A Janus Bilayer Portland Cement‐Based Moisture‐Electricity Generator via Hydrogen‐Bonding Network Regulation

The ubiquitous interaction between ambient moisture and built environments presents a compelling opportunity for continuous energy harvesting through moisture‐electricity generation (MEG). However, current MEG materials fail to satisfy high‐power demands in buildings because hydrogen bonds, indispensable for the structural integrity of soft carbon‐chain networks, severely restrict water diffusion, and thus bottleneck MEG performance. Hydrated Portland cement, featuring a robust silicate backbone, allows aggressive modulation of the water hydrogen‐bonding network (HBN), emerging as an ideal platform for higher performance. Here, we developed a Portland cement‐based moisture‐electricity generator (CMEG) via a facile asymmetric acid etching strategy, extending MEG to cementitious material systems. The resulting CMEG presents a Janus bilayer architecture with a stark gradient in hygroscopicity across the layers to drive the unidirectional diffusion of water molecules. Mechanistically, the etching process induces the breakage of HBN, which unlocks ultrafast water diffusion throughout the top layer and thus accelerates selective ion transport toward the bottom layer. Remarkably, CMEG delivers an extremely high short‐circuit current density of 723 µA/cm 2 and output power density of 112.5 µW/cm 2 . Furthermore, CMEG demonstrates exceptional scalability, modular integration capabilities and nearly identical mechanical strength to that before acid etching, proving its giant potential for future self‐powered buildings and infrastructures.