Water-Evaporation-Induced Electric Generators Built from Electrospun Carbon Nanofiber Mats

Abstract

Electricity generation from evaporation-driven water flow in porous nanomaterials is a promising approach for harvesting renewable energy. Driven by capillary action and continuous water evaporation, water flow in the pores of a partially submerged porous film is sustained and the flow carries along ions dissociated from pore walls, giving rise to a streaming potential and current. Water-evaporation-induced generators (WEIGs) are constructed to harness these currents and electricity. However, past WEIGs suffer from poor mechanical robustness, handling limitations, and low output power. A novel material is developed and used to construct powerful and easy-to-handle WEIGs. Herein, the progress towards the fabrication of a novel free-standing porous carbon nanofiber mat (CNM) for the construction of powerful WEIGs is described. CNMs are prepared from carbonizing electrospun polyacrylonitrile nanofiber mats and then treating them with oxygen plasma. Chapter 2 systematically investigates how the generated short-circuit current (Is) and open-circuit voltage (Vo) of WEIGs change with the structural parameters of CNMs. Under optimized conditions, these WEIGs generate a maximum aerial power density of 83 nW.cm-2, which exceeds that of existing WEIGs by almost 10-fold. Next, in search of WEIGs that would operate in seawater, the performance of devices with different electrode combinations operating in NaCl solutions is investigated. Traditionally, inert graphite (C) electrodes are used to construct WEIGs. However, we report on C/metal and metal/metal WEIGs that feature either a carbon or a corroding metal [Cu, St (steel), Al] as the top/bottom electrodes. The asymmetric environments and potential differences between the top and bottom electrodes of a WEIG facilitate metal corrosion in NaCl solution. While the WEIG configuration facilitates metal corrosion, the metal corrosion empowers the WEIG. These Galvanic WEIGs outperform traditional WEIGs by thousands of times in power outputs. High output power is essential for the entry of WEIGs into the renewable energy market. The voltage, current, and output power of Galvanic WEIGs can be further increased by adding series and parallel connections to multiple devices. This research brings WEIGs one step closer to practical utilization.