Nanostructured carbon electrocatalyst supports for intermediate-temperature fuel cells: Single-walled versus multi-walled structures

It is unknown if nanostructured carbons possess the requisite electrochemical stability to be used as catalyst supports in the cathode of intermediate-temperature solid acid fuel cells (SAFCs) based on the CsH₂PO₄ electrolyte. To investigate this application, single-walled carbon nanohorns (SWNHs) and multi-walled carbon nanotubes (MWNTs) were used as supports for Pt catalysts in SAFCs operating at 250 ^°C. SWNH-based cathodes display greater maximum activity than their MWNT-based counterparts at a cell voltage of 0.8 V, but are unstable in the SAFC cathode as a consequence of electrochemical carbon corrosion. MWNT-based cells are resistant to this effect and capable of operation for at least 160 h at 0.6 V and 250 ^°C. Cells fabricated with nanostructured carbon supports are more active (52 mA cm⁻¹ vs. 28 mA cm⁻¹ at 0.8 V) than state-of-the-art carbon-free formulations while simultaneously displaying enhanced Pt utilization (40 mA mg_Pt⁻¹ vs. 16 mA mg_Pt⁻¹ at 0.8 V). These results suggest that MWNTs are a viable support material for developing stable, high-performance, low-cost air electrodes for solid-state electrochemical devices operating above 230 ^°C.