Abstract • Bi2O3 cannot directly activate PMS. • Bi2O3 loading increased the specific surface area and conductivity of CoOOH. • Larger specific surface area provided more active sites for PMS activation. • Faster electron transfer rate promoted the generation of reactive oxygen species. • 1O2 was identified as dominant ROS in the CoOOH@Bi2O3/PMS system. Cobalt oxyhydroxide (CoOOH) has been turned out to be a high-efficiency catalyst for peroxymonosulfate (PMS) activation. In this study, CoOOH was loaded on bismuth oxide (Bi2O3) using a facile chemical precipitation process to improve its catalytic activity and stability. The result showed that the catalytic performance on the 2,4-dichlorophenol (2,4-DCP) degradation was significantly enhanced with only 11 wt% Bi2O3 loading. The degradation rate in the CoOOH@Bi2O3/PMS system (0.2011 min−1) was nearly 6.0 times higher than that in the CoOOH/PMS system (0.0337 min−1). Furthermore, CoOOH@Bi2O3 displayed better stability with less Co ions leaching (16.4% lower than CoOOH) in the PMS system. These phenomena were attributed to the Bi2O3 loading which significantly increased the conductivity and specific surface area of the CoOOH@Bi2O3 composite. Faster electron transfer facilitated the redox reaction of Co (III) / Co (II) and thus was more favorable for reactive oxygen species (ROS) generation. Meanwhile, larger specific surface area furnished more active sites for PMS activation. More importantly, there were both non-radical (1O2) and radicals (SO4−•, O2−•, and OH•) in the CoOOH@Bi2O3/PMS system and 1O2 was the dominant one. In general, this study provided a simple and practical strategy to enhance the catalytic activity and stability of cobalt oxyhydroxide in the PMS system.