To further investigate the intrinsic mechanism, the CBNP and Cu strips are characterized before and after discharging (short-circuiting) the device for 12 h under intermittent supply of water. As shown in the Raman spectra in Figure , the wet-end Cu strip after discharge exhibits several obvious peaks in the range of 100 to 1500 cm -1 as compared with pristine Cu. The peaks at 148 and 220 cm -1 correspond to the Cu-O vibrations of Cu 2 O, and the peaks at 298 and 615 cm -1 correspond to the Cu-O vibrations of CuO, while the peaks at 535 and 1035 cm -1 can be respectively ascribed to the Cu-OH and CO 3 2-vibrations of Cu 2 CO 3 (OH) 2 . From the SEM and energy dispersive spectroscopy (EDS) images in Figure , the formation of some O-containing substances after discharge can be observed. These observations confirm that the Cu strip at the wet end undergoes an oxidation reaction at the Cu-water interface, which plays a vital role in the output performance of the AWIEG. The CBNP-coating before and after the reaction was also characterized by Raman spectroscopy. As calculated from the Raman spectra in Figure , the intensity ratio of D band at 1313 cm -1 and G band at 1578 cm -1 (I D /I G ) increases slightly from 1.42 before charge to 1.51 after discharge, suggesting a small decrease of sp 2 hybridized carbon atoms after discharging. This result is further confirmed by X-ray photoelectron spectroscopy (XPS) analysis (Figure ), which demonstrate an increased ratio of sp 3 C-C bonds, indicating that some sp 2 C=C bonds of CBNP are electrochemically reduced after discharging. Note that ambient oxygen that is dissolved in water and/or adsorbed on CBNP may also participate in the electrochemical reactions and affect the electricity generation of the AWIEG. To investigate this, the output voltage of the AWIEG was measured with oxygen-free water in an Ar-filled glove box. As shown in Figure , the output voltage shows an obvious decrease compared with that measured in the ambient environment, indicating the active contribution of oxygen to the electrochemical reactions and the electricity generation of the AWIEG. It should be noted that the dissolved CO 2 in water can also participate in the reactions and affect the output voltage and the final products on the Cu surface (e.g., Cu 2 CO 3 (OH) 2 ). Based on these results, the underlying mechanism for the AWIEG with a pair of Cu current collectors is proposed and illustrated in Figure . The generated voltage can be ascribed to the potential difference between the CBNP-water and Cu-water interfaces in the wet region, where electrochemical (redox) half-reactions occur similarly to those in galvanic corrosion cells. These reactions would cause electron movement from Cu to CBNP when they are electrically connected via a circuit, generating an electrical current (Figure ). It is believed that the AWIEG using other current collectors would undergo similar electrochemical reactions at solid-water interfaces, which convert the chemical energy of active materials (CBNP and O 2 ) and current collectors into electricity.