Experimental measurement technique for the assessment of the fuel crossover diffusion coefficient in the membrane electrode assembly of a direct methanol fuel cell

Since the cross-over still seems to be the main issue of the direct methanol fuel cells, an experimental evaluation of the diffusive cross-over is performed. Even if the relationship of the rate through the membrane is the sum of the three terms of diffusive, osmotic and drag, the diffusive component is also present at open circuit lowering the Open Circuit Voltage of the single cell up to 50 % with respect to the Nernst potential. The goal of the research is to develop a direct measurement technique of the crossover that can provide the effective values of the parameters that characterize the membrane electrode assembly. The experimental set up consists in the pressure, flow and temperature control and acquisition using Labview. A sensitive analysis for three values of temperatures at 60°C, 65°C and 70°C is performed for first. Then, a small overpressure was generated in the cathode side by a valve located at the cathode outlet. A set of pressure were analysed for 0, 30 and 90 mbar of overpressure at the cathode. The tested fuel cell has a commercial Nafion 117 membrane and carbon paper gas diffusion layers 700 cm2 large. Preliminary results show that the differential concentration term seems to be significantly larger than the osmotic term. The diffusion coefficients are useful for fuel cell modelling and for the calibration of the operating conditions in the sensor less DMFC systems

Assessment of innovative reforming procedures for biogas obtained from organic fraction of solid municipal waste

In the present paper reforming technologies for the treatment of biogas from municipal solid wastes are discussed. An approach based on the well-known ASPEN Plus software was adopted for the simulation of the whole process, assuming equilibrium conditions for the reactions development. The well-established steam-reforming, the dry reforming and an innovative two-steps reforming (including the basics of both models) were considered. A preliminary assessment was carried out comparing the predictions and experimental results of the steam-reforming procedure of diesel fuel. Then, the validated model was applied to the different schemes. The dry reforming (at 800 °C) showed better reforming efficiency if compared to steam reforming (at 600°C). However, carbon deposition occurs when dry reforming is in play. On the other hand, the two-steps technique demonstrated to be able to solve the problem of carbon deposition guaranteeing a very good efficiency

Assessment of CO2 bubble generation influence on direct methanol fuel cell performance

Fuel cells fed directly by liquid methanol represent a class of suitable devices for supply portable small power applications. To become a market attractive technology some issues must be properly addressed and resolved. The presence of gaseous CO2 generated in the anode channels is the main issue as it can hinder the free surface of the Gas Diffusion Layer reducing the active area and the methanol flux through the porous media towards the catalyst layer. In this work the influence of gas phase fraction on the cell performance and the relationship with the operating parameters such as air flow rate, methanol-water solution flow rate and current density is investigated. The characterization of CO2 bubbles flow in the anode channel is carried out

Development of Improved Passive Configurations of DMFC with Reduced Contact Resistance

Abstract The Direct Methanol Fuel Cell (DMFC) represents today an appropriate solution for powering portable applications and small electronic devices, due to: 1) its compactness, 2) the high power density when compared with batteries and 3) the facility in transporting proper quantities of fuel (generally a liquid mixture of methanol and water). In order to further reduce the DMFCs size, passive configurations without external pumps and auxiliary devices are actively studied. Oxygen is supplied from the surrounding air while methanol-water solution is stored into a built-in tank in contact with the gas diffusion layer (GDL) that is constantly kept wet. Such configurations have a lower current density, roughly around 10÷30 mA/cm2, when compared with active configuration (40÷80 mA/cm2). It is then important to improve the baseline performance (power and efficiency) of such cells by optimizing all system components. Here we aim at reducing the effects of the contact resistance between GDL and current collectors by carrying out a sensitivity analysis on a number of relevant cells parameters such as:. assembly shape, gaskets, current collectors materials and open ratios. Analysis will be carried out at different molar concentrations (1 to 4 M) of the water-methanol solution used as fuel

Hydroxyapatite–Silicon Scaffold Promotes Osteogenic Differentiation of CGF Primary Cells s

