Feasibility of ultra-low Pt loading electrodes for high temperature proton exchange membrane fuel cells based in phosphoric acid-doped membrane

Factors as the Pt/C ratio of the catalyst, the binder content of the electrode and the catalyst deposition method were studied within the scope of ultra-low Pt loading electrodes for high temperature proton exchange membrane fuel cells (HT-PEMFCs). The Pt/C ratio of the catalyst allowed to tune the thickness of the catalytic layer and so to minimize the detrimental effect of the phosphoric acid flooding. A membrane electrode assembly (MEA) with 0.05 mg_Ptcm⁻² at anode and 0.1 mg_Ptcm⁻² at cathode (0.150 mg_Ptcm⁻² in total) attained a peak power density of 346 mW cm⁻². It was proven that including a binder in the catalytic layer of ultra-low Pt loading electrodes lowers its performance. Electrospraying-based MEAs with ultra-low Pt loaded electrodes (0.1 mg_Ptcm⁻²) rendered the best (peak power density of 400 mW cm⁻²) compared to conventional methods (spraying or ultrasonic spraying) but with the penalty of a low catalyst deposition rate.     

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.     

Chemically and thermally reduced graphene oxide supported Pt catalysts prepared by supercritical deposition

Reduced graphene oxide (RGO) is used in many energy applications, especially in Polymer Electrolyte Membrane (PEM) fuel cells, as carbon sourced catalyst support materials. In this study, thermally (T-RGO) and chemically (C-RGO) reduced GO support materials were synthesized for utilization in PEM fuel cells. Pt catalysts were synthesized using supercritical carbon dioxide (SCCO₂) deposition technique over synthesized support materials. Physical (BET, SEM-EDX, FTIR, RAMAN, XRD, TEM, ICP-MS and optical tensiometer) and electrochemical (CV, PEM fuel cell test) characterizations of synthesized support materials and corresponding Pt catalysts were performed. The differences between the structures of thermally and chemically reduced graphene oxide supports and their Pt catalysts were investigated. The ECSA values of the Pt/T-RGO and Pt/C-RGO catalysts are 19.86 m² g^?1 and 6.31 m² g^?1, respectively. The current and power density values of the Pt/T-RGO and Pt/C-RGO catalysts at 0.6 V are 84 mA cm^?2, 80 mA cm^?2 and 50 mW cm^?2, 45 mW cm^?2, respectively. Pt/T-RGO and Pt/C-RGO catalysts showed similar trend in PEMFC environment.     

Investigation of sintered stainless steel fiber felt as gas diffusion layer in proton exchange membrane fuel cells

The feasibility of using sintered stainless steel fiber felt (SSSFF) as gas diffusion layer (GDL) in proton exchange membrane fuel cells (PEMFCs) is evaluated in this study. The SSSFF is coated with an amorphous carbon (a-C) film by closed field unbalanced magnetron sputter ion plating (CFUBMSIP) to enhance the corrosion resistance and reduce the contact resistance. The characteristics of treated SSSFF, including microscopic morphology, mechanical properties, electrical conductivity, electrochemical behavior and wettablity characterization, are systematically investigated and summarized according to the requirements of GDL in PEMFC. A membrane electrode assembly (MEA) with a-C coated SSSFF-15 GDL is fabricated and assembled with a-C coated stainless steel bipolar plates in a single cell. The initial peak power density of the single cell is 877.8 mW cm⁻² at a current density of 2324.9 mA cm⁻². Lifetime test of the single cell over 200 h indicates that the a-C coating protects the SSSFF-15 GDL from corrosion and decreases the performance degradation from 30.6% to 6.3%. The results show that the SSSFF GDL, enjoying higher compressive modulus and ductility, is a promising solution to improve fluid permeability of GDL under compression and PEMFC durability.     

Preparation and performance of a nano-honeycomb cathode for microtubular solid oxide fuel cells

The effect of a nano-honeycomb cathode on the performance of a microtubular solid oxide fuel cell is investigated. We successfully prepared nano-honeycomb cathodes with high unsealing pore porosity (～64.6%) and high structural strength by freeze casting, which improved the adsorption and dissociation of oxygen. We added gadolinium doped ceria (GDC) nanopowder to the lanthanum strontium cobalt ferrite (LSCF) cathode material. The cell performance of the nano-cell structure of the GDC-LSCF cathode is significantly improved compared to a traditional GDC-LSCF cathode with a spongy porous structure. At 750 °C, the current density is 1450 mA cm^?2 and the power density is 475 mW cm^?2, which is better than that of conventional cathode structures. We discussed the effects of the honeycomb structure on the cell, including the migration of silver paste as a cathodic collector to the GDC-LSCF interface and the improvement of the activity of the oxygen electrodes.     

