Alessandra D’Epifanio

High proton conduction in grain-boundary-free yttrium-doped barium zirconate films grown by pulsed laser deposition

Reducing the operating temperature in the 500-750 °C range is needed for widespread use of solid oxide fuel cells (SOFCs). Proton-conducting oxides are gaining wide interest as electrolyte materials for this aim. We report the fabrication of BaZr(0.8)Y(0.2)O(3-δ) (BZY) proton-conducting electrolyte thin films by pulsed laser deposition on different single-crystalline substrates. Highly textured, epitaxially oriented BZY films were obtained on (100)-oriented MgO substrates, showing the largest proton conductivity ever reported for BZY samples, being 0.11 S cm(-1) at 500 °C. The excellent crystalline quality of BZY films allowed for the first time the experimental measurement of the large BZY bulk conductivity above 300 °C, expected in the absence of blocking grain boundaries. The measured proton conductivity is also significantly larger than the conductivity values of oxygen-ion conductors in the same temperature range, opening new potential for the development of miniaturized SOFCs for portable power supply.

Vertical TiO2 Nanorods as a Medium for Stable and High-Efficiency Perovskite Solar Modules

Perovskite solar cells employing CH3NH3PbI3-xClx active layers show power conversion efficiency (PCE) as high as 20% in single cells and 13% in large area modules. However, their operational stability has often been limited due to degradation of the CH3NH3PbI3-xClx active layer. Here, we report a perovskite solar module (PSM, best and av. PCE 10.5 and 8.1%), employing solution-grown TiO2 nanorods (NRs) as the electron transport layer, which showed an increase in performance (∼5%) even after shelf-life investigation for 2500 h. A crucial issue on the module fabrication was the patterning of the TiO2 NRs, which was solved by interfacial engineering during the growth process and using an optimized laser pulse for patterning. A shelf-life comparison with PSMs built on TiO2 nanoparticles (NPs, best and av. PCE 7.9 and 5.5%) of similar thickness and on a compact TiO2 layer (CL, best and av. PCE 5.8 and 4.9%) shows, in contrast to that observed for NR PSMs, that PCE in NPs and CL PSMs dropped by ∼50 and ∼90%, respectively. This is due to the fact that the CH3NH3PbI3-xClx active layer shows superior phase stability when incorporated in devices with TiO2 NR scaffolds.

Using olive mill wastewater to improve performance in producing electricity from domestic wastewater by using single-chamber microbial fuel cell.

Improving electricity generation from wastewater (DW) by using olive mill wastewater (OMW) was evaluated using single-chamber microbial fuel cells (MFC). Doing so single-chambers air cathode MFCs with platinum anode were fed with domestic wastewater (DW) alone and mixed with OMW at the ratio of 14:1 (w/w). MFCs fed with DW+OMW gave 0.38 V at 1 kΩ, while power density from polarization curve was of 124.6 mW m(-2). The process allowed a total reduction of TCOD and BOD5 of 60% and 69%, respectively, recovering the 29% of the coulombic efficiency. The maximum voltage obtained from MFC fed with DW+OMW was 2.9 times higher than that of cell fed with DW. DNA-fingerprinting showed high bacterial diversity for both experiments and the presence on anodes of exoelectrogenic bacteria, such as Geobacter spp. Electrodes selected peculiar consortia and, in particular, anodes of both experiments showed a similar specialization of microbial communities independently by feeding used.

Sulfonated Polyether Ether Ketone-Based Composite Membranes Doped with a Tungsten-Based Inorganic Proton Conductor for Fuel Cell Applications

