Enhancing power generation for carbon black film device based on optimization of liquid capillary flow

Power generation via spontaneous water evaporation is considered as one potential solution to the energy and pollution issues in very recent years. The efforts to harvest this type of green energy have been made in the previous works, which proved the different functional materials can be used for the energy harvesting device. However, few studies focused on the capillary flow of liquid inside the devices, which should be a key factor in the process of electricity generation. In this work, four carbon black film devices with different geometries are designed and fabricated. From the experimental test, it is found the optimization of device geometry is an efficient approach for improving the electricity output performance, and an increase of 200% in the generated open-circuit voltage can be achieved. In addition, three different types of capillary grooves are etched on the Al2O3 substrates through ultrafast laser micromachining, which is to further improve the liquid capillary flow inside the devices and reduce the flow losses. A voltage output of 188 mV can be realized in the device with the fractal tree-like capillary grooves, which obtains a 652% improvement compared to the original one. By connecting eight independent carbon black film devices in series, a portable electronic calculator can be powered, which shows the potential application of this new energy harvesting technique.