• Journal of Powder Materials
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• v.27 no.1
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• pp.63-71
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• 2020

It is necessary to fabricate uniformly dispersed nanoscale catalyst materials with high activity and long-term stability for polymer electrolyte membrane fuel cells with excellent electrochemical characteristics of the oxygen reduction reaction and hydrogen oxidation reaction. Platinum is known as the best noble metal catalyst for polymer electrolyte membrane fuel cells because of its excellent catalytic activity. However, given that Pt is expensive, considerable efforts have been made to reduce the amount of Pt loading for both anode and cathode catalysts. Meanwhile, the atomic layer deposition (ALD) method shows excellent uniformity and precise particle size controllability over the three-dimensional structure. The research progress on noble metal ALD, such as Pt, Ru, Pd, and various metal alloys, is presented in this review. ALD technology enables the development of polymer electrolyte membrane fuel cells with excellent reactivity and durability.

• Advances in Energy Research
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• v.2 no.2
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• pp.73-84
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• 2014

Fuel cells of proton exchange membrane type (PEMFC) working with hydrogen in the anode and ambient air in the cathode ('air breathing') have been prepared and characterized. The cells have been studied with variable thickness of the cathode catalyst layer ($L_{CL}$), maintaining constant the platinum and ionomer loads. Polarization curves and electrochemical active area measurements have been carried out. The polarization curves are analyzed in terms of a model for a flooded passive air breathing cathode. The analysis shows that $L_{CL}$ affects to electrochemical kinetics and mass transport processes inside the electrode, as reflected by two parameters of the polarization curves: the Tafel slope and the internal resistance. The observed decrease in Tafel slope with decreasing $L_{CL}$ shows improvements in the oxygen reduction kinetics which we attribute to changes in the catalyst layer structure. A decrease in the internal resistance with $L_{CL}$ is attributed to lower protonic resistance of thinner catalyst layers, although the observed decrease is lower than expected probably because the electronic conduction starts to be hindered by more hydrophilic character and thicker ionomer film.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.16 no.3
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• pp.133-140
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• 2007

A 2-D model of fluid flow, mass transport and electrochemistry is analysed to examine the effect of current density at the current collector depending on active layer thickness of catlyst in polymer elecrolyte fuel cells. The finite element method is used to solve the continuity, potential and Maxwell-Stefan equations in the flow channel and gas diffusion electrode regions. For the material behavior of electrode reactions in the active catalyst layers, the agglomerate model is implemented to solve the diffusion-reaction problem. The calculated model results are described and compared with the different thickness of active catalyst layers. The significance of the results is discussed in the viewpoint of the current collecting capabilities as well as mass transportation phenomena, which is inferred that the mass transport of reactants dictates the efficiency of the electrode in the present analysis.

• Transactions of the Korean hydrogen and new energy society
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• v.31 no.5
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• pp.444-452
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• 2020

This study investigated the cathode catalyst of direct borohydride/hydrogen peroxide fuel cells for space exploration. Various catalysts such as Au, Ag, and Ni were supported on multiwalled carbon nanotubes (MWCNTs). Various techniques, such as transmission electron microscopy, Brunauer-Emmett-Teller method, scanning electron microscopy, and X-ray diffraction were conducted to investigate the characteristics of the catalysts. Fuel cell tests were performed to evaluate the performance of the catalysts. Ag/MWCNTs exhibited better catalytic activity than the Ni/MWCNTs and better catalytic selectivity of the Au/MWCNTs. Ag/MWCNTs presented good catalytic activity and selectivity even at an elevated operating temperature. The performance of Ag/MWCNTs was also stable for up to 60 minutes.

• Korean Chemical Engineering Research
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• v.49 no.6
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• pp.775-780
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• 2011

5-cell DMFC stack was fabricated and operated with the load of 4 A for 4000 hrs. After 4000 hrs operation peak power density of the stack reduced by 27.3%. Two of the five cells did now show performance degradation, the performance of other two was reduced by 40% and the performance of the other decreased by 60%. The amount of performance degradation of each cell by long-term operation did not correlate with the position in the stack. Platinum particle size in the anode catalyst layer of the MEA with the strongest degradation increased and the increase was severer on the position of methanol inlet than on the position of methanol outlet. However, platinum particle size in the cathode catalyst layers did not changed for all the MEA'. Ruthenium crossover from the anode catalyst layer to the cathode catalyst layer through the membrane was observed after 4,000 hrs operation by SEM-EDX and it occurred for all MEA' regardless of the degree of performance degradation. Atomic ratio of ruthenium to platinum in the cathode catalyst layer was the highest in the MEA with the strongest performance degradation.

