# Ag-Cellulose Hybrid Filler for Boosting the Power Output of a Triboelectric Nanogenerator
## 1 Introduction  
With the rapid growth of the Internet of things (IoTs), micro/nano sensors, as well as portable and wearable electronic devices, are extensively developed, requiring massive energy demand. The triboelectric nanogenerator (TENG) is a new energy technology which is promising as an effective power source to sustain these new generation electronics by converting mechanical energy into electricity [1, 2]. With a combination of two physical phenomena--contact electrification and electrostatic induction--TENG generates an alternating current electricity with many significant advantages, including high output voltage, cost-effectiveness, a simple fabrication process, and numerous operation modes [3]. This gives TENG the potential for application in diverse fields, such as micro/nano power sources, self-powered sensors, large-scale blue energy, and direct high-voltage power sources.  
Biodegradable and biocompatible TENGs have recently received increasing interest due to their potential application in various fields [4]. Numerous natural material-based TENGs were developed, such as those derived from natural wood [5], natural leaves [6], silk [7], cellulose [8, 9], lignin [10], and chitosan [11]. Natural rubber (NR) and cellulose are the two natural polymers that have gained increasing attention for the fabrication of biodegradable and biocompatible TENGs [9, 12, 13, 14, 15]. NR, or polyisoprene, is a natural polymer with a chemical formula of cis-1, 4-polyisoprene, which is obtained from the _Hevera brasiliensis_ tree [16]. NR is used as raw material for the production of many industrial goods due to its good flexibility, high tensile strength, and low cost. The majority of NR products involve their subject to mechanical force; thus, NR is one of the attractive materialsfor TENG fabrication, replacing the synthetic polymers such as polytetrafluoroethylene (PTFE) [17], polydimethylsiloxane (PDMS) [18], polyvinylidenefluoride (PVDF) [19], and polyimide (Kapton) [20], which are non-biodegradable and expensive.  
According our previous study [21], cellulose fiber (CF) was employed to modify NR, which was found to effectively improve TENG performance due to its electron donating property [22; 23], which is preferred for tribopositive materials. Regarding many appealing aspects of cellulose-based materials, including significant bioavailability, good mechanical properties, insolubility in common organic solvents--which is ideal for structural engineering materials--and low cost [24; 25; 26], it is promising for modifying NR to develop the NR-based TENG with enhanced power output, which is crucial for realizing the potential application of TENGs.  
As for improving the energy conversion efficiency of TENG, diverse approaches were proposed to modify triboelectric polymers, including surface/internal structure modification [18; 27; 28], chemical functionalization [29], and improving charge capacitance of the triboelectric layer by filling it with metal nanoparticles and high dielectric constant materials [18; 30; 31; 32]. For the case of metal nanoparticles filling, Ag nanoparticles were extensively used to enhance the energy conversion efficiency of triboelectric polymers [32; 33; 34; 35; 36]. In this work, the hybrid material composed of cellulose fiber and Ag nanoparticles was synthesized and used as a filler for NR triboelectric film. Cellulose fibers were derived from sugarcane leaves, one of the major agricultural wastes from sugarcane farm, which were employed synergistically as a filler for NR and a capping agent for Ag nanoparticles. The Ag nanoparticle content in the composites was optimized. The contribution of CF-Ag hybrid filler was investigated and discussed. The applications of the fabricated NR-CF-Ag TENG as a power source were also demonstrated. Since NR and sugarcane are industrial crops in many countries, the success of this research would contribute to the bio-circular-green economy regarding the development of green and sustainable energy.