Morphological influence of graphitic carbon nanofibers by N–F dual-doping on Pt electrocatalytic activity and stability for oxygen reduction reaction in polymer electrolyte membrane fuel cells

Morphology of carbon nanofibers significantly effects Pt nanoparticles dispersion and specific interaction with the support, which is an important aspect in the fuel cell performance of the electrocatalysts. This study emphasizes, the defects creation and structural evolution comprised due to N–F co-doping on graphitic carbon nanofibers (GNFs) of different morphologies, viz. GNF-linearly aligned platelets (L), antlers (A), herringbone (H), and their specific interaction with Pt nanoparticle in enhancing the oxygen reduction reaction (ORR). GNFs–NF–Pt catalysts exhibit better ORR electrocatalytic activity, superior durability that is solely ascribed to the morphological evolution and the doped N–F heteroatoms, prompting the charge density variations in the resultant carbon fiber matrices. Amongst, H–NF–Pt catalyst performed outstanding ORR activity with exceptional electrochemical stability, which shows only 20 mV loss in the half-wave potential whilst 100 mV loss for Pt/C catalyst on 20,000 potential cycling. The PEMFC comprising H–NF–Pt as cathode catalyst with minimum loading of 0.10 mg cm^?2, delivers power density of 0.942 W cm^?2 at current density of 2.50 A cm^?2 without backpressures in H₂–O₂ feeds. The H–NF–Pt catalyst owing to its hierarchical architectures, performs well in PEMFC at the minimized catalyst loading with outstanding stability that can significantly decrease total price for the fuel cell.     

Power generation using an activated carbon fiber felt cathode in an upflow microbial fuel cell

An activated carbon fiber felt (ACFF) cathode lacking metal catalysts is used in an upflow microbial fuel cell (UMFC). The maximum power density with the ACFF cathode is 315 mW m⁻², compared to lower values with cathodes made of plain carbon paper (67 mW m⁻²), carbon felt (77 mW m⁻²), or platinum-coated carbon paper (124 mW m⁻², 0.2 mg-Pt cm⁻²). The addition of platinum to the ACFF cathode (0.2 mg-Pt cm⁻²) increases the maximum power density to 391 mW m⁻². Power production is further increased to 784 mW m⁻² by increasing the cathode surface area and shaping it into a tubular form. With ACFF cutting into granules, the maximum power is 481 mW m⁻² (0.5 cm granules), and 667 mW m⁻² (1.0 cm granules). These results show that ACFF cathodes lacking metal catalysts can be used to substantially increase power production in UMFC compared to traditional materials lacking a precious metal catalyst.     

Ultra-low Pt loading for proton exchange membrane fuel cells by catalyst coating technique with ultrasonic spray coating machine

This paper reports use of an ultrasonic spray for producing ultra-low Pt load membrane electrode assemblies (MEAs) with the catalyst coated membrane (CCM) fabrication technique. Anode Pt loading optimization and rough cathode Pt loading were investigated in the first stage of this research. Accurate cathode Pt coating with catalyst ink using the ultrasonic spray method was investigated in the second stage. It was found that 0.272 mg_Pt/cm² showed the best observed performance for a 33 wt% Nafion CCM when it was ultrasonically spray coated with SGL 24BC, a Sigracet manufactured gas diffusion layer (GDL). Two different loadings (0.232 and 0.155 mg_Pt/cm²) exposed to 600 mA/cm² showed cathode power mass densities of 1.69 and 2.36 W/mg_Pt, respectively. This paper presents impressive cathode mass power density and high fuel cell performance using air as the oxidant and operated at ambient pressure.     

Performance enhancement of polymer electrolyte membrane fuel cell by PtCo3 nanoporous film as high mass-specific power density catalyst using laser deposition and processing

This study demonstrates the performance of polymer electrolyte membrane fuel cell (PEMFC) can be significantly enhanced with laser deposited and processed PtCo₃ nanoporous film as the catalyst layer. The PtCo₃ nanoporous film is fabricated by first depositing a thin film of stacked PtCo₃ nanoparticles on gas diffusion layer using pulsed laser deposition and then subjecting the film to scanning continuous-wave laser processing. The heating by the scanning laser beam increases electrochemical surface area substantially, which could be ascribed to formation of Pt skin on each nanoparticle via Pt surface segregation. Furthermore, the durability of the catalyst under accelerated degradation test is greatly enhanced, which may be attributed to inhibition of Co leaching by the Pt skin and strengthening of the contacts between nanoparticles caused by concomitant sintering effect. Application of such catalyst to the cathode of a PEMFC exhibits a 2.4-fold increase in current density with respect to that without laser processing, raising the cathode mass-specific power density to 8.79 kW g⁻¹ with 1 atm oxygen and 12.0 kW g⁻¹ with 1.5 atm oxygen.     

