Influence of Pt Loading and Cell Potential on the HF Ohmic Resistance of an Nb-Doped SnO₂-Supported Pt Cathode for PEFCs

Abstract

We measured highly accurate ohmic resistances of single cells at high frequency (HF) using Pt/Nb-SnO2 cathodes under several different conditions, including various cathode potentials and various atmospheres, in order to study the relationships between the ohmic resistances of single cells and the electrical conductivity of the Pt/Nb-SnO2 catalyst for polymer electrolyte fuel cells (PEFCs). The ohmic resistance of a cell using Pt/Nb-SnO2 increased with increasing cathode potential, in the range of typical cathode operation (0.4 V to 1.0 V vs. the reversible hydrogen electrode). The increase of Pt loading on the Nb-SnO2 support from 9 wt% to 17 wt% was effective in decreasing the ohmic resistance and in improving the cell performance. We propose that Pt oxidation might impede the effect of shrinking the depletion layer of the Nb-SnO2 surface. The addition of graphitized carbon black (GCB) to the Pt/Nb-SnO2 cathode was able to improve the cell performance by constructing both electronic pathways and gas diffusion pathways in the catalyst layer, under low and high current density operation, respectively. The performance of the Pt/Nb-SnO2 + GCB cathode was superior to that of the Pt/GCB cathode due to these effects.

Synthesis and Evaluation of Ni Catalysts Supported on BaCe0.5Zr0.3−xY0.2NixO3−δ with Fused-Aggregate Network Structure for the Hydrogen Electrode of Solid Oxide Electrolysis Cell

“…For example, in the case of Pt loaded on Nb doped SnO 2 , these values increased abruptly over a Pt loading amount of 7 wt %. We also proved that the reason why the electrochemical activity increased in this way over the threshold amount of metal loading was that there was a diminution of the effect of an insulating depletion layer on the nanoparticle surface [37,41]. We supposed that, under the Ni loading amount of 10 vol %, the insulating depletion layer on the BCZYN nanoparticle surface disturbed the reaction on the hydrogen electrode, and thus, the current density for Ni/BCZYN (x = 0.03) did not show a significant difference compared to that for Ni/BCZYN (x = 0).…”

“…The transmission electron microscopy (TEM) images of BCZYN (x = 0 and 0.03) nanoparticles are shown in the inset of Figure 2(a). The nanoparticles were partially fused with nearest neighbors and constructed chain-like microstructures, the fused-aggregate network structure referred to earlier [35][36][37][38][39][40][41]. The XRD profiles of Ni/BCZYN (x = 0 and 0.03) CLs sintered at 1000 °C in 4% hydrogen atmosphere (N2 balance) are also displayed in Figure 2(c).…”

“…BCZYN (x = 0 and 0.03) nanoparticle powders with a fused-aggregate network structure were prepared by the flame oxide synthesis method [35][36][37][38][39][40][41]. Briefly, reagent grade Ba, Ce, Zr, Y, and Ni 2-ethylhexanoates (Nihon Kagaku Sangyo Co. Ltd., Tokyo, Japan) were mixed in desired ratios with terpene oil as starting materials.…”

“…Furthermore, rutile-structured oxide nanoparticles with a fused-aggregate network structure were developed, whose microstructure was similar to that of carbon black and had the ability to provide effective gas diffusion pathways, electron transport pathways and high surface area [35][36][37][38][39][40][41]. We expected that nanoparticles with the fused-aggregate network structure would also be well suited for these design concepts for the CLs of a hydrogen electrode in a proton-conducting SOEC.…”

Improvement of Cell Performance in Low-Pt-Loading PEFC Cathode Catalyst Layers with Pt/Ta-SnO2Prepared by the Electrospray Method

“…Both gas flow rates were 100 mL min −1 . Based on our previous AC impedance measurements with a Pt/Ta-SnO 2 -cathode cell, 35 the high frequency (HF) ohmic resistance was measured at 10 kHz under load by use of a digital ac milliohmmeter (Model 356E, Tsuruga Electric. Co.).…”