PtCo, a Durable Catalyst for Automotive PEMFC?

Abstract

Carbon supported Pt and PtCo alloy cathodes have been evaluated under the DoE proscribed accelerated MEA durability protocol (0.7 - 0.9 V iR free, square wave cycle, H2/air). The Pt MEA showed reasonable stability up to 2500 cycles, after which significant performance loss was observed. Post mortem analysis indicated that this was due to Pt sintering and dissolution. The PtCo MEA showed similar stability up to 2500 cycles showing a mass activity of twice that of the Pt MEA. However, after this, activity loss was observed to a value similar to pure Pt, without significant loss in electrochemical area. The MEA was tested to 83,000 cycles with only a gradual further activity loss. Post-mortem analysis showed only modest Pt sintering and loss of Pt into the membrane. This early loss of PtCo activity has been correlated with surface loss of Co through activity testing of acid pre-leached catalysts.

Activity and Stability of Pt Monolayer Core Shell Catalysts

“…Pt alloy materials can demonstrate around 2x Pt only activity for the Oxygen Reduction Reaction (ORR) however, such materials fall short of the activity required in advanced ORR catalyst materials [2,3]. Pt alloys are generally prepared via an annealing treatment, which produces larger catalyst particles (3-5nm) with reduced susceptibility to surface area loss during voltage cycles compared to highly dispersed Pt catalysts (1-2nm) [3,4].…”

“…Pt alloy materials can demonstrate around 2x Pt only activity for the Oxygen Reduction Reaction (ORR) however, such materials fall short of the activity required in advanced ORR catalyst materials [2,3]. Pt alloys are generally prepared via an annealing treatment, which produces larger catalyst particles (3-5nm) with reduced susceptibility to surface area loss during voltage cycles compared to highly dispersed Pt catalysts (1-2nm) [3,4]. The addition of alloying elements to Pt may also enhance the intrinsic stability of the catalyst by reducing Pt oxide growth and dissolution at higher potentials, however loss of surface base metal from alloy materials under cyclic regimes is a source of performance loss over time in PEMFC systems [3].…”

“…DFT modelling studies have been used to probe the surface segregation of different Pt(shell)/M(core) systems in the presence of oxygen and a Pt/Ir(core) was found to show surface segregation of Pt even in the presence of absorbed oxygen [13]. DFT calculations on Pt 3 M alloys [14] in vacuum show Pt segregation occurs for M= Pd or Ir, however the segregation energy of the Pt 3 Pd system is small, indicating surface segregation of Pd could be likely, especially in the presence of oxygen.…”

Electrochemical Stability and Oxidation Mechanism of Carbon Support for PEM Fuel Cell

“…More recently, challenging durability targets for catalysts, and hence carbon supports, have been proposed for PEFCs for automotive applications. Catalysts must survive repeated potential cycling and exposure to high potentials during idle/open circuit potential conditions (7). In this study, an attempt has been made to use the electrochemical quartz crystal microbalance (EQCM) as a tool to identify the oxidation state of carbon in acidic medium.…”

Estudo de eletrocatalisadores nanoestruturados de Pt/C e Pt-Co/C depositados em carbono de alta área superficial: efeitos morfológicos e composicionais frente à reação de redução de oxigênio

“…Há estudos teóricos de estabilidade[65], estudos que fizeram os testes composta por três eletrodos em eletrólito líquido; neste caso o eletrodo de trabalho consiste em eletrodos de disco com uma camada fina de catalisador[2,[67][68][69]. Sobre os procedimentos de envelhecimento acelerado pode-se destacar os que utilizam a ciclagem de potencial em diferentes perfis, como por exemplo, ondas quadradas[66,70,71] e ondas triangulares[1,69]. Alem do mais, os envelhecimentos têm sido feitos também sob atmosfera de oxigênio ou sob gás inerte, porém em ambos os casos os resultados indicam valores próximos de perda de área ativa, e assim sendo, por conveniência a maioria dos envelhecimentos eletroquímicos são feitos sob gás inerte[72].…”