Bioinspired Oxygen Functional Group Density Governs Hydrovoltaic Energy Harvesting for Soil–Moisture–Driven Plant Monitoring

ABSTRACT Hydrovoltaic generators convert ambient water flow into electricity, yet their power output has plateaued for lack of a quantitative link between surface chemistry and electrokinetic performance. Here we identify oxygen functional group density as that missing descriptor. The design is inspired by plant root cell walls, where oxygen‐rich ─COOH and ─OH groups electrostatically recruit mobile cations to drive nutrient uptake. We translate this chemical logic into a Cellulose‐scaffolded Oxygen‐functionalized Hydrovoltaic Generator (CO‐HyGEN), pairing a long‐fiber Hanji cellulose scaffold with a graphene oxide interface. Across a graded series of carbon architectures, physicochemical, surface‐electronic, and electrochemical signatures converge on a consistent picture: zeta potential, work function, hydrovoltaic output, and charge‐storage response exhibit systematic dependence on the oxygen functional group density. Beyond passive wettability, the oxygen‐rich graphene oxide interface behaves as an electrochemically active participant rather than an inert conduit, strengthening the electrical double layer through denser electrostatic recruitment of counterions, consistent with its more negative zeta potential and higher work function. Deployed around the root zone of a living plant, CO‐HyGEN arrays autonomously harvest soil moisture to power wireless Bluetooth sensing, demonstrating a plant‐electronics symbiosis that extends interface‐engineered hydrovoltaics toward bio‐integrated energy systems.