Up-Scaling the Pt Hollow Nanoparticle Materials: From the Laboratory Synthesis up to Large PEMFC Cell Integration

Abstract

Proton Exchange Membrane Fuel Cell (PEMFC) technologies have focused much attention over the last decades as energy sources for both stationary and transportation applications. Their electrical performances have now reached a sufficient level for the deployment in specific markets. However, higher power densities are needed to decrease the size of the stack, and to reduce the total cost and/or to take into account the high degradation of the electrical performance during operation [1]. PEMFC performances are usually ruled out by the cathode side where the sluggish Oxygen Reduction Reaction (ORR) is processed. Moreover, the stability of the nanomaterials is also a concern in the harsh operating conditions of a PEMFC cathode [1]. The formation of hollow Pt/C particles was reported after degradation of Pt3Co/C alloys in PEMFC on-site operation [2]. Having unveiled the enhanced ORR activity of such nanostructures, LEPMI recently developed a simple “one pot” method to synthesize hollow PtNi nanoparticles supported on high surface area carbon (PtNi/C). The best porous hollow PtNi/C nanocatalysts achieved 6-fold and 9-fold enhancement in mass and specific activity for the ORR, respectively over standard solid Pt/C nanocrystallites of the same size [3] (liquid electrolyte). Upscaling the synthesis process is now a key-step to integrate these hollow nanoparticles into Membrane Electrode Assemblies (MEAs). Step-by-step development of the synthesis enabled to reach a 10-fold upscale of the synthesis corresponding to ca. 4 g of catalyst per batch (Figure 1). Combined physical and electrochemical characterizations were performed to ensure that the initial structure and the intrinsic properties of the hollow PtNi/C nanoparticles were maintained (Figure2). In parallel, different experimental conditions were also experimented to optimize the overall manufacturing process. This material upscaling also rendered possible the use of classical electrodes manufacturing processes for MEAs such as bar coating and screen printing, similarly to commercial catalysts. The first measurements performed in 25 cm² single cells demonstrated promising results for MEA using hollow PtNi/C at the cathode (Figure 3). Moreover, after an accelerated stress test designed to test the robustness of the metal nanoparticles [4], the MEA performance became higher than that of the Pt/C-based reference MEA. This is particularly true at high efficiency (up to medium current densities), which tends to confirm the interest of such nanostructures on the long-term. Complementary characterizations revealed that the utilization factor of the hollow catalyst is only 50%, and can be improved by optimizing the cathode catalyst layer formulation before integrating these new materials in larger MEAs and finally into representative PEMFC stacks. References : [1]: L. Dubau, L. Castanheira, F. Maillard, M. Chatenet, O. Lottin, G. Maranzana, J. Dillet, A. Lamibrac, J.-C. Perrin, E. Moukheiber, A. Elkaddouri, G. De Moor, C. Bas, L. Flandin, N. Caqué., Wiley Interdisciplinary Reviews: Energy and Environment,2014, 3, 540-560. [2]: L. Dubau, J. Durst, F. Maillard, L. Guétaz, M. Chatenet, J. André, E. Rossinot, Electrochim. Acta 2011, 56, 10658-10667. [3]: L. Dubau, T. Asset, R. Chattot, C. Bonnaud, V. Vanpeene, J. Nelayah, F. Maillard, ACS Catal. 2015, 5, 5333-5341 [4]: L. Castanheira, W.O. Silva, F.H. Lima, A. Crisci, L. Dubau, F. Maillard, ACS Catal. 2015, 5, 2184-2194 Figure 1