Development and Application of SnP₂O₇-based Proton Conductors to Intermediate-temperature Fuel Cells

Abstract

Much attention has been devoted to efforts to operate polymer electrolyte fuel cells (PEFCs) at temperatures above 100℃ in order to avoid the problem of serious CO poisoning of the anode catalyst. It is also of great con cern to operate PEFCs under low-humidity conditions, because the space and energy required for external humidi fication are eliminated or minimized in the fuel cell system. Thus, proton-conducting materials that can satisfy the above criteria have been proposed, developed, and evaluated worldwide. In particular, recent research efforts have been increasingly focusing on the design of anhydrous proton conductors, since these materials, at least in principle, do not need the presence of water as a charge carrier. We have recently found that In, Al, or Mg-doped SnP2O7 show high proton conductivities＞10-1 S・cm -1 between 150 and 350℃ under water-free conditions. Attempts to apply these materials as electrolytes in some electrochemical devices were also made. This paper presents an overview of the current status of doped SnP2O7 with principal emphasis on the materials aspect. In addition, the benefits of intermediate-temperature fuel cells using these materials are briefly summarized in terms of cell design, electrolyte and electrode materials.

Ionic conduction in Sn1−xScxP2O7 for intermediate temperature fuel cells

“…Nagao et al reported that the conductivities of AP 2 O 7 (A = Sn, Ti, Ge, Si) increased in the order of Ge 4+ < Si 4+ < Ti 4+ < Sn 4+ in unhumidified air [9], and that proton-conducting Sn 1−x R x P 2 O 7 (R = Al 3+ , In 3+ ) were also applied to some electrochemical reactors, such as H 2 /air fuel cell, selective catalytic reduction of NO x , direct oxidation of methane to methanol, and gas sensors, etc. [13][14][15][16][17][18]. Chen et al reported that Sn 0.9 In 0.1 P 2 O 7 can conduct both protons and oxide-ions in the temperature range from 403 to 503 K [19].…”

Ionic conduction in undoped SnP2O7 at intermediate temperatures

“…at intermediate temperatures (373-573 K) [7][8][9][10][11][12][13][14][15][16][17][18][19][20]. Hibino et al reported that SnP 2 O 7 and Sn 0.9 In 0.1-P 2 O 7 exhibit high protonic conductivities of above 10 − 2 S cm − 1 from 348 to 573 K and above 10 − 1 S cm − 1 from 398 to 573 K under unhumidified conditions, respectively [7,8].…”

CsH2PO4/Polyvinylidene Fluoride Composite Electrolytes for Intermediate Temperature Fuel Cells

“…6,7 Polymer electrolytes are not applicable in ITFCs due to their dehydration or chemical degradation at temperatures above 100 • C, causing low conductivity or system deterioration. 8,9 Thus, inorganic electrolytes are needed for fuel cells operating at these intermediate temperatures. As most of the inorganic conductors exhibit very low conductivity at temperatures below 1000 • C, 10 to find electrolytes with promising conductivity at temperatures between 200-600 • C is crucial to the development and commercialization of ITFCs.…”