Non-precious metal electrocatalysts with atomically dispersed transition metal sites have shown promising performance for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells. The Fe-N-C catalysts, with single iron atom coordinated by nitrogen atoms (FeN_x) on carbonaceous supports, exhibits outstanding ORR activity as compared to its other metal counterparts (M-N-C). ^[1] The Fe-N-C catalysts synthesized via sacrificial support method (SSM) showed superior ORR performance and this family of Fe-N-C electrocatalysts is so far the only commercially available PGM-free catalysts for fuel cell application. ^[2] For membrane electrode assembly (MEA) performance, the pore structure ^[3] and surface hydrophobicity ^[4] of the carbon matrix are of particular significance, because the high current throughput requires good oxygen transport and well-controlled water management on cathodes. In this talk, we present the local hydrophobicity of SSM-based Fe-N-C electrocatalysts ^[1] and its impact on the ORR macrokinetics in MEA. Specifically, nitrogen physisorption and water vapor physisorption were used to study the pore morphology and the local surface hydrophobicity, respectively. As shown in Figure 1, the sacrificial templated Fe-N-C catalyst showed a large amount of mesoporosity while its surface was very hydrophobic, as indicated by the little water uptake through whole pressure range. Such porosity and local hydrophobicity features were further correlated to its macrokinetic performance in a study of water partial pressure dependence under MEA configuration.

Reference

[1] T. Asset and P. Atanassov, Joule, 2020, 4, 33.

[2] https://pajaritopowder.com

[3] Y. Huang, Y. Chen, M. Xu, T. Asset, P. Tieu, A. Gili, D. Kulkarni, V. de Andrade, F. de Carlo, H. S. Barnard, A. Doran, D. Y. Parkinson, X. Pan, P. Atanassov, and I. Zenyuk, Materials Today, 2021, 47, 53.

[4] L. Liu, S. J. Tan, T. Horikawa, D. D. Do, D. Nicholson and J. Liu, Adv Colloid Interface Sci, 2017, 250, 64.