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.     

Synthesis and characterization of carbon nanotubes supported platinum nanocatalyst for proton exchange membrane fuel cells

Multi-walled carbon nanotubes (MWCNTs) were used as catalyst support for depositing platinum nanoparticles by a wet chemistry route. MWCNTs were initially surface modified by citric acid to introduce functional groups which act as anchors for metallic clusters. A two-phase (water-toluene) method was used to transfer PtCl₆²⁻ from aqueous to organic phase and the subsequent sodium formate solution reduction step yielded Pt nanoparticles on MWCNTs. High-resolution TEM images showed that the platinum particles in the size range of 1-3 nm are homogeneously distributed on the surface of MWCNTs. The Pt/MWCNTs nanocatalyst was evaluated in the proton exchange membrane (PEM) single cell using H₂/O₂ at 80 °C with Nafion-212 electrolyte. The single PEM fuel cell exhibited a peak power density of about 1100 mW cm⁻² with a total catalyst loading of 0.6 mg Pt cm⁻² (anode: 0.2 mg Pt cm⁻² and cathode: 0.4 mg Pt cm⁻²). The durability of Pt/MWCNTs nanocatalyst was evaluated for 100 h at 80 °C at ambient pressure and the performance (current density at 0.4 V) remained stable throughout. The electrochemically active surface area (64 m² g⁻¹) as estimated by cyclic voltammetry (CV) was also similar before and after the durability test.     

Functionalizing carbon nanotubes for proton exchange membrane fuel cells electrode

In recent years, carbon nanotubes (CNTs) have been increasingly considered as an advanced metal catalyst support for proton exchange membrane fuel cells (PEMFCs), owing to their outstanding physical and mechanical characteristics. However, the effective attachment of metal catalysts, uniformly dispersed onto the CNT surface, remains a formidable challenge because of the inertness of the CNT walls. Therefore, the surface functionalization of CNTs seems necessary in most cases in order to enable a homogeneous metal deposition. This review presents the different surface functionalization approaches that provide efficient avenues for the deposition of metal nanoparticles on CNTs, for the application of catalyst supports in PEMFCs with improved reactivity.     

High loading and monodispersed Pt nanoparticles on multiwalled carbon nanotubes for high performance proton exchange membrane fuel cells

Composite electrodes consisting of Pt nanoparticles-supported on multiwalled carbon nanotubes grown directly on carbon paper (Pt/CNTs/carbon paper) have been synthesized by a new method using glacial acetic acid as a reducing agent. Transmission electron microscopy (TEM) images show that the Pt nanoparticles with high density and relative small in size (2–4 nm) were monodispersed on the surface of CNTs. X-ray photoelectron spectroscopy (XPS) analysis indicates that the glacial acetic acid acts as a reducing agent and has the capability of producing a high density of oxygen-containing functional groups on the surface of CNTs that leads to high density and monodispersion of Pt nanoparticles. Compared with standard Pt/C electrode, the Pt/CNT/carbon paper composite electrodes exhibit higher electrocatalytic activity for methanol oxidation reaction and higher single-cell performance in a H₂/O₂ fuel cell.     

Tungsten oxide nanowires grown on carbon paper as Pt electrocatalyst support for high performance proton exchange membrane fuel cells

Tungsten oxide nanowires (W₁₈O₄₉ NWs) were directly grown on carbon paper by chemical vapor deposition. Well-dispersed Pt nanoparticles, with a size distribution from 2 to 4 nm, were deposited on the surface of W₁₈O₄₉ NWs through a simple reductive process. The resulting Pt/W₁₈O₄₉ NW/carbon paper composites formed a three-dimensional electrode structure. In comparison to conventional Pt/C electrocatalyst, the Pt/W₁₈O₄₉ NW/carbon paper composite exhibited higher electrocatalytic activity toward the oxygen reduction reaction and better CO tolerance in a single cell polymer electrolyte membrane fuel cell.     

Hierarchy carbon paper for the gas diffusion layer of proton exchange membrane fuel cells

This communication described the fabrication of a hierarchy carbon paper, and its application to the gas diffusion layer (GDL) of proton exchange membrane (PEM) fuel cells. The carbon paper was fabricated by growing carbon nanotubes (CNTs) on carbon fibers via covalently assembling metal nanocatalysts. Surface morphology observation revealed a highly uniform distribution of hydrophobic materials within the carbon paper. The contact angle to water of this carbon paper was not only very large but also particularly even. Polarization measurements verified that the hierarchy carbon paper facilitated the self-humidifying of PEM fuel cells, which could be mainly attributed to its higher hydrophobic property as diagnosed by electrochemical impedance spectroscopy (EIS).     

