Abstract
This research prepared two types of graphene sheet through microwave plasma torch chemical vapor deposition method (MPT-CVD). We fine- tuned the parameters of process and controlled strength of plasma to manipulate the defects of graphene and found a correlation between nitrogen configuration and defect density. The nitrogen plasma has been demonstrated to effectively dope N atoms onto graphene sheets. The distribution of the N-doping types can be tuned by control of the graphene defect density and the nitrogen plasma power to generate multiple functionalities of the resultant materials. The medium-quality graphene doped at a high-power nitrogen plasma exhibits the highest electrocatalytic activity toward the oxygen reduction reaction (ORR) with a mean electron-transfer number of 3.94 which is comparable to that of platinum. The high-quality graphene doped at a low-power nitrogen plasma shows the high activity and selectivity for simultaneously detecting uric acid (UA), ascorbic acid (AA), and dopamine (DA) and detecting limit is 2.5 μM due to the high content of the pyridinic-N structure. We also produced the binder-free, vertically grown graphene-nano-walls (GNW) and nitrogen-doped graphene-nano-walls (NGNW) electrodes respectively provide good examples for extending the upper potential limit of a positive electrode of EDLCs from 0.1 V to 1.5 V (vs. Ag/AgNO3) as well as the lower potential limit of a negative electrode of EDLCs from -2.0 V to ca. -2.5 V in 1 M Tetraethyl ammonium tetrafluoroborate (TEABF4)/propylene carbonate (PC) compared to ACs. This newly designed asymmetric EDLC exhibits a cell voltage of 4 V, specific energy of 53 Wh kg-1 and specific power of 8 kW kg-1 and ca. 100% capacitance retention after 10,000 cycles charge-discharge.