Self‑Powered All‑Fiber Hydrogen Sensor via Whispering Gallery Mode Microcavity and Built‑in Electric Field Synergy.

Fiber‑optic hydrogen sensors offer intrinsic safety and remote operation, yet their application is constrained by expensive spectrometers and complex demodulation. Here, we present a self-powered all‑fiber hydrogen sensor (SAHS) that integrates optical excitation, electrical readout and gas detection on a single fiber tip, enabling remote and room‑temperature sensing at zero bias. By constructing a whispering gallery mode (WGM)-enhanced lateral ZnO/PEDOT:PSS n-p heterojunction on the fiber tip, we achieve synergy between the localized optical field and the built‑in electric field. The WGM microcavity confines and recycles incident light, markedly enhancing light-matter interaction and photogeneration on the tiny fiber tip. Meanwhile, the lateral built‑in field efficiently dissociates the photogenerated carriers, producing a substantial photocurrent without any external voltage. The self‑powered sensor exhibits outstanding room‑temperature H2 detection under 380 nm light excitation upon Pd functionalization, with a detection limit of ∼19 ppm and response/recovery times of 30 s and 7 s, respectively. This light‑activated, electrically‑read‑out architecture eliminates costly optical demodulation equipment, offering a low‑cost, user‑friendly and intrinsically safe solution for advanced hydrogen energy monitoring.