Effects of surface chemical states of carbon nanotubes supported Pt nanoparticles on performance of proton exchange membrane fuel cells

This study synthesized platinum (Pt) nanoparticles supported on carbon nanotubes (CNTs) using a microwave-assisted polyol method. The oxidation treatment of CNTs introduced primarily -OH and -COOH groups to the CNTs, thereby enhancing the reduction of Pt ionic species, resulting in smaller Pt particles with improved dispersion and attachment properties. The Pt particles supported on oxidized CNTs displayed superior durability to those on pristine CNTs or commercially available Pt/C. These improvements are most likely associated with the percentage of metallic Pt in the particles. After 400 cycles, the losses of electrochemical surface area in Pt nanoparticle supported on oxidized CNTs and pristine CNTs catalysts were 66 and 84%, respectively, of that associated with commercial Pt/C. A single proton exchange membrane fuel cell using Pt supported on oxidized CNTs at the cathode with a total catalytic loading of 0.6 Pt mg cm⁻² exhibited the highest power density of 890 mW cm⁻² and displayed a lower mass transfer loss, compared to Pt/C.     

Highly uniform platinum nanoparticles supported on graphite nanoplatelets as a catalyst for proton exchange membrane fuel cells

Graphite nanoplatelets (GNPs), which consist of layers of graphene, are an ideal electrocatalyst support due to their high electrical and thermal conductivity, excellent chemical stability, and easy availability. However, GNPs are somewhat chemically inert, which makes the even deposition of catalytic metal nanoparticles on their surface difficult. In this paper, we present a facile method to prepare highly uniform Pt nanoparticles on GNPs, which are decorated with 1-pyrenecarboxylic acid (PCA). When the hydrophobic pyrene group of the PCA is adsorbed on the surface of GNPs via π–π interaction, its carboxylic group can serve as an anchor for the Pt deposition. This decoration facilitates a narrow size profile, which is centered at approximately 2–3 nm, and an even spatial distribution on the GNPs surface for the Pt nanoparticles. The resultant Pt/GNPs catalyst exhibits a noticeably higher durability and electrochemical activity than the commonly used Pt/C catalyst and is therefore a promising cathodic catalyst for proton exchange membrane fuel cells.     

Surfactant-assisted synthesis of platinum nanoparticle catalysts for proton exchange membrane fuel cells

High-performance platinum nanoparticle catalysts (Pt–NPCs) remain the most widespread applied electrocatalysts for oxygen reduction reaction (ORR). Here, cetyltrimethylammonium bromide (CTAB), a surface-controlling agent, is introduced to modulate the microstructure and size of Pt nanoparticles (NPs) via a microwave-assisted heating process. The Pt-NPC assisted by 5 wt% CTAB exhibits the highest mass activity (MA) of 0.072 A mg_Pt^?1 and specific activity (SA) of 0.077 mA cm^?2, higher than those of commercial Pt/C (0.023 A mg_Pt^?1 and 0.035 mA cm^?2). Transmission electron microscopy (TEM) results indicate that Pt NPs are uniformly dispersed onto carbon supports with an average size of 2.39 nm. When applied in membrane electrode assembly (MEA), it exhibits the highest power density of 1.142 W cm^?2, which is about 1.24 times larger than that of commercial Pt/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.     

Dodecylamine-modified carbon supports for cathode in proton exchange membrane fuel cells

In this investigation, hydrophobic dodecylamine-modified carbon supports are prepared for proton exchange membrane fuel cells by organic synthesis. Well-dispersed Pt-Ru nanoparticles, with a narrow size distribution, are then deposited on the dodecylamine-modified carbon supports by methanol reduction to serve as cathodic catalysts. These dodecylamine-modified catalysts are separately mixed with either a commercial catalyst or unmodified catalyst to provide hydrophobic channels to convey the reaction gas to the active sites in the catalyst layer. The best cathode composite catalyst, containing 20-40 wt% of modified-catalyst, gives approximate 30% increase in the maximum power density, comparing to E-TEK catalyst (125 mW cm⁻²). The increase in the maximum power density is attributed to higher activity and lower resistance. This result is discussed in the context of AC-impedance and proton conductivity analysis.     

