Effect of Fuel Cell Operating Potential Window on Pt/C Catalyst Durability
Typ
Examensarbete för masterexamen
Master's Thesis
Master's Thesis
Program
Materials chemistry (MPMCN), MSc
Publicerad
2023
Författare
Hjern, Astrid
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
The proton exchange membrane fuel cell is a potential key player in reducing green house gas emissions. There is, however, a need for further improvements in Pt on
carbon support catalyst (Pt/C) durability and costs. The purpose of this thesis is
to improve catalyst durability by investigating what upper potential limit (UPL)
voltage clipping should be implemented during load cycling. It is further investi gated how scan rate affects catalyst durability. Based on previous research, possible
causes and pathways of Pt degradation are discussed. Three catalysts from different
producers with varying support surface area are examined with accelerated stress
tests (ASTs) using triangular wave . One AST was performed with a scan rate of
250 mV/s in the potential window of 0.6 to 1.0 V. Four ASTs were performed with
a scan rate of 50 mV/s with a set lower potential limit (LPL) of 0.6 and varying
UPL between 0.7-1.0 V. The electrochemical surface area (ECSA) is calculated to
track catalyst degradation at specific intervals during the ASTs.
The degradation of the catalyst increases with a higher scan rate from 23 to 26%
for scan rates of 50 mV/s and 250 mV/s, respectively. All three catalysts show a
decrease in degradation when the UPL is lowered from 1.0 to 0.8 V. With decreased
UPL a thinner oxide layer is formed. The degradation increases for two catalysts
at UPL 0.7, possibly due to error sources in the method. The Pt/C catalyst with a
support area of 750 m2/g displayed the lowest degradation possibly due to a large
inter-particle distance. The primary degradation mechanisms for platinum in the
potential window of 0.6 and 1.0 V are commonly described as Pt dissolution and
agglomeration. Based on the results, it can be concluded that a decreasing UPL
in the region 1.0 to 0.8 V and increasing support area results in lower catalyst
degradation. However, the influence of initial ECSA variations, low coating quality,
and ink age questions the accuracy of the results. Therefore, it would be beneficial
to repeat the current tests with a more controllable method.
Beskrivning
Ämne/nyckelord
Proton exchange membrane fuel cell, accelerated stress test, triangular wave, electrochemical surface area, rotating disk electrode, upper potential limit, scan rate, Pt/C.