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...

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General rightsThis document is made available in accordance with publisher policies. Please cite only the published version using the reference above. AbstractAlignment of magnetic particles into a viscous fluid by a homogeneous magnetic field has been studied both experimentally and theoretically, but very few studies have investigated the effects of viscosity changes on the capability of achieving complex fibre assemblies in composite materials. In this paper, we study the alignment of short carbon fibres into a viscous matrix whose viscosity is made dependent on the time, in order to simulate the curing process of the composite. A simple model is derived which gives the evolution of fibre position and orientation in terms of the external field and shows good agreement with the experimental evidence on nickel coated carbon fibres embedded in PDMS. The model is used to predict the fibre distribution at curing and hence could be a useful tool to predict the mechanical, electrical and magnetic properties of the composite. A closed form expression of the minimum magnetic field intensity necessary to achieve the * Corresponding author

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The non-isothermal, two-phase membrane electrodes assembly numerical model previously developed in Part I [J. Electrochem. Soc., 164, 6, F530 (2017)] is validated by comparing to experimentally measured electrochemical performance data under various operating conditions. Water accumulation in catalyst layer (CL) and gas diffusion layer (GDL) are also compared to the neutron and X-ray imaging data and shown to be in agreement. Water fluxes at cathode and anode boundaries and phase change induced flow are analyzed and compared to experimental data. Simulation results indicate that when liquid water is present, reactant transport in the catalyst layer is the key factor limiting fuel cell performance. The model shows that at high relative humidity, 80 • C is the optimal operating temperature in order to delay water accumulation without degrading performance due to oxygen dilution by water vapor. The impact of CL and GDL hydrophilic volume fraction, hydrophobic contact angle and pore size distribution on performance are also studied. Results suggest that when liquid water is present, GDL parameters have minimal effect on performance and a CL should have a large hydrophobic contact angle, a low hydrophilic volume fraction, and large pore radius. Improving water management in polymer electrolyte fuel cell (PEFCs) is critical to achieving higher efficiency and power density, which are crucial for increasing range and reducing stack size, cost and weight in automobile applications. In order to understand water transport in PEFCs, develop improved water and heat management strategies, and design advanced gas diffusion layer (GDL), micro-porous layer (MPL) and catalyst layer (CL) micro-structures, advanced numerical models are required both at the macro-2 and micro-scales. 3Several two-phase, non-isothermal membrane electrode assembly (MEA) models have been developed over the past decades.4-8 A promising approach to include micro-structural details in MEA models has been the recent development of pore size distribution (PSD) based mathematical models for analyzing two-phase flow in porous electrodes models. 1,[9][10][11][12] In all previous work however, the PSD model was either not integrated in a complete membrane electrode assembly (MEA) model 9,11,12 or was integrated only in a one-dimensional model. 10,13 As a result, detailed validation of the numerical models has seldom been performed, and it has been mainly based on its capability to reproduce polarization curves 4,6,10 A two-dimensional model is required in order to study the validity of the water distribution in channel and land regions.In Reference 1, the authors introduced a mixed wettability pore size distribution based mathematical model for analyzing two-phase flow in porous electrodes. The pore size distribution and membrane electrode assembly models were validated by comparison to experimental polarization curves from literature data. The model however was not validated in terms of its ability to accurately estimate cell performance and cell resistance un...

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Propylene glycol was used as an additive to enhance the porosity and performance of catalyst layers (CL) fabricated using inkjet printing. Compared to the previously used additive, ethylene glycol based ink, the modified recipe helped in improving the CL porosity by 10 -20% and the in-situ performance by 50-100 mV at high current densities. The performance for PG based CLs was found to increase with decreasing ionomer/carbon (I/C) ratio, with I/C ratio of 0.5 showing the best performance. A setup based on Archimedes principle is used to measure the CL porosity, that is based on weighing the sample in n-octane and deionized water to determine the solid and bulk volumes respectively. Overall, the work improves on the previously reported inkjet printed CL performance and addresses the concern of low porosity by modifying the ink recipe.

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