Effect of PTFE nanoparticles in catalyst layer with high Pt loading on PEM fuel cell performance

In this study, Polytetrafluoroethylene (PTFE) was added to catalyst layer structure. This modification was aimed at facilitating excess water removal from the cathode catalyst layer with high Pt loading (1.2 mg/cm(2)). The weight percentage of PTFE in the catalyst inks varied from zero to 30. Membrane electrode assemblies were prepared with a commercial catalyst containing 70 wt % Pt on carbon, by ultrasonic spray coating technique. PEM fuel cell performance testing was carried out with two different membrane electrode assembly configuration in order to identify the effect of PTFE in anode and cathode catalyst layer structures on water transport mechanism and cell performance. In the first configuration (MEA1), PTFE nanoparticles were added to anode and cathode catalyst layers. In the second configuration (MEA2), PTFE nanoparticles were added only on cathode catalyst layer. PEM fuel cell tests were carried out at both H-2/O-2 and H-2/Air gas-feeding modes. Electrochemical characterization with impedance spectroscopy was carried out to investigate the influence of PTFE nanoparticles on reaction kinetics and mass transport. PTFE nanoparticles in catalyst layers of 5PTFE_AC provided meso-macro hydrophobic channeling, providing enhanced water management compared to conventional catalyst layers. Higher hydro-phobicity in cathode catalyst layer coupled with high airflow rate promotes increased back diffusion rate of water, diminishing flooding at cathode GDL. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved

Influence of FEP nanoparticles in catalyst layer on water management and performance of PEM fuel cell with high Pt loading

In this study, fluorinated ethylene propylene (FEP) nanoparticles were added to catalyst layer (CL) to facilitate excess water removal from the triple phase boundary in high Pt loading (1.2 mg/cm(2)) proton exchange membrane fuel cell (PEMFC) electrodes. The loading of PEP in the catalyst ink was varied from zero to 30 weight percentage. High-performance electrodes for anode and cathode were prepared by ultrasonic spray coating technique with a commercial catalyst containing 70 wt. % Pt on carbon. Different membrane electrode assemblies (MEAs) were prepared in order to differentiate the influence of hydrophobic nanoparticles on water transport and cell performance. In the first configuration (MEA1), FEP nanoparticles were added to both anode and cathode catalyst layers (cCLs). In the second configuration (MEA2), FEP nanoparticles were added only to cCL. PEM fuel cell tests were carried out at both H-2/O-2 and H-2/Air gas-feeding modes. Impedance spectroscopy results have revealed the influence of FEP nanoparticles on reaction kinetics and mass transport limitations. The addition of FEP nanoparticles decreased Pt utilization due to the isolation of Pt particles, therefore, cell performance decreased. Electrochemical impedance spectroscopy results have shown increasing back diffusion rate of water, and diminishing flooding at cathode GDL at high airflow rate. FEP nanoparticles in the cCLs of 10FEP_C, 5FEP_C at H-2/O-2 feeding mode and in the CLs of 5FEP_AC, 5FEP_C at H-2/Air feeding mode provide meso-macro hydrophobic channeling, which mitigates flooding compared to conventional catalyst layers. For anode and cathode catalyst layer including 30 wt. % FEP nanoparticles (30FEP_AC), capillary pressure increased due to high hydrophobicity, accordingly, liquid water concentration at anode catalyst layer/membrane interface decreased and this caused membrane dehydration. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved

