Assimilation of highly porous sulfonated carbon nanospheres into Nafion Ò matrix as proton and water reservoirs Bing Guo a , Siok Wei Tay b , Zhaolin Liu b , Liang Hong a,b, * a Department of Chemical & Biomolecular Engineering, National University of Singapore, 10 Kent Ridge Crescent, Singapore 119260, Singapore b Institute of Materials Research and Engineering, 3 Research Link, Singapore 117602, Singapore article info Article history: Received 18 April 2012 Received in revised form 22 July 2012 Accepted 24 July 2012 Available online 11 August 2012 Keywords: Sulfonic acid Porous nanocarbon particles Composite membrane PEM fuel cell Crosslinking abstract A unique form of carbon nanospheres possessing an immense number of micropores and pendant surface sulfonic acid groups was synthesized and used as an effective filler to enhance proton transfer in Nafion Ò membrane at elevated temperatures. The synthesis of the filler involved the formation of polypyrrole nanoparticles and pyrolysis of them to generate carbon nanospheres (CN). Alkaline etching was then carried out to create the porous structure, and the resulting porous carbon nanospheres were then sulfonated to attain the sulfonated porous carbon nanospheres (sPCN, 1300 m 2 /g, 6.9 mmol-SO 3 H/g). Dispersion of a substantially small amount of sPCN in a Nafion matrix brought about a cross-adsorption between the hydrophilic side-chain of Nafion molecules and sPCN. This causes the formation of a cross-linking network with sPCN junctions. The scope of this network, however, decreased with the increase in the sPCN loading from 1 to 2 wt% due to a reduction in extent of the cross-adsorption. The sPCN loading of 1 wt% reached the highest crosslinking degree that displayed the maximum enhancement on proton trans- port. It can be attributed to the role of the sPCN crosslinking junctions in keeping moisture and supplying protons. The characterizations of glass transition behaviour, hydrophilic microenvironments, and proton conductivity under low humidity levels reflected the impact of crosslinking extent. In the single H 2 -PEMFC test at 70  C using dry H 2 /O 2 , 1 wt %-sPCN Nafion composite membrane manifested a power density of 571 mW/cm 2 as compared to the pristine Nafion membrane that showed uppermost value of 388 mW/cm 2 . Copyright ª 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. 1. Introduction A sulfonated perfluoropolymer membrane such as Nafion loses moisture under low humidity conditions when it is used in a proton exchange membrane fuel cell (PEM-FC) operated in the temperature range of 70e120  C. Dehydration in Nafion membrane results in low proton mobility and hence poorer fuel cell performance. To over- come this drawback, incorporation of inorganic nano- particles such as SiO 2 or TiO 2 into the membrane offered a simple solution [1e4] relying on the physical interactions between Nafion polymer chains and filler particles. However, * Corresponding author. Department of Chemical & Biomolecular Engineering, National University of Singapore, 10 Kent Ridge Crescent, Singapore 119260, Singapore. Fax: þ65 6779 1936. E-mail address: chehongl@nus.edu.sg (L. Hong). Available online at www.sciencedirect.com journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy 37 (2012) 14482 e14491 0360-3199/$ e see front matter Copyright ª 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ijhydene.2012.07.112