The increase of autonomous motes for the Internet of Things (IoT) leads to an increasing demand for sustainable and compact energy sources in order to supply them. A typical power requirement for future nodes is in the range of 100 μW and less. In this field, it is also important to reduce the environmental footprint and avoid fossil fuels.
Emerging as a concept in the 1970’s, the so-called "blue energy" or "salinity gradient power" is harvesting the free energy released during the mixing of waters with different saline concentrations. For instance, the mixing of freshwater and seawater near estuaries can be harvested with devices implementing this concept. This clean and green energy is not producing any waste.
Several approaches have been proposed to collect the blue energy. Most of them are based on semi-permeable or ionic-conducting membranes. This thesis will be investigating the use of porous silicon as specific embodiment for the salt/fresh water separation and mixing control.
Porous silicon is obtained by the electrochemical etching of monocristalline silicon. This step is well-known in the micro and nanofabrication cleanrooms of UCL (WINFAB) and results in nanochannels perforating the silicon substrate. The objective of the thesis will be targeted at fabricating and characterizing porous silicon membranes, and perform surface treatments to change the conducting properties of the substrate. A test bench will be set up to test the energy harvesting of different membranes and various electrode configurations.