High-Current Hydrovoltaic Devices Enabled by Synergistic Physicochemical Processes via a Dynamic Liquid-Hydrogel Interface

Electricity generation from interfacial molecular motion holds great promise for harvesting micro/nano energy for carbon neutrality and sustainable off-grid power. Carbon materials and noble metals are normally treated as chemically inert electrodes even in such systems, potentially overestimating physical contributions and underutilizing chemical processes. Here, we achieve an ultrahigh current output via a dynamic liquid-hydrogel interface through a synergistic physicochemical approach, by bridging a static graphite electrode and a dynamic hydrogel-coated platinum electrode in saline. The hydrogel film containing poly(acrylic acid) is critical to both processes. Polyanionic poly(acrylic acid) serves as a proton reservoir, neutralizing hydroxide ions from the oxygen reduction reaction at the platinum surface (oxygen is ubiquitous in air), thereby providing a continuous chemical current; sharp ion concentration gradients form near the hydrogel/saline interface due to the Donnan effect, enabling physical charge separation by liquid flow during periodic immersion-withdrawal cycles. Overall, this design delivers a direct-current output with a peak current density of 2432 µA cm⁻² and a transferred charge density over 1000 mC m⁻² per cycle, surpassing existing counterparts. This work offers new insight into constructing high-performance hydrovoltaic devices as green, scalable energy sources for self-powered miniaturized systems and emerging energy infrastructures.