Niobium-doped SnO 2 is selected as an alternative carbon-free support material to negate carbon corrosion in polymer electrolyte fuel cells (PEFCs) electrocatalysts. The durability is measured using a membrane electrode assembly (MEA) over 60,000 start-stop cycles at high potential, equating to the lifetime of fuel cell vehicles. Using the Nb-doped SnO 2 support results in retention of 99% of the initial cell voltage. The current-voltage characteristics are improved by adding carbon nanofibers as fillers in the Nb-doped SnO 2 , indicating that electronic conduction in the electrocatalyst layer is critical in the application of metal oxide-supported electrocatalysts.Platinum nanoparticles homogeneously decorated on carbon black is widely utilized as an electrocatalyst in polymer electrolyte fuel cells (PEFCs). 1,2 Carbon black is an attractive support material due to its high electrical conductivity and large surface area. However, during PEFC operation the cathode potential can reach 1.5 V vs RHE (V RHE ) under start-stop conditions, resulting in severe carbon corrosion. [3][4][5][6][7] To remedy this, electronically conducting metal oxides have been proposed as alternative support materials. Tentative results using Nb-doped TiO 2 , Sn-doped In 2 O 3 , and Sb-doped SnO 2 electrocatalyst supports have already been reported. and ITO (indium tin oxides) 8,24 have been proposed as oxide-based support materials with high resistance to corrosion. The case for such corrosion-resistant support materials becomes even more pertinent in the move toward higher PEFC operation temperature. 25,26 SnO 2 is a popular alternative support material because of its thermochemical stability. [10][11][12]14,27 Doping Nb into SnO 2 is an effective method to increase the electrical conductivity. 14 We reported that 2 mol% Nb doped into SnO 2 exhibits the highest electrical conductivity. 14 No significant degradation in the performance of Ptdecorated SnO 2 or Pt-decorated Nb-doped SnO 2 powder was observed in electrochemical half-cell tests conducted over 60,000 cycles, in an accelerated durability test simulating the harsh start-stop conditions of fuel cell vehicles. Despite the excellent durability, low electrical conductivity in such metal oxides generally leads to poor cell performance. Additionally, evaluation in MEAs is essential in order to demonstrate the feasibility of using metal oxide supports in practical fuel cell applications. However, there are very few papers reporting MEA performance and cycling durability of Pt-decorated metal oxide electrocatalysts. [8][9][10][11][12][13][14][15][16] Here, we present electrochemical performance and start-stop voltage cycling durability of MEAs with Pt-decorated, Nb-doped-SnO 2 cathode electrocatalysts. We also report the effect of using carbon fiber filler in the electrocatalyst layers in order to improve electron conductivity. ExperimentalPreparation and characterization.-Metal oxides were synthesized via an ammonia co-precipitation method, using SnCl 2 · 2H 2 O

Carbon black is commonly used as an electrocatalyst support material in polymer electrolyte fuel cells (PEFCs). However, during the fuel cell start-stop cycles, carbon is known to be oxidized electrochemically. In the present study, SnO2 has been selected as a candidate for the support material, and the relation between SnO2 preparation conditions and electrochemical properties is analyzed.

SnO2 can act an alternative PEFC electrocatalyst support to the conventional carbon black, for preventing catalyst support corrosion. In this study, current-voltage characteristics of MEAs with SnO2 support are improved by controlling the content of electron-conductive fillers and proton-conductive Nafion ionomer.

Possible alternative electrocatalyst support materials to the conventional carbon black have been examined. Among others, doped-SnO2 can be a promising support for Pt nanoparticles well connected to the oxide with a certain crystallographic orientation. Pt/doped SnO2 exhibits suitable voltage cycle durability, while further improvement in oxygen reduction reaction (ORR) activity is still desired.

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