Intrinsically microporous polymer slows down fuel cell catalyst corrosion

The limited stability of fuel cell cathode catalysts causes a significant loss of operational cell voltage with commercial Pt-based catalysts, which hinders the wider commercialization of fuel cell technologies. We demonstrate beneficial effects of a highly rigid and porous polymer of intrinsic microporosity (PIM-EA-TB with BET surface area 1027 m² g^− 1) in accelerated catalyst corrosion experiments. Porous films of PIM-EA-TB offer an effective protective matrix for the prevention of Pt/C catalyst corrosion without impeding flux of reagents. The results of electrochemical cycling tests show that the PIM-EA-TB protected Pt/C (denoted here as PIM@Pt/C) exhibit a significantly enhanced durability as compared to a conventional Pt/C catalyst.     

A completely spray-coated membrane electrode assembly

We present a proton exchange membrane fuel cell (PEMFC) manufacturing route, in which a thin layer of polymer electrolyte solution is spray-coated on top of gas diffusion electrodes (GDEs) to work as a proton exchange membrane. Without the need for a pre-made membrane foil, this allows inexpensive, fast, large-scale fabrication of membrane-electrode assemblies (MEAs), with a spray-coater comprising the sole manufacturing device. In this work, a catalyst layer and a membrane layer are consecutively sprayed onto a fibrous gas diffusion layer with applied microporous layer as substrate. A fuel cell is then assembled by stacking anode and cathode half-cells with the membrane layers facing each other. The resultant fuel cell with a low catalyst loading of 0.1 mg Pt/cm² on each anode and cathode side is tested with pure H₂ and O₂ supply at 80 °C cell temperature and 92% relative humidity at atmospheric pressure. The obtained peak power density is 1.29 W/cm² at a current density of 3.25 A/cm². By comparison, a lower peak power density of 0.93 W/cm² at 2.2 A/cm² is found for a Nafion NR211 catalyst coated membrane (CCM) reference, although equally thick membrane layers (approx. 25 μm), and identical catalyst layers and gas diffusion media were used. The superior performance of the fuel cell with spray-coated membrane can be explained by a decreased low frequency (mass transport) resistance, especially at high current densities, as determined by electrochemical impedance spectroscopy.     

Preparation process for improving cathode electrode structure in direct methanol fuel cell

The cathode electrode structure of the direct methanol fuel cell (DMFC) was improved by a novel catalyst ink preparation method. Regulation of the solvent polarity in the cathode catalyst ink caused increases in the electrochemical active surface (EAS) for the oxygen reduction reaction (ORR) as well as decreases in the methanol crossover effect. In a two-step preparation, agglomerates consisting of catalyst and Nafion ionomers were decreased in size, and polar groups in the ionomers formed organized networks in the cathode catalyst layer. Despite Pt catalysts in the cathode being only 0.5 mg cm^? 2, the maximum power density of the improved membrane electrode assembly (MEA) was 120 mW cm^? 2, at 3 M methanol, which was much larger than that of traditional MEA (67 mW cm^? 2).     

Sulfur doped reduced graphene oxide as metal-free catalyst for the oxygen reduction reaction in anion and proton exchange fuel cells

Sulfur doped reduced graphene oxide (S-rGO) is investigated for catalytic activity towards the oxygen reduction reaction (ORR) in acidic and alkaline electrolytes. X-ray photoelectron spectroscopy shows that sulfur in S-rGO is predominantly integrated as thiophene motifs within graphene sheets. The overall sulfur content is determined to be approximately 2.2 at.% (elemental analysis). The catalytic activity of S-rGO towards the ORR is investigated by both rotating disc electrode (RDE) and polymer electrolyte fuel cell (PEFC) measurements. RDE measurements reveal onset potentials of 0.3 V and 0.74 V (vs. RHE) in acidic and alkaline electrolyte, respectively. In a solid electrolyte fuel cell with S-rGO as cathode material, this is reflected in an open circuit voltage of 0.37 V and 0.78 V and a maximum power density of 1.19 mW/cm² and 2.38 mW/cm² in acidic and alkaline polymer electrolyte, respectively. This is the first report investigating the catalytic activity of a sulfur doped carbon material in both acidic and alkaline liquid electrolyte, as well as in both proton and anion exchange polymer electrolyte fuel cells.     

