Carbon Corrosion in Proton-Exchange Membrane Fuel Cells: Effect of the Carbon Structure, the Degradation Protocol, and the Gas Atmosphere Luis Castanheira, †,‡ Wanderson O. Silva, § Fabio H.B. Lima, § Alexandre Crisci, Δ,⊥ Laetitia Dubau,* ,†,‡ and Fre ́ de ́ ric Maillard* ,†,‡ † Univ. Grenoble Alpes, LEPMI, F-38000 Grenoble, France ‡ CNRS, LEPMI, F-38000 Grenoble, France § Instituto de Química de Sã o Carlos, Universidade de Sã o Paulo, CEP 13560-970, CP 780 Sã o Carlos, SP, Brazil Δ Univ. Grenoble Alpes, SIMAP, F-38000 Grenoble, France ⊥ CNRS, SIMAP, F-38000 Grenoble, France * S Supporting Information ABSTRACT: The impact of the carbon structure, the aging protocol, and the gas atmosphere on the degradation of Pt/C electrocatalysts were studied by electrochemical and spectro- scopic methods. Pt nanocrystallites loaded onto high-surface area carbon (HSAC), Vulcan XC72, or reinforced-graphite (RG) with identical Pt weight fraction (40 wt %) were submitted to two accelerated stress test (AST) protocols from the Fuel Cell Commercialization Conference of Japan (FCCJ) mimicking load-cycling or start-up/shutdown events in a proton-exchange membrane fuel cell (PEMFC). The load- cycling protocol essentially caused dissolution/redeposition and migration/aggregation/coalescence of the Pt nanocrystallites but led to similar electrochemically active surface area (ECSA) losses for the three Pt/C electrocatalysts. This suggests that the nature of the carbon support plays a minor role in the potential range 0.60 < E < 1.0 V versus RHE. In contrast, the carbon support was strongly corroded under the start-up/shutdown protocol (1.0 < E < 1.5 V versus RHE), resulting in pronounced detachment of the Pt nanocrystallites and massive ECSA losses. Raman spectroscopy and differential electrochemical mass spectrometry were used to shed light on the underlying corrosion mechanisms of structurally ordered and disordered carbon supports in this potential region. Although for Pt/HSAC the start-up/shutdown protocol resulted into preferential oxidation of the more disorganized domains of the carbon support, new structural defects were generated at quasi-graphitic crystallites for Pt/RG. Pt/Vulcan represented an intermediate case. Finally, we show that oxygen affects the surface chemistry of the carbon supports but negligibly influences the ECSA losses for both aging protocols. KEYWORDS: proton-exchange membrane fuel cells (PEMFCs), carbon corrosion, catalyst support corrosion, accelerated stress testing, durability of PEMFC materials, degradation mechanisms I n the search for renewable energy sources, different possibilities (solar power plants, wind turbines, geothermal, and ocean energy) are currently being implemented. The largest drawback for renewable energy sources is their intermittency, which implies the need of flexible electro- chemical storage and conversion systems to accommodate the energy demand. Hydrogen (H 2 ), with a mass energy density of 140 MJ kg −1 , 1 is the most relevant contender to store renewable electrical energy produced in excess in the H−H bond. In case the energy demand exceeds the production, this chemical energy may then be converted back into electrical energy thanks to a proton-exchange membrane fuel cell (PEMFC). 2 However, PEMFCs still suffer from the insufficient durability of their constitutive materials: the carbon supported Pt or Pt-M nanocrystallites (Pt/C or Pt-M/C, M being an early or late transition metal) used as electrocatalysts, the proton- exchange membrane (PEM), the ionomer, and the gas-diffusion layers. 3−5 The physicochemical and electrochemical analyses performed on aged membrane electrode assemblies 4−17 or model PEMFC electrodes aged in accelerated stress tests protocols (ASTs) 14,18−22 have unveiled several degradation mechanisms for the Pt-based nanocrystallites: (i) dissolution/ redeposition via electrochemical Ostwald ripening, 23,24 (ii) chemical reduction of the Pt z+ ions produced by the electrochemical Ostwald ripening into electrically disconnected Pt crystallites in the proton-exchange membrane or in the Received: December 9, 2014 Revised: February 16, 2015 Published: February 23, 2015 Research Article pubs.acs.org/acscatalysis © 2015 American Chemical Society 2184 DOI: 10.1021/cs501973j ACS Catal. 2015, 5, 2184−2194