Synergistic effect of a Berlin green framework for highly efficient moisture-electric energy transformation†

We developed a novel moisture-induced power generator (MPG) by utilizing Berlin green (BG) as an active material to enhance its moisture-electric energy transformation (MEET) performance. The bilayer-based MPG device was fabricated by stacking a BG/graphene oxide/cellulose nanofiber (BGC) composite layer on a NaCl/cellulose nanofiber (NC) composite layer. Moisture adsorption onto the NC layer triggered the dissociation and spontaneous diffusion of the sodium ions toward the BGC layer due to the ion concentration gradient. The adsorption of positive sodium ions onto the BGC layer induced electron transfer from the counter electrode through the external wire, generating electricity. Furthermore, the insertion of sodium ions into the BG framework reduced BG to Prussian blue, generating additional electricity. This synergistic interplay of physical and electrochemical processes resulted in excellent MEET performance: 1.17 V and 2770 μA cm⁻² at 90% relative humidity. These values are two and ten times higher than those of the bilayer MPG without BG, respectively. In particular, the current density of BGC–NC is the highest value that has been reported to date.