• 한국전기화학회:학술대회논문집
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• 2004.06a
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• pp.71-74
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• 2004

• Korean Chemical Engineering Research
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• v.57 no.4
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• pp.512-518
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• 2019

To develop a membrane electrode assembly (MEA) with lower Pt loading and higher performance in proton exchange membrane fuel cells (PEMFCs), it is an important research issue to understand interfacial structure of Pt/C catalyst and ionomer and design the catalyst layer structure. In this study, we prepared short-side-chain Nafion-based ionomer dispersion using propylene glycol (PG) as a solvent instead of water which is commonly used as a solvent for commercially available ionomers. Cathode catalyst layers with different ionomer content from 20 to 35 wt% were prepared using the ionomer dispersion for the fabrication of four different MEAs, and their fuel cell performance was evaluated. As the ionomer content increased to 35 wt%, the performance of the prepared MEAs increased proportionally, unlike the commercially available water-based ionomer, which exhibited an optimum at about 25 wt%. Small size micelles and slow evaporation of PG in the ionomer dispersion were effective in proton transfer by inducing the formation of a uniformly structured catalyst layer, but the low oxygen permeability problem of the PG-based ionomer film should be resolved to improve the MEA performance.

• Korean Journal of Materials Research
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• v.28 no.11
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• pp.646-652
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• 2018

During a long-term operation of polymer electrolyte membrane fuel cells(PEMFCs), the fuel cell performance may degrade due to severe agglomeration and dissolution of metal nanoparticles in the cathode. To enhance the electrochemical durability of metal catalysts and to prevent the particle agglomeration in PEMFC operation, this paper proposes a hybrid catalyst structure composed of PtCo alloy nanoparticles encapsulated by porous carbon layers. In the hybrid catalyst structure, the dissolution and migration of PtCo nanoparticles can be effectively prevented by protective carbon shells. In addition, $O_2$ can properly penetrate the porous carbon layers and react on the active Pt surface, which ensures high catalytic activity for the oxygen reduction reaction. Although the hybrid catalyst has a much smaller active surface area due to the carbon encapsulation compared to a commercial Pt catalyst without a carbon layer, it has a much higher specific activity and significantly improved durability than the Pt catalyst. Therefore, it is expected that the designed hybrid catalyst concept will provide an interesting strategy for development of high-performance fuel cell catalysts.

• Applied Chemistry for Engineering
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• v.21 no.6
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• pp.697-701
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• 2010

We investigate the cell performance and characteristics of a direct formic acid fuel cell (DFAFC) using palladium (Pd) as a catalyst for anode. Pd is deposited on the electrolyte using the "direct paint" method. From a continuous three time-test of the polarization curve of the DFAFC, it is found that the catalytic activity of Pd and the cell performance of DFAFC steadily degrade as the tests are proceeded. This behavior may be due to the deactivation of Pd by formate (COOH) and hydroxyl (OH) groups, which are electrochemically dissociated from formic acid solution. Estimations of the degradation, followed by reactivation in activity of Pd catalyst and DFAFC cell performance are implemented by linear voltage sweep tests going in both positive and negative directions. When the maximum voltage of 1.0 V versus DHE is applied to the cell while a linear voltage sweep test going in negative directions, the activity of Pd catalyst and the DFAFC cell performance recover by the rehabilitation in activity of the deactivated Pd.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2822-2827
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• 2008

Among the main components of PEM fuel cell, the functions of GDL are to transport reactants from the channel to the catalyst and remove reaction products from the catalyst and transport heat from the catalyst to the channels in the flow filed plate. Permeability of GDL is known to make it possible to enhance the gas transport through GDL, devoting to get better performance. In this paper, three dimensional numerical simulation of the fuel cell by the permeability of GDL is presented by using a FLUENT modified to include the electrochemical behavior. Results show that as permeability is higher than $10^{-12}m^2$, gradients of temperature distribution, oxygen molar concentration and current density distribution in MEA were decreased. Although heat generation was increased as high permeability, MEA's temperature was lower than the low permeability of GDL. This seems because that convection was higher affects in mass and heat transfer process than diffusion as permeability of GDL is increases.