In situ diagnostics for water transport in proton exchange membrane fuel cells

Proton exchange membrane fuel cells (PEMFCs) have attracted considerable attention as energy-conversion systems for future applications in vehicles and for on-site power generation. Major technical challenges exist in achieving a high cell performance over a wide range of operating conditions, such as various cell current densities, operating temperatures, and relative humidities of the supplied gases. Correct water management is critical to achieving a high power density, long-term operation, and increased robustness in PEMFCs. Aspects such as the swelling of the membrane by water, the generation and accumulation of liquid water inside the fuel cells, and the discharge of accumulated water need to be clarified to ensure a fundamental understanding of water transport in PEMFCs. In this article, we examine the state of art regarding in situ diagnostics, particularly visualization techniques, for probing the behaviour of water in PEMFCs, with attention to neutron radiography, X-ray imaging, magnetic resonance imaging, and optical visualization techniques. The recent rapid development of in situ imaging techniques with high spatial and temporal resolutions provides a novel platform for the development of PEMFCs.     

Effect of carbon black concentration in carbon fiber paper on the performance of low-temperature proton exchange membrane fuel cells

This study uses fuel cell gas diffusion layers (GDLs) made from carbon fiber paper containing carbon black in proton exchange membrane fuel cells (PEMFCs) in order to determine the relationship between carbon black content and fuel cell performance. The connection between fuel cell performance and the carbon black content of the carbon fiber paper is discussed, and the effects of carbon black on the carbon fiber paper's thickness, density, and surface resistivity are investigated. When a carbon fiber paper GDL contains 10 wt% phenolic resin and 2% carbon black, and reaction area was 25 cm² and operating temperature 40 °C, tests show that a carbon electrode fuel cell could achieve 1026.4 mA cm⁻² and maximum power of 612.8 mW cm⁻² under a 0.5 V load.     

Electrochemical carbon corrosion in high temperature proton exchange membrane fuel cells

Electrochemical carbon corrosion occurring in a high temperature proton exchange membrane fuel cell (HT-PEMFC) operating under non-humidification conditions was investigated by measuring CO₂ generation using on-line mass spectrometry and comparing the results with a low-temperature proton exchange membrane fuel cell (LT-PEMFC) operated under fully humidified conditions. The experimental results showed that more CO₂ was measured for the HT-PEMFC, indicating that more electrochemical carbon corrosion occurs in HT-PEMFCs. This observation is attributed to the enhanced kinetics of electrochemical carbon corrosion due to the elevated operating temperature in HT-PEMFCs. Additionally, electrochemical carbon corrosion in HT-PEMFCs showed a strong dependence on water content. Therefore, it is critical to remove the water content in the supply gases to reduce electrochemical carbon corrosion.     

In situ diagnosis of micrometallic proton exchange membrane fuel cells using microsensors

This work utilizes the microsensors that are fabricated on metallic bipolar plates to measure temperature and humidity in an operating micro-proton exchange membrane fuel cell (PEMFC). Bipolar plates were constructed of stainless steel (SS-304), and the flow channel was formed on a stainless steel substrate by wet etching. The micro-temperature and humidity sensors were fabricated using micro-electro-mechanical-systems (MEMS) technology. The sensors were located on the flow channel rib.     

Stable support based on highly graphitic carbon xerogel for proton exchange membrane fuel cells

Highly graphitic carbon xerogel (GCX) is prepared by the modified sol-gel polymerization process using cobalt nitrate as the catalyst, followed by high temperature treatment at 1800 °C. The as-prepared GCX is explored as a stable support for Pt in proton exchange membrane fuel cells. The results of N₂ sorption measurement and X-ray diffraction analysis (XRD) reveal that GCX has a better mesoporous structure and a preferably higher degree of graphitization, compared with the commercial XC-72 carbon black. The transmission electron microscopy (TEM) image indicates that Pt nanoparticles are well dispersed on GCX and exhibit relatively narrow size distribution. Accelerated aging test (AAT) based on potential cycling is used to investigate the durability of the as-prepared Pt/GCX in comparison with the commercial Pt/C. Electrochemical analysis demonstrates that the catalyst with GCX as a support exhibits an alleviated degradation rate of electrochemical active surface area (39% for Pt/GCX and 53% for Pt/C). The results of single cell durability tests indicate that the voltage loss of Pt/GCX at 100 mA cm⁻² is about 50% lower than that of Pt/C. GCX is expected to be a corrosion resistant electrocatalyst support.     

