Berlin Green-Coated Cellulose Paper for Hydrovoltaic Electricity and Solar Steam Cogeneration

Generating both freshwater and electricity from solar energy offers a promising solution to the global challenges of freshwater scarcity and energy demand. Evaporation-induced electricity generation is a key technology in advancing sustainable energy technologies. However, it faces limitations such as low output power, complex fabrication processes, and inefficiency with highly concentrated water like seawater. In this study, we introduce a solution by fabricating a dual-layered structure consisting of Berlin green (BG) and carbon black (CB) coated onto a cellulose paper substrate (PS) (CB/BG@PS). This structure enables simultaneous water-induced electricity generation and solar-induced freshwater production. By leveraging the electrokinetic effect and the electrochemical energy produced by the interaction of salt ions with BG, the short-circuit current of the CB/BG@PS device is significantly enhanced compared to CB@PS based on the electrokinetic effect alone. A single CB/BG@PS device with an active area of 3 cm × 3 cm can sustainably output a short-circuit current of ∼48 μA and an open-circuit voltage of ∼410 mV when operating in a 0.6 M NaCl solution. Simultaneously, it achieves an evaporation rate of 2.1 kg m–2 h–1 under 1 sun illumination. Moreover, the combined voltage of six series-connected CB/BG@PS devices is sufficient to power some electronic devices. These findings demonstrate the potential of the proposed device for simultaneous desalination and ocean energy harvesting.