Room-Temperature Ammonia Gas Sensing Using Mixed-Valent CuCo₂O₄ Nanoplatelets: Performance Enhancement through Stoichiometry Control

Abstract

We report the sensing properties of an interesting ternary oxide CuCo₂O₄ (CCO) which comprises two earth-abundant transition elements, both capable of supporting multiple valence states. We have used a synthesis protocol, which renders unique nanoplatelet-type morphology but with a degree of biphasic character (CuO as a secondary phase in addition to the defect-spinel Cu_1-<i>x</i> Co₂O₄). This sample constitution can be controlled through the use of cation off-stoichiometry, and the same also influence the sensing response significantly. In particular, a Co 10 at. % excess CCO (CCO-Co(10)) case exhibits a good response (∼7.9% at 400 ppm) for NH₃ gas with a complete recovery at room temperature (23 °C, ±1 °C) in 57% RH. The material performance was investigated for other gases such as H₂S, NO₂, and CO. A good response is observed for H₂S and NO₂ gases but without a recovery; however, for CO, a poor response is noted. Herein, we discuss the specific results for ammonia sensing for the CCO-Co(10) case in detail via the use of different characterizations and outline the difference between the cases of the single-phase defect-stabilized material versus nonpercolating biphasic material.