Platinum-macrocycle co-catalyst for electro-oxidation of formic acid

In this work, a new promoter, tetrasulfophthalocyanine (FeTSPc), one kind of environmental friendly material, was found to be very effective in both inhibiting self-poisoning and improving the intrinsic catalysis activity, consequently enhancing the electro-oxidation current during the electro-oxidation of formic acid. The cyclic voltammograms test showed that the formic acid oxidation peak current density has been increased about 10 times compared with that of the Pt electrode without FeTSPc. The electrochemical double potential step chronoamperometry measurements revealed that the apparent activity energy decreases from 20.64 kJ mol⁻¹ to 17.38 kJ mol⁻¹ after Pt electrode promoted by FeTSPc. The promoting effect of FeTSPc may be owed to the specific structure and abundant electrons of FeTSPc resulting in both the steric hindrance of the formation of poisoning species (CO) and intrinsic kinetic enhancement. In the single cell test, the performance of DFAFC increased from 80 mW cm⁻² mg⁻¹ (Pt) to 130 mW cm⁻² mg⁻¹ after the anode electrode adsorbed FeTSPc.     

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.     

Promotion of PtIr and Pt catalytic activity towards ammonia electrooxidation through the modification of Zn

Zn is introduced into Pt and PtIr electrodes by applying potential cycles to their corresponding polycrystalline microdisc electrodes in a ZnCl₂-containing ionic liquid bath. Scanning-electron microscopy and energy-dispersive X-ray microanalysis studies show that nanostructured PtIrZn and PtZn layers created on the microdisc electrodes contain approximately 5 wt% Zn. Cyclic voltammetric studies reveal that PtZn and PtIrZn are significantly more active towards electrochemical ammonia oxidation in alkaline media than virgin Pt and PtIr electrodes. The PtIrZn electrode demonstrates a low onset potential of 0.30 V vs RHE and a high exchange current density of 4.3 × 10^− 8 A cm^− 2, which is favorably comparable to state-of-the-art electrocatalyts for the same reaction. The catalytic activity promotion by the Zn modification may be related to the inhibition of the hydrogen electrochemistry. PtIrZn appears therefore to be a very promising anode catalyst for direct ammonia fuel cells and ammonia electrolysis.     

Ultra-low platinum loading high-performance PEMFCs using buckypaper-supported electrodes

The microstructure of the catalyst layer in proton exchange membrane fuel cells (PEMFCs) greatly influences catalyst (Pt) utilization and cell performance. We demonstrated a functionally graded catalyst layer based on a double-layered carbon nanotube/nanofiber film- (buckypaper) supported Pt composite catalyst to approach an idealized microstructure. The gradient distribution of Pt, electrolyte and porosity along the thickness effectively depresses the transport resistance of proton and gas. A rated power of 0.88 W/cm² at 0.65 V was achieved at 80 °C with a low Pt loading of 0.11 mg/cm² resulting in a relatively high Pt utilization of 0.18g_Pt/kW. The accelerated degradation test of catalyst support showed a good durability of buckypaper support because of the high graphitization degree of carbon nanofibers.     

Enhancement of the performances of a single concentric glucose/O2 biofuel cell by combination of bilirubin oxidase/Nafion cathode and Au–Pt anode

This work deals with a novel preparation method of bilirubin oxidase/2,2′-azinobis-3-ethylbenzothiazoline-6-sulfonic acid electrode. The enzyme and its mediator were adsorbed on carbon Vulcan XC-72R before their immobilization into a Nafion^® matrix. Promising results were obtained when this biocathode was associated with Au₇₀Pt₃₀ nanoparticles as anode in a single concentric glucose/O₂ biofuel cell (BFC). The latter BFC delivered at 37 °C a power density of 90 μW cm^?2 for a cell voltage of 0.4 V in phosphate buffer (pH 7.4) containing 0.01 M glucose. Moreover, the electrical performances were increased with the concentration of glucose by generating up to 190 μW cm^?2 for a cell voltage of 0.52 V when the concentration of the renewable fuel reached 0.7 M.     

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.     

