Photoenergy harvesting by ammonium molybdate soft hydrogel drops

Photoenergy harvesting is promising to power Internet-of-Things (IoT) sensors, freeing the limitations of wired power sources or batteries, enabling bio-integrated devices. However, existing photoenergy harvesting systems are restricted to solid or liquid configurations-limiting biocompatibility and space utilization-which makes obtaining flexible, biocompatible, light-harvesting devices a significant challenge. In this paper, inspired by natural ion gradient diffusion in organisms, offering an ion-hydrogel drops-based photoenergy harvesting base on ammonium molybdate. Through the photochemical process of ammonium molybdate, the electric potential of the device is regulated by the altered ion gradient and the redox pairs ( ${{[\mathrm{Mo}}_7{O}_{24}]}^{6-}$ / ${{[\mathrm{Mo}}_{14}{O}_{46}]}^{10-}$ ), to generate energy. When exposed to excitation light, a photo driven ammonium molybdate-hydrogel photoenergy harvester (PAPH) can generate an open-circuit potential of ~250 mV, and it can still obtain a considerable output power for milliseconds to thousands of seconds after the termination of the initial illumination. The reversible hydrogel droplets network allows for the recovery and fabrication of arbitrary structures of the PAPH. We further demonstrate the scalable PAPH networks can on-demand regulation of cell epithelial growth factor secretion and receptor expression, stimulate the cell proliferation, thereby facilitating biological tissue wound repair. This ionic hydrogel opens a new avenue for flexible, photoenergy harvesting, biocompatible devices.