Synthesis and characterization of platinum nanoparticles on in situ grown carbon nanotubes based carbon paper for proton exchange membrane fuel cell cathode

Multi-walled carbon nanotubes (MWCNTs) based micro-porous layer on the carbon paper substrates was prepared by in situ growth in a chemical vapor deposition setup. Platinum nanoparticles were deposited on in situ grown MWCNTs/carbon paper by a wet chemistry route at <100 °C. The in situ MWCNTs/carbon paper was initially surface modified by silane derivative to incorporate sulfonic acid–silicate intermediate groups which act as anchors for metal ions. Platinum nanoparticles deposition on the in situ MWCNTs/carbon paper was carried out by reducing platinum (II) acetylacetonate precursor using glacial acetic acid. High resolution TEM images showed that the platinum particles are homogeneously distributed on the outer surface of MWCNTs with a size range of 1–2 nm. The Pt/MWCNTs/carbon paper electrode with a loading of 0.3 and 0.5 mg Pt cm⁻² was evaluated in proton exchange membrane single cell fuel cell using H₂/O₂. The single cells exhibited a peak power density of 600 and 800 mW cm⁻² with catalyst loadings of 0.3 and 0.5 mg Pt cm⁻², respectively with H₂/O₂ at 80 °C, using Nafion-212 electrolyte. In order to understand the intrinsically higher fuel cell performance, the electrochemically active surface area was estimated by the cyclic voltammetry of the Pt/MWCNTs/carbon paper.     

Experimental study of commercial size proton exchange membrane fuel cell performance

Commercial sized (16 × 16 cm² active surface area) proton exchange membrane (PEM) fuel cells with serpentine flow chambers are fabricated. The GORE-TEX® PRIMEA 5621 was used with a 35-μm-thick PEM with an anode catalyst layer with 0.45 mg cm⁻² Pt and cathode catalyst layer with 0.6 mg cm⁻² Pt and Ru or GORE-TEX® PRIMEA 57 was used with an 18-μm-thick PEM with an anode catalyst layer at 0.2 mg cm⁻² Pt and cathode catalyst layer at 0.4 mg cm⁻² of Pt and Ru. At the specified cell and humidification temperatures, the thin PRIMEA 57 membrane yields better cell performance than the thick PRIMEA 5621 membrane, since hydration of the former is more easily maintained with the limited amount of produced water. Sufficient humidification at both the cathode and anode sides is essential to achieve high cell performance with a thick membrane, like the PRIMEA 5621. The optimal cell temperature to produce the best cell performance with PRIMEA 5621 is close to the humidification temperature. For PRIMEA 57, however, optimal cell temperature exceeds the humidification temperature.     

Performance and degradation of high temperature polymer electrolyte fuel cell catalysts

An investigation of carbon-supported Pt/C and PtCo/C catalysts was carried out with the aim to evaluate their stability under high temperature polymer electrolyte membrane fuel cell (PEMFC) operation. Carbon-supported nanosized Pt and PtCo particles with a mean particle size between 1.5 nm and 3 nm were prepared by using a colloidal route. A suitable degree of alloying was obtained for the PtCo catalyst by using a carbothermal reduction. The catalyst stability was investigated to understand the influence of carbon black corrosion, platinum dissolution and sintering in gas-fed sulphuric acid electrolyte half-cell at 75 °C and in PEMFC at 130 °C. Electrochemical active surface area and catalyst performance were determined in PEMFC at 80 °C and 130 °C. A maximum power density of about 700 mW cm⁻² at 130 °C and 3 bar abs. O₂ pressure with 0.3 mg Pt cm⁻² loading was achieved. The PtCo alloy showed a better stability than Pt in sulphuric acid after cycling; yet, the PtCo/C catalyst showed a degradation after the carbon corrosion test. The PtCo/C catalyst showed smaller sintering effects than Pt/C after accelerated degradation tests in PEMFC at 130 °C.     

