Abstract:

Objective: The purpose of this study is to prepare natural wood into a Janus wood-based functional material with an asymmetric structure via chemical modification methods, so as to endow it with excellent hydrovoltaic power generation performance, thereby reducing the dependence of hydrovoltaic technology on non-degradable or expensive nanomaterials, and providing new design ideas for the development of high-performance and long-life wood-based hydrovoltaic generators. Method: Natural balsa wood was selected as the substrate and cut along the direction perpendicular to the growth of trees to retain its natural micro-channels and expose the intrinsic anisotropic structure. Firstly, the negatively charged carboxyl groups were selectively introduced on the surface of wood fiber by TEMPO oxidation reaction. Further functionalization was performed by citric acid esterification reaction to construct different charge densities within the material. Subsequently, two kinds of wood with different degrees of modification were assembled to successfully prepare a water volt generator with Janus structure with significant differences in charge density, stable microstructure, and green simplified preparation process. Result: The microstructure analysis showed that highly ordered and aligned ion nanochannels were formed inside the modified wood, and the inner wall of the channel was rich in functional groups such as dissociative carboxyl groups, which provided an ideal path for the selective and rapid transport of ions. The open circuit voltage of the water volt generator based on the Janus wood-based material was able to reach up to 184 mV, which is about 3.5 times that of the natural wood (the output voltage is only 53 mV). At the same time, its output power density was increased to 0.29 nW·cm^?2. With seven water volt power generation units integrated in series, the cumulative output voltage was able to reach as high as 1.44 V, which can successfully drive a small calculator to work stably, which preliminarily proves its practical potential in power supply for micro-electronic devices. Conclusion: This work has successfully transformed natural wood into high-performance hydrovoltaic power generation materials through a novel strategy of two-step continuous chemical modification to construct a Janus gradient structure. This study not only provides a new material design idea for the development of low-cost, biodegradable green energy conversion devices, but also shows the great application prospects of wood-based functional materials in the field of sustainable energy.

Key words: natural balsa wood, hydrovoltaic generator, double-layer structure, TEMPO oxidation, esterification modification