Effect Band Gap of Chitosan Film in Converting Water Vapour Into Electrical Current

Abstract

In this study, a device called a water vapour cell has been successfully fabricated. A water vapour cell consists of patterned silver on the top layer, chitosan film in the middle, titanium in the bottom layer and isolator substrate as the cover. Chitosan films utilized as a conversion material which works based on direct chemical interactions between chitosan film surface and water vapour to generate electrical current. The chitosan concentration was varied from 0%, 1%, 2%, 3%, 3.25%, 3.5%, 3.75%, 4%, 4.25% and 4.5% (w/v), respectively. The energy conversion properties of a water vapour cell were conducted by exposing water vapour into a water vapour cell. The water vapour was represented by a percentage of relative humidity (RH) which varied from 30% - 90% at 27 °C until 24 hours. It was proven that no electrical current was generated by water vapour cell with 0% chitosan film, while the other concentrations generated stable electrical current once exposed to ≤70% RH. However, the electrical current started to increase and achieved a stable state after 13-11 hours when exposed to ≥70% RH. The highest electrical current was generated 15.31 microampere (μA) achieved by 4% chitosan film under 90% RH exposure. The optical band gap and SEM characterization result indicated that the addition of chitosan concentration higher or equal to 4.25% showed the presence of aggregates which decreased chitosan film band gap into 3.22 and 3.53 eV. Therefore, the higher than 4% concentrations of chitosan have an effect on the physical structure which decreasing the band gap and electrical current.