Assessment of Platinum Dissolution from a Pt/C Fuel Cell Catalyst: An Electrochemical Quartz Crystal Microbalance Study

Abstract

The stability of different types of platinum surfaces in the presence of chloride was evaluated by applying a potential of 1.2 V vs reversible hydrogen electrode while the associated mass change in the Pt electrode was monitored with an electrochemical quartz crystal microbalance. The platinum metal surfaces based on the particles and films show a large difference toward dissolution when exposed to small amounts of chloride. While an electrodeposited platinum metal film showed no degradation in a sulfuric acid solution containing 10 ppm of chloride, an electrode made from a fuel cell catalyst (50 wt % Pt/C) lost 10% of its platinum content over a 24 h period when exposed to a sulfuric acid solution containing 10 ppm of chloride. At a chloride concentration of 20 ppm, the onset potential of the Pt oxide formation increased ∼200mV compared to an electrode in a chloride-free solution. The degradation of nanoparticles thus appears to be much more significant than for the electrodeposited platinum electrodes.

Stability of carbon nanofibre-supported platinum catalysts in the presence of chloride under controlled mass-transfer conditions

“…Li et al [14] investigated the effects of trace amounts of chlorine in PEM fuel cells to address the possibility of using hydrogen from the chlor-alkali industry as a fuel in PEM fuel cells. In line with our results [13], Li et al [14] also found a significant, non-recoverable loss in electrochemical surface area (ECSA). This group later investigated the loss of ECSA in catalysts of fuel cell catalysts (46 wt.…”

“…However, for nanosized Pt particles the corrosion rate can be significant, as was shown by our electrochemical quartz crystal microbalance (EQCM) [13] in which an electrode made from a fuel cell catalyst (50 wt. % Pt/C) lost 10 % of its platinum content over a 24 h period when exposed to a sulfuric acid solution containing 10 ppm of chloride and at a constant potential of 1.2 V vs. a reversible hydrogen electrode (RHE).…”

“…The duration of these experiments is therefore much shorter than those in Ref. [13], and a direct comparison is difficult. However, the almost instantaneous 50 % loss even at 50 ppm in Ref.…”

“…However, the almost instantaneous 50 % loss even at 50 ppm in Ref. [13] would seem to indicate that chloride is more aggressive during potentiostatic hold than during cycling. Later results in a PEM fuel cell appears to indicate that also the mass transfer is affected by chloride contaminations [16].…”

Towards Practical Applications of EQCN Experiments to Study Pt Anchor Sites on Carbon Surfaces

“…Some attempts have been made at depositing a Pt/C ink onto a gold-coated quartz crystal [14,15]. However, these systems are difficult to calibrate since precise loadings are required to ensure that the quartz crystal oscillations are not drastically different from measurement to measurement.…”