Influence of Cathode Catalyst Layer with SiO2-Coated Pt/Ketjen Black Catalysts on Performance for Polymer Electrolyte Fuel Cells

Abstract

In this study, we investigated the effect of silica (SiO2) layer included in a cathode catalyst layer (CL) on the performance for polymer electrolyte fuel cells (PEFCs). Porous carbons such as Ketjen black (KB) have been widely used as a support for Pt catalysts in PEFCs. Such KB-supported Pt catalyst (Pt/KB) was used as a cathode CL with low ionomer content (a condition of low proton conductivity). The Pt/KB was then coated with SiO2. In addition, the Pt/KB and SiO2-coated Pt/KB (SiO2-Pt/KB) were measured and analyzed under relative humidity (RH) conditions (100% and 20%). The catalyst ink of SiO2-Pt/KB showed higher stability and dispersion compared to Pt/KB, due to the hydrophilic surface characteristics of SiO2, which act as a binder-like ionomer. The performance of the SiO2-Pt/KB at 100% RH, was significantly lower than that of Pt/KB, whereas the performance of the Pt/KB at 20% RH, was significantly improved by SiO2 coating. This is due to an increase in the proton conductivity, which can be attributed to the hydrophilic properties of SiO2. Based on these results, the effect of SiO2 coating on performance, depending on carbon supports of SiO2-coated Pt/Carbon catalysts, could be evaluated.

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

“…Distinct from the transition-metal oxides stated above, silica (typical-metal oxide) is neither oxidized by ·OH radicals nor reduced by H 2 . It has been reported that the incorporation of SiO 2 –NPs in a Nafion membrane increased the σ H , specifically at low relative humidity (RH), due to its hygroscopic property. , Recently, Inoue et al added silica NPs to the anode and cathode CLs of gas diffusion electrodes (GDE) to increase the effective utilization of Pt catalysts under low RH conditions, , while Park et al reported an increase in the cell performance by coating an SiO 2 layer on Pt/C cathode catalysts . On the basis of these results, it is envisioned that the addition of hygroscopic silica NPs leads to a longer residence time of H 2 O 2 molecules within the anode CL, leading to a longer lifetime of the Nafion membrane, as well as an increase in the effective utilization of the Pt catalyst.…”

“…14,15 Recently, Inoue et al added silica NPs to the anode and cathode CLs of gas diffusion electrodes (GDE) to increase the effective utilization of Pt catalysts under low RH conditions, 16,17 while Park et al reported an increase in the cell performance by coating an SiO 2 layer on Pt/C cathode catalysts. 18 On the basis of these results, it is envisioned that the addition of hygroscopic silica NPs leads to a longer residence time of H 2 O 2 molecules within the anode CL, leading to a longer lifetime of the Nafion membrane, as well as an increase in the effective utilization of the Pt catalyst.…”

Tolerance of Silicon Oxide‐Coated Pt/C Catalyst Toward CO and H2S Contamination in Hydrogen for Proton Exchange Membrane Fuel Cells

“…At lower concentrations and adjusted ionomer contents in the cathode electrode, SiO 2 ‐containing MEAs can provide better performances at low RH conditions, but also limited mass transport at high RH values and current densities. [ 23,24 ] In the present work, the effect on water retention appears to excel effect of the SiO 2 on electronic or reactant diffusion resistances visible in the slightly better performance in neat H 2 .…”

“…The measured Si loading of %0.6 wt% is low as compared to values ranging from 0.3 to 40 wt% reported in other studies on similar types of SiO 2 coatings. [18,19,[21][22][23][24]26] The comparably low concentration is assumed to either stem from adsorption of APTES and TEOS on container surfaces during the coating process or from unreacted reagent removed during the washing procedure at the end of the hydrolysis step. Whether the electrocatalyst stability and performance are enhanced, likely depends on the thickness, pore structure, and hydrophilicity of the SiO 2 coating, being a function of the precursor types, their amount and on the settings during the fabrication process.…”

“…[18,19] When employed on electrocatalysts, such SiO 2 coatings showed to protect the catalysts from dissolution and improved the PEMFC performance particularly at low relative humidity (RH) conditions. [20][21][22][23][24][25][26] In these regards, Yu et al used this coating over PtRu catalysts to protect the Ru from dissolution, such that the catalyst maintained the improved CO tolerance during accelerated stress tests. [20] Aside from the application as a coating, SiO 2 can also be integrated as an additive to the proton exchange membrane (PEM) or electrode in form of silica particles or aerogel, or as a mesoporous support for the metal catalyst.…”