Carbon Support Microstructure Impact on High Current Density Transport Resistances in PEMFC Cathode

Abstract

Cell voltages at high current densities (HCD) of an operating proton-exchange membrane fuel cell (PEMFC) cathode suffer from losses due to the local-O2 and bulk-H+ transport resistances in the catalyst layer. Particularly, the microstructure of high surface area carbon (HSC) support upon which both the platinum catalyst and ionomer are dispersed play a pivotal role in controlling the reactant transport to the active site in the catalyst layer. In this study, we perform a systematic analysis of the underlying microstructure of platinum-cobalt catalyst dispersed on various HSC supports in terms of their surface area and pore-size distribution. The carbon microstructure was found to strongly influence the PtCo nanoparticle dispersion, catalyst layer ionomer distribution and transport losses governing the performance at HCD. Catalyst layer electrochemical diagnostics carried out to quantify local-O2 transport resistance and bulk-H+ transport resistance in the cathode were found to be directly correlated to the micropore (<2 nm) and macropore (>8 nm) surface areas of the carbon support, respectively. Finally, a 1D-performance model has been developed to assimilate our understanding of the catalyst layer microstructure and transport resistances at HCD.

Dense Pt Nanowire Electrocatalyst for Improved Fuel Cell Performance Using a Graphitic Carbon Nitride‐Decorated Hierarchical Nanocarbon Support

“…More interestingly, this catalyst also demonstrates high power/performance compared with the state-of-the-art electrocatalysts, Pt(20 wt%)NPs/VC (JM), Pt(40 wt%)NPs/Hi-spec (JM), and Pt(50 wt%)NPs/HSAC (Tanaka), which is very important in reducing the size and cost of the fuel cell stack. [49] Last but not the least, it is worth noting that in this study, neither the amount of g-CN nor the macroporosity of the MPC support were optimized, thus it is likely that the electrocatalytic performance of g-CN@MPC-supported Pt NW catalysts can still be further increased. Furthermore, Pt metal and Pt alloys (e.g., Pt 3 Ni) with other morphologies (e.g., Nanoframe) which have demonstrated ultrahigh electrocatalytic activity toward the ORR [4,50] can be incorporated into g-CN@MPC to further enhance the electrocatalytic activity and electrochemical stability of this electrocatalyst approach.…”

Interpreting Ionic Conductivity for Polymer Electrolyte Fuel Cell Catalyst Layers with Electrochemical Impedance Spectroscopy and Transmission Line Modeling

“…GrC carbon support (MEA 1 and MEA 2) has almost no internal porosity, which results in a low total surface area, where all the Pt particles distribute on the surface of the support. For MEA 3, according to Nagappan et al, 26 high surface area carbon (HSC) support has around 3-5 times higher total surface area than Vulcan carbon support due to its high internal porosity. Figure 7a shows the effective ionic conductivities for MEA 1 and MEA 2 (properties defined in Table I).…”

“…At low RH, MEA 3 with the HSC support showed lower effective ionic conductivity. It was shown recently by Ramaswamy et al 26 that surface area of smaller meso-pores (> 8 nm) of the carbon support determines the continuity and uniformity of the ionomer distribution in the catalyst layer. The GrC carbon support in MEA 2 has less to no meso-pores compared to the HSC used in MEA 3, which results in a larger effective ionic conductivity of MEA 2.…”

Effects of PEMFC Operational History under Dry/Wet Conditions on Additional Voltage Losses due to Ionomer Migration

“…However, this location ensures that the Pt surface is in contact with the ionomer, leading to adsorption of sulfonic acid groups and poisoning effects. 13,14 Based on such observations, Harzer et al 13 suggested that an ideal catalyst ought to have most of the Pt particles outside for good mass transport, while having a small fraction of internal Pt to increase total mass activity. Similar results have also been obtained by other researchers.…”