Performance of plasma sputtered fuel cell electrodes with ultra-low Pt loadings

Ultra-low Pt content PEMFC electrodes have been manufactured using magnetron co-sputtering of carbon and platinum on a commercial E-Tek^® uncatalyzed gas diffusion layer in plasma fuel cell deposition devices. Pt loadings of 0.16 and 0.01 mg cm^?2 have been realized. The Pt catalyst is dispersed as small clusters with size less than 2 nm over a depth of 500 nm. PEMFC test with symmetric electrodes loaded with 10 μg cm^?2 led to maximum reproducible power densities as high as 0.4 and 0.17 W cm^?2 with Nafion^®212 and Nafion^®115 membranes, respectively.     

Poly(vinyl alcohol) separators improve the coulombic efficiency of activated carbon cathodes in microbial fuel cells

High-performance microbial fuel cell (MFC) air cathodes were constructed using a combination of inexpensive materials for the oxygen reduction cathode catalyst and the electrode separator. A poly(vinyl alcohol) (PVA)-based electrode separator enabled high coulombic efficiencies (CEs) in MFCs with activated carbon (AC) cathodes without significantly decreasing power output. MFCs with AC cathodes and PVA separators had CEs (43%–89%) about twice those of AC cathodes lacking a separator (17%–55%) or cathodes made with platinum supported on carbon catalyst (Pt/C) and carbon cloth (CE of 20%–50%). Similar maximum power densities were observed for AC-cathode MFCs with (840 ± 42 mW/m²) or without (860 ± 10 mW/m²) the PVA separator after 18 cycles (36 days). Compared to MFCs with Pt-based cathodes, the cost of the AC-based cathodes with PVA separators was substantially reduced. These results demonstrated that AC-based cathodes with PVA separators are an inexpensive alternative to expensive Pt-based cathodes for construction of larger-scale MFC reactors.     

Platinum nanoparticles supported on nitrobenzene-functionalised graphene nanosheets as electrocatalysts for oxygen reduction reaction in alkaline media

A systematic study on the electrocatalytic properties of Pt nanoparticles supported on nitrobenzene-modified graphene (Pt-NB/G) as catalyst for oxygen reduction reaction (ORR) in alkaline solution was performed. Graphene nanosheets were spontaneously grafted with nitrophenyl groups using 4-nitrobenzenediazonium salt. The electrocatalytic activity towards the ORR and stability of the prepared catalysts in 0.1 M KOH solution have been studied and compared with that of the commercial Pt/C catalyst. The results obtained show that the NB-modified graphene nanosheets can be good Pt catalyst support with high stability and excellent electrocatalytic properties. The specific activity of Pt-NB/G for O₂ reduction was 0.184 mA cm⁻², which is very close to that obtained for commercial 20 wt% Pt/C catalyst (0.214 mA cm⁻²) at 0.9 V vs. RHE. The Pt-NB/G hybrid material promotes a four-electron reduction of oxygen and can be used as a promising cathode catalyst in alkaline fuel cells.     

Comparison of performances of bioanodes modified with graphene oxide and graphene–platinum hybrid nanoparticles

The performances of graphene oxide (GO) and graphene–platinum hybrid nanoparticles (Gr-Pt hybrid NPs) were compared for biofuel cell (BFC) systems. This is the first study that constitutes these nanomaterials in BFC systems. For this purpose, fabricated bioanodes were combined with laccase modified biocathode in a single cell membraneless BFC. Power and current densities of these systems were calculated as 2.40 μW cm^− 2 and 211.90 μA cm^− 2 for GO based BFC and 4.88 μW cm^− 2 and 246.82 μA cm^− 2, for Gr-Pt hybrid NPs based BFC. As a result, a pioneer study which demonstrates the effective performances of combination of graphene with Pt was conducted.     