Platinum decorated aligned carbon nanotubes: Electrocatalyst for improved performance of proton exchange membrane fuel cells

This study aims to improve the performance of proton exchange membrane fuel cells (PEMFCs) using carbon nanotubes as scaffolds to support nanocatalyst for power generation over prolonged time periods, compared to the current designs. The carbon nanotubes are prepared using chemical vapor deposition and decorated by platinum nanoparticles (Pt-NPs) using an amphiphilic approach. The PEMFC devices are then constructed using these aligned carbon nanotubes (ACNTs) decorated with Pt-NPs as the cathode. The electrochemical analyses of the PEMFC devices indicate the maximum power density reaches to 860 mW cm⁻² and current density reaches 3200 mA cm⁻² at 0.2 V, respectively, when O₂ is introduced into cathode. Importantly, the Pt usage was decreased to less than 0.2 mg cm⁻², determined by X-ray energy dispersive spectroscopy and X-ray photoelectron spectroscopy as complimentary tools. Electron microscopic analyses are employed to understand the morphology of Pt-ACNT catalyst (with diameter of 4-15 nm and length from 8 to 20 μm), which affects PEMFC performance and durability. The Pt-ACNT arrays exhibit unique alignment, which allows for rapid gas diffusion and chemisorption on the catalyst surfaces.     

Platinum nanoparticles embedded in layer-by-layer films from SnO2/polyallylamine for ethanol electrooxidation

Self-assembled films from SnO₂ and polyallylamine (PAH) were deposited on gold via ionic attraction by the layer-by-layer (LbL) method. The modified electrodes were immersed into a H₂PtCl₆ solution, a current of 100 μA was applied, and different electrodeposition times were used. The SnO₂/PAH layers served as templates to yield metallic platinum with different particle sizes. The scanning tunnel microscopy images show that the particle size increases as a function of electrodeposition time. The potentiodynamic profile of the electrodes changes as a function of the electrodeposition time in 0.5 mol L⁻¹ H₂SO₄, at a sweeping rate of 50 mV s⁻¹. Oxygen-like species are formed at less positive potentials for the Pt–SnO₂/PAH film in the case of the smallest platinum particles. Electrochemical impedance spectroscopy measurements in acid medium at 0.7 V show that the charge transfer resistance normalized by the exposed platinum area is 750 times greater for platinum electrode (300 kΩ cm²) compared with the Pt–SnO₂/PAH film with 1 min of electrodeposition (0.4 kΩ cm²). According to the Langmuir–Hinshelwood bifunctional mechanism, the high degree of coverage with oxygen-like species on the platinum nanoparticles is responsible for the electrocatalytic activity of the Pt–SnO₂/PAH concerning ethanol electrooxidation. With these features, this Pt–SnO₂/PAH film may be grown on a proton exchange membrane (PEM) in direct ethanol fuel cells (DEFC).     

Preparation of Pt/zeolite–Nafion composite membranes for self-humidifying polymer electrolyte fuel cells

A novel Pt/zeolite–Nafion (PZN) polymer electrolyte composite membrane is fabricated for self-humidifying polymer electrolyte membrane fuel cells (PEMFCs). A uniform dispersion of Pt nanoparticles with an average size of 3 nm is achieved by ion-exchange of the zeolite HY. The Pt nanoparticles embedded in the membrane provide the catalytic sites for water generation, whereas the zeolite HY-supported Pt particles absorbs water and make it available for humidification during cell operation at elevated temperature. Compared with the performance of ordinary membranes, the performance of cells with PZN membranes is improved significantly under dry conditions. With dry H₂ and O₂ at 50 °C, the PZN membrane with 0.65 wt.% of Pt/zeolite (0.03 mg Pt cm⁻²) gives 75% of the performance obtained at 0.6 V with the humidified reactants at 75 °C. Impedance analysis reveales that an increase in charge-transfer resistance is mainly responsible for the cell performance loss operated with dry gases.     

Direct alkaline fuel cell for multiple liquid fuels: Anode electrode studies

A direct alkaline fuel cell with a liquid potassium hydroxide solution as an electrolyte is developed for the direct use of methanol, ethanol or sodium borohydride as fuel. Three different catalysts, e.g., Pt-black or Pt/Ru (40 wt.%:20 wt.%)/C or Pt/C (40 wt.%), with varying loads at the anode against a MnO₂ cathode are studied. The electrodes are prepared by spreading the catalyst slurry on a carbon paper substrate. Nickel mesh is used as a current-collector. The Pt–Ru/C produces the best cell performance for methanol, ethanol and sodium borohydride fuels. The performance improves with increase in anode catalyst loading, but beyond 1 mg cm⁻² does not change appreciably except in case of ethanol for which there is a slight improvement when using Pt–Ru/C at 1.5 mA cm⁻². The power density achieved with the Pt–Ru catalyst at 1 mg cm⁻² is 15.8 mW cm⁻² at 26.5 mA cm⁻² for methanol and 16 mW cm⁻² at 26 mA cm⁻² for ethanol. The power density achieved for NaBH₄ is 20 mW cm⁻² at 30 mA cm⁻² using Pt-black.     

