Barbara Mecheri

Engineering materials and biology to boost performance of microbial fuel cells: a critical review

In less than a decade the levels of performance of microbial fuel cells (MFCs) in terms of current output, voltage, and power density have grown tremendously according to steady exponential trends. Achievements occurred over the past 2–3 years have been particularly impressive. This is due partly to a better understanding of the biological aspects of this multidisciplinary technology, but also to systematic work undertaken by several research groups worldwide aimed at improving and optimizing aspects related to materials and system configuration. Aim of this review is to outline the current perspective about MFCs by focusing on the recent major advances in the areas of materials and engineering. MFCs are promising devices to address sustainability concerns both in terrestrial and space applications.

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.

Thick Soft Tissue Reconstruction on Highly Perfusive Biodegradable Scaffolds

The lack of a vascular network and poor perfusion is what mostly prevents three-dimensional (3D) scaffolds from being used in organ repair when reconstruction of thick tissues is needed. Highly-porous scaffolds made of poly(L-lactic acid) (PLLA) are prepared by directional thermally induced phase separation (dTIPS) starting from 1,4-dioxane/PLLA solutions. The influence of polymer concentration and temperature gradient, in terms of imposed intensity and direction, on pore size and distribution is studied by comparison with scaffolds prepared by isotropic TIPS. The processing parameters are optimized to achieve an overall porosity for the 3D scaffolds of about 93% with a degree of interconnectivity of 91%. The resulting pore network is characterized by the ordered repetition of closely packed dendrite-like cavities, each one showing stacks of 20 microm large side lamellar branches departing from 70 microm diameter vertical backbones, strongly resembling the vascular patterns. The in vitro biological responses after 1 and 2 weeks are evaluated from mesenchymal (bone marrow stromal) cells (MSC) static culturing. A novel vacuum-based deep-seeding method is set up to improve uniform cell penetration down to scaffold thicknesses of over 1 mm. Biological screenings show significant 3D scaffold colonization even after 18 h, while cellular retention is observed up to 14 d in vitro (DIV). Pore architecture-driven cellular growth is accompanied by cell tendency to preserve their multi-potency towards differentiation. Confluent tissues as thick as 1 mm were reconstructed taking advantage of the large perfusion enhanced by the highly porous microstructure of the engineered scaffolds, which could successfully serve for applications aimed at vascular nets and angiogenesis.

Tuning hierarchical architecture of 3D polymeric scaffolds for cardiac tissue engineering

Tissue engineering combines the fields of engineering, chemistry, biology, and medicine to fabricate replacement tissues able to restore, maintain, or improve structurally and functionally damaged organs. The approach of regenerative medicine is of paramount importance for treating patients with severe cardiac diseases. For successful exploitation, the challenge for cardiac regenerative medicine is to identify the suitable combination between the best cell source for cardiac repair and the design of the optimal scaffold as a template for tissue replacement. Adult stem cells have the potential to improve regenerative medicine with their peculiar feature to self-renew and differentiate into various phenotypes. Insights into the stem cell field lead to the identification of the suitable scaffold features that enhance the ex vivo proliferation and differentiation of stem cells. Scaffolds composed of natural and/or synthetic polymers can organise stem cells into complex architectures that mimic native tissues. To achieve this, a proper design of the chemical, mechanical, and morphological characteristics of the scaffold at different length scales is needed to reproduce the tissue complexity at the cell-scaffold interface. Hierarchical porosities are needed in a single construct, at the millimetre scale to help nutrition and vascularisation, at the micrometer scale to accommodate cells, and at the nanometre scale to favour the expression of extra-cellular matrix components. The present study has been undertaken to setup strategies to integrate stem cells and tailored scaffolds, as a tool to control cardiac tissue regeneration. Among the many available techniques for scaffold fabrication, porogen leaching, phase separation, and electrospinning were selected as low-cost and user-friendly technologies to fabricate tuneable, hierarchically porous matrices that mimic aspects of the cell native surroundings. The biological validation of these scaffolds was performed by implanting adult stem cells.

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.

Design of iron(II) pthalocyanine (FePc) derived oxygen reduction electrocatalysts for high power density microbial fuel cells

Abstract Iron(II) phthalocyanine (FePc) deposited onto two different carbonaceous supports was synthesized through an unconventional pyrolysis‐free method. The obtained materials were studied in the oxygen reduction reaction (ORR) in neutral media through incorporation in an air‐breathing cathode structure and tested in an operating microbial fuel cell (MFC) configuration. Rotating ring disk electrode (RRDE) analysis revealed high performances of the Fe‐based catalysts compared with that of activated carbon (AC). The FePc supported on Black‐Pearl carbon black [Fe‐BP(N)] exhibits the highest performance in terms of its more positive onset potential, positive shift of the half‐wave potential, and higher limiting current as well as the highest power density in the operating MFC of (243±7) μW cm−2, which was 33 % higher than that of FePc supported on nitrogen‐doped carbon nanotubes (Fe‐CNT(N); 182±5 μW cm−2). The power density generated by Fe‐BP(N) was 92 % higher than that of the MFC utilizing AC; therefore, the utilization of platinum group metal‐free catalysts can boost the performances of MFCs significantly.

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.

Tuning Structural Changes in Glucose Oxidase for Enzyme Fuel Cell Applications

Stabilization and electrical contacting of redox enzymes with electrodes are fundamental requirements for bioelectronics devices, including biosensors and enzyme fuel cells (EFCs). In this study, we show increased glucose oxidase (GOx) stability by immobilization with Nafion. The immobilization process affected GOx conformation but was not detrimental to its activity, which was maintained for more than 120 days. The GOx/Nafion system was interfaced to a carbon cloth electrode and assembled in a prototypal EFC fed with glucose. Polarization and power density curves demonstrated that GOx/Nafion system was able to generate power, exploiting a Nafion-assisted electron transfer process to the electrode. Our findings are consistent with the onset of pH-dependent conformational equilibrium for the enzyme secondary structure and its active site. Significantly, the protective effect exerted by Nafion on the enzyme structure may be tuned by varying parameters such as the pH to fabricate durable EFCs with good electrocatalytic performance.

Nafion/Tin Oxide Composite Membranes for Direct Methanol Fuel Cells

Composite Nafion-based membranes were prepared and characterized, using hydrated tin oxide as a filler. Water Uptake and proton conductivity were measured as a function of temperature. Methanol crossover through reference Nafion and composite membranes was evaluated by a voltametric method and the electrochemical performance of the membranes was assessed by tests in a single direct methanol fuel cell (DMFC). The formation of the composite improved the properties of Nafion matrix in terms of methanol crossover and DMFC performance, allowing to identify Nafion membrane with 10wt% tin oxide as a suitable electrolyte to be used in a DMFC device operating at T ≥ 90°C. ©The Electrochemical Society.