Fuel cells hold the potential to provide a zero-emission power source for future automotive applications. However, their widespread commercialization is hampered by the insufficient activity and durability of both the anode and cathode electrocatalysts. In this case, aerogels derived from catalytically active noble metals seem to be promising electrocatalyst candidates to overcome these problems.^[1] Metallic aerogels combine the advantages of metals and aerogels, such as the metallic backbone (enables rapid electron transfer), large surface area (provides more reactive sites), high porosity (accelerates mass transfer), and self-supportability (eliminates support corrosion), which unleashed tremendous potential in electrocatalysis.

Recently, we studied the self-assembly of noble metal nanoparticles (e.g. Pt, Pd, Au) into aerogel structures and their electrocatalytic properties. Pure Pd and bimetallic PdPt aerogels achieved by a spontaneous gelation method showed improved performance in both anode (ethanol oxidation, EOR) and cathode (oxygen reduction, ORR) reactions.^[2-3] In addition, Pd aerogels synthesized via a controlled gelation method showed a promoted bio-fuel cell application.^[4-5]

For noble-metal electrocatalysts, the regulation of the morphology and alloying with transition metals remain the most efficient ways to meet the industrial requirements. Thus, this presentation will focus on our recent progress on the design of multimetallic aerogel electrocatalysts based on catalytically beneficial morphologies and transition-metal doping. Starting from alloyed PdNi hollow nanospheres (HNSs) as the building blocks, the resulting PdNi HNS aerogels combine the advantages of the aerogel structure, the hollow interior and the alloying effect.^[6] The morphology and shell thickness are strongly dependent on their composition which can be tuned by controlling the Ni/Pd precursor ratios. The Pd₈₃Ni₁₇ HNS aerogels are electrochemically more accessible and show an up to 5.6- and 4.2- fold improved mass and specific activity for EOR as compared to Pd/C. We further expanded this system to ternary NiPdPt aerogels showing improved ORR kinetics and stability.^[7] Additionally, the morphology evolution is under investigation.

References
[1] W. Liu, A. K. Herrmann, N. C. Bigall, P. Rodriguez, D. Wen, M. Oezaslan, T. J. Schmidt, N. Gaponik, A. Eychmüller, Acc. Chem. Res. 2015, 48, 154-162.
[2] W. Liu, A. K. Herrmann, D. Geiger, L. Borchardt, F. Simon, S. Kaskel, N. Gaponik, A. Eychmüller, Angew. Chem. Int. Ed. 2012, 51, 5743-5747.
[3] W. Liu, P. Rodriguez, L. Borchardt, A. Foelske, J. Yuan, A. K. Herrmann, D. Geiger, Z. Zheng, S. Kaskel, N. Gaponik, R. Kotz, T. J. Schmidt, A. Eychmüller, Angew. Chem. Int. Ed. 2013, 52, 9849-9852.
[4] D. Wen, A. K. Herrmann, L. Borchardt, F. Simon, W. Liu, S. Kaskel, A. Eychmüller, J. Am. Chem. Soc. 2014, 136, 2727-2730.
[5] D. Wen, W. Liu, A. K. Herrmann, A. Eychmüller, Chem. Eur. J. 2014, 20, 4380-4385.
[6] B. Cai, D. Wen, W. Liu, A-K Herrmann, A. Benad and A. Eychmüller, Angew. Chem. Int. Ed. 2015, 54, 13101-13105.
[7] B. Cai, D. Wen, W. Liu, A. Benad, T. J. Schmidt, A. Govorov and A. Eychmüller, submitted.