Enhancing Hydrovoltaic Power Generation through Coupled Heat and Light-Driven Surface Charge Dynamics

Abstract

Harnessing natural evaporation offers a sustainable and untapped pathway for next-generation energy technologies. Here, we present a unified physical and experimental framework for evaporation-driven hydrovoltaic (EDHV) systems that decouples and systematically controls the key interfacial processes underlying electricity generation from ambient heat and sunlight. By introducing an intermediate ion-conducting layer, we spatially and functionally separate the evaporative top interface from the silicon-dielectric nanopillar array at the bottom, enabling independent modulation of evaporation, ion transport, and interfacial chemical equilibrium. This decoupling strategy enhances device performance, facilitating the study of thermal and photo-induced charge generation, and improving ion migration and electricity generation. We develop a predictive equivalent electrical circuit model that captures the coupling between these processes through a transfer capacitance term, which we derive analytically as a function of geometric and material parameters. Our study reveals that capacitive photocharging and thermally modulated surface equilibria, rather than Faradaic or photothermal effects, are the dominant drivers of energy conversion when interfacial environments are adequately engineered. The device achieves a state-of-the-art open-circuit voltage of 1 V and a peak power density of 0.25 W/m2 at a 0.1 M salt concentration. Strategic variation of doping reveals that increasing silicon doping enhances voltage by 28% and power by 1.6 times, while switching the dielectric shell from TiO2 to Al2O3 boosts voltage (power) by up to 1.9 times (3.6 times). These findings offer insights for enhancing EDHV devices and suggest strategies that consider environmental conditions, water salinity, and material engineering to better harness waste heat and sunlight.