Simple Summary: The aim of this study was to identify new and innovative strategies to improve the tissue-regeneration process. Concentrated growth factor (CGF) is an autologous biomaterial rich in growth factors and multipotent stem cells. The purpose of our study was to evaluate the osteogenic differentiation of CGF primary cells in the presence of a hydroxyapatite–silicon scaffold, which represents a very interesting material in the field of bone reconstructive surgery. Our findings showed that the hydroxyapatite–silicon scaffold provided support to primary CGF cells by enhancing osteogenic differentiation. These data suggest interesting perspectives in the use of CGF together with scaffolds in the field of regenerative medicine. Abstract: The application of scaffolding materials together with stem cell technologies plays a key role in tissue regeneration. Therefore, in this study, CGF (concentrated growth factor), which represents an autologous and biocompatible blood-derived product rich in growth factors and multipotent stem cells, was used together with a hydroxyapatite and silicon (HA-Si) scaffold, which represents a very interesting material in the field of bone reconstructive surgery. The aim of this work was to evaluate the potential osteogenic differentiation of CGF primary cells induced by HASi scaffolds. The cellular viability of CGF primary cells cultured on HA-Si scaffolds and their structural characterization were performed by MTT assay and SEM analysis, respectively. Moreover, the matrix mineralization of CGF primary cells on the HA-Si scaffold was evaluated through Alizarin red staining. The expression of osteogenic differentiation markers was investigated through mRNA quantification by real-time PCR. We found that the HA-Si scaffold was not cytotoxic for CGF primary cells, allowing their growth and proliferation. Furthermore, the HASi scaffold was able to induce increased levels of osteogenic markers, decreased levels of stemness markers in these cells, and the formation of a mineralized matrix. In conclusion, our results suggest that HA-Si scaffolds can be used as a biomaterial support for CGF application in the field of tissue regeneration

Simulation of fluid dynamic and electric field in a direct methanol fuel cell

This  paper  represents  the  first step  of  a  comprehensive  analysis of the influence of CO2 in the DMFC channels. The  flow  is  treated  as  gaseous  (and  not  as  liquid‐gaseous  mixture)  to  separately  assess  the  importance  of several  parameters, such  as  methanol  concentration,  mass  flow,  current  density.  In  the  model  mass  transport  of  the  different species and the electric field inside the fuel cell are  considered.  The  3D  computational  model  with  multicomponent flow is solved using COMSOL Multiphysics  software. The set of governing equations is composed by: a)  Maxwell‐Stefan equation for species transport; b) Brinkman  equation  to  calculate  momentum  in  porous  media;  c)  Butler‐Volmer  equation  to  calculate  the  current  density  over the  catalyst  layers  allowing the  achievement  of the  quantity  of  generated/consumed  species.  The  equations  system is validated against available experimental data. The  V/I characteristic of the cell, species distributions, velocity  fields  and  current  density  distributions  will  be  discussed.  The  generation  and  the  dispersion  of  CO2  in  the  anode  channel is also analyzed

Analisi del funzionamento di una direct methanol fuel cell (dmfc) soggetta all'effetto del fenomeno di cross-over

Le fuel cells alimentate con metanolo rappresentano un’interessante soluzione di conversione energetica per applicazioni che richiedano potenze elettriche contenute associate ad alta densità di energia ed alta efficienza. Questo è il caso tipico dei dispositivi portatili. Lo schema con alimentazione diretta a metanolo risulta il più diffuso data la semplificazione impiantistica e la maggiore compattezza che ne deriva. Il sistema di equazioni che descrivono il funzionamento della Direct Methanol Fuel Cell (DMFC) è stato sviluppato in ambiente COMSOL®. Tale modello permette di analizzare le peculiarità di questa tecnologia. In particolare si studierà il crossover del combustibile non reagito dall’anodo al catodo. Questo fenomeno risulta essere il limite principale per raggiungere elevati valori di efficienza in questi sistemi energetici e può provocare fenomeni corrosivi nel comparto catodico. L’entità di tale fenomeno è dipendente dall’effetto di tre componenti: quella relativa alla resistenza elettro-osmotica, dovuta al trascinamento di molecole di metanolo da parte degli ioni H+ attraverso la membrana; quella relativa alla componente diffusiva, caratterizzata dal gradiente di concentrazione; quella relativa alla componente convettiva, dovuta al gradiente di pressione. Le specie chimiche presenti nelle semireazioni sono tre all’anodo (CH3OH, H2O e CO2) e tre al catodo (N2, O2 e H2O). Gli ioni sono considerati esistenti solo all’interno della membrana. Nell’equazione di Maxwell-Stefan sono stati inseriti tre opportuni coefficienti di diffusione binaria, per ciascun elettrodo, necessari alla costruzione di una matrice che governi tale fenomeno. La semireazione all’anodo è endotermica, mentre quella al catodo è esotermica e pertanto il flusso di calore dal catodo verso l’anodo risulta un aspetto chiave della gestione termica. Il flusso termico viene calcolato tenendo conto del differenziale di produzione di calore tra anodo e catodo allo scopo di mappare la temperatura (utile per l’individuazione di hot spot o elevati gradienti termici) ed analizzare configurazioni che potrebbero indurre malfunzionamenti del dispositivo