Enhancing the surface activity of Co3O4 by gallium doping to increase the sensitivity of conductometric CO gas sensors

Increasing the surface activity of p-type oxide semiconductors, especially for Co₃O₄, is essential but challenging to improve the sensing performances toward CO. Herein, a strategy is proposed aiming to increase the surface activity of Co₃O₄ toward the oxidation of CO through gallium doping by utilizing the wet impregnation and freeze-drying approach. The synthesized Ga-doped Co₃O₄ (Ga-Co₃O₄) features a hierarchical structure assembled by nanosheets and a large surface area (65.39 m²/g), which ensures high-efficiency gas interaction and high response to CO. Moreover, the results demonstrate that this strategy promotes the formation of oxygen vacancies and increases the ratio of Co³⁺/Co²⁺ in Co₃O₄, resulting in an enhanced response of 5.8 toward 100 ppm CO, which is markedly higher than that of the bare Co₃O₄ (1.08). The sensor based on Ga-Co₃O₄ also presents excellent selectivity toward CO in various interfering gases and a wide concentration detection range of 1–900 ppm. The improved CO sensing performance can be put down to the increased surface activity of Co₃O₄ via tailoring the content of oxygen vacancy and Co³⁺ active sites. This study provides new perspectives and strategies for improving the gas-sensing properties of p-type oxide semiconductors.