Enhanced catalytic properties from platinum nanodots covered carbon nanotubes for proton-exchange membrane fuel cells

An efficient fabrication method for carbon nanotube (CNT)-based electrode with a nanosized Pt catalyst is developed for high efficiency proton-exchange membrane fuel cells (PEMFC). The integrated Pt/CNT layer is prepared by in situ growth of a CNT layer on carbon paper and subsequent direct sputter-deposition of the Pt catalyst. Both scanning electron microscopy (SEM) and transmission electron microscopy (TEM) demonstrate that this Pt/CNT layer consists of a highly porous CNT layer covered by well-dispersed Pt nanodots with a narrow size distribution. Compared with conventional gas-diffusion layer assisted electrodes, the CNT-based electrode with a Pt/CNT layer acting as a combined gas-diffusion layer and catalyst layer shows pronounced improvement in polarization tests. A high maximum power density of 595 mW cm⁻² is observed for a low Pt loading of 0.04 mg cm⁻² at the cathode.     

Preparation and operation of gas diffusion electrodes for high-temperature proton exchange membrane fuel cells

Gas diffusion electrodes for high-temperature PEMFC based on acid-doped polybenzimidazole membranes were prepared by a tape-casting method. The overall porosity of the electrodes was tailored in a range from 38% to 59% by introducing porogens into the supporting and/or catalyst layers. The investigated porogens include volatile ammonium oxalate, carbonate and acetate and acid-soluble zinc oxide, among which are ammonium oxalate and ZnO more effective in improving the overall electrode porosity. Effects of the electrode porosity on the fuel cell performance were investigated in terms of the cathodic limiting current density and minimum air stoichiometry, anodic limiting current and hydrogen utilization, as well as operations under different pressures and temperatures.     

Metal oxide nanoparticles synthesized by pulsed laser ablation for proton exchange membrane fuel cells

We report on the development of a modified gas diffusion layer for fuel cells consisting of a simple or teflonized carbon cloth pulsed laser deposited with metal oxide nanostructures designed to operate both as co-catalyst, and oxidic support for other electrochemically active catalysts. We selected TiO₂, ZnO and Al₂O₃ doped (2 wt.%) ZnO which were uniformly distributed over the surface of gas diffusion layers in order to improve the catalytic activity, stability and lifetime, and reduce the production costs of proton exchange membrane fuel cells. We evidenced by scanning electron microscopy and energy dispersive spectroscopy that our depositions consisted of TiO₂ nanoparticles while in the case of ZnO and Al₂O₃ doped (2 wt.%) ZnO transparent quasi-continuous films were synthesized.     

Preparation and performance of nano silica/Nafion composite membrane for proton exchange membrane fuel cells

Composite membranes made from Nafion ionomer with nano phosphonic acid-functionalised silica and colloidal silica were prepared and evaluated for proton exchange membrane fuel cells (PEMFCs) operating at elevated temperature and low relative humidity (RH). The phosphonic acid-functionalised silica additive obtained from a sol–gel process was well incorporated into Nafion membrane. The particle size determined using transmission electron microscope (TEM) had a narrow distribution with an average value of approximately 11 nm and a standard deviation of ±4 nm. The phosphonic acid-functionalised silica additive enhanced proton conductivity and water retention by introducing both acidic groups and porous silica. The proton conductivity of the composite membrane with the acid-functionalised silica was 0.026 S cm⁻¹, 24% higher than that of the unmodified Nafion membrane at 85 °C and 50% RH. Compared with the Nafion membrane, the phosphonic acid-functionalised silica (10% loading level) composite membrane exhibited 60 mV higher fuel cell performance at 1 A cm⁻², 95 °C and 35% RH, and 80 mV higher at 0.8 A cm⁻², 120 °C and 35% RH. The fuel cell performance of composite membrane made with 6% colloidal silica without acidic group was also higher than unmodified Nafion membrane, however, its performance was lower than the acid-functionalised silica additive composite membrane.