One type is moisture-induced electricity generators (MIEGs), which generate electricity based on the interaction between ubiquitous moisture and active materials with ionizable groups such as graphene oxide (GO), carboxylated cellulose nanofibrils (CNFs), and polyelectrolytes. The generated voltage of MIEGs is generally explained as the potential difference induced by directional ion diffusion across the film of the active material. For example, Qu et al. demonstrated a series of MIEGs that is composed of a pair of electrodes and hygroscopic materials with a chemical-gradient structure. The other type is water-induced electricity generators (WIEGs) based on concentration/temperature gradient of salty liquid water or the interactions between liquid water and electrically conductive solids. Carbon materials such as carbon black nanoparticles (CBNPs), carbon nanotubes (CNTs), and graphene are generally used as the active materials for fabricating WIEGs. For example, Xue et al. developed a CBNP-based WIEG that can generate a voltage up to 1 V, which was claimed to arise from water evaporation.