Performance enhancement of air-breathing proton exchange membrane fuel cell through utilization of an effective self-humidifying platinum-carbon catalyst

One issue with air-breathing proton exchange membrane fuel cells (AB-PEMFCs) is that the reactants are not externally humidified, and thus the membrane or the catalyst layers might dry out due to electro-osmotic drag, diffusion and evaporation at the opening cathode. This results in a drop in internal ionic conductivity and thus in cell performance. Here, the preparation and characterization of self-humidifying carbon-supported Pt catalyst using citric acid modified carbon black (CA-CB) as the catalyst support are reported. Pt/CA-CB is highly hydrophilic due to the functional groups attached on the carbon support, which endows the ability to retain water in the membrane electrolyte assembly (MEA) and thereby help to improve the performance of AB-PEMFCs. A maximum power density of 204 mW cm⁻² can be achieved in an air-breathing PEMFC stack using Pt/CA-CB, a thick polymer membrane (NRE212) and a circular opening cathode. A 23.4% enhancement in the output power density is obtained by using Pt/CA-CB in place of a commercial catalyst when oblique slit cathodes are employed. This self-humidifying catalyst is particularly suitable for portable PEMFC applications.     

Study of the influence of Nafion/C composition on electrochemical performance of PEM single cells with ultra-low platinum load

The electrochemical performance of membrane electrode assemblies (MEAs) with ultra-low platinum load (0.02 mg_Pt cm^?2) and different compositions of Nafion/C in the catalytic layer have been investigated. The electrodes were fabricated depositing the catalytic ink, prepared with commercial catalyst (HiSPEC 2000), onto the gas diffusion layers by wet powder spraying. The MEAs were electrochemically tested using current-voltage curves and electrochemical impedance spectroscopy measurements. The experiments were carried out at 70 °C in H₂/O₂ and H₂/air as reactant gases at 1 and 2 bar pressure and 100% of relative humidity. For all MEAs tested, power density increases when the gasses pressure is increased from 1 to 2 bar. On the other hand, power density also increased when oxygen is used instead of air as oxidant gas in cathode. The lower power density (34 mW cm^?2) and power per Pt loading (0.86 kW g_Pt^?1) corresponds to the MEA prepared without Nafion in anode and cathode catalytic layers working with hydrogen and air at 1 bar pressure as reactants gas. The MEA with 30% wt Nafion/C reached the highest power density (422 mW cm^?2) and power per Pt loading (10.60 kW g_Pt^?1) using hydrogen and oxygen at 2 bar pressure. Finally, electrode surface microstructure and cross sections of MEAs were analyzed by Scanning Electron Microscopy (SEM). Examination of the electrodes, revealed that the most uniform ionomer network surface corresponds to the electrode with 40 wt% Nafion/C, and MEA ionomer-free catalytic layer shows delamination, it leads to low electrochemical performance.     

Pt nanowire growth induced by Pt nanoparticles in application of the cathodes for Polymer Electrolyte Membrane Fuel Cells (PEMFCs)

Improving cathode performance at a lower Pt loading is critical in commercial PEMFC applications. A novel Pt nanowire (Pt-NW) cathode was developed by in-situ growth of Pt nanowires in carbon matrix consisting Pt nanoparticles (Pt-NPs). Characterization of TEM and XRD shows that the pre-existing Pt-NPs from Pt/C affect Pt-NW morphology and crystallinity and Pt profile crossing the matrix thickness. The cathode with Pt-NP loading of 0.005 mg_Pt-NP cm^?2 and total cathode Pt loading of 0.205 mg_Pt cm^?2 has the specific current density of 89.56 A g_Pt^?1 at 0.9 V, which is about 110% higher than that of 42.58 A g_Pt^?1 of the commercial gas diffusion layer (GDE) with Pt loading of 0.40 mg cm^?2. When cell voltage is below 0.48 V, the Pt-NW cathode has better performance than the commercial GDE. It is believed that the excellent performance of the Pt-NW cathode is attributed to Pt-NP induction, therefore producing unique Pt-NW structure and efficient Pt utilization. A Pt-NW growth mechanism was proposed that Pt precursor diffuses into the matrix consisting of pre-existent Pt-NPs by concentration driving, and Pt-NPs provide priority sites for platinum depositing at early stage and facilitate Pt-NW growth.     