Characterization and single cell testing of Pt/C electrodes prepared by electrodeposition

Electrodes for proton exchange membrane fuel cells (PEMFC) have been prepared by the electrodeposition method. For this task, the electrodeposition of platinum is carried out on a carbon black substrate impregnated with an ionomer, proton conducting, medium. Before electrodeposition, the substrate is submitted to an activation process to increase the hydrophilic character of the surface to a few microns depth.Electrodeposition of platinum takes place inside the generated surface hydrophilic layer, resulting in a continuous phase covering totally or partially carbon substrate grains. Cross sectional images show a decay profile of platinum towards the interior of the substrate, reflecting a deposition process limited by diffusion of PtCl₆²⁻ through the porous substrate. Electrodes with different platinum loads have been prepared, and membrane electrode assemblies (MEA) have been mounted with the electrodeposited electrodes as cathode and other standard components (commercial anode and Nafion^R 117 membrane). The electrochemically active surface area determined from hydrogen underpotential deposition charge, is lower on the electrodeposited electrodes than on standard electrodes. However, single cell testing shows higher mass specific activity on electrodeposited cathodes with low and intermediate Pt load (below 0.05 mg Pt cm⁻²).     

Inkjet printing of carbon supported platinum 3-D catalyst layers for use in fuel cells

We present a method of using inkjet printing (IJP) to deposit catalyst materials onto gas diffusion layers (GDLs) that are made into membrane electrode assemblies (MEAs) for polymer electrolyte fuel cell (PEMFC). Existing ink deposition methods such as spray painting or screen printing are not well suited for ultra low (<0.5 mg Pt cm⁻²) loadings. The IJP method can be used to deposit smaller volumes of water based catalyst ink solutions with picoliter precision provided the solution properties are compatible with the cartridge design. By optimizing the dispersion of the ink solution we have shown that this technique can be successfully used with catalysts supported on different carbon black (i.e. XC-72R, Monarch 700, Black Pearls 2000, etc.). Our ink jet printed MEAs with catalyst loadings of 0.020 mg Pt cm⁻² have shown Pt utilizations in excess of 16,000 mW mg⁻¹ Pt which is higher than our traditional screen printed MEAs (800 mW mg⁻¹ Pt). As a further demonstration of IJP versatility, we present results of a graded distribution of Pt/C catalyst structure using standard Johnson Matthey (JM) catalyst. Compared to a continuous catalyst layer of JM Pt/C (20% Pt), the graded catalyst structure showed enhanced performance.     

Performance of a direct methanol alkaline membrane fuel cell

A study of a direct methanol fuel cell (DMFC) operating with hydroxide ion conducting membranes is reported. Evaluation of the fuel cell was performed using membrane electrode assemblies incorporating carbon-supported platinum/ruthenium anode and platinum cathode catalysts and ADP alkaline membranes. Catalyst loadings used were 1 mg cm⁻² Pt for both anode and cathode. The effect of temperature, oxidant (air or oxygen) and methanol concentration on cell performance is reported. The cell achieved a power density of 16 mW cm⁻², at 60 °C using oxygen. The performance under near ambient conditions with air gave a peak power density of approximately 6 mW cm⁻².     

Ni–Pt/C as anode electrocatalyst for a direct borohydride fuel cell

In this study, a series of Ni–Pt/C and Ni/C catalysts, which were employed as anode catalysts for a direct borohydride fuel cell (DBFC), were prepared and investigated by XRD, TEM, cyclic voltammetry, chronopotentiometry and fuel cell test. The particle size of Ni₃₇–Pt₃/C (mass ratio, Ni:Pt = 37:3) catalyst was sharply reduced by the addition of ultra low amount of Pt. And the electrochemical measurements showed that the electro-catalytic activity and stability of the Ni₃₇–Pt₃/C catalysts were improved compared with Ni/C catalyst. The DBFC employing Ni₃₇–Pt₃/C catalyst on the anode (metal loading, 1 mg cm⁻²) showed a maximum power density of 221.0 mW cm⁻² at 60 °C, while under identical condition the maximum power density was 150.6 mW cm⁻² for Ni/C. Furthermore, the polarization curves and hydrogen evolution behaviors on all the catalysts were investigated on the working conditions of the DBFC.     

