catalyst, indicating its potential application as a non-metal cathode catalyst for the alkaline direct methanol fuel cell.