Self‐Sustained Electricity Generation from Ambient Moisture Enabled by Step‐Gradient Polysaccharide Films

Abstract Moisture electricity generator (MEG) has emerged as a promising technology to directly harvest energy from the ambient atmosphere. However, their practical applications remain limited by inefficient ion transport. In this work, a high‐performance, polysaccharide‐based step‐gradient MEG (SG‐MEG) is presented, fabricated by the sequential multilayer casting‐drying of polysaccharide materials with varying functional group densities. This design creates an intrinsic step‐wise ionic gradient, promoting ion dissociation and diffusion. As a result, a single unit can sustain an open‐circuit voltage of 0.78 V for over 1300 h, a milliamp‐scale short‐circuit current density of 1.1 mA cm −2 and an improved power density of 15.49 µW cm −2 (1291 W m⁻ 3 ), representing a ten‐fold enhancement compared to conventional MEG. Numerical simulations and experimental analyses confirm that the enhanced performance arises from the high functionalization of polysaccharide and the facilitated ion diffusion enabled by the step gradient.The multifunctionality of SG‐MEG is demonstrated in practical applications, including self‐powered respiration monitoring, direct powering of low‐power electronics, and integration with energy storage systems for autonomous devices such as a self‐cruising boat and a water‐level alarm. This work offers a new paradigm for the design of high‐performance, bio‐based MEGs and advances their application.