Electrochemical Top-Down Synthesis of Nanostructured Electrocatalysts for Polymer Electrolyte Membrane Fuel Cells

Abstract

Nanostructured catalysts are a promising class of materials to meet the requirements for the energy transition away from fossil fuels towards alternative, carbon-free, energy carriers, such as hydrogen. These catalyst materials boost the efficiency of energy conversion devices, such as fuel cells or electrolyzers, by accelerating their fundamental electrochemical reactions. Bottom-up synthetic routes for nanostructured materials often involve multiple synthesis steps and the use of surfactants, reducing agents or stabilizers. This results in complex and extensive synthesis protocols.[1] In recent years, a novel top-down synthesis approach to form metal nanoparticles has been established, in which bulk metal wires are immersed in an electrolyte and subsequently subjected to a high alternating potential. This leads to the generation of nanoparticles dispersed in the electrolyte.[2] There is no need for reducing agents, surfactants, or precursor solutions. The complete synthesis can be performed in one pot involving one main step with consequent washing and drying of the nanoparticles.In this study, we synthesized Pt-based nanoparticles supported on Vulcan® carbon support (Pt/C) and tested their electrochemical activity towards the oxygen reduction reaction (ORR) for polymer electrolyte membrane fuel cells (PEMFCs). Firstly, we elucidated the influence of synthesis parameters such as potential amplitude, frequency, electrolyte composition, and concentration on the size and shape of Pt nanoparticles.[3] We continued with the synthesis of more complex nanostructures, such as Pt alloy nanoparticles. This introduces strain and ligand effects at the surface of the nanoparticles, which increases the electrocatalytic activity for the ORR. We demonstrated the facile, simple, and surfactant-free synthesis of highly active PtxPr/C[4] and PtxCu/C, as two examples for Pt alloy catalysts for the ORR, and give an outlook on other systems, such as PtxGd/C.