Water-Evaporation-Induced Electric Generator Built from Carbonized Electrospun Polyacrylonitrile Nanofiber Mats

Abstract

Electricity has been generated from evaporation-driven water flow in films of carbon soot particles and other porous media. This paper reports the placement of carbon nanofiber mats (CNMs) on fiberglass screens for the construction of efficient water-evaporation-induced generators (WEIGs). These CNMs are prepared from carbonizing electrospun polyacrylonitrile nanofiber mats and then treating them with oxygen plasma. After electrode attachment to the two ends of a CNM, one electrode is immersed into water. Water rises in the mat due to capillary action and evaporates from the mat surface due to thermal energy provided by the environment. The steady rise of water pushes the dissociated ions of the surface functionalities upward, resulting in a streaming current and an electric potential. This paper investigates how the generated short-circuit current, I s, and open-circuit voltage, V o, of the WEIG change with structural parameters of the CNMs. Under optimized conditions, these CNMs produce electricity at an areal power density of 83 nW/cm2, which is almost 10 times those offered by some existing ones. Thus, the easy-to-handle CNMs are an attractive porous scaffold for WEIGs.

Evaporation-driven electrokinetic energy conversion: Critical review, parametric analysis and perspectives

“…Moreover, the SCC increased about 5 times when temperature increased from 24˚C to 55˚C in quantitative agreement with the increase in saturated-vapor pressure [24]. Further positive correlations with temperature [19,29,47] and airflow rate [12,13,28,29,47] have been observed. Many studies have also reported on deteriorating performance with increasing ambient relative humidity [12,13,28,34,49,51].…”

“…However, these reactions were studied only in acidic media, so it remains unclear if they could effectively occur in the typically pH-neutral solutions. Besides, some studies used non-carbon electrode materials (for example, copper foil [28], Au, Ag, ITO [29]) but the results were qualitatively similar to obtained with carbon-based electrodes.…”

“…This is in line with the largest experimental values reported up to date (see, for example, [24]) although in most cases the power densities were essentially lower. Thus for instance, they were around 150 µW/m 2 [50], 100 µW/m 2 [51], 130 µW/m 2 [13], 800 µW/m 2 [28], or 80 µW/m 2 [29]. Such sub-optimal performance could be primarily due to over-voltages and sluggish kinetics of electrode reactions as well as low EK-conversion efficiencies caused by insufficient surface charge-densities in very dilute electrolyte solutions used in the experiments.…”

“…In this section, we will formulate (and qualitatively compare with published experiments) a simple model for the description of the configuration, which has been mostly studied experimentally up to date. Although some elementary expressions for basic electrokinetic phenomena of streaming potential and streaming current in this context were considered previously [16,18,28,29,47,48], no attempts to formulate a consistent model have been made. The configuration is schematically represented in Fig.…”

“…On the other hand, in several studies the films were thinner than the assumed 100 µm, which had to give rise to shorter fully-wet zones. The existence of an optimal film length (based on qualitative considerations and experimental data) was suggested in [28,34].…”