Sulfonated polyether ether ketone (SPEEK)-based composite membranes doped with hydrated tungsten oxide were prepared and studied for proton exchange membrane applications. Hydrated tungsten oxide (W O3 ·2 H2 O) was synthesized via acidic hydrolysis of sodium tungstate and its structure and physicochemical features were investigated by thermogravimetric analysis (TG), X-ray diffraction (XRD), and electrochemical impedance spectroscopy (EIS). SPEEK/ W O3 ·2 H2 O composite membranes were prepared by mixing proper amounts of SPEEK and hydrated W O3 in dimethylacetamide as casting solvent. The composite membranes were characterized by XRD, TG-DTA, EIS, and water uptake measurements as a function of the oxide content in the membrane. In particular, XRD patterns as well as TG measurements indicated the existence of a coordinative interaction between the water molecules of tungsten oxide and the SPEEK sulfonic acid groups. This interaction lead to the enhancement of the membrane proton conductivity, as well as of their properties, from the point of view of heat resistance and water solubility. In fact, the addition of tungsten oxide resulted in higher proton conductivity, improved heat resistance, and lower water solubility.

Ormosil/Sulfonated Polyetheretherketone-Based Hybrid Composite Proton Conducting Membranes

A modified silane bearing a sulfonic acid function (sulfonated diphenylsilanediole, SDPSD) was prepared and characterized. The resulting ormosil was mixed with sulfonated polyetheretherketone (SPEEK) with high degree of sulfonation (0.9) leading to homogeneous composite membranes. The formation of the composite substantially modified the properties of SPEEK in terms of water uptake and solubility. The structural and electrochemical performance of the components and of the composite were investigated with thermogravimetric analysis, field emission scanning electron microscopy, H-1 and Si-29 nuclear magnetic resonance, both in solution and in the solid state, and electrochemical impedance spectroscopy. Both conductivity values, as high as 0.1 S cm(-1), and H-1 diffusion coefficients of the composite SPEEK/SDPSD demonstrated that it possesses good proton transport characteristics up to 120 S C, and it is then suitable for application as an electrolyte in polymer electrolyte fuel cells operating at intermediate temperature

Composite Ormosil/Nafion Membranes as Electrolytes for Direct Methanol Fuel Cells

Composite Ormosil/Nafion membranes were prepared and characterized for use as electrolytes in direct methanol fuel cells (DMFCs). An organosilane derivative (sulfonated diphenylsilanediol, SDPSD) was selected as a filler of the Nafion matrix. The composite membranes were characterized by electrochemical impedance spectroscopy, differential scanning calorimetry, and solvent uptake measurements. The composite membranes exhibited higher proton conductivity and enhanced stability than the reference unfilled Nafion membrane, due to the occurrence of an effective interaction between the filler and the polar cluster of the polymer matrix. Polarization curves in a DMFC were acquired and the results showed that the performance of the composite membrane was superior to that of unfilled Nafion due to a reduced methanol permeation rate, as well as to enhanced proton conductivity and thermal stability of the membrane. Due to its satisfactory properties, the composite Nafion/SDPSD membrane has a potential use as electrolyte in DMFCs operating at intermediate temperatures.

Development of glucose oxidase-based bioanodes for enzyme fuel cell applications

We fabricated an enzyme fuel cell (EFC) device based on glucose as fuel and glucose oxidase (GOx) as biocatalyst. As a strategy to improve GOx stability, preserving at the same time the enzyme catalytic activity, we propose an immobilization procedure to entrap GOx in a polymer matrix based on Nafion and multiwalled carbon nanotubes. Circular dichroism (CD) spectra were recorded to study changes in the 3D structure of GOx that might be generated by the immobilization procedure. The comparison between the CD features of GOx immobilized and free in solution indicates that the shape of the spectra and position of peaks do not significantly change. The bioelectrocatalytic activity toward glucose oxidation of immobilized GOx was studied by cyclic voltammetry and chronoamperometry experiments. Such electrochemical experiments allow monitoring the rate of GOx-catalyzed glucose oxidation and extrapolating GOx kinetic parameters. Results demonstrate that immobilized GOx has high catalytic efficiency, due the maintaining of regular and well-ordered structure of the immobilized enzyme, as indicated by spectroscopic findings. Once investigated the electrode structure–property relationship, an EFC device was assembled using the GOx-based bioanode, and sulfonated poly ether ether ketone as electrolyte membrane. Polarization and power density curves of the complete EFC device were acquired, demonstrating the suitability of the immobilization strategy and materials to be used in EFCs.

