Performance and stability of PtCo alloy catalysts in high-temperature polymer electrolyte membrane fuel cells

Abstract

High-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) suffer from fast catalyst degradation and catalyst poisoning by phosphate anions. Their performance can be tuned by alloying Pt with a less noble metal and by choosing an appropriate catalyst support and preparation method. To address this, we investigate the performance of two novel PtCo intermetallic alloy catalysts supported either on carbon black or reduced graphene oxide (rGO), prepared by double passivation galvanic displacement method, appropriate thermal annealing and ex situ chemical activation. The catalysts were used on the cathode and/or anode of a single cell (H₂/O₂, 180°C, 144 h) to shed light on the Co lifecycle in HT-PEMFCs. I-U curves as well as electrochemical impedance spectroscopy showed that their use on the cathode improved cell performance, partly also due to Co dissolution, providing higher surface area and more active sites. On the other hand, when they were used on the anode and on both electrodes, the cell performance was marked by severely inhibited mass transport due to Co phosphate formation. XRF and XAS showed that regardless of where a PtCo catalyst is used, Co at least partly dissolves and is transported to the other electrode, affecting the cell performance.