CNTs are inert without any functionalization and do not have any positive effects. To functionalize, the CNTs were ultrasonicated in a 3:1 concentrated H2SO4 and HNO3 solution for three hours. Next, the required amount of CNT (0.5 mg/cm2) was dispersed in the small amount of ethanol. This resulted in a stable dispersed CNT ink solution. The ink was brushed on the surface of carbon paper and then dried at 100oC for one hour, in order to eliminate any residual water