Tetsuya Mashio

The Analysis of Performance Loss with Low Platinum Loaded Cathode Catalyst Layers

An analysis of the performance loss with low platinum loaded cathode catalyst layers (CCLs) was conducted. A modified 1-D calculation model in the CCL was developed in this study, where newly developed oxygen transport resistance in the direction from pores in the CCL to platinum surface (RO2,CCL-micro) and the effect of platinum oxide coverage on RO2,CCL-micro were taken into account. As a result, the increased voltage loss with low platinum loaded CCLs was demonstrated by the modified 1-D calculation model. The analysis results indicated that the oxygen transport loss caused by RO2,CCL-micro became a dominant factor of the performance loss with the low platinum loaded CCLs.

Analysis of Reactant Gas Transport in Catalyst Layers; Effect of Pt-loadings

An analytical in-situ technique was utilized to evaluate reactant gas transport resistance (Rother) in catalyst layers (CLs). It was found that Rother was increased with the decrease of Pt-loadings of the CLs although their thickness was decreased. Effective Knudsen diffusion coefficient was calculated from the pore size distribution and the porosity. It was estimated almost steady regardless of the Pt-loadings. To understand the increase of Rother, a simple transport model was established including Knudsen diffusion resistance in secondary pores and the local transport resistance around the Pt surface. Knudsen diffusion resistance should be decreased in lower Pt-loadings because of the shorter transport length. On the other hand, it was considered that the local transport resistance was increased with decreasing of the effective Pt surface area. Hence, that the effective Pt surface area might be one of the important factors for Rother in the CLs, especially in the lower Pt-loadings.

Surface oxide growth on platinum electrode in aqueous trifluoromethanesulfonic acid

Platinum in the form of nanoparticles is the key and most expensive component of polymer electrolyte membrane fuel cells, while trifluoromethanesulfonic acid (CF3SO3H) is the smallest fluorinated sulfonic acid. Nafion, which acts as both electrolyte and separator in fuel cells, contains -CF2SO3H groups. Consequently, research on the electrochemical behaviour of Pt in aqueous CF3SO3H solutions creates important background knowledge that can benefit fuel cell development. In this contribution, Pt electro-oxidation is studied in 0.1 M aqueous CF3SO3H as a function of the polarization potential (E(p), 1.10 ≤ E(p) ≤ 1.50 V), polarization time (t(p), 10(0) ≤ t(p) ≤ 10(4) s), and temperature (T, 278 ≤ T ≤ 333 K). The critical thicknesses (X1), which determines the applicability of oxide growth theories, is determined and related to the oxide thickness (d(ox)). Because X1 > d(ox) for the entire range of E(p), t(p), and T values, the formation of Pt surface oxide follows the interfacial place-exchange or the metal cation escape mechanism. The mechanism of Pt electro-oxidation is revised and expanded by taking into account possible interactions of cations, anions, and water molecules with Pt. A modified kinetic equation for the interfacial place exchange is proposed. The application of the interfacial place-exchange and metal cation escape mechanisms leads to an estimation of the Pt(δ+)-O(δ-) surface dipole (μ(PtO)), and the potential drop (V(ox)) and electric field (E(ox)) within the oxide. The Pt-anion interactions affect the oxidation kinetics by indirectly influencing the electric field within the double layer and the surface oxide.