context: The wettability of electrodes is well known as an important characteristic governing the interaction between the electrolyte and electrode as well as the charge transfer at the interface. As shown in Fig. S6,† the water contact angle (WCA) of COG is measured to be 0°, and the total spreading and penetration time (TSPT) of a water drop is about 3.17 s, indicating the inherent hydrophilicity of the COG. This should be attributed to the presence of some heteroatoms in natural reed straw, leading to heteroatom doping during the carbonization process and hence improved hydrophilicity of carbon materials. In contrast, the TSPT of COG@Zn, porous COG@MnO2 and bulk COG@MnO2 is reduced to 0.92 s, 0.42 s and 0.54 s, respectively. The results indicate that the surface wettability of the electrodes has been enhanced from hydrophilic to super-hydrophilic with the incorporation of MnO2 and Zn nanosheets. As is well known, MnO2 and Zn are inherently hydrophilic. In this case, the nanosheet structure increases the roughness of the material's surface, thereby further improving the hydrophilicity of the material. This favors the accessibility of the electrolyte at the surface of the electrodes and the charge transfer between them, giving rise to enhanced electrochemical performance.