Oxygen Reduction on Metal-Free Nitrogen-Doped Carbon Nanowall Electrodes

A plasma-enhanced chemical vapor deposition (PECVD) process using a CH 4 :H 2 gas mixture creates vertically aligned carbon nanowalls (CNWs) on glassy carbon (GC) and Si substrates. Metal catalysts are not required for the nucleation and growth of CNWs on the substrates. The PECVD deposition temperatures and reaction times alter the morphology and thickness of the resulting CNW layer. A low-pressure, post-processing N 2 :Ar plasma treatment dopes the CNWs with nitrogen, and X-ray photoelectron spectroscopy measurements demonstrate that nitrogen is present at 4–20 atomic% with varying CN x bonding configurations dependent upon processing conditions. Raman spectroscopy shows relatively high intensity disorder bands (I D ) compared to lower intensity graphitic bands (I G ) indicating small crystalline domains. Rotating disk electrode voltammetry results show that the number of electrons ( n ) and kinetic current density ( j k ) of the oxygen reduction reaction both increase with nitrogen content. In addition, n and j k increase with thickness of the nitrogen-containing CNW deposit. The results indicate that nitrogen-doped CNWs have higher electrochemical reactivity than their non-doped counterparts.