A novel MEA architecture for improving the performance of a DMFC

Direct methanol fuel cell (DMFC) consisting of a double-catalytic layered membrane electrode assembly (MEA) provide higher performance than that with the traditional MEA. This novel structured MEA includes a hydrophilic inner catalyst layer and a traditional electrode with an outer catalyst layer, which was made using both catalyst coated membrane (CCM) and gas diffusion electrode (GDE) methods. The inner catalyst was PtRu black on anode and Pt black on cathode. The outer catalyst was carbon supported Pt–Ru/Pt on anode and cathode, respectively. Thus in the double-catalytic layered electrodes three gradients were formed: catalyst concentration gradient, hydrophilicity gradient and porosity gradient, resulting in good mass transfer, proton and electron conducting and low methanol crossover. The peak density of DMFC with such MEA was 19 mW cm⁻², operated at 2 M CH₃OH, 2 atm oxygen at room temperature, which was much higher than DMFC with traditional MEA.     

Anti-flooding cathode catalyst layer for high performance PEM fuel cell

Water management in cathode catalyst layer (CCL) plays an important role in the PEM fuel cell operation. A novel anti-flooding CCL is developed with the addition of oxygen permeable and hydrophobic dimethyl silicone oil (DSO) into the catalyst layer (CL) to improve the water balance and oxygen transport within the cathode. With the addition of 0.5 mg cm^?2 DSO in the CCL, the ability of water management has been enhanced greatly compared to that with a normal cathode. Electrochemical impedance spectroscopy has been employed to characterize the electrochemical behavior of the single fuel cell. The results show that the increased hydrophobicity of the CCL by DSO modification effectively expels water out of the voids of CCL. In addition, DSO in the CCL enhances oxygen accessibility to the CCL, thus improving the performance of the PEM fuel cell significantly.     

High performance solid oxide fuel cells with electrocatalytically enhanced (La,Sr)MnO3 cathodes

The conventionally mixed LSM–YSZ, LSM impregnated YSZ (LSM + YSZ) and Pd impregnated LSM–YSZ (Pd + LSM–YSZ) cathodes, were prepared and evaluated by electrochemical impedance spectroscopy and single cell testing. The electrochemical performance of the impregnated cathodes have been significantly boosted due to the formation of nano-sized LSM and Pd particles on the YSZ and LSM–YSZ substrates, respectively, and in turn, the increased area of the triple phase boundary (TPB) where the O₂ reduction reaction occurs, the power densities as high as 1.42 and 0.83 W cm^?2 at 750 °C were achieved from single cells with the Pd + LSM–YSZ and LSM + YSZ cathodes, respectively, in contrast to 0.20 W cm^?2 from the single cell with the conventional LSM–YSZ cathode. Suggesting the Pd + LSM–YSZ and LSM + YSZ cathodes can be well used for the intermediate temperature solid oxide fuel cells (IT-SOFCs).     

A novel single electrode supported direct methanol fuel cell

In this paper a single electrode supported direct methanol fuel cell (DMFC) is fabricated and tested. The novel architecture combines the elimination of the polymer electrolyte membrane (PEM) and the integration of the anode and cathode into one component. The thin film fabrication involves a sequential deposition of an anode catalyst layer, a cellulose acetate electronic insulating layer and a cathode catalyst layer onto a single carbon fibre paper substrate. The single electrode supported DMFC has a total thickness of 3.88 × 10^?2 cm and showed a 104% improvement in volumetric specific power density over a two electrode DMFC configuration under passive conditions at ambient temperature and pressure (1 atm, 25 °C).     

A novel single phase cathode material for a proton-conducting SOFC

A novel single phase BaCe_0.5Bi_0.5O_3 ? δ (BCB) was employed as a cathode material for a proton-conducting solid oxide fuel cell (SOFC). The single cell, consisting of a BaZr_0.1Ce_0.7Y_0.2O_3 ? δ (BZCY7)-NiO anode substrate, a BZCY7 anode functional layer, a BZCY7 electrolyte membrane and a BCB cathode layer, was assembled and tested from 600 to 700 °C with humidified hydrogen (～3% H₂O) as the fuel and the static air as the oxidant. An open-circuit potential of 0.96 V and a maximum power density of 321 mW cm^?2 were obtained for the single cell. A relatively low interfacial polarization resistance of 0.28Ω cm² at 700 °C indicated that the BCB was a promising cathode material for proton-conducting SOFCs.     

