(289b) The Evolution of Multi-Functional Nanoporous Metal Composite Electrocatalysts

The unique physicochemical properties of nanoscale materials and the continual development of synthesis and fabrication techniques has led to a renaissance in the production of complex catalytic materials with increasing degrees of multi-functionality. Nanoporous metals are an interesting subset of nanoscale electrocatalytic materials as they possess a high surface-to-volume ratio, are intrinsically conductive, are core-shell in nature, and their morphology, composition and compositional gradient are readily tuned through a manipulation of dealloying conditions. Here we present our mechanism for the formation and evolution of nanoporous metal morphology and their application to the catalysis of several elementary electrochemical reactions including the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER)¹. Nanoporous metals are inherently metastable. In addition to the standard mechanisms of catalyst deactivation and surface area loss including Ostwald ripening and coalescence, surface energy driven coarsening is a new pathway for the loss of electrochemically active surface area in nanoporous materials. With a better understanding of the interplay between nanoporous structure coarsening and transition metal corrosion, we can propose strategies to mitigate coarsening and improve operational catalyst stability. Additional utility of these porous materials lies in the ability to take advantage of the interior volume of the nanoporous metals, incorporating a material that can address the various kinetic limitations of the catalyst. Here we demonstrate the use of hydrophobic, protic ionic liquids on the ORR where the unique properties of the ionic liquid aid the optimization of the interaction between catalyst, reactive intermediates and water.

¹ Snyder, J.; Livi, K. & Erlebacher, J. Adv. Funct. Mater. 23, 5494-5501 (2013).