Simulation on cathode catalyst layer in proton exchange membrane fuel cell: Sensitivity of design parameters to cell performance and oxygen distribution

The microstructure tuning of the cathode catalyst layer (CCL) is crucial for proton exchange membrane fuel cell (PEMFC) performance. However, a great number of studies have been devoted to the qualitative analysis of CCL design parameters and there is a lack of quantitative studies. In this paper, a cross-dimensional PEMFC agglomerate model is developed to investigate the sensitivities of the CCL design parameters to cell performance and oxygen distribution. Although the results exhibit that the impact of Pt loading on cell performance accounts for 50.7%, the total impact of the Pt radius and I/C ratio (I/C) is as high as 44.9% under the current density of 1000 mA cm^?2. In addition, the variation in I/C directly affects the CCL porosity and thickness of the ionomer on the Pt surface, which determines the oxygen distribution. Typically, under a current density of 1000 mA cm^?2, the impacts of I/C on the average and standard deviation of oxygen concentration account for 42.3% and 51.3%, respectively. The sensitivities of the parameters evolve with the increase in the current density. Pt loading and I/C dominate the cell performance, respectively, with 1200 mA cm^?2 as the demarcation point. This study points out the optimization direction for the design of high-performance CCL.     

Effect of catalyst layer with zeolite on the performance of a proton exchange membrane fuel cell operated under low-humidity conditions

Proton exchange membrane fuel cells (PEMFCs) employ a proton conductive membrane as the separator to transport a hydrogen proton from the anode to the cathode. The membrane's proton conductivity depends on the water content in the membrane, which is affected by the operating conditions. A membrane electrode assembly (MEA) that can self-sustain water is the key component for developing a light-weight and compact PEMFC system without humidifiers. Hence, zeolite is employed to the anode catalyst layer in this study. The effect of the gas diffusion layer (GDL) materials, catalyst loading, binder loading, and zeolite loading on the MEA performance is investigated. The MEA durability is also investigated through the electrochemical impedance spectroscopy (EIS) method. The results suggest that the MEA with the SGL28BCE carbon paper, Pt loadings of 0.1 and 0.7 mg cm^?2 in the anode and cathode, respectively, Nafion-to-carbon weight ratio of 0.5, and zeolite-to-carbon weight ratio of 0.3 showed the best performance when the cell temperature is 60 °C and supplies with dry hydrogen and air from the environment. According to the impedance variation measured by EIS, the MEA with zeolite in the anode catalyst layer shows higher and more stable performance than those without zeolite.     

Performance optimization of ultra-low platinum loading membrane electrode assembly prepared by electrostatic spraying

To improve the utilization of platinum and reduce the manufacturing cost of proton exchange membrane fuel cell (PEMFC), the electrostatic spraying was used to prepare the cathode catalyst layer of membrane electrode assembly (MEA) with platinum loading varying from 0.1 to 0.01 mg cm^?2. The performance of fuel cell was tested and analyzed by electrochemical impedance and polarization curve. Our results show that the platinum carbon (Pt/C) particles deposited by electrostatic spraying were well dispersed and the microporous structure of catalyst layer (CL) were relatively uniform. Replacing the CCS type MEA (catalyst coated on gas diffusion layer substrate) with the CCM type MEA (catalyst coated on proton exchange membrane) can reduce its electrochemical impedance and improve the power density of fuel cell. Compared to the Pt/C catalyst with a platinum mass fraction of 60%, a lower platinum-carbon ratio catalyst is more conducive to the uniform dispersion of catalyst particles and efficient utilization of platinum in the preparation of MEA with ultra-low platinum loading. However, their difference in peak power density decreases with the increase of platinum loading. Besides, increasing the back pressure can improve the performance of fuel cell, when the back pressure increased to 0.15 Mpa and the feeding gases were set as H₂/O₂, the peak power density of 0.56 W cm^?2 was obtained by the MEA with cathode platinum loading of 0.01 mg cm^?2, which is corresponding to the cathode platinum utilization of 56 kW·g_Pt^?1_cathode.     

Cobalt oxyphosphide as oxygen reduction electrocatalyst in proton exchange membrane fuel cell

The cobalt oxyphosphides supported on carbon black were prepared using incipient wetness method and characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The possibility of their application as the electrocatalyst for oxygen reduction reaction (ORR) in proton exchange membrane fuel cell (PEMFC) was investigated and the electrocatalytic activities were evaluated by the electrochemical measurements and single cell test, respectively. The electrocatalyst presents attractive catalytic activity towards ORR and good stability in acid media and exhibits an onset potential for oxygen reduction as high as 0.69 V (RHE) in H₂SO₄ solution. The maximum power density obtained in a H₂/O₂ PEMFC is 57 mW cm⁻² with Co₄P₂O₉/C loading of 1.13 mg cm⁻². No significant performance degradation is observed over 50 h of continuous fuel cell operation. The combination of heteroatom P with nanostructured oxides with high stability, excellent functionality and low cost which are prerequisites for large-scale applications, probably provide a new solution for the critical challenge of finding effective cathode materials for PEMFC.     