Synthesis of highly active nanostructured PtRu electrocatalyst with three-dimensional mesoporous silica template

Nanostructured PtRu material has been successively synthesized via chemical co-reduction of hexachloroplatinic acid and ruthenium trichloride using three-dimensional (3D) hexagonal mesoporous SBA-12 silica as a solid template, and has been studied as an electrocatalyst toward methanol electro-oxidation. The ordered nanostructure of the PtRu particles has been disclosed by transmission electron micrographs and is characterized by regular pores of ca. 3.0 ± 0.3 nm in diameter separated by walls of ca. 3.0 ± 0.3 nm thick. X-ray diffraction and energy dispersive X-ray spectroscope studies indicate that the PtRu material comprises of complicated phases rather than a single alloy phase of Pt and Ru. The specific electrochemical surface area of the nanostructured powder measured using both CO and underpotential deposited Cu stripping techniques is 74–78 m² g^–1, higher than that of unsupported precious metal catalysts prepared using standard techniques. The combination of high surface area and periodic nanostructure of the templated PtRu makes it an interesting promising fuel cell electrocatalyst. This has been demonstrated by the high activity of the templated PtRu towards the methanol electrooxidation. Therefore the solid template route based on 3D mesoporous silica with controlled pore size and high pore interconnectivity provides an interesting alternative to produce promising high-surface-area electrode materials.     

Development of micro-tubular SOFCs with an improved performance via nano-Ag impregnation for intermediate temperature operation

Micro-tubular solid-oxide fuel cell consisting of a 10-μm thick (ZrO₂)_0.89(Sc₂O₃)_0.1(CeO₂)_0.01 (ScSZ) electrolyte on a support NiO/(ScSZ) anode (1.8 mm diameter, 200 μm wall thickness) with a Ce_0.8Gd_0.2O_1.9 (GDC) buffer-layer and a La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ (LSCF)/GDC functional cathode has been developed for intermediate temperature operation. The functional cathode was in situ formed by impregnating the well-dispersed nano-Ag particles into the porous LSCF/GDC layer using a citrate method. The cells yielded maximum power densities of 1.06 W cm⁻² (1.43 A cm⁻², 0.74 V), 0.98 W cm⁻² (1.78 A cm⁻², 0.55 V) and 0.49 W cm⁻² (1.44 A cm⁻², 0.34 V), at 650, 600 and 550 °C, respectively.     

Fabrication of a large area cathode-supported thin electrolyte film for solid oxide fuel cells via tape casting and co-sintering techniques

A large area cathode-supported electrolyte film, comprising porous (La_0.8Sr_0.2)_0.95MnO₃ (LSM95) cathode substrate, LSM95/Zr_0.89Sc_0.1Ce_0.01O_2?x (SSZ) cathode active layer, and SSZ electrolyte, has been successfully fabricated by tape casting and co-sintering techniques. The interface reaction between cathode and electrolyte was inhibited by using A-site deficient LSM. A dense enough SSZ thin film with a thickness of ～26 μm was obtained at 1250 °C. By using Pt as anode, the obtained single cell reached the maximum power density of 0.54 W cm^?2 at 800 °C in O₂/humidified H₂, with open circuit voltage (OCV) value of 1.08 V.     

