In another study, Chen et al. prepared the N, Se co-doped graphene by hydrothermal method accompanied by the subsequent thermal annealing of hydrothermal treated GO with required amounts of diphenyl selenide and urea at 800 °C for 2 h in N2 flow and attained a specific capacitance of 302.9 F g -1 which is appreciably higher compared to N (150.2 F g -1 ) and Se-doped graphene (183.9 F g -1 ) in 6 M KOH solution and also shown in Fig. [677]. The content of nitrogen from the XPS in the NGA and NSeGA are 7.25 and 5.89 atom%, respectively. On the other hand, the content of the selenium in SeGA and NSeGA are 3.68 and 2.13 atom%, respectively. It has apparently inferred that content of both nitrogen and selenium atoms in the NSeGA are lower when compared to the single-doped samples. This suggesting that the N, Se co-doping reaction is competitive, which arise as a result of both the dopants tend to react with the limited defect sites over graphene rather than with the sp 2 -carbon lattice.