Physical insights into alkaline overall water splitting with NiO microflowers electrodes with ultra-low amount of Pt catalyst

Electrochemical water splitting represents a promising alternative to conventional carbon-based energy sources. The hydrogen evolution reaction (HER) is a key process, still if conducted in alkaline media, its kinetics is slow thus requiring high amount of Pt based catalysts. Extensive research has been focused on reducing Pt utilization by pursuing careful electrode investigation. Here, a low-cost chemical methodology is reported to obtain large amount of microflowers made of interconnected NiO nanowalls (20 nm thick) wisely decorated with ultralow amounts of Pt nanoparticles. These decorated microflowers, dispersed onto graphene paper by drop casting, build a high performance HER electrode exhibiting an overpotential of only 66 mV at current density of 10 mA cm^?2 under alkaline conditions. Intrinsic activity of catalyst was evaluated by measuring the Tafel plot (as low as 82 mV/dec) and turnover frequencies (2.07 s^?1 for a Pt loading of 11.2 μg cm^?2). The effect of Pt decoration has been modelled through energy band bending supported by electrochemical analyses. A full cell for alkaline electrochemical water splitting has been built, composed of Pt decorated NiO microflowers as cathode and bare NiO microflowers as anode, showing a low potential of 1.57 V to afford a current density of 10 mA cm^?2 and a good long-term stability. The reported results pave the way towards an extensive utilization of Ni based nanostructures with ultralow Pt content for efficient electrochemical water splitting.     

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.     

Modified La0.6Sr0.4Co0.2Fe0.8O3-δ cathodes with the infiltration of Er0.4Bi1.6O3 for intermediate-temperature solid oxide fuel cells

Aiming to lower the activation energy and expedite the oxygen reduction reaction (ORR) process of La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF) cathodes for application in intermediate-temperature solid oxide fuel cells (IT-SOFCs), Er_0.4Bi_1.6O₃ (ESB) modified LSCF was prepared by infiltrating using organic solvents. The infiltration of ESB dramatically reduces the polarization resistances of LSCF cathodes (from 0.27 to 0.11 Ω cm² at 700 °C, from 0.58 to 0.25 Ω cm² at 650 °C), and lowers their activation energy (from 100.28 to 97.15 kJ mol^?1). Also, ESB makes the rate-limiting step of LSCF cathodes at high frequency change from the charge transfer process on the cathode to the adsorption and diffusion of oxygen on cathode surface. The single cell with ESB infiltrated LSCF cathodes shows a peak power density of 469 mW cm^?2 at 700 °C using humid hydrogen and air as fuels and oxidants, respectively, as well as a good short-term stability for 50 h.     

Effects of basic gas diffusion layer components on PEMFC performance with capillary pressure gradient

The gas diffusion layer (GDL) is composed of a substrate and a micro-porous layer (MPL), and is treated with polytetrafluoroethylene (PTFE) to promote water discharge. Additionally, the MPL mainly consists of carbon black and PTFE. In other words, the optimal design of these elements has a dominant effect on the polymer electrolyte membrane fuel cell (PEMFC) performance. For the GDL, it is crucial to prevent water flooding, and the water flux within the GDL is strongly affected by the capillary pressure gradient. In this study, the PEMFC performance was systematically investigated by varying the substrate PTFE content, MPL PTFE content, and MPL carbon loading per unit area. The effects of each experimental variable on the PEMFC performance and especially on the capillary pressure gradient were quantitatively analyzed when the GDLs were manufactured by the doctor blade manufacturing method. The experimental results indicated that as the PTFE content of the anode and cathode GDL increased, the PEMFC performance deteriorated due to the deformation of the porosity and tortuosity of the GDL. Additionally, the PEMFC performance improved as the MPL PTFE content of the cathode GDL increased at low relative humidity (RH), but the PEMFC performance tendency was reversed at high RH. Further, the MPL carbon loading of 2 mg/${\text{cm}}^2$ demonstrated the best performance, and the advantages and disadvantages of the MPL carbon loading were identified. In addition, the effects of each experimental variable on liquid water, water vapor, and gas permeability were investigated.