On the Electrochemical Stability of PtRu Alloy Electrodes in Aqueous Acidic Baths: A Strategy for Recycling Pt and Ru

Abstract

PtRu alloy nanoparticles supported on high surface area carbon material (PtRu/C) are common electrocatalysts used for the hydrogen oxidation reaction at polymer electrolyte membrane fuel cell (PEMFC) anodes. The recovery of these precious metals at the end of the lifetime of fuel cells is important for their further applications in a sustainable energy technology scenario. Here, new mechanisms for efficient recycling of the spent catalyst are proposed and examined based on the potentiodynamic dissolution of PtRu/C in chloride containing—and in chloride free dilute acidic baths, respectively, such as in 0.1 M HCl and 1 M H2SO4. During potential cycling, Ru exhibits a higher stability than Pt in 0.1 M HCl. This is in contrast to a relatively lower stability of Ru under potentiodynamic treatment in the absence of Cl−. For example, the % dissolutions of Pt and Ru are observed to be ∼72% and ∼33% during potential cycling between 0.2 and 1.6 V for 50 cycles at a scan rate of 100 mV s−1, in 0.1 M HCl. On the other hand, for similar initial Pt and Ru loadings, the corresponding dissolution values for Pt and Ru after potential cycling between 0.2 and 1.6 V for 10k cycles at a scan rate of 1 V s−1 in 1 M H2SO4 are observed to be ∼27% and ∼61%, respectively. This difference of behaviors is attributed to the formation and stability of soluble Pt and Ru species during potential cycling. The fast dissolution of Pt and higher stability of Ru found during potential cycling in dilute HCl may be explored towards separation of Pt and Ru and for separable recoveries from spent alloy catalysts. Finally, it is observed that the Pt and Ru dissolution rates during potential cycling may be enhanced through inhibition of redeposition of the dissolved species by using Cu as a surface switching species.