Berlin Green-Coated\nCellulose Paper for Hydrovoltaic\nElectricity and Solar Steam Cogeneration

Generating both freshwater and electricity\nfrom solar energy offers\na promising solution to the global challenges of freshwater scarcity\nand energy demand. Evaporation-induced electricity generation is a\nkey technology in advancing sustainable energy technologies. However,\nit faces limitations such as low output power, complex fabrication\nprocesses, and inefficiency with highly concentrated water like seawater.\nIn this study, we introduce a solution by fabricating a dual-layered\nstructure consisting of Berlin green (BG) and carbon black (CB) coated\nonto a cellulose paper substrate (PS) (CB/BG@PS). This structure enables\nsimultaneous water-induced electricity generation and solar-induced\nfreshwater production. By leveraging the electrokinetic effect and\nthe electrochemical energy produced by the interaction of salt ions\nwith BG, the short-circuit current of the CB/BG@PS device is significantly\nenhanced compared to CB@PS based on the electrokinetic effect alone.\nA single CB/BG@PS device with an active area of 3 cm × 3 cm can\nsustainably output a short-circuit current of ∼48 μA\nand an open-circuit voltage of ∼410 mV when operating in a\n0.6 M NaCl solution. Simultaneously, it achieves an evaporation rate\nof 2.1 kg m<sup>–2</sup> h<sup>–1</sup> under 1 sun\nillumination. Moreover, the combined voltage of six series-connected\nCB/BG@PS devices is sufficient to power some electronic devices. These\nfindings demonstrate the potential of the proposed device for simultaneous\ndesalination and ocean energy harvesting.