Summary A comprehensive 3D, multiphase, and nonisothermal model for a proton exchange membrane fuel cell has been developed in this study. The model has been used to investigate the effects of the size of the parallel‐type cathode flow channel on the fuel cell performance. The flow‐field plate, with the numerically predicted best performing cathode flow channel, has been built and experimentally tested using an in‐house fuel cell test station. The effects of the operating conditions of relative humidity, pressure, and temperature have also been studied. The results have shown that the fuel cell performs better as the size of the cathode flow channel decreases, and this is due to the increased velocity that assists in removing liquid water that may hinder the transport of oxygen to the cathode catalyst layer. Further, the modelled fuel cell was found to perform better with increasing pressure, increasing temperature, and decreasing relative humidity; the respective results have been presented and discussed. Finally, the agreement between the modelling and the experimentally data of the best performing cathode flow channel was found to be very good.

A numerical model for a PEM fuel cell has been developed and used to investigate the effect of some of the key parameters of the porous layers of the fuel cell (GDL and MPL) on its performance. The model is comprehensive as it is three-dimensional, multiphase and non-isothermal and it has been well-validated with the experimental data of a 5 cm² active area-fuel cell with/without MPLs. As a result of the reduced mass transport resistance of the gaseous and liquid flow, a better performance was achieved when the GDL thickness was decreased. For the same reason, the fuel cell was shown to be significantly improved with increasing the GDL porosity by a factor of 2 and the consumption of oxygen doubled when increasing the porosity from 0.40 to 0.78. Compared to the conventional constant-porosity GDL, the graded-porosity (gradually decreasing from the flow channel to the catalyst layer) GDL was found to enhance the fuel cell performance and this is due to the better liquid water rejection. The incorporation of a realistic value for the contact resistance between the GDL and the bipolar plate slightly decreases the performance of the fuel cell. Also the results show that the addition of the MPL to the GDL is crucially important as it assists in the humidifying of the electrolyte membrane, thus improving the overall performance of the fuel cell. Finally, realistically increasing the MPL contact angle has led to a positive influence on the fuel cell performance.

Water is the key element that defines and individualizes our planet. Relative to body weight, water represents 70% or more for the majority of all species on Earth. Taking care of water as a whole is equivalent with taking care of the entire biodiversity or the whole of humanity itself. Water quality is becoming an increasingly important component of terrestrial life, hence intensive work is being conducted to develop sensors for detecting contaminants and assessing water quality and characteristics. Our bibliometric analysis is focused on water quality sensors based on carbon nanotubes and highlights the most important objectives and achievements of researchers in recent years. Due to important measurement characteristics such as sensitivity and selectivity, or low detection limit and linearity, up to the ability to measure water properties, including detection of heavy metal content or the presence of persistent organic compounds, carbon nanotube (CNT) sensors, taking advantage of available nanotechnologies, are becoming increasingly attractive. The conducted bibliometric analysis creates a visual, more efficient keystones mapping. CNT sensors can be integrated into an inexpensive real-time monitoring data acquisition system as an alternative for classical expensive and time-consuming offline water quality monitoring. The conducted bibliometric analysis reveals all connections and maps all the results in this water quality CNT sensors research field and gives a perspective on the approached methods on this specific type of sensor. Finally, challenges related to integration of other trends that have been used and proven to be valuable in the field of other sensor types and capable to contribute to the development (and outlook) for future new configurations that will undoubtedly emerge are presented.

Various flow field designs have been numerically investigated to evaluate the effect of pattern and the cross-sectional dimensions of the channel on the performance of a large active area PEM fuel cell. Three types of multiple-serpentine channels (7-channels, 11-channels and 14-channels) have been chosen for the 200 cm 2 fuel cell investigated and numerically analysed by varying the width and the land of the channel. The CFD simulations showed that as the channel width decreases, as in the 14channels serpentine case, the performance improves, especially at high current densities where the concentration losses are dominant. The optimum configuration, i.e. the 14-channels serpentine, has been manufactured and tested experimentally and a very good agreement between the experimental and modelling data was achieved. 4 channel depths have been considered (0.25, 0.4, 0.6 and 0.8 mm) in the CFD study to determine and the effects on the pressure drop and water content is described. Up to 7 % increase in the maximum reported current density has been achieved for the smallest depth and this due to the better removal of excess liquid water and better humidification of the membrane. Also, the influence of the air flow rate has been evaluated: the current density at 0.6V increased by around 25% when air flow rate was increased 4 times; this is attributed to better removal of excess liquid water.

Numerical simulations based on ANSYS Fluent software were carried out in order to investigate the effect of the clamping force and MPL addition on the fuel cell performance. The influence of the required gas diffusion layer (GDL) compression, during assembly process, onto fuel cell performance is investigated by considering four cases (0%, 15.7 %, 31.5%, 47.4%) and the optimum compression ratio was obtained (31.5%). The study revealed that the GDL compression and intrusion into the channels affect the fuel cell performance and some aspects related to its influence on liquid saturation are presented. Then, our study analyzed the role of the micro porous layer (MPL) inserted between catalyst layer (CL) and GDL and it found that an improvement in the cell performance can be achieved since it can help to reduce the ohmic and the concentration polarization losses.