Visible light active hydrogen modified (HM)-n-TiO2 thin films for photoelectrochemical splitting of water

Visible light active hydrogen modified n-type titanium oxide (HM-n-TiO₂) thin films were synthesized by thermal oxidation of Ti metal sheet (Alfa Co. 0.25 mm thick) in an electric oven followed by incorporation of hydrogen electrochemically under cathodic polarization at ?1.6 V vs Pt. The photoresponse of the HM-n-TiO₂ was evaluated by measuring the rate of water splitting reaction to hydrogen and oxygen in terms of photocurrent density, J_p. The optimized electric oven-made n-TiO₂ and HM-n-TiO₂ photoelectrodes showed photocurrent densities of 0.2 mA cm^?2 and 1.60 mA cm^?2, respectively, at a measured potential of ?0.4 V vs Pt at illumination intensity of 100 mW cm^?2 from a 150 W xenon lamp. This indicated an eightfold increase in photocurrent density for HM-n-TiO₂ compared to oven-made n-TiO₂ at the same measured electrode potential. The band-gap energy of HM-n-TiO₂ was found to be 2.7 eV compared to 2.82 eV for electric oven-made n-TiO₂ and a mid-gap band at 1.67 eV above the valence band was also observed. The HM-n-TiO₂ thin film photoelectrodes were characterized using photocurrent density under monochromatic light illumination and UV–Vis spectral measurements.     

Impact of reforming catalyst on the anodic polarisation resistance in single-chamber SOFC fed by methane

This paper emphasises the electrochemical and catalytic properties of a Ni–10% GDC (10% gadolinium-doped ceria) cermet anode of a single-chamber solid oxide fuel cell (SC-SOFC). Innovative coupling of electrochemical impedance spectroscopy with gas chromatography measurements was carried out to characterise the anode material using an operando approach. The experiments were conducted in a symmetric anode/electrolyte/anode cell prepared by slurry coating resulting in 100 μm-thick anode layers. The electrochemical performance was assessed using a two-electrode arrangement between 400 °C and 650 °C, in a methane-rich atmosphere containing CH₄, O₂ and H₂O in a 14:2:6 volumetric ratio. The insertion of a Pt–CeO₂ based catalyst with high specific surface area inside the cermet layer was found to promote hydrogen production from the Water Gas Shift reaction and consequently to improve the electrochemical performances. Indeed, a promising polarisation resistance value of 12 Ω cm² was achieved at 600 °C with a catalytic loading of only 15 wt.%.     

Titanium-supported nanoporous bimetallic Pt–Ir electrocatalysts for formic acid oxidation

Novel titanium-supported nanoporous network bimetallic Pt–Ir/Ti electrocatalysts (S1:Pt₅₉Ir₄₁/Ti, S2:Pt₄₄Ir₅₆/Ti, S3:Pt₂₂Ir₇₈/Ti) have been successfully fabricated by the hydrothermal process. The nanoparticles of Pt and Ir were deposited on the titanium substrates in the presence of formaldehyde as a reduction agent. The electrocatalytic activity of these electrocatalysts towards formic acid oxidation in 0.5 M H₂SO₄ + 0.5 M HCOOH solutions was investigated using cyclic voltammograms (CVs), linear sweep voltammograms (LSVs), chrono amperometry and electrochemical impedance spectroscopy (EIS). The CVs of S1, S2 and S3 exhibit two anodic peaks in the forward scan and one anodic peak in the reverse scan which are similar to the pure Pt. Their LSVs show that the three samples present significantly high current densities of formic acid oxidation compared to the Pt electrode. It is observed from the chrono amperometric measurements at potential 600 mV that the sample S2 delivers a steady-state current density that is 545 times larger than that for the pure Pt electrode. EIS analysis shows that the impedances on both the imaginary and real axes of S1, S2 and S3 are much lower than those of the pure Pt. Among the three samples (S1, S2 and S3), S2 exhibits the highest electrocatalytic activity towards the formic acid oxidation.     

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.     

