Suppression of Membrane Degradation Accompanied with Increased Output Performance in Fuel Cells by Use of Silica-Containing Anode Catalyst Layers

Abstract

Polymer electrolyte membranes (PEMs) for fuel cells are chemically degraded by the attack of •OH radicals generated from the decomposition of H 2 O 2 , which is predominantly produced at the Pt/C hydrogen anode. The incorporation of conventional radical scavengers into the PEM suffers from a decrease in the output performance. We, for the first time, demonstrate that the addition of hygroscopic silica nanoparticles (NPs) to the Pt/C anode catalyst layer provides a remarkably prolonged (ca. 4 times) lifetime of a Nafion membrane in an accelerated stress test and open circuit voltage (OCV) holding at 90 °C, accompanied by improved output (I−E) performances at low relative humidity. It has been found that the use of silica NPs decreases H 2 O 2 formation rate from the OCV to a practical H 2 oxidation potential in a half-cell using 0.1 M HClO 4 at 90 °C and provides reduced ohmic resistance (increase in water content) and effective utilization of Pt cathode catalyst in a single cell, by which the improvement of the durability of the PEM and increased output performance are explained rationally.

Impact of Pt-Loading and Carbon Support of Pt/C Anode Catalysts on Membrane Degradation Rate in Fuel Cells

“…Figure 4 shows the potential dependence of j(H 2 O 2 ) on the type of Pt/C catalyst. The values of j(H 2 O 2 ) for all catalysts increased with decreasing potential and reached the highest level at 0 V vs RHE (corresponding to the OCV condition in the single cell), consistent with the tendency described in our previous works by use of Pt/C (various d Pt ), 12 Pt/C with addition of silica, 14 and Pt skin-PtCo/C. 15 Based on such a potential-dependence of j(H 2 O 2 ) at E ⩽ 0.1 V, the production of H 2 O 2 was correlated with the onset for the formation of overhydrogen H OPD on the Pt surface, which was observed by in situ FTIR.…”

“…S3) changed in a similar fashion to those in our previous work. 14 Hence, the behaviors shown in Fig. 3 are characteristics of the chemical degradation of the Nafion-PEM by •OH radical to emit F − ions, which accompanies the decrease in the thickness of the PEM (or pinhole formation), 6,[13][14][15][16] by which j(H 2 ) increases and OCV decreases.…”

“…14 Hence, the behaviors shown in Fig. 3 are characteristics of the chemical degradation of the Nafion-PEM by •OH radical to emit F − ions, which accompanies the decrease in the thickness of the PEM (or pinhole formation), 6,[13][14][15][16] by which j(H 2 ) increases and OCV decreases. A recovery of the OCV was observed for the cell with Pt 50 /GCB anode every 200 h, where the j(H 2 ) and ECSA of the Pt catalysts were evaluated by LSV and CV, respectively.…”

“…Testing protocols.-Each CCM was mounted in a single cell with a geometric electrode area of 29.2 cm 2 of the type standardized by the Japan Automobile Research Institute (JARI). After conditioning the single cell, the chemical stability of the PEM was examined via an AST in which the single cell was maintained at open circuit voltage (OCV) in H 2 /air under conditions identical to those in our previous work, 14 i.e., T cell = 90 °C with 40% RH and a backpressure of 160 kPa-G (see section S2 of the Supplementary Materials). The AST was continued until the OCV decreased to 0.85 V (ca.…”

“…The H 2 O 2 production rate j(H 2 O 2 ), kinetically-controlled area specific activity for the HOR (j k ), and mass activity for the HOR (MA k ) at various Pt/C anodes were measured with hydrodynamic voltammetry in 0.1 M HClO 4 using the CFDE technique at 90 °C. 14,15 Details for the CFDE measurements are described in section S3 of the Supplementary Materials.…”