Enhanced hydrovoltaic energy conversion via optimized tubular MnO₂-activated carbon composites

Recently, hydrovoltaic energy harvesting has emerged as a sustainable approach to convert water-solid interfacial interactions into usable electricity under ambient conditions, However, the combined potential of manganese dioxide (MnO₂) and activated carbon (AC) in this context remains largely unexplored. A systematic study conducted here led to the fabrication and optimization of a tubular hydrovoltaic device composed of MnO₂ and AC to enhance energy conversion efficiency. New insights into the structural and morphological characterizations, adapted to the hydrovoltaic mechanism, confirmed the uniform integration of crystalline MnO₂ within the activated carbon matrix, providing both hydrophilicity and a high surface area for effective water transport and electrokinetic activity. Justifying the critical role of physical dimensions, device geometry was first optimized using silicone tubes of varying lengths (2 cm, 3.5 cm, and 5 cm), in that the 3.5 cm device exhibited the most favorable balance between capillary-driven water flow and evaporation, thereby enabling continuous hydration-evaporation cycles and stable ion migration. In-depth tuning of the MnO₂​/AC ratio established that the 3:1 composition achieved the highest open-circuit voltage (1.12 V) and short-circuit current (0.19 mA), producing a peak power of 56 μW by leveraging the uniform MnO₂​ dispersion within the AC framework to promote efficient electrical double layer formation and sustained ion gradient establishment. The device demonstrated long-term operational stability over three months, scalability through series connections (up to 2.58 V with three devices), and practical utility by successfully charging capacitors of various capacitances and powering an LED. Highlighting the synergistic role of MnO₂​ and AC in advancing hydrovoltaic energy harvesting, these findings bridge a critical gap in the application of composite materials, underscoring their promise for self-powered and sustainable electronic applications.