Use of cellulose-based carbon aerogels as catalyst support for PEM fuel cell electrodes: Electrochemical characterization

New nanostructured carbons have been developed through pyrolysis of organic aerogels, based on supercritical drying of cellulose acetate gels. These cellulose acetate-based carbon aerogels (CA) are activated by CO₂ at 800 °C and impregnated by PtCl₆²⁻; the platinum salt is then chemically or electrochemically reduced. The resulting platinized carbon aerogels (Pt/CA) are characterized with transmission electron microscopy (TEM) and electrochemistry. The active area of platinum is estimated from hydrogen adsorption/desorption or CO-stripping voltammetry: it is possible to deposit platinum nanoparticles onto the cellulose acetate-based carbon aerogel surface in significant proportions. The oxygen reduction reaction (ORR) kinetic parameters of the Pt/CA materials, determined from quasi-steady-state voltammetry, are comparable with that of Pt/Vulcan XC72R. These cellulose acetate-based carbon aerogels are thus promising electrocatalyst support for PEM application.     

Ultra low Pt-loading electrode prepared by displacement of electrodeposited Cu particles on a porous carbon electrode

Ultra low Pt-loading and high Pt utilization electrodes were prepared by displacement of electrodeposited Cu on a porous carbon electrode. Copper particles were electrodeposited on a porous carbon electrode (PCE) by four-step deposition (FSD) at first. The size and dispersion of deposited Cu particles were markedly improved with application of the FSD. The Cu deposits were then displaced by platinum as dipping a Cu/PCE in a platinum salt solution. Sequentially, Pt particles supported on the PCE were obtained. The Pt/PCE electrode prepared via the FSD of Cu overcomes the problem of the hydrogen evolution reaction accompanied with direct platinum electrochemical deposition, and has a high Pt dispersion. The single cell consisting of the electrodes Pt/PCE via the FSD of Cu outputs a power of 0.45 W cm⁻² with ultra low Pt loadings of 0.196 mg cm⁻² MEA (0.098 mg cm⁻² per each side of the MEA) at no backpressure of reactant gases.     

Performance of a miniaturized silicon reformer-PrOx-fuel cell system

A fuel cell made with silicon is operated with hydrogen supplied by a reformer and a preferential oxidation (PrOx) reactor those are also made with silicon. The performance and durability of the fuel cell is analyzed and tested, then compared with the results obtained with pure hydrogen. Three components of the system are made using silicon technologies and micro electro-mechanical system (MEMS) technology. The commercial Cu-ZnO-Al₂O₃ catalyst for the reformer and the Pt-Al₂O₃ catalyst for the PrOx reactor are coated by means of a fill-and-dry method. A conventional membrane electrode assembly composed of a 0.375 mg cm⁻² PtRu/C catalyst for the anode, a 0.4 mg cm⁻² Pt/C catalyst for the cathode, and a Nafion™ 112 membrane is introduced to the fuel cell. The reformer gives a 27 cm³ min⁻¹ gas production rate with 3177 ppm CO concentration at a 1 cm³ h⁻¹ methanol feed rate and the PrOx reactor shows almost 100% CO conversion under the experimental conditions. Fuel cells operated with this fuel-processing system produce 230 mW cm⁻² at 0.6 V, which is similar to that obtained with pure hydrogen.     

Development of high performance carbon composite catalyst for oxygen reduction reaction in PEM Proton Exchange Membrane fuel cells

Highly active and stable carbon composite catalysts for oxygen reduction in PEM fuel cells were developed through the high-temperature pyrolysis of Co–Fe–N chelate complex, followed by the chemical post-treatment. A metal-free carbon catalyst was used as the support. The carbon composite catalyst showed an onset potential for oxygen reduction as high as 0.87 V (NHE) in H₂SO₄ solution, and generated less than 1% H₂O₂. The PEM fuel cell exhibited a current density as high as 0.27 A cm⁻² at 0.6 V and 2.3 A cm⁻² at 0.2 V for a catalyst loading of 6.0 mg cm⁻². No significant performance degradation was observed over 480 h of continuous fuel cell operation with 2 mg cm⁻² catalyst under a load of 200 mA cm⁻² as evidenced by a resulting cell voltage of 0.32 V with a voltage decay rate of 80 μV h⁻¹. Materials characterization studies indicated that the metal–nitrogen chelate complexes decompose at high pyrolysis temperatures above 800 °C, resulting in the formation of the metallic species. During the pyrolysis, the transition metals facilitate the incorporation of pyridinic and graphitic nitrogen groups into the carbon matrix, and the carbon surface doped with nitrogen groups is catalytically active for oxygen reduction.     

