Porous Co 3 O 4 /SnO 2 quantum dot (QD) heterostructures with abundant oxygen vacancies and Co 2+ ions for highly efficient gas sensing and oxygen evolution reaction.

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.