Carbon-Free Pt Electrocatalysts Supported on SnO[sub 2] for Polymer Electrolyte Fuel Cells

Abstract

Carbon-free Pt-based electrocatalysts supported on semiconducting SnO 2 ͑Pt/SnO 2 ͒ have been developed for polymer electrolyte fuel cells ͑PEFCs͒ by various electrochemical and microstructural characterizations. Pt/SnO 2 exhibited comparable currentvoltage characteristics to conventional Pt electrocatalysts and, in particular, a considerable tolerance against 10,000 cycles of voltages up to 0.9 and 1.3 V RHE ͑RHE denotes reversible hydrogen electrode͒ vs the RHE. These results indicate that the carbon-free oxide-supported Pt/SnO 2 can be a promising alternative electrocatalyst with long-term durability against voltage cycling up to higher potentials, as a possible fundamental solution to the PEFC degradation caused by carbon support corrosion.Polymer electrolyte fuel cells ͑PEFCs͒ are environmentally compatible promising power sources possibly for automotive, stationary, and portable applications, 1 where Pt-based electrocatalysts supported on carbon black are widely used. While carbon black is the state-of-the-art support material, 2 corrosion of the carbon-based electrocatalyst support is one of the important technological issues that should be solved to improve the long-term durability of the PEFC systems. Oxidation-induced carbon support corrosion in cathode electrocatalysts occurs especially under high potential conditions associated with ͑i͒ start-up and shutdown, ͑ii͒ potential cycling, and ͑iii͒ open-circuit preservation of the PEFCs. 3-9 Anode electrocatalyst layers could be under a higher potential in the start-up situation, 4 which may also cause carbon support corrosion. For automotive applications, frequent voltage cycling during the operation should be tolerated, including high potential conditions beyond 1.0 V RHE ͑RHE denotes reversible hydrogen electrode͒. Tolerance against potential cycling is also essential for stationary PEFC systems probably operated in the daily start-and-stop mode for a decade. 9 Because carbon black ͑graphite͒ is thermochemically unstable under higher potential conditions, 10 alternative carbon-free electrocatalyst support materials are desired to be developed for PEFCs with a long-term durability. Various oxides have been evaluated as possible PEFC electrocatalyst support materials, including TiO 2 , 11 Ti 4 O 7 , 12,13 WO 3 , 14 and SnO 2 . [15][16][17][18][19] Electrocatalyst support materials are used as the mixture with strongly acidic electrolyte materials, e.g., Nafion; thermochemical stability is required under such acidic conditions during the lifetime of the cells. Among various oxides relatively stable under such conditions, we have selected SnO 2 known as a broad-band oxide semiconductor with high electronic conductivity and electronic mobility used, e.g., for transparent conductors and gas sensors, the conductivity of which could be further increased, e.g., by oxygen deficiency and extrinsic impurity doping. [20][21][22] The pH-potential diagram ͑so-called Pourbaix diagram 10 ͒ of the Sn-H 2 O system at 80°C thermochemically calculated indicated that SnO 2 is...

SnO2 nanocluster supported Pt catalyst with high stability for proton exchange membrane fuel cells

“…After the high potential oxidation, the Pt/SnO 2 reserved as much as 89.7% of its initial ECA and the CV of SnO 2 seldom changed, indicating that the use of SnO 2 as a catalyst support significantly improved the catalyst resistance against high potential. According to the literature [16,17], SnO 2 is the most stable compound in the Sn-H 2 O system at 80 • C which is similar to typical PEMFC operation conditions.…”

“…Tin oxide (SnO 2 ), with n-type semiconducting property and good electrochemical stability, has been proposed as a potential catalyst support material for fuel cell application [10][11][12][13][14][15][16][17][18]. Previous studies have shown that SnO 2 can promote the electro-oxidation of CO, methanol, and ethanol due to the formation of OH species at low potentials and the strengthened metal-support interaction [19,20].…”

“…There are also works reporting the usage of SnO 2 as a stable catalyst support for the oxygen reduction reaction (ORR). Zhang et al [16] and Masao et al [17] investigated the electrochemical stability of SnO 2 nanoparticles as PEMFC cathode catalyst support, and found that SnO 2 had much higher corrosion resistance than carbon. As catalyst support, the stability of SnO 2 as the catalyst support for hydrogen oxidation in PEMFCs also needs to be studied in detail.…”

Oxygen Reduction Reaction Activity and Durability of Pt Catalysts Supported on Titanium Carbide

“…So far, electronic conductive oxides or nitrides have been examined as stable supports for PEFCs, e.g., Pt/SnO2 [18,19], Pt/TiO2 [20][21][22][23], Pt/Ti4O7 [24,25], Pt/TiN [26], among others. The support materials used are typically in the form of nanoparticles with HSA to disperse Pt catalyst particles uniformly, but the use of HSA supports often leads to a high contact resistance between the particles.…”

High Capacity of SnO2 Nanoparticles Decorated Graphene as an Anode for Lithium-Ion Batteries

“…4,5 To address these problems, many efforts have been devoted to investigate new electrode materials and design new nanostructures of electrode material. [6][7][8][9] Particularly, metal oxide/graphene composites are emerging as a kind of promising materials for lithium-ion batteries because these materials have superior electrical conductivities than graphite. Among them, tin oxide (SnO 2 ) has attracted much attention because of its high lithium storage capacity up to 782 mAhg −1 , more than twice as that of graphite.…”