Evaluation of Carbon Support Corrosion Using Accelerated Stress Protocol and Impedance Spectroscopy

Abstract

Proton Exchange Membrane Fuel Cell (PEMFC) gathering momentum again in various commercial applications has made scientists evaluate its components rigorously.[1–3] In this context, evaluation of the electrocatalyst and its supports has been vital. As widely investigated and accepted, carbonaceous materials are generally preferred as support due to their promising intrinsic characteristics like good electrical conductivity and higher surface area. The metal-support interaction plays a vital role in the catalytic activity and durability of electrocatalyst. Functionalization or inducing defects on these carbon support surface materials are much essential to achieve better impregnation of Pt nanoparticles with improved adherence. It also aids in achieving well dispersed nucleation of Pt on the support and hence exhibits enhanced electrochemical performance.[4] However, the carbon supports are susceptible to corrosion under PEMFC conditions and get accelerated when the fuel cell generates voltages > 1.2 V during start-up/shut-down and gross fuel starvation. This condition leads to deterioration of electrocatalyst layer through various mechanisms such as Pt dissolution, Ostwald ripening, coalescence via particle migration which ultimately leads to decreased electrochemical performance and durability of PEMFC. The stability of electrocatalyst and carbon corrosion resistant property of support material has an integral role in substantiating the longevity of fuel cell performance. Hence, understanding the role of carbon supports in corrosion, after functinalization becomes essential. Herein, we have attempted to evaluate the carbon supports rigoursly under functionalized and non-functionalized conditions. The protocol employed is an accelerated stress test (AST) of potential cycling between 1.0 V – 1.5 V vs. RHE for 5,000 cycles formulated by the U.S. Department of Energy.[5] The studies were also supported by carrying out dynamic electrochemical impedance spectroscopy near the oxidation potential of carbon. The corrosion behaviour of functionalized forms of carbon were found to be more corrosive than their respective non-functionalized forms due to surface oxygenated species. However, the functionalized form of acetylene black showed one order less in the corossion current compared to the conventional Vulcan carbon (Fig 1). In additon, the durability of acetylene black based carbon supported Pt electrocatalysts exhibited remarkable durability with less than 40% loss in their electrochemical surface area after the AST protocol study, satisfying the set DoE targets for 2020. Based on our results, we propose that the functionalized acetylene black will be a promising excellent corrosive resistance support for Pt electrocatlyst in PEMFCs with enhanced performance and also durability.