Microbial fuel cell cathode with dendrimer encapsulated Pt nanoparticles as catalyst

In this paper, we investigated the use of polyamidoamine (PAMAM) dendrimer-encapsulated platinum nanoparticles (Pt-DENs) as a promising type of cathode catalyst for air-cathode single chamber microbial fuel cells (SCMFCs). The Pt-DENs, prepared via template synthesis method, have uniform diameter distribution with size range of 3-5 nm. The Pt-DENs then loaded on to a carbon substrate. For comparison, we also electrodeposited Pt on carbon substrate. The calculation shows that the loading amount of Pt-DENs on carbon substrate is about 0.1 mg cm⁻², which is three times lower than that of the electrodeposited Pt (0.3 mg cm⁻²). By measuring batch experiments, the results show that Pt-DENs in air-cathode SCMFCs have a power density of 630 ± 5 mW m⁻² and a current density of 5200 ± 10 mA m⁻² (based on the projected anodic surface area), which is significantly better than electrodeposited Pt cathodes (power density: 275 ± 5 mW m⁻² and current density: 2050 ± 10 mA m⁻²). Additionally, Pt-DENs-based cathodes resulted in a higher power production with 129.1% as compared to cathode with electrodeposited Pt. This finding suggests that Pt-DENs in MFC cathodes is a better catalyst and has a lower loading amount than electrodeposited Pt, and may serve as a novel and alternative catalyst to previously used noble metals in MFC applications.     

An investigation of Pt alloy oxygen reduction catalysts in phosphoric acid doped PBI fuel cells

A study of a phosphoric acid doped polybenzimidazole (PBI) membrane fuel cell using commercial carbon supported, Pt alloy oxygen reduction catalysts is reported. The cathodes were made from PTFE bonded carbon supported Pt alloys without PBI but with phopshoric acid added to the electrode for ionic conductivity. Polarisation data for fuel cells with cathodes made with alloys of Pt with Ni, Co, Ru and Fe are compared with those with Pt alone as cathode at temperatures between 120 and 175 °C. With the same loading of Pt enhancement in cell performance was achieved with all alloys except Pt-Ru, in the low current density activation kinetics region of operation. The extent of enhancement depended upon the operating temperature and also the catalyst loading. In particular a Pt-Co alloy produced performance significantly better than Pt alone, e.g. a peak power, with low pressure air, of 0.25 W cm⁻² with 0.2 mg Pt cm⁻² of a 20 wt% Pt-Co catalyst.     

Performance increase of microfluidic formic acid fuel cell using Pd/MWCNTs as catalyst

This paper shows that the combination of an O₂ saturated acidic fluid setup (O₂-setup) and a composite of Pd nanoparticles supported on multiwalled-carbon nanotubes (Pd/MWCNTs) as anode catalyst material, results in the improvement of microfluidic fuel cell performance. Microfluidic fuel cells were constructed and evaluated at low HCOOH concentrations (0.1 and 0.5 M) using Pd/V XC-72 and Pd/MWCNTs as anode and Pt/V XC-72 as cathode electrode materials, respectively. The results show a higher power density (2.9 mW cm⁻²) for this cell when compared to the value reported in the literature that considers a commercial Pd/V XC-72 and 3.3 mW cm⁻² using a Pd/MWCNTs with a 50% less Pd loading than that commercial Pd/V XC-72.     

Direct borohydride fuel cell using Ni-based composite anodes

In this study, nickel-based composite anode catalysts consisting of Ni with either Pd on carbon or Pt on carbon (the ratio of Ni:Pd or Ni:Pt being 25:1) were prepared for use in direct borohydride fuel cells (DBFCs). Cathode catalysts used were 1 mg cm⁻² Pt/C or Pd electrodeposited on activated carbon cloth. The oxidants were oxygen, oxygen in air, or acidified hydrogen peroxide. Alkaline solution of sodium borohydride was used as fuel in the cell. High power performance has been achieved by DBFC using non-precious metal, Ni-based composite anodes with relatively low anodic loading (e.g., 270 mW cm⁻² for NaBH₄/O₂ fuel cell at 60 °C, 665 mW cm⁻² for NaBH₄/H₂O₂ fuel cell at 60 °C). Effects of temperature, oxidant, and anode catalyst loading on the DBFC performance were investigated. The cell was operated for about 100 h and its performance stability was recorded.