Porous Co3O4/SnO2 quantum dot (QD) heterostructures with abundant oxygen vacancies and Co2+ ions for highly efficient gas sensing and oxygen evolution reaction

Abstract

Porous Co₃O₄/SnO₂ quantum dot (QD) heterojunctions with a strong synergistic effect are successfully synthesized in this paper. Owing to the strong synergistic effect between Co₃O₄ and SnO₂QDs, Co₃O₄/SnO₂QD heterostructures possess more Co²⁺ ions for a faster Co²⁺/Co⁰ redox reaction in the process of sensing of reducing gases and electrochemical reactions, and more oxygen vacancies for more active sites and reduced charge transfer resistance on the surface. These advantages are demonstrated to significantly enhance the gas sensitivity to xylene and greatly improve the catalysis for the oxygen evolution reaction (OER). As a catalyst for the OER, Co₃O₄/SnO₂QD (1 : 1) heterostructures exhibit the highest current density, lowest onset potential, largest active surface area and remarkable durability in alkaline electrolytes. The sensitivity of Co₃O₄/SnO₂QD (1 : 1) heterostructures to 100 ppm xylene is almost 10 times higher than that of pure Co₃O₄ nanosheets and 3 times higher than that of SnO₂QDs. In addition, Co₃O₄/SnO₂QD (1 : 1) heterostructure sensors exhibit excellent gas selectivity, long-term stability and markedly high response to low concentrations of xylene at low operating temperatures.