Flexible and Tailorable Moisture–Electric Generators Realized by Arsenic Concentration Gradient in 2D Black As _x P Nanosheet Sponge

ABSTRACT

Moisture‐enabled electric generators (MEGs) can harvest atmospheric water and convert humidity into electricity, but their application is hindered by low and unstable output. Herein, we exploit the compositional tunability of two‐dimensional black arsenic phosphorus ( b ‐As _x P) to construct asymmetric MEGs by integrating b ‐As _x P nanosheets but their application is hindered into a high‐density polyurethane sponge. The graded As distribution creates distinct surface physicochemical properties while preserving the crystalline lattice, enabling directional water adsorption and asymmetric proton transport. The MEGs show pronounced humidity‐responsive output over a wide relative humidity range. At ∼80% relative humidity, a 4.0 × 1.0 × 0.5 cm ³ device delivers an open‐circuit voltage of 186 mV and a short‐circuit current density of 0.44 µA cm ⁻² . Polyvinyl alcohol encapsulation enhances device hygroscopicity and suppresses b ‐As _x P oxidation, improving stability and mitigating concerns associated with arsenic oxidation. Comparative experiments and theoretical calculations indicate that composition‐dependent interactions between water molecules and arsenic/phosphorus sites establish the asymmetric ionic environment and electrical output. The devices show excellent flexibility and scalability, delivering stable output even at a nearly folded state and 2.7 V from 28 serially connected units. This work highlights the concentration‐tunable characteristics of 2D elemental alloys and provides a composition‐gradient strategy for flexible moisture‐energy systems.