Pyridinic nitrogen induced compressed bilayer graphene for oxygen reduction reaction

Despite the emergence of nitrogen-doped graphene as a noble-metal free electrocatalyst for oxygen reduction reaction, its participation in the electrochemical conversion mechanism is not well-established. In the present study, functionalities of the nitrogen species on the oxygen reduction activity of bilayer graphene were investigated by combining atom-specific X-ray spectroscopy, Raman spectroscopy, and density functional theory calculations with electrochemical activity tests in alkaline media. Among various nitrogen species, pyridinic nitrogen as the dominant species improved the electrochemical activity of bilayer graphene, which was followed by graphene bilayers doped with graphitic nitrogen in majority. Polarization curves revealed a significantly high electrocatalytic oxygen reduction activity of the nitrogen-doped bilayer graphene where the pyridinic nitrogen was the major dopant. This improved activity was confirmed by the lowest overpotential and Tafel slope (78.9 mV/dec). The enhanced interaction of graphene bilayers doped with pyridinic nitrogen is shown to be the main reason for this improvement.