In the present investigation, porous carbon fiber paper as a gas diffusion layer (GDL) of polymer electrolyte membrane fuel cell was modified by nano-structuring. It was modified by incorporating multiwall carbon nanotubes (MWCNTs) in chopped carbon fiber preform by two approaches; first by incorporating in the matrix phase and second by the in-situ growth of MWCNTs on the carbon fiber preform by chemical vapor deposition technique, followed by impregnation of phenolic resin and processed to carbonization at 1000 and 1800 degrees C.The effect of MWCNTs incorporation was ascertained by characterizing carbon fiber paper by various techniques. It is found that incorporation of MWCNTs reveals an increase in electrical conductivity from 66 S/cm to 175 S/cm and flexural modulus from 5 GPa to 20 GPa. The extent of increase in electrical conductivity was greater in MWCNTs mixed with phenolic resin as compared to MWCNTs grown over the carbon fiber preform. There is a significant improvement in power density from 361 to 594 mW/cm(2) of MWCNTs grown based GDL. The BET contact angle increases the hydrophobicity of GDL, reduced the blockage of gas diffusion path. Also, higher value of electrical conductivity, surface area and optimal pore sizes results in the enhancement of I-V performance. (C) 2019 Elsevier Ltd. All rights reserved.