Improvement of DMFC Electrode Kinetics by Using Nanohorns Catalyst Support

One of the factors limiting direct methanol fuel cells (DMFC) performance is the slow kinetics of methanol oxidation at the anode. The importance of the catalyst support for fuel cells has been recognized and different forms of carbon have been suggested. Single wall nanohorns (SWNH) are a new class of carbon with a similar graphitic structure of carbon nanotubes. They are self-assembling materials that produce aggregates of about 100 nm. In the present study, the comparison of the performance of a DMFC equipped with electrocatalysts supported on a commercial carbon black and on SWNH was carried out. The SWNH were synthesized by the arc discharge method in air. The deposition of the Pt and Pt/Ru catalysts on the carbon supports was accomplished by using ethylene glycol as reducing agent. The synthesized catalyst nanoparticles have a very small diameter size (ca. 2.5 nm) and they are uniformly distributed on both carbon supports. The supported electrode catalysts were tested in a DMFC and results indicate that employing SWNH is very promising showing catalytic activities 60 % higher.

Electrocatalysts Based on Iron Phthalocyanine and Polyindole Supported on Carbon Nanotubes for Oxygen Reduction in DMFCs

Novel electrocatalysts from iron phthalocyanine (FePc) and polyindole (PID) supported on carbon nanotubes (CNTs) have been synthesized for oxygen reduction reaction (ORR) in Direct Methanol Fuel Cell (DMFC). Two synthetic strategies have been proposed: i) preparation of PID on CNTs (PID/CNTs) through indole polymerization followed by the mechanical mixing of PID/CNTs with FePc (FePc_PID/CNTs); and ii) dispersion of polymerized PID, FePc, and CNTs in methanol and subsequent drying (FePc/PID/CNTs). The morphology of prepared catalysts was examined by SEM, and the electrochemical activity towards ORR was evaluated by cyclic voltammetry. FePc/PID/CNTs catalysts were found to have higher activity than that of FePc_PID/CNTs, due to a better dispersion of PID and FePc on carbon support, as demonstrated by SEM. Furthermore, in comparison with platinum on carbon black the prepared PID-based catalysts exhibited a stable ORR potential in both H2SO4 and H2SO4 + CH3OH solution. These new iron-based catalysts are thus promising to substitute platinum/carbon black at the cathode side of DMFC.

Oxygen Reduction Reaction Electrocatalysts Derived from Iron Salt and Benzimidazole and Aminobenzimidazole Precursors and Their Application in Microbial Fuel Cell Cathodes

In this work, benzimidazole (BZIM) and aminobenzimidazole (ABZIM) were used as organic-rich in nitrogen precursors during the synthesis of iron–nitrogen–carbon (Fe–N–C) based catalysts by sacrificial support method (SSM) technique. The catalysts obtained, denoted Fe-ABZIM and Fe-BZIM, were characterized morphologically and chemically through SEM, TEM, and XPS. Moreover, these catalysts were initially tested in rotating ring disk electrode (RRDE) configuration, resulting in similar high electrocatalytic activity toward oxygen reduction reaction (ORR) having low hydrogen peroxide generated (<3%). The ORR performance was significantly higher compared to activated carbon (AC) that was the control. The catalysts were then integrated into air-breathing (AB) and gas diffusion layer (GDL) cathode electrode and tested in operating microbial fuel cells (MFCs). The presence of Fe–N–C catalysts boosted the power output compared to AC cathode MFC. The AB-type cathode outperformed the GDL type cathode probably because of reduced catalyst layer flooding. The highest performance obtained in this work was 162 ± 3 μWcm–2. Fe-ABZIM and Fe-BZIM had similar performance when incorporated to the same type of cathode configuration. Long-term operations show a decrease up to 50% of the performance in two months operations. Despite the power output decrease, the Fe-BZIM/Fe-ABZIM catalysts gave a significant advantage in fuel cell performance compared to the bare AC.