environmental protection, infrastructure monitoring, and security, dramatically changing people's lives. [5,8] Meanwhile, the rapid increase of portable electronics calls for new demand of power supply. The traditional energy sources to power these devices are batteries and capacitors, [9] which need to be frequently replaced or charged. For trillions of electronic devices widely distributed, replacing batteries or frequent charging would be a challenging and high-cost task. [10] To address this problem, we desperately need a sustainable energy supply solution.Integrating the energy harvesting device with the energy storage device to form a self-powered system seems like an ideal solution. [11] When two dissimilar materials come into contact, charge transfer will occur due to the distinct surface electron affinity, creating opposite charges on their surfaces. [12] This common physical phenomenon is called the triboelectric effect, generally considered harmful and needs to be prevented. [13] In 2012, Wang's group first reported the triboelectric nanogenerator (TENG), a novel energy harvesting device that can convert mechanical energy into electricity based on triboelectric effect and electrostatic induction. [14] According to the working mechanisms, TENG can be divided into four basic modes: vertical contact-separation (CS) mode, lateral-sliding (LS) mode, single-electrode (SE) mode, and freestanding triboelectric-layer (FT) mode. [15] Based on these four modes, all kinds of mechanical energy can be harvested, such as human movement, vibration, wind, flowing water, water wave, and more. [16] Since its invention, the TENG is regarded as a revolutionary breakthrough toward energy conversion and utilization, has attracted considerable attention. [17] A TENG mainly consists of substrate (which provides support), [18] triboelectric layers (which generate the triboelectric charge), [19] and electrodes (which generate the induced charge). In principle, any two materials with distinct electron affinity can be utilized as triboelectric layers to fabricate a TENG, resulting in diverse materials choices. [20] However, most of the current triboelectric materials used in TENGs are synthetic polymer films, which are nonrenewable and non-biodegradable. For example, polyamide (PA) and polyformaldehyde are commonly used as positive triboelectric layers, while polydimethylsiloxane (PDMS) and polytetrafluoroethylene (PTFE) are usually applied as negative triboelectric layers. [21] With the enhancement of Developing new energy technology is a significant challenge in the context of the energy crisis. As a novel energy conversion device to convert mechanical energy into electricity, the triboelectric nanogenerator (TENG) has attracted significant attention in the past few years. The choice of component materials directly affects the cost, environmental performance, output performance, and preparation process of a TENG. In recent years, cellulose paper has become an ideal material for fabricating a TENG due to its lightweight, bio...