Pseudocapacitive polypyrrole–nanocellulose composite for sugar-air enzymatic fuel cells

Efficient, new combination of a bioelectrocatalytic and a pseudocapacitive cellulose-based composite material is reported. The anode comprising Gluconobacter sp. fructose dehydrogenase physically adsorbed on Cladophora sp. Algae nanocellulose/polypyrrole composite provides large catalytic oxidation currents due to large effective surface area of the composite material, and enables storing of the charge. Supercapacitor properties are useful for larger current demands e.g. during switching on–off the devices. Mediatorless catalytic oxidation current densities as high as 14 mA cm^− 2 at potentials as negative as − 0.17 V vs. Ag/AgCl constitute the best anode performance without using mediators reported to date. The fuel cell with GCE cathode covered with laccase adsorbed on naphthylated multiwalled carbon nanotubes, exhibits improved parameters: open circuit voltage of 0.76 V, and maximum power density 1.6 mW cm^− 2.     

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.     

Oxygen reduction reaction activities of Ni/Pt(111) model catalysts fabricated by molecular beam epitaxy

Oxygen reduction reaction (ORR) activities were evaluated for clean Pt(111) and Ni/Pt(111) model catalysts fabricated by molecular beam epitaxy. Exposure of clean Pt(111) to 1.0 L CO at 303 K produced linear-bonded and bridge-bonded CO-Pt IR bands at 2093 and 1858 cm^? 1. In contrast, 0.3-nm-thick Ni deposited on Pt(111) at 573 K (573 K-Ni_0.3 nm/Pt(111)) produced broad IR bands for adsorbed CO at around 2070 cm^? 1; the separation of reflection high-energy electron diffraction (RHEED) streaks is slightly wider for 573 K-Ni_0.3 nm/Pt(111) than for the clean Pt(111). For 823 K-Ni_0.3 nm/Pt(111), the separation of the RHEED streaks is the same as that for the Pt(111), and a single sharp IR band due to adsorbed CO is located at 2082 cm^? 1. The results suggest that for the 823 K-Ni_0.3 nm/Pt(111), a Pt-enriched outermost surface (Pt-skin) was formed through surface segregation of the substrate Pt atoms. ORR activities for the 573 K- and 823 K-Ni_0.3 nm/Pt(111) as determined from linear sweep voltammetry curves were five times and eight times higher than that for clean Pt(111), respectively, demonstrating that Pt-skin generation is crucial for developing highly active electrode catalysts for fuel cells.     

Hydrogen oxidation reaction on thin platinum electrodes in the polymer electrolyte fuel cell

A method for measuring the kinetics of the hydrogen oxidation reaction (HOR) in a fuel cell under enhanced mass transport conditions is presented. The measured limiting current density was roughly 1600 mA cm_Pt^? 2, corresponding to a rate constant of the forward reaction in the Tafel step of 0.14 mol m^? 2 s^? 1 at 80 °C and 90% RH. The exchange current density for the HOR was determined using the slope at low overvoltages and was found to be 770 mA cm_Pt^? 2. The high values for the limiting and exchange current densities suggest that the Pt loading in the anode catalyst can be reduced further without imposing measurable voltage loss.     

Cyanamide-derived non-precious metal catalyst for oxygen reduction

Cyanamide was used in the preparation series of metal–nitrogen–carbon (M–N–C) oxygen reduction catalysts. The best catalyst, treated at 1050 °C, shows good performance versus previously reported non-precious metal catalysts with an OCV ~ 1.0 V and a current density of 105 mA/cm² (iR-corrected) at 0.80 V in H₂/O₂ fuel cell testing (catalyst loading: 4 mg cm^? 2). Although nitrogen content has been previously correlated positively with ORR activity, no such trend is observed here for any nitrogen type. The combined effects of nitrogen and sulfur incorporation into the carbon may account for the high activity of the 1050 °C catalyst.     

