Preparation and characterization of graphene oxide based membranes as possible Gas Diffusion Layers for PEM fuel cells with enhanced surface homogeneity

The aim of this work is to define and optimize a process to produce a membrane made of reduced graphene oxide, r-GO, aiming to use it as Gas Diffusion Layer, GDL, in a Polymer Electrolyte Membrane Fuel Cell, PEMFC. Some works have reported that r-GO could reach conductivity values of about 104S/m; by using the "self-assembling" properties of GO, it would be possible to obtain a GDL with enhanced homogeneity, which maintains a good electronic conductivity. A reduction process of GO in aqueous solution was developed in order to get the desired conductivity value of the final product. The membrane was characterized through several techniques to assess key parameters and to understand its properties. In this work it was possible to obtain a membrane which has a maximum contact angle of 86° and a conductivity of about 421 S/m

Supercapacitor Sizing for Fast Power Dips in a Hybrid Supercapacitor—PEM Fuel Cell System

Polymer electrolyte membrane fuel cell (PEM FC) operation is likely to be characterized by voltage dips on timescales shorter than 1 s, arising from temporary flooding of gas channels or porous layers, particularly when the FC is operated at high humidity levels. If supercapacitors are employed in hybrid systems, they can make up for the temporary lack of energy produced by the FC. However, the steep slopes of the voltage dips affect the energy that can be actually delivered by the supercapacitor because of its series impedance, and this should be taken into account when sizing it. This paper presents a simplified approach for sizing the supercapacitor, based on some observed peculiar features of the FC dips, which allow a simple but accurate model for the evaluation of the supercapacitor response to such dips. The validity of such an approach is supported by simulation and experimental results performed on a single PEM FC and on a supercapacitor

PEM Fuel Cell Drying and Flooding Diagnosis With Signals Injected by a Power Converter

In this paper, a low-cost approach for polymer electrolyte membrane fuel cell (FC) drying and flooding diagnosis based on power converter ripple is presented, suitable to be implemented in commercial applications. If proper signal processing algorithms are employed, the high-frequency ripple inherently produced by switch-mode converters allows one to monitor the FC ohmic resistance, which is a good indicator for membrane drying, while an ad hoc switching control of the converter allows one to monitor also the low-frequency impedance, which is an indicator for cell flooding. This technique is tested with a dc/dc boost converter directly connected to a single cell, discussing how different FC operation modes (such as constant current or constant voltage) may affect the sensitivity required to the diagnostic algorithm to correctly recognize drying and flooding occurrences

Diagnosis of PEM Fuel Cell Drying and Flooding Based on Power Converter Ripple

This paper discusses the possibility to use the current ripple introduced by switch mode power converters for low-cost monitoring of polymer electrolyte membrane (PEM) fuel cell (FC) state-of-health, suitable for commercial applications that cannot afford dedicated instrumentation. In more details, an estimate of the ohmic resistance, which is a good indicator of the membrane water content, can be obtained from the high-frequency ripple response by data processing in the frequency domain, while lower frequency ripple at 100/120 Hz (when present) is in the typical frequency range of activation processes. All the available impedance estimates, together with the dc voltage measurement, can be used to promptly detect FC drying and flooding, that are the two opposite failure modes as far as water balance is concerned. The proposed diagnostic approach is tested on a single PEM FC in drying and flooding conditions, by emulating three-phase and single-phase inverter ripples by means of an electronic load

Combining Electrical and Pressure Measurements for Early Flooding Detection in a PEM Fuel Cell

Water flooding is one of the main causes of performance degradation for polymer electrolyte membrane fuel cells (FCs), and its prompt detection is therefore important to guarantee optimal FC operation. This paper aims at comparing the most common methods for flooding diagnosis, which are based on electrical or gas pressure measurements. Their differences in terms of sensitivity to flooding are investigated, primarily focusing on their suitability for its early detection. In particular, the differences between anodic and cathodic pressure drop measurements are highlighted, as well as their relationship with the FC electrical output. The experimental results show that cathodic pressure measurements are the most convenient choice for early flooding detection. Measurements have been performed on a single cell, since it allows an easier interpretation of the results, although the applicability of the considered methods to FC stacks for commercial applications is also discussed