Hydrovoltaic Electricity Generators: A Comprehensive Overview of Chemical and Architectural Designs

Hydrovoltaic electricity generators (HEGs) have emerged as a class of distinctive green energy harvesters that convert the energy of ubiquitous water, including moisture and liquid water, into electricity through water-induced interfacial processes at solid-gas and solid-liquid interfaces. While early studies primarily focused on empirical material screening, recent advances have increasingly demonstrated that HEG performance is governed by the coupled interplay between interfacial chemistry and architectural design. Chemically, proton dissociation, surface charge regulation, ion-solvation dynamics, and electric double layer formation govern charge separation and transport at molecular scale. Architecturally, hierarchical and deliberately engineered structures, including pore design, asymmetric configurations, and multilayer coupling, can be implemented across one- to three-dimensional device formats, thereby dictating water distribution, ion diffusion, and mechanical integrity. This review establishes a unified chemical-architectural framework that correlates interfacial molecular processes with device-level architectures and macroscopic electrical outputs. We categorize representative HEG systems according to their structural motifs while elucidating the governing physicochemical mechanisms that drive energy conversion. Building on this foundation, we identify key design principles and functional objectives toward high-output, durable, and multifunctional HEGs. Finally, we outline future directions emphasizing synergistic chemical control and architectural innovation to realizing intelligent, sustainable, and scalable hydrovoltaic energy systems.