High performance cathode-supported SOFC with perovskite anode operating in weakly humidified hydrogen and methane

A high performance cathode-supported solid oxide fuel cell (SOFC), suitable for operating in weakly humidified hydrogen and methane, has been developed. The SOFC is essentially made up by a YSZ/LSM composite supporting cathode, a thin YSZ film electrolyte, and a GDC-impregnated La_0.75Sr_0.25Cr_0.5Mn_0.5O₃ (LSCM) anode. A gas tight thin YSZ film (∼27 μm) was formed during the co-sintering of cathode/electrolyte bi-layer at 1200 °C. The cathode-supported SOFC developed in this study showed encouraging performance with maximum power density of 0.182, 0.419, 0.628 and 0.818 W cm⁻² in air/3% H₂O–97% H₂ (and 0.06, 0.158, 0.221 and 0.352 W cm⁻² in air/3% H₂O–97% CH₄) at 750, 800, 850 and 900 °C, respectively. Such performance is close to that of the cathode-supported cell (0.42 W cm⁻² vs. 0.455 W cm⁻² in humidified H₂ at 800 °C) developed by Yamahara et al. [Solid State Ionics 176 (2005) 451–456] with a Co-infiltrated supporting LSM-YSZ cathode, a (Sc₂O₃)_0.1(Y₂O₃)_0.01(ZrO₂)_0.89 (SYSZ) electrolyte of 15 μm in thickness and a SYSZ/Ni anode, indicating that the performance of the GDC-impregnated LSCM anode is comparable to that made of Ni cermet while stable in weakly humidified methane fuel.     

Electrochemical behavior of a micro-patterned Si anode/LiV3O8 secondary cell

Using a micro-patterned Si plate, a Li secondary cell was assembled and tested for its electrochemical properties. A micro-patterned Si plate was made by photolithography. This was followed by Pt coating and Li deposition. With a non-lithiated LiV₃O₈ cathode, a Li-deposited micro-patterned Si anode was assembled as a secondary cell. The cell exhibited an initial charge/discharge capacity of about 220 mAh g^? 1 at a current density of 0.1 C-rate and it continued for more than 100 cycles without failure. The morphologies of Li deposition/dissolution in the anode were observed via scanning electron microscopy (SEM). Dendrite behavior of the Li metal was not observed on the anode during the cyclic process.     

Switchable electrode functionalized with an azobenzene-containing copolymer thin film using the Langmuir–Schaefer technique for a “smart” uric acid/air fuel cell

A new photoswitchable electrode triggered by a brief light signal was fabricated by depositing an azobenzene-containing copolymer on an indium tin oxide substrate decorated with gold nanoparticles. The polymer formed a compact, complete thin film on the electrode surface using the Langmuir–Schaefer technique and offered reversible and stable switching performance. The conductivity and hydrophilicity of the electrode changed under UV/visible light due to the photoisomerization of the azobenzene moieties in the polymer film, influencing electron transfer and mass transport at the electrode. The electrochemical characterization demonstrated that the electrode exhibited reversibly switchable electrochemical behavior. In its active state, the as-prepared electrode possessed efficient electrocatalytic capability towards uric acid oxidation with a maximum anodic current density of 0.97 mA·cm^− 2. The uric acid/air fuel cell assembled from the photo-triggered anode and a Pt/C-modified cathode operated with an open circuit voltage of 0.12 V and a maximum power density of 41.33 μW·cm^− 2. The cell exhibited reversible switching performance (four cycles) and high stability: after one month the power output was 94.2% of the original maximum value.     

Power generation using an activated carbon and metal mesh cathode in a microbial fuel cell

An inexpensive activated carbon (AC) air cathode was developed as an alternative to a platinum-catalyzed electrode for oxygen reduction in a microbial fuel cell (MFC). AC was cold-pressed with a polytetrafluoroethylene (PTFE) binder to form the cathode around a Ni mesh current collector. This cathode construction avoided the need for carbon cloth or a metal catalyst, and produced a cathode with high activity for oxygen reduction at typical MFC current densities. Tests with the AC cathode produced a maximum power density of 1220 mW/m² (normalized to cathode projected surface area; 36 W/m³ based on liquid volume) compared to 1060 mW/m² obtained by Pt catalyzed carbon cloth cathode. The Coulombic efficiency ranged from 15% to 55%. These findings show that AC is a cost-effective material for achieving useful rates of oxygen reduction in air cathode MFCs.