Effective factors improving catalyst layers of PEM fuel cell

Cathode catalyst layer has an important role on water management across the membrane electrode assembly (MEA). Effect of Pt percentage in commercial catalyst and Pt loading from the viewpoint of activity and water management on performance was investigated. Physical and electrochemical characteristics of conventional and hydrophobic catalyst layers were compared. Performance results revealed that power density of conventional catalyst layers (CLs) increased from 0.28 to 0.64 W/cm(2) at 0.45 V with the increase in Pt amount in commercial catalyst from 20% to 70% Pt/C for H-2/Air feed. In the case of H-2/O-2 feed, power density of CLs increased from 0.64 to 1.29 W/cm(2) at 0.45 V for conventional catalyst layers prepared with Tanaka. Increasing Pt load from 0.4 to 1.2 mg/cm(2), improved kinetic activity at low current density region in both feeding conditions. Scattering electron microscopy (SEM) images revealed that thickness of the catalyst layers (CLs) increases by increasing Pt load. Electrochemical impedance spectroscopy (EIS) results revealed that thinner CLs have lower charge transfer resistance than thicker CLs. Inclusion of 30 wt % Polytetrafluoroethylene (PTFE) nanoparticles in catalyst ink enhanced cell performance for the electrodes manufactured with 20% Pt/C at higher current densities. However, in the case of 70% Pt/C, performance enhancement was not observed. Cyclic voltammetry (CV) results revealed that 20% Pt/C had higher (77 m(2)/g) electrochemical surface area (ESA) than 70% Pt/C (65 m2/g). In terms of hydrophobic powders, ESA of 3OPTFE prepared with 70% Pt/C was higher than 3OPTFE prepared with 20 %Pt/C. X-Ray Diffractometer (XRD) results showed that diameter of Pt particles of 20% Pt/C was 2.5 nm, whereas, it was 3.5 nm for 70% Pt/C, which confirms CV results. Nitrogen physisorption results revealed that primary pores of hydrophobic catalyst powder prepared with 70% Pt/C was almost filled (99%) with Nafion and PTFE. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved

Improved PEM fuel cell performance with hydrophobic catalyst layers

Flooding of catalyst layers is one of the major issues, which effects performance of low temperature proton exchange membrane fuel cells (PEMFC). Rendering catalyst layers hydrophobic one may improve the performance of PEMFC depending on Pt percentage in the catalyst and Polytetrafluoroethylene (PTFE) loading on the electrode. In this study, effect of hydrophobicity in catalyst layers on performance has been investigated by comparing performances of membrane electrode assemblies prepared with 48% Pt/C. Ultrasonic coating technique was used to manufacture highly efficient electrodes. Power density at 0.45 V increased by the addition of PTFE, from 0.95 to 1.01 W/cm(2) with H-2/O-2 feed; while it slightly increased from 0.52 W/cm(2) to 0.53 W/cm(2) with H-2/Air feed. Addition of PTFE to catalyst layers while keeping Pt loading constant, enhanced performance providing improved water management. Kinetic activity increased by decreasing Nafion loading from 0.37 mg/cm(2) to 0.25 mg/cm(2) while introducing PTFE (0.12 mg/cm(2)) to the electrode. Electrochemical impedance spectroscopy (EIS) results proved that charge transfer resistance decreased with hydrophobic catalyst layers for H-2/O-2 feed. This is attributed to enhanced water management due to PTFE presence. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved

High performance PEM fuel cell catalyst layers with hydrophobic channels

Polymer electrolyte membrane fuel cell performance has been enhanced with efficient water management by modification of the structure of the catalyst layer. Polytetrafluoroethylene (PTFE) was added to the catalyst layer structure by using two-step catalyst ink preparation method. Physical and electrochemical characterization of catalyst layers with hydrophobic nanoparticles were investigated via TGA-DTA, XRD, nitrogen physisorption, SEM, TEM, EDX analysis, and cyclic voltammetry technique. In addition, performance tests of MEAs were carried out. Catalyst layer structure after performance tests was observed by SEM analysis. Tubular open-ended mesopores have been constructed through the catalysts with hydrophobic nanoparticle addition. PTFE addition to the catalyst layer structure decreased both electrochemical surface area and Pt utilization. Mesoporous hydrophobic channels in the catalyst layer provided decreasing mass transport limitations at higher current densities, by this way, power density of Pt/C-Nafion/PTFE catalyst enhanced. It is concluded that mesoporous hydrophobic channels through the catalyst layer facilitate water removal. Copyright (c) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved

Biohydrogen production in an outdoor panel photobioreactor on dark fermentation effluent of molasses

Hydrogen is regarded as an ideal energy carrier if it is produced from renewable resources such as biomass. Sequential operation of dark and photofermentation allows a highly efficient production of hydrogen from biomass, as maximal conversion of the energy in the carbohydrates to hydrogen can be achieved. In this study photofermentative hydrogen production was carried out in a solar panel photobioreactor by Rhodobacter capsulatus wild type (DSM 1710) and Rhodobacter capsulatus hup(-) (YO3) strain on the molasses dark fermentation effluents which were obtained using an extreme thermophile Caldicellusiruptor saccharolyticus in the dark fermentation step. Continuous hydrogen production on the molasses dark fermentation effluents was achieved up to 55 days with R. capsulatus wild type and 75 days with R. capsulatus hup(-) in outdoor conditions during summer 2009, in Ankara Turkey. The maximum hydrogen yield obtained using R. capsulatus hup- was 78% (of the theoretical maximum) and the maximum hydrogen productivity was 0.67 mmol H-2/L-c.h. The maximum hydrogen productivity and yield of the wild type strain on the molasses dark fermentation effluents were 0.50 mmol H-2/L-c.h and 50%, respectively. The changes in climatic conditions, particularly daily global solar radiation, affected the hydrogen productivity and yield. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved

