Development of Flexible Methylcellulose/Cellulose Acetate-Based Triboelectric Nanogenerators with AlFe2O4 and CuMnO2 Nanoparticle Coatings for Enhanced Energy Harvesting

Wood is one of the most used materials in the world, from its applications in building structures, furniture, food flavorings, to even the paper this is printed on. One of the earliest usages of wood by man was energy generation by combustion. As time passed, and mankind developed, we turned to other sources of energy, such as coal, natural gas, and nuclear energy, which happen to be the three main sources of energy production in the USA. However, these predominantly used energy generation methods contribute a lot to wastewater/air pollution and greenhouse gas production. In order to prevent this, and to reduce the amount of greenhouse gas emissions and pollution, many alternative energy resources have been investigated. One of these alternatives discovered during the last decade are triboelectric nanogenerators, commonly referred to as TENGs . As these devices were investigated and studied, a list known as the triboelectric series was formed, based on the ability of various materials to gain or donate electrons. Cellulose, a wood-derived polymer, happens to fall near the middle of this list, slightly to the positive side. In this study we investigated both cellulose and its derivatives, methylcellulose and cellulose acetate, in combination with CuMnO2 delafossite and AlFe2O4 spinel to manufacture a TENG device.<br/>TENGs are devices composed of two layers with opposing charges, one negatively charged and one positively charged, that produce electricity when the two layers contact each other. This voltage is produced by the triboelectric effect and electrostatic induction. The former is when different materials become charged after coming in contact with another through friction. One will gain electrons and the other will lose electrons, which creates a current. The latter is when materials with different charges separate, in this case charges created by the triboelectric effect, and create an electric potential difference which generates a current once more. This is why TENGs produce voltage upon both contact and separation. By maximizing the charge difference and surface area of the two layers, more voltage can be produced.<br/>Cellulose is considered a slightly positive material, which means it tends to lose electrons, based on its chemical structure. However, in order to maximize voltage production, we synthesized methylcellulose and cellulose acetate, the former being more negative than standard cellulose, and the latter more positive. These derivatives were then used to make hydrogel films,. Metals are highly conductive and durable materials, and have high electron mobility, traits essential to a good TENG. By depositing metallic nanoparticle compounds onto the surface of the cellulose derivative films, the charge difference, surface area, and electron mobility of the respective films can be enhanced. Copper and manganese are relatively negative on the triboelectric series, meaning they are likely to gain electrons. On the other hand, aluminum and iron are more positive, and easily donate electrons.<br/>Given this we synthesized CuMnO2 delafossite and AlFe2O4 spinel nanoparticles using hydrothermal process, that when deposited onto the methylcellulose and cellulose acetate films respectively, will enhance their negative and positive charge respectively as well as their contact surface area. Once complete, a TENG device surrounded by a 3D printed chassis is produced, and then connected to an oscilloscope and triboelectric testing commences. The produced TENGs generated a much higher voltage than our control TENGs made of plain cellulose, plain methylcellulose and cellulose acetate, and plain cellulose deposited with AlFe2O4 and CuMnO2. Further studies must be conducted in order to investigate the capacitance properties of these cellulose derivatives, as well as their ability to conduct electricity. Nonetheless, the usage and application of cellulose derivatives seems to be a promising and unique direction for future TENG research.