Carbon Corrosion in Proton-Exchange Membrane Fuel Cells: Effect of the Carbon Structure, the Degradation Protocol, and the Gas Atmosphere

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 spectroscopic 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.

Effects of Pd Nanoparticle Size and Solution Reducer Strength on Pd/C Electrocatalyst Stability in Alkaline Electrolyte

“…54 The 50% ECSA loss estimated for Pt/C after correction from the characterization steps is much larger than the values calculated after subtraction of the impact of steps of characterization for the Pd/C electrocatalysts (of ca. 8% and 5% for Pd/C#1 and Pd/C#2, respectively).…”

Influence of thermal treatments on the stability of Pd nanoparticles supported on graphitised ordered mesoporous carbons

“…In practice, this means that the higher the exposed carbon surface, the higher the corrosion rate. In other words, a carbon material with high specific capacitance is more prone to corrosion unless its structure is more graphitic and/or there is a higher density of resistant surface carbon moieties [28,29]. Apparently, the differences encountered in carbon corrosion among the graphitised CMK-3s of the present work are more correlated to the electrochemical surface area rather than other parameters like graphitisation or surface chemistry.…”

“…Recent investigations have also individuated an important corrosion phenomena at the anode side in transient operating conditions of fuel feeding [27]. The corrosion rate of carbon materials increases with their surface area, carbon disordering degree and with a high percentage of labile surface carbon moieties [28,29]. However, the degradation rate can be significantly slowed down by graphitisation treatments at high temperature (1100-2000 °C) without compromising the advantage of a highly mesoporous texture [30][31][32].…”

Sb-Doped SnO2Aerogels Based Catalysts for Proton Exchange Membrane Fuel Cells: Pt Deposition Routes, Electrocatalytic Activity and Durability

“…For example, a loss of electrochemical surface area (ECSA) is monitored over time, which is mainly caused by migration/aggregation of Pt nanoparticles on the carbon support, 3,4 Pt dissolution/redeposition (electrochemical Ostwald ripening) [5][6][7][8] and/or catalyst support corrosion leading to detachment of Pt nanoparticles. [9][10][11][12][13][14] The latter process, the electrochemical carbon oxidation reaction (COR), is thermodynamically favorable at potentials higher than 0.2 V vs. the reversible hydrogen electrode (RHE) according to Reaction 1: C + 2 H 2 O → CO 2 + 4 H + + 4 e − E • = 0.207 V vs. RHE [1] At temperatures below 100…”