Supportless Pt catalysts have several advantages over conventional carbon-supported Pt catalysts in that they are not susceptible to carbon corrosion. However, the need for high Pt loadings in membrane electrode assemblies (MEAs) to achieve state-of-the-art fuel cell performance has limited their application in proton exchange membrane fuel cells. Herein, we report a new approach to the design of a supportless Pt catalyst in terms of catalyst layer architecture, which is crucial for fuel cell performance as it affects water management and oxygen transport in the catalyst layers. Large Pt hollow spheres (PtHSs) 100 nm in size were designed and prepared using a carbon template method. Despite their large size, the unique structure of the PtHSs, which are composed of a thin-layered shell of Pt nanoparticles (ca. 7 nm thick), exhibited a high surface area comparable to that of commercial Pt black (PtB). The PtHS structure also exhibited twice the durability of PtB after 2000 potential cycles (0-1.3 V, 50 mV/s). A MEA fabricated with PtHSs showed significant improvement in fuel cell performance compared to PtB-based MEAs at high current densities (>800 mA/cm). This was mainly due to the 2.7 times lower mass transport resistance in the PtHS-based catalyst layers compared to that in PtB, owing to the formation of macropores between the PtHSs and high porosity (90%) in the PtHS catalyst layers. The present study demonstrates a successful example of catalyst design in terms of catalyst layer architecture, which may be applied to a real fuel cell system.

In this study, we address the catalytic performance of variously sized Pt nanoparticles (NPs) (from 1.7 to 2.9 nm) supported on magnéli phase titanium oxide (MPTO, Ti4O7) along with commercial solid type carbon (VXC-72R) for oxygen reduction reaction (ORR). Key idea is to utilize a robust and electrically conductive MPTO as a support material so that we employed it to improve the catalytic activity and durability through the strong metal-support interaction (SMSI). Furthermore, we increase the specific surface area of MPTO up to 61.6 m2 g−1 to enhance the SMSI effect between Pt NP and MPTO. After the deposition of a range of Pt NPs on the support materials, we investigate the ORR activity and durability using a rotating disk electrode (RDE) technique in acid media. As a result of accelerated stress test (AST) for 30k cycles, regardless of the Pt particle size, we confirmed that Pt/MPTO samples show a lower electrochemical surface area (ECSA) loss (<20%) than that of Pt/C (~40%). That is explained by the increased dissolution potential and binding energy of Pt on MPTO against to carbon, which is supported by the density functional theory (DFT) calculations. Based on these results, we found that conductive metal oxides could be an alternative as a support material for the long-term fuel cell operation.

Magnéli phase titanium oxides (MPTOs), possess high electrical conductivity and chemical stability, are promising support materials for the development of novel electrocatalyst in polymer electrolyte fuel cells (PEFCs). Despite MPTO's extremely low specific surface area (1 m2/g or less), high Pt loading (40 wt%) and excellent Pt particle-size distribution were obtained by the modified borohydride method. The reasons were discussed and compared with polyol method. Membrane electrode assembly (MEA) performance of those Pt/MPTO catalysts were found to be 169.7 and 366.2 mA/cm2 at 0.7 V for H2/air and H2/O2, respectively. The accelerated stress tests (ASTs) showed superior durability of the Pt/MPTO catalyst as a cathode electrode. After 10,000 cycles of high-voltage cycling test from 0.9 V and 1.3 V RHE, no significant performance degradation of the Pt/MPTO electrode was observed comparing with Pt/C. Thus, MPTOs can be considered as a good substitute of carbon supports in fuel cells.

High surface area Magnèli Phase Titanium Oxides (MPTOs), synthesized by high temperature reduction and mechanical milling of TiO2 as a catalyst support material for a polymer electrolyte fuel cells (PEFCs). Pt as an active metal distributed on the prepared supports by impregnation-reduction method. The catalyst structure and composition of the Pt/HS_MPTO were determined by X-ray diffractometer (XRD), Field Emission Transmission Electron Spectroscopy (FE-TEM) and Inductively Coupled Plasma-Atomic Emission Spectrometer (ICP). The catalytic activity for the oxygen reduction reaction (ORR) and stability against high potential were examined and compared with commercial Pt/C catalyst. The durability of Pt/HS_MPTO catalysts was examined by potential holding at 1.3 V for 24 h. Pt/HS_MPTO catalyst showed nearly no changes in the half-wave potentials representing much higher durability compared to the commercial Pt/C catalysts.

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Supportless Pt black is an attractive oxygen reduction reaction (ORR) catalyst for polymer electrolyte fuel cells (PEFCs) due to its merits such as no concern of support corrosion at high potentials and high durability against Pt dissolution at frequent potential change conditions. However, when the Pt black catalysts were fabricated as MEAs the performance is still lower than the current Pt/C catalysts and they have difficulty in reducing Pt content in the MEAs. In the present study, we have prepared sub-micron size Pt hollow spheres as an alternative catalyst layer architecture for PEFC MEAs. The big Pt spheres were employed to make 3-dimensional catalyst layer architectures and to enhance oxygen transport in catalyst layers, and hollow type Pt was made to reduce Pt content and to facilitate water management. 200 nm Pt hollow spheres with 10 nm shell thickness were prepared using carbon sphere templates. The Pt hollow spheres revealed comparable ORR performance with commercial Pt/C catalyst in a half cell test. Catalyst layer fabrication was also performed using the catalysts by optimizing the catalyst slurries and its fuel cell performance at different operating conditions and durability will be discussed based on single cell test results.