CBNP is chosen as the active material for WIEG because it is a nanostructured material that has a high specific surface area and interaction with water. A flexible, hydrophilic, and porous mixed-cellulose-ester (MCE) membrane fully coated by CBNPs (denoted as CBNP f /MCE membrane) is fabricated via vacuum filtration, as shown in Figure . The scanning electron microscope (SEM) image (Figure ) shows that CBNPs are sparsely distributed on the porous MCE membrane. To assemble a CBNP-based traditional WIEG (TWIEG) similar to previous reports, two conductive strips as the current collectors were placed at both ends of a rectangular CBNP f /MCE membrane. Then a certain amount of water was dropped on one end (denoted as the wet end) of the membrane near the current collector. To investigate the effect of current collectors on the output voltage of the TWIEG, eight kinds of conductive strips of aluminum (Al), zinc (Zn), nickel (Ni), copper (Cu), silver (Ag), platinum (Pt), gold (Au), and graphite/polyvinylidene fluoride (PVDF) (GP) are combined into different pairs of current collectors. The output voltage and current curves of the TWIEGs are shown in Figure and Figure , respectively. As shown in Figure , no voltage is generated for both the pure MCE membrane after adding water and the TWIEG before adding water, indicating the vital roles of CBNP and water in the electricity generation. According to these curves, the average output voltage of the TWIEG is calculated and summarized in Figure . As indicated by the blue columns, the TWIEG using current collectors with higher electrochemical activity generates higher output voltage, suggesting that the electrochemical activity of current collectors also plays a key role in electricity generation. It is worth noting that quite low voltages are generated when using noble Ag, Au, and Pt as the electrodes. The generated voltage might be ascribed to the previously claimed weak interactions between CBNPs and water that induce streaming potential. To further figure out the mechanism, the current collector at the wet end was fixed as a Zn strip while the one at the dry end varied. As illustrated by the red columns, the average output voltage shows no significant difference when using different current collectors at the dry end. This demonstrates that the output voltage of the TWIEG is determined by the potential difference between two ends, which can be attributed to the different electrochemical reactions that occurred at the solid-water interfaces in the wet region. Then the CBNP f /MCE membrane is separated into five equal portions to evaluate the influence of the inner resistance on the output performance of TWIEG. The voltage E x0 between points 0 (the wet end) and x (x=1, 2, 3, 4, or 5) is recorded (Figure ). As the distance between the two current collectors increases, the average E x0 decreases almost linearly (Figure ), which can be explained by the inset electric circuit model in Figure . The wet section (S 10 ) can be considered as a power source while the dry section S x1 (x=2, 3, 4, or 5) as a variable resistor. The total resistance of section S x0 increases as the distance between the two current collectors increases, hence the measured E x0 decreases. The above results indicate that the presence of asymmetric solid-water interfaces at two ends of the wet region could be a vital factor for voltage generation. To prove this, 10 µL of water was dropped in the middle of a CBNP f /MCE membrane. As shown in Figure , no voltage is generated because water does not contact metal strips, making both ends of the wet region dry CBNP layers.