(Invited) Design and Synthesis of Nano-Porous / Nano-Structured Electrochemical Interfaces with Application in the Fuel Cell Catalysis

Abstract

The drive toward efficient and durable fuel cells is founded on the design, synthesis, characterization, and testing of a variety of catalysts that in most cases include either Pt or Pd or a combination of both. Given the high cost and scarcity of these metals it is essential to either find a cost-effective alternative or to minimize as much as possible the amount of Pt / Pd in developed catalysts of interest. The route of amount minimization has been firstly approached by synthesizing catalysts in the form of nanoparticles. Nanoparticles are undoubtedly superior to other type of materials applicable in catalysis with their large surface area to volume ratio and unique physical and chemical properties. At the same time, they are also associated with some drawbacks like material loss during synthesis, surface contamination that is difficult to deal with, mechanical disconnection from the carrier electrode, and / or aggregation in time of exploitation. Such unwanted developments lead to a rapid reduction of the electrochemically active surface area (ECSA) and thus, to loss of activity and poor durability.A way to address these drawbacks is to employ electrochemical approaches for synthesizing the catalytically active layer directly on the carrier electrode. Such approach would not only provide for better adhesion and contamination free surface but would also enable a complete control over the amount of the deposited material along with its surface structure and composition thus reducing the overall synthetic cost. The electrochemical means normally include electrodeposition of a binary / ternary alloy layer with controlled thickness and elemental composition followed by a selective oxidative dissolution (de-alloying) of the less / least noble metal to create a continuous nanoporous film with tunable pore and ligament size in the single-digit nanometer range (1-4). Finally, as-synthesized film may either be employed directly as catalyst (3-7) or be subjected to an additional surface functionalization for boosting its activity and/or durability (1, 2, 8-10).This talk will introduce the use of electrochemical means in the design and synthesis of continuous nanoporous alloy catalysts based on Pt-(1, 9), Pd-(7, 10), and Au-(2, 6) with application in small organic molecule oxidation, oxygen reduction in alkaline media, and nitrate electroreduction reactions, respectively. The discussed synthetic approaches will include bulk alloy electrodeposition, electrochemical de-alloying, and electrochemical atomic layer deposition for sub-monolayer to a few layers surface functionalization. The presentation of each catalyst will include electrochemical and ultra-high vacuum-based characterization, followed by standard performance tests of the activity and durability of said catalysts in the respective applications. Finally, aspects of the catalysts’ performance along with hypothesized mechanistic views will be critically discussed in comparison with other nanoparticulate and/or nanostructured counterpart catalysts in the literature. References D. A. McCurry, M. Kamundi, M. Fayette, F. Wafula and N. Dimitrov, Acs Appl Mater Inter, 3, 4459 (2011).Y. Xie and N. Dimitrov, Acs Omega, 3, 17676 (2018).Y. Xie and N. Dimitrov, Appl Catal B-Environ, 263, 118366 (2020).Y. Xie, Y. Yang, D. A. Muller, H. D. Abruna, N. Dimitrov and J. Y. Fang, Acs Catal, 10, 9967 (2020).Y. Xie, C. Li, S. A. Razek, J. Y. Fang and N. Dimitrov, Chemelectrochem, 7, 569 (2020).H. Yang, J. X. Xia, L. Bromberg, N. Dimitrov and M. S. Whittingham, J Solid State Electr, 21, 463 (2017).Y. Xie, C. Li, E. Castillo, J. Fang and N. Dimitrov, Electrochimica Acta, 138306 (2021).L. Bromberg, M. Fayette, B. Martens, Z. P. Luo, Y. Wang, D. Xu, J. Zhang, J. Fang and N. Dimitrov, Electrocatalysis, 4, 24 (2013).J. X. Xia, I. Achari, S. Ambrozik and N. Dimitrov, Mater Res Bull, 85, 1 (2017).I. Achari and N. Dimitrov, Electrochem, 1, 4 (2020).