Influence of FEP nanoparticles in catalyst layer on water management and performance of PEM fuel cell with high Pt loading

In this study, fluorinated ethylene propylene (FEP) nanoparticles were added to catalyst layer (CL) to facilitate excess water removal from the triple phase boundary in high Pt loading (1.2 mg/cm(2)) proton exchange membrane fuel cell (PEMFC) electrodes. The loading of PEP in the catalyst ink was varied from zero to 30 weight percentage. High-performance electrodes for anode and cathode were prepared by ultrasonic spray coating technique with a commercial catalyst containing 70 wt. % Pt on carbon. Different membrane electrode assemblies (MEAs) were prepared in order to differentiate the influence of hydrophobic nanoparticles on water transport and cell performance. In the first configuration (MEA1), FEP nanoparticles were added to both anode and cathode catalyst layers (cCLs). In the second configuration (MEA2), FEP nanoparticles were added only to cCL. PEM fuel cell tests were carried out at both H-2/O-2 and H-2/Air gas-feeding modes. Impedance spectroscopy results have revealed the influence of FEP nanoparticles on reaction kinetics and mass transport limitations. The addition of FEP nanoparticles decreased Pt utilization due to the isolation of Pt particles, therefore, cell performance decreased. Electrochemical impedance spectroscopy results have shown increasing back diffusion rate of water, and diminishing flooding at cathode GDL at high airflow rate. FEP nanoparticles in the cCLs of 10FEP_C, 5FEP_C at H-2/O-2 feeding mode and in the CLs of 5FEP_AC, 5FEP_C at H-2/Air feeding mode provide meso-macro hydrophobic channeling, which mitigates flooding compared to conventional catalyst layers. For anode and cathode catalyst layer including 30 wt. % FEP nanoparticles (30FEP_AC), capillary pressure increased due to high hydrophobicity, accordingly, liquid water concentration at anode catalyst layer/membrane interface decreased and this caused membrane dehydration. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved

Effective factors improving catalyst layers of PEM fuel cell

Cathode catalyst layer has an important role on water management across the membrane electrode assembly (MEA). Effect of Pt percentage in commercial catalyst and Pt loading from the viewpoint of activity and water management on performance was investigated. Physical and electrochemical characteristics of conventional and hydrophobic catalyst layers were compared. Performance results revealed that power density of conventional catalyst layers (CLs) increased from 0.28 to 0.64 W/cm(2) at 0.45 V with the increase in Pt amount in commercial catalyst from 20% to 70% Pt/C for H-2/Air feed. In the case of H-2/O-2 feed, power density of CLs increased from 0.64 to 1.29 W/cm(2) at 0.45 V for conventional catalyst layers prepared with Tanaka. Increasing Pt load from 0.4 to 1.2 mg/cm(2), improved kinetic activity at low current density region in both feeding conditions. Scattering electron microscopy (SEM) images revealed that thickness of the catalyst layers (CLs) increases by increasing Pt load. Electrochemical impedance spectroscopy (EIS) results revealed that thinner CLs have lower charge transfer resistance than thicker CLs. Inclusion of 30 wt % Polytetrafluoroethylene (PTFE) nanoparticles in catalyst ink enhanced cell performance for the electrodes manufactured with 20% Pt/C at higher current densities. However, in the case of 70% Pt/C, performance enhancement was not observed. Cyclic voltammetry (CV) results revealed that 20% Pt/C had higher (77 m(2)/g) electrochemical surface area (ESA) than 70% Pt/C (65 m2/g). In terms of hydrophobic powders, ESA of 3OPTFE prepared with 70% Pt/C was higher than 3OPTFE prepared with 20 %Pt/C. X-Ray Diffractometer (XRD) results showed that diameter of Pt particles of 20% Pt/C was 2.5 nm, whereas, it was 3.5 nm for 70% Pt/C, which confirms CV results. Nitrogen physisorption results revealed that primary pores of hydrophobic catalyst powder prepared with 70% Pt/C was almost filled (99%) with Nafion and PTFE. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved