Novel Miniature DMFC With Monolithic Si Electrodes

2009 ◽  
Author(s):  
Masanori Hayase ◽  
Yosuke Saito
Keyword(s):  
Metal Layer ◽  
Catalyst Layer ◽  
Pt Catalyst ◽  
Galvanic Replacement ◽  
Porous Si ◽  
Si Substrate ◽  
Catalyst Layers ◽  
Novel Structure ◽  
Si Wafer ◽  
Immersion Plating

A through-chip porous Ru-Pt catalyst layer was fabricated on a Si wafer and a novel miniature DMFC (Direct Methanol Fuel Cell) was realized. Recently, we found that porous noble metal layer can be synthesized on Si substrate by immersion plating on a porous Si. In order to realize a DMFC with our novel structure, a porous Ru layer was synthesized on the Si substrate using the immersion plating on the porous Si, then Pt was deposited by galvanic replacement reaction on the porous Ru. The porous Ru-Pt structure showed catalytic activity on methanol oxidization. A through-chip porous Ru-Pt layer was fabricated on a Si wafer by plasma etching and monolithic electrodes with catalyst layers and fuel channels were realized. A preliminary DMFC prototype successfully demonstrated power generation of 2mW/cm2.

scholarly journals Transport and Electrochemical Interface Properties of Ionomers in Low-Pt Loading Catalyst Layers: Effect of Ionomer Equivalent Weight and Relative Humidity

Molecules ◽  
2020 ◽  
Vol 25 (15) ◽  
pp. 3387
Author(s):  
Sushmit Poojary ◽  
Muhammad Naoshad Islam ◽  
Udit N. Shrivastava ◽  
Edward P. L. Roberts ◽  
Kunal Karan
Keyword(s):  
Relative Humidity ◽  
Catalyst Layer ◽  
Reduction Reaction ◽  
Pt Catalyst ◽  
Significant Finding ◽  
Equivalent Weight ◽  
Catalyst Layers ◽  
Kinetic Activity ◽  
Orr Kinetics ◽  
Low Pt Loading

Catalyst layer (CL) ionomers control several transport and interfacial phenomena including long-range transport of protons, local transport of oxygen to Pt catalyst, effective utilization of Pt catalyst, electrochemical reaction kinetics and double-layer capacitance. In this work, the variation of these properties, as a function of humidity, for CLs made with two ionomers differing in side-chain length and equivalent weight, Nafion-1100 and Aquivion-825, was investigated. This is the first study to examine humidity-dependent oxygen reduction reaction (ORR) kinetics in-situ for CLs with different ionomers. A significant finding is the observation of higher ORR kinetic activity (A/cm2Pt) for the Aquivion-825 CL than for the Nafion-1100 CL. This is attributed to differences in the interfacial protonic concentrations at Pt/ionomer interface in the two CLs. The differences in Pt/ionomer interface is also noted in a higher local oxygen transport resistance for Aquivion-825 CLs compared to Nafion-1100 CLs, consistent with stronger interaction between ionomer and Pt for ionomer with more acid groups. Similar dependency on Pt utilization (ratio of electrochemically active area at any relative humidity (RH) to that at 100% RH) as a function of RH is observed for the two CLs. As expected, strong influence of humidity on proton conduction is observed. Amongst the two, the CL with high equivalent weight ionomer (Nafion-1100) exhibits higher conduction.

scholarly journals Effect of Photoillumination on Gold-Nanoparticle-Assisted Chemical Etching of Silicon

2018 ◽  
Vol 2018 ◽  
pp. 1-5 ◽  
Author(s):  
Ming-Hua Shiao ◽  
Chou-Pu Lai ◽  
Bo-Huei Liao ◽  
Yung-Sheng Lin
Keyword(s):  
Chemical Etching ◽  
Substrate Surface ◽  
Lag Time ◽  
Localized Surface Plasmon ◽  
Etching Time ◽  
Galvanic Replacement ◽  
Si Substrate ◽  
Replacement Reaction ◽  
Aspect Ratios ◽  
Si Wafer

Metal-assisted chemical etching (MacEtch) has attracted considerable attention for its ability to fabricate micro- and nanostructures with high aspect ratios and its applications in other microelectromechanical fields. However, few studies have reported the effect of photoillumination on MacEtch. In this study, gold nanoparticles (GNPs) were deposited on the surface of a Si wafer by using the fluoride-assisted galvanic replacement reaction, and then, the effect of photoillumination on the MacEtch of the Si wafer was investigated. The etched depth increased linearly with etching time from 0–45 min and was considerably larger in the illuminated area than the nonilluminated area. A lag time was observed for the MacEtch of the nonilluminated area. However, no lag time was observed in the illuminated area. The trapping of light by the GNPs on the Si substrate surface during the MacEtch process enhanced the etching efficiency due to localized surface plasmon resonance.

scholarly journals Microstructure Investigation of Polymer Electrolyte Fuel Cell Catalyst Layers Containing Perfluorosulfonated Ionomer

Membranes ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 466
Author(s):  
Maito Koga ◽  
Hidetoshi Matsumoto ◽  
Mitsunori Kunishima ◽  
Masatoshi Tokita ◽  
Hiroyasu Masunaga ◽  
...  
Keyword(s):  
Polymer Electrolyte ◽  
Proton Exchange Membrane ◽  
Catalyst Layer ◽  
Proton Exchange ◽  
Polymer Electrolyte Fuel Cell ◽  
Pt Catalyst ◽  
X Ray ◽  
Catalyst Layers ◽  
X Ray Scattering ◽  
Ray Scattering

Perfluorosulfonated ionomers are the most successful ion-exchange membranes at an industrial scale. One recent, cutting-edge application of perfluorosulfonated ionomers is in polymer electrolyte fuel cells (PEFCs). In PEFCs, the ionomers are used as a component of the catalyst layer (CL) in addition to functioning as a proton-exchange membrane. In this study, the microstructures in the CLs of PEFCs were characterized by combined synchrotron X-ray scattering and transmission electron microscopy (TEM) analyses. The CL comprised a catalyst, a support, and an ionomer. Fractal dimensional analysis of the combined ultrasmall- and small-angle X-ray scattering profiles indicated that the carbon-black-supported Pt catalyst (Pt/CB) surface was covered with the ionomer in the CL. Anomalous X-ray scattering revealed that the Pt catalyst nanoparticles on the carbon surfaces were aggregated in the CLs. These findings are consistent with the ionomer/catalyst microstructures and ionomer coverage on the Pt/CB surface obtained from TEM observations.

scholarly journals Effect of Stratification of Cathode Catalyst Layers on Durability of Proton Exchange Membrane Fuel Cells

Energies ◽  
2021 ◽  
Vol 14 (10) ◽  
pp. 2975
Author(s):  
Zikhona Nondudule ◽  
Jessica Chamier ◽  
Mahabubur Chowdhury
Keyword(s):  
Fuel Cells ◽  
Proton Exchange Membrane ◽  
Electrochemical Impedance ◽  
Catalyst Layer ◽  
Cost Effective ◽  
Proton Exchange ◽  
Membrane Electrode ◽  
Potential Cycling ◽  
Catalyst Layers ◽  
Exchange Membrane

To decrease the cost of fuel cell manufacturing, the amount of platinum (Pt) in the catalyst layer needs to be reduced. In this study, ionomer gradient membrane electrode assemblies (MEAs) were designed to reduce Pt loading without sacrificing performance and lifetime. A two-layer stratification of the cathode was achieved with varying ratios of 28 wt. % ionomer in the inner layer, on the membrane, and 24 wt. % on the outer layer, coated onto the inner layer. To study the MEA performance, the electrochemical surface area (ECSA), polarization curves, and electrochemical impedance spectroscopy (EIS) responses were evaluated under 20, 60, and 100% relative humidity (RH). The stratified MEA Pt loading was reduced by 12% while maintaining commercial equivalent performance. The optimal two-layer design was achieved when the Pt loading ratio between the layers was 1:6 (inner:outer layer). This MEA showed the highest ECSA and performance at 0.65 V with reduced mass transport losses. The integrity of stratified MEAs with lower Pt loading was evaluated with potential cycling and proved more durable than the monolayer MEA equivalent. The higher ionomer loading adjacent to the membrane and the bi-layer interface of the stratified catalyst layer (CL) increased moisture in the cathode CL, decreasing the degradation rate. Using ionomer stratification to decrease the Pt loading in an MEA yielded a better performance compared to the monolayer MEA design. This study, therefore, contributes to the development of more durable, cost-effective MEAs for low-temperature proton exchange membrane fuel cells.

scholarly journals Formation and Evaluation of Silicon Substrate with Highly-Doped Porous Si Layers Formed by Metal-Assisted Chemical Etching

2021 ◽  
Vol 16 (1) ◽  
Author(s):  
Yijie Li ◽  
Nguyen Van Toan ◽  
Zhuqing Wang ◽  
Khairul Fadzli Bin Samat ◽  
Takahito Ono
Keyword(s):  
Electrical Conductivity ◽  
Seebeck Coefficient ◽  
Contact Resistance ◽  
Power Factor ◽  
Chemical Etching ◽  
Porous Si ◽  
Si Substrate ◽  
Si Substrates ◽  
Output Performance ◽  
Metal Assisted Chemical Etching

AbstractPorous silicon (Si) is a low thermal conductivity material, which has high potential for thermoelectric devices. However, low output performance of porous Si hinders the development of thermoelectric performance due to low electrical conductivity. The large contact resistance from nonlinear contact between porous Si and metal is one reason for the reduction of electrical conductivity. In this paper, p- and n-type porous Si were formed on Si substrate by metal-assisted chemical etching. To decrease contact resistance, p- and n-type spin on dopants are employed to dope an impurity element into p- and n-type porous Si surface, respectively. Compared to the Si substrate with undoped porous samples, ohmic contact can be obtained, and the electrical conductivity of doped p- and n-type porous Si can be improved to 1160 and 1390 S/m, respectively. Compared with the Si substrate, the special contact resistances for the doped p- and n-type porous Si layer decreases to 1.35 and 1.16 mΩ/cm2, respectively, by increasing the carrier concentration. However, the increase of the carrier concentration induces the decline of the Seebeck coefficient for p- and n-type Si substrates with doped porous Si samples to 491 and 480 μV/K, respectively. Power factor is related to the Seebeck coefficient and electrical conductivity of thermoelectric material, which is one vital factor that evaluates its output performance. Therefore, even though the Seebeck coefficient values of Si substrates with doped porous Si samples decrease, the doped porous Si layer can improve the power factor compared to undoped samples due to the enhancement of electrical conductivity, which facilitates its development for thermoelectric application.

scholarly journals A Molecular Model of PEMFC Catalyst Layer: Simulation on Reactant Transport and Thermal Conduction

Membranes ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 148
Author(s):  
Wenkai Wang ◽  
Zhiguo Qu ◽  
Xueliang Wang ◽  
Jianfei Zhang
Keyword(s):  
Thermal Conductivity ◽  
Proton Exchange Membrane ◽  
Molecular Model ◽  
Phase Interface ◽  
Catalyst Layer ◽  
Md Simulations ◽  
Distribution Functions ◽  
Proton Exchange ◽  
Pt Catalyst ◽  
Reaction Efficiency

Minimizing platinum (Pt) loading while reserving high reaction efficiency in the catalyst layer (CL) has been confirmed as one of the key issues in improving the performance and application of proton exchange membrane fuel cells (PEMFCs). To enhance the reaction efficiency of Pt catalyst in CL, the interfacial interactions in the three-phase interface, i.e., carbon, Pt, and ionomer should be first clarified. In this study, a molecular model containing carbon, Pt, and ionomer compositions is built and the radial distribution functions (RDFs), diffusion coefficient, water cluster morphology, and thermal conductivity are investigated after the equilibrium molecular dynamics (MD) and nonequilibrium MD simulations. The results indicate that increasing water content improves water aggregation and cluster interconnection, both of which benefit the transport of oxygen and proton in the CL. The growing amount of ionomer promotes proton transport but generates additional resistance to oxygen. Both the increase of water and ionomer improve the thermal conductivity of the C. The above-mentioned findings are expected to help design catalyst layers with optimized Pt content and enhanced reaction efficiency, and further improve the performance of PEMFCs.

Water Management in PEMFC With Ultra-Thin Catalyst-Layers

2013 ◽  
Author(s):  
Prodip K. Das ◽  
Adam Z. Weber
Keyword(s):  
Water Management ◽  
Proton Exchange Membrane ◽  
Removal Rate ◽  
Catalyst Layer ◽  
Proton Exchange ◽  
Cathode Side ◽  
Water Capacity ◽  
Catalyst Layers ◽  
Modeling Data ◽  
Low Pt Loading

A two-dimensional non-isothermal multi-physics proton-exchange-membrane fuel-cell (PEMFC) modeling has been undertaken to investigate the interplay between the platinum (Pt) loading, water-capacity, water transport and cell performance at low operating temperatures (< 40 °C). Two ultra-thin catalyst layers (CLs), traditional Pt/C with extremely low Pt loading and nano-structured thin-film (NSTF), have been the main focus in the present model. Modeling data are compared with experimental polarization curves for both NSTF and traditional Pt/C CLs. Using the model, the interplay between the inherent CL water-capacity versus its removal rate through either the anode or cathode side of the PEMFC is explored. The controlling parameters for the water removal and accumulation (e.g., thickness of catalyst layer, existence of microporous layer, etc.) are also analyzed and the tradeoff between these parameters elucidated with a path towards efficient water management for ultra-thin CLs.

Effects of Catalysts Supporting Layer on Carbon Nanotubes Growth

2005 ◽  
Author(s):  
K. P. Yung ◽  
J. Wei ◽  
B. K. Tay
Keyword(s):  
Carbon Nanotubes ◽  
Vapor Deposition ◽  
Metal Layer ◽  
Chemical Vapor ◽  
Nitrogen Atmosphere ◽  
Thermal And Mechanical Properties ◽  
Catalyst Layers ◽  
Supporting Layer ◽  
Hot Filament ◽  
Deposited Films

Due to their extraordinary electrical, thermal and mechanical properties, carbon nanotubes have been foreseen as potential materials for electronics devices in the future. To integrate carbon nanotubes in electronic applications, carbon nanotubes would need to be grown on different metal layer. In this study, carbon nanotubes growth with Ni as catalyst on three different support layers, Cu, Al and Cr, by hot filament chemical vapor deposition (HFCVD) is reported. The nanotubes were grown using C2H2 acetylene as carbon feedstock, in a hydrogen and nitrogen atmosphere. The catalyst layers and their support layers were deposited by magnetron sputtering technique. Deposited films were annealed at 600 °C for 10 minutes before exposing to C2H2 for the growth of nanotubes at same temperature for another 10 minutes. The effects of the support layer have been investigated with reference to nanotubes formation. The morphology and microstructure of the films were measured and analyzed by scanning electron microscopy (SEM) and Raman spectrometer. It was found that reaction of the catalyst with its supporting layer has significant effects on the growth of nanotubes. For Cu or Cr as support layer, its effect on the nanotubes growth was minimal. However Al support layer prevented the growth of carbon nanotubes. The possible mechanisms for the observed results are proposed.

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