Amperometric biosensors based on deposition of gold and platinum nanoparticles on polyvinylferrocene modified electrode for xanthine detection

In this study, new xanthine biosensors, XO/Au/PVF/Pt and XO/Pt/PVF/Pt, based on electroless deposition of gold(Au) and platinum(Pt) nanoparticles on polyvinylferrocene(PVF) coated Pt electrode for detection of xanthine were presented. The amperometric responses of the enzyme electrodes were measured at the constant potential, which was due to the electrooxidation of enzymatically produced H₂O₂. Compared with XO/PVF/Pt electrode, XO/Au/PVF/Pt and XO/Pt/PVF/Pt exhibited excellent electrocatalytic activity towards the oxidation of the analyte. Effect of Au and Pt nanoparticles was investigated by monitoring the response currents at the different deposition times and the different concentrations of KAuCl₄ and PtBr₂. Under the optimal conditions, the calibration curves of XO/Au/PVF/Pt and XO/Pt/PVF/Pt were obtained over the range of 2.5 × 10^?3 to 0.56 mM and 2.0 × 10^?3 to 0.66 mM, respectively. The detection limits were 7.5 × 10^?4 mM for XO/Au/PVF/Pt and 6.0 × 10^?4 mM for XO/Pt/PVF/Pt. The effects of interferents, the operational and the storage stabilities of the biosensors and the applicabilities of the proposed biosensors to the drug samples analysis were also evaluated.     

A direct borohydride–peroxide fuel cell using a Pd/Ir alloy coated microfibrous carbon cathode

A direct borohydride fuel cell with a Pd/Ir catalysed microfibrous carbon cathode and a gold-catalysed microporous carbon cloth anode is reported. The fuel and oxidant were NaBH₄ and H₂O₂, at concentrations within the range of 0.1–2.0 mol dm⁻³ and 0.05–0.45 mol dm⁻³, respectively. Different combinations of these reactants were examined at 10, 25 and 42 °C. At constant current density between 0 and 113 mA cm⁻², the Pd/Ir coated microfibrous carbon electrode proved more active for the reduction of peroxide ion than a platinised-carbon one. The maximum power density achieved was 78 mW cm⁻² at a current density of 71 mA cm⁻² and a cell voltage of 1.09 V.     

Low Pt content Pt–Ru–Ir–Sn quaternary catalysts for anodic methanol oxidation in DMFC

In this communication we report our research work on low Pt content Pt–Ru–Ir–Sn quaternary catalysts for use in DMFC anodes. The carbon-supported quaternary metal alloy catalyst was synthesized according to the solution reduction method and was deposited onto a carbon fiber paper or a carbon aerogel nanofoam to form the anode for direct methanol fuel cells. The Pt loading of the electrode is 0.1 mg/cm². The testing results from a three-electrode electrochemical cell show that the simultaneous use of higher Ir (25–35 wt.%) and Sn (10 wt.%) content gives satisfactory stability and higher activity for methanol oxidation than the commercially available E-TEK anode (80%[0.5Pt 0.5Ru]/C on carbon cloth). Energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), scanning electron microscope (SEM), and Bruner–Emmett–Teller method (BET) measurements were carried out to characterize the composition, structure, morphology, and surface area of the developed catalysts.     

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.     

A microfluidic glucose biofuel cell to generate micropower from enzymes at ambient temperature

A Y-shaped microfluidic channel is applied for the first time to the construction of a glucose/O₂ biofuel cell, based on both laminar flow and biological enzyme strategies. During operation, the fuel and oxidant streams flow parallel at gold electrode surfaces without convective mixing. At the anode, the glucose oxidation is performed by the enzyme glucose oxidase whereas at the cathode, the oxygen is reduced by the enzyme laccase, in the presence of specific redox mediators. Such cell design protects the anode from an interfering parasite reaction of O₂ at the anode and offers the advantage of using different streams of oxidant and fuel for optimal performance of the enzymes. Electrochemical characterizations of the device show the influence of the flow rate on the output potential and current density. The maximum power density delivered by the assembled biofuel cell reached 110 μW cm^?2 at 0.3 V with 10 mM glucose at 23 °C. The microfluidic approach reported here demonstrates the feasibility of advanced microfabrication techniques to build an efficient microfluidic glucose/O₂ biofuel cell device.