The high-temperature proton exchange membrane fuel cell (HT-PEMFC) conducts protons through the hydrogen bond network established by the polymer and phosphoric acid (PA), which reduces the dependence on humidity and allows its operating temperature to be higher than 100°C ^[1]. A higher operating temperature is conducive to improve catalyst activity, reducing carbon dioxide adsorption on the catalyst thus reducing the requirement for hydrogen purity, and convenient water management ^[2]. As the most widely commercialized HT-PEMFC proton exchange membrane material, the performance and durability of Polybenzimidazole (PBI) still need to be improved. In particular, it has insufficient proton conductivity, insufficient mechanical properties, and phosphoric acid leaching issues under high acid doping level ^[3][4][5].

The doping of functionalized graphene oxide in the PBI membrane can build additional proton transfer channels, promote proton hopping and act as a trap for PA to reduce its leaching by virtue of abundant functional groups of functionalized GO ^[6][7][8]. Among the groups that can be used for functionalization, the phosphoric acid group has become one of the most promising due to its strong hydrogen bonding and water retention ability ^[9][10][11]. Phosphonated graphene oxide (PGO) is usually synthesized by further phosphonation of GO obtained by chemical exfoliation ^[6][7]. Chemical exfoliation methods usually require the long-term action of strong acids and strong oxidants ^[12]. The safety and environmental issues caused by those methods can not be underestimated. And the two-step synthesis method of PGO has a long reaction period.

This work achieved the rapid, safe, and large-yield production of electrochemically exfoliated PGO by using a 3D printed reactor, ammonium dihydrogen phosphate as the electrolyte and natural graphite flakes as the raw material. The two-step electrochemical exfoliation method of producing GIC with concentrated sulfuric acid as the first electrolyte is also used to synthesize electrochemical exfoliated (E)GO. 1.5wt% EGO or PGO was doped in the PBI membrane to explore the effect of different GO on the performance and durability of the PBI- membrane-based HT-PEMFC. Compared with pure PBI, the doping of EGO and PGO increases the peak power density of HT-PEMFC by 17.4% and 35.4%, respectively.

[1] Y.-L. Ma, J.S. Wainright, M.H. Litt, R.F. Savinell, Journal of The Electrochemical Society 2004, 151, A8.

[2] H. Su, S. Pasupathi, B. Bladergroen, V. Linkov, B.G. Pollet, International Journal of Hydrogen Energy 2013, 38, 11370.

[3] S. Galbiati, A. Baricci, A. Casalegno, R. Marchesi, International Journal of Hydrogen Energy 2013, 38, 6469.

[4] S.H. Eberhardt, F. Marone, M. Stampanoni, F.N. Büchi, T.J. Schmidt, Journal of Synchrotron Radiation 2014, 21, 1319.

[5] Q. He, X. Yang, W. Chen, S. Mukerjee, B. Koel, S. Chen, Physical Chemistry Chemical Physics 2010, 12, 12544.

[6] J. Yang, C. Liu, L. Gao, J. Wang, Y. Xu, R. He, RSC Advances 2015, 5, 101049.

[7] C. Xu, Y. Cao, R. Kumar, X. Wu, X. Wang, K. Scott, Journal of Materials Chemistry 2011, 21, 11359.

[8] Y. Cai, Z. Yue, S.X.-J. of A.P. Science, undefined 2017, Wiley Online Library 2017, 134, 44986.

[9] E. Abouzari-Lotf, H. Ghassemi, A. Shockravi, T. Zawodzinski, D. Schiraldi, Polymer 2011, 52, 4709.

[10] E. Abouzari-Lotf, M. Zakeri, M.M. Nasef, M. Miyake, P. Mozarmnia, N.A. Bazilah, N.F. Emelin, A. Ahmad, Journal of Power Sources 2019, 412, 238.

[11] S. Some, I. Shackery, S.J. Kim, S.C. Jun, Chemistry - A European Journal 2015, 21, 15480.

[12] C. Xu, Y. Cao, R. Kumar, X. Wu, X. Wang, K. Scott, Journal of Materials Chemistry 2011, 21, 11359.