Highly Sensitive Rice‐Grain–Shaped β‐MnO₂ Nano Crystallites for Ammonia Detection in Vapor and Liquid Phases

ABSTRACT In this study, β‐MnO₂ films were synthesized and assessed for dual applications in ammonia vapor sensing and electrocatalytic oxidation in alkaline media. XRD confirmed a tetragonal phase, while FESEM revealed a uniform nanostructure, enhancing surface reactivity. XPS verified material purity and oxidation state. Gas sensing tests at 350°C showed fast, stable, and repeatable responses with strong selectivity. The sensing mechanism involved NH₃ adsorption and reaction with chemisorbed oxygen, modulating electrical conductivity. Long‐term stability confirmed robust performance. Electrochemical studies via cyclic voltammetry in 0.5 M NaOH indicated increased oxidation currents with rising NH₃ concentrations, evidencing effective electrocatalysis. The β‐MnO₂ electrode promoted NH₃ oxidation, generating electrons and nitrogen gas through OH − mediated electron transfer at the electrode–electrolyte interface. This dual‐functional capability highlights β‐MnO₂ as a cost‐effective, versatile material for real‐time ammonia detection in both gas and liquid phases, with potential applications in environmental monitoring and alkaline fuel cell systems.