Elucidation of Performance Recovery for Platinum-Group Metal Free Cathodes in Fuel Cells

Abstract

Platinum group metal (PGM)-free oxygen reduction reaction (ORR) catalysts for proton exchange membrane fuel cells (PEMFCs) continue to demonstrate significant advances in electrocatalytic activity. However, the initial cell high performances cannot be retained over an extended period. We show that fuel cell performance can be electrochemically recovered in-situ, without having to disassemble or disconnect the fuel cell. This was achieved through a set of experiments that included cyclic voltammetry with variations in upper voltage limits and constant potential holds with variation of voltage and time durations. We found that by depriving the cathode of oxygen and applying a low voltage (less than 0.25 V) to the cell, performance can be recovered. Using a reaction kinetics model analysis, the activity decay as well as the recovery and activity enhancement were separated into two sets of sites, one set with a rapid performance decay and a second with a more durable activity. Through a detailed analysis of potential dependence, we show that the voltage requirements to recover the two sites are also different, with the stable sites requiring a lower, more reductive potential that generates greater amounts of reduction current. We hypothesize this is due to electrochemically cleaning the surface of the catalyst from a poisoning species and restoring a percentage of the original active sites. Furthermore, our CV analysis shows the recovery procedure increases the amount of redox active Fe species.