Analysis of Inkjet Printed PEFC Electrodes with Varying Platinum Loading

Abstract

PEFC electrodes manufactured using inkjet printing are investigated. Cell performance, Tafel slope, reaction order and local oxygen transport resistance of electrodes with varying Pt loadings of 0.014 to 0.113 mg/cm 2 are studied in order to understand the nonlinear relationship between loading and performance. The performance increase with Pt loading was substantially reduced above Pt loadings of 0.08 mg/cm 2 . Electrochemical active area of the electrodes decreased from 66.4 to 40.4 m 2 /g as the Pt loading increased from 0.026 to 0.113 mg/cm 2 . Below the transition voltage of 0.8 V i R f ree , the Tafel slope was found to be a function of the Pt loading and oxygen partial pressure. The kinetic performance dependence on p O 2 was quantified by measuring the total reaction order. Oxygen transport resistance evaluated from limiting current experiments revealed its dependence on the inlet relative humidity of the reactants. The local oxygen transport resistance was found to drop from 5.93 ± 3.16 s/cm to 3.43 ± 1.67 s/cm as the humidity increased from 50% to 90%. Hydrogen polymer electrolyte fuel cells (PEFCs) are a zero emission and efficient energy conversion technology for transportation, stationary and electronic applications. The current generation of fuel cell vehicles provide quick start-up, long-range and increased durability. The high and unstable cost of platinum (Pt), which is the commonly used catalyst, however hinders its commercial prospects, especially when compared to the internal combustion engine. The cost of Pt is responsible for over 34% of the fuel cell stack cost.1 Less than 10-20% of the catalyst is however estimated to be utilized during the operation of a conventional catalyst layer (CL) due to mass and charge transport limitations.2 Re-designing the CL to improve these transport limitations has the potential to achieve better Pt utilization, i.e., generate more current per gram of catalyst. The CL fabrication process governs its utilization efficiency, microstructure and Pt loading in the electrodes.The effect of Pt loading on electrodes manufactured by spraying, using film applicators, sputtering as well as inkjet printing has been studied in the literature. [3][4][5][6][7][8][9][10][11][12][13][14][15] Results show that fuel cell performance is severely degraded at low Pt loading, 3,6,12,16 and that an optimal value of Pt loading exists above which the performance gains are not very significant. 4,12 The reason for the reduced performance of low loading electrodes has thus far mainly been attributed to a high oxygen mass transport resistance at the reaction site. 12,[17][18][19][20][21][22] The source of this resistance is still under debate. Oxygen dissolution in the ionomer, 23 densification of the ionomer layer near the ionomer/Pt interface, 24 and catalyst/oxygen interactions at the catalyst site 20 have been proposed as causes for this local mass transport barrier. These results indicate that in order to understand the performance degradation of low loading electrodes, and to comp...

A Mixed Wettability Pore Size Distribution Based Mathematical Model for Analyzing Two-Phase Flow in Porous Electrodes

“…The liquid water concentration (cm 3 /g · carbon) reported by Deevanhxay et al 19 is converted to liquid water saturation by first subtracting the OCV water concentration (0.22 cm 3 /g · carbon), multiplying the result by the carbon density (1.9 g/cm 3 ) reported in Ref. 24 and finally multiplying by the ratio between solid phase (the carbon black only) and void phase. The soft X-ray data 19 in Figure 8b shows a continuous decrease of water saturation from the GDL to the membrane side, whereas a slight increase in saturation is observed near the GDL side from the numerical prediction.…”

Experimental and Theoretical Analysis of Ink Dispersion Stability for Polymer Electrolyte Fuel Cell Applications

“…Details regarding the experimental procedure have been described in our previous work. 5 The averaged true density value of carbon black, ρ p , was found to be 1.69 ± 0.21 g/cm 3 based on 4 independent tests using an intrusion pressure of up to 33,000 psi.…”

“…1,2 The CL ink is usually a mixture of carbonsupported platinum particles, ionomer and a dispersion medium (DM). Ink stability, defined as the ability of particles to remain dispersed in the DM, and a reduced aggregate size are critical to deposition methods such as inkjet printing [3][4][5][6] and spray coating. 1,7,8 Inkjet printing allows for controlled spacial resolution, 6 however in order to create appropriate droplet sizes, the ink has to be ejected from micrometer size nozzles, 5 easily resulting in nozzle clogging.…”

Unexpected Performance of Inkjet‐Printed Membrane Electrode Assemblies for Proton Exchange Membrane Fuel Cells

“…[6] Thus, inkjet printing presents a pathway toward low catalyst loading MEAs without expensive equipment and controlled environmental conditions of sputtering and without materials loss and the masking of spray coating. [10] Furthermore, the structure of low-loading inkjet-printed MEAs in the CCM configuration is such that transport characteristics are largely invariant to significant differences in Nafion binder concentration. [8] A small body of work provides evidence of the promise of inkjetprinted MEAs.…”