Insights into the multiple active sites in Bi-Co bimetallic oxide for a deeper understanding of nitrate electroreduction to ammonia

The electrochemical nitrate reduction reaction (NO 3 RR) is a promising approach for nitrate removal and NH 3 production at ambient conditions. The development of various types of efficient electrocatalysts, especially bimetallic oxides with the advantages of superior durability and excellent catalytic activity, have become a research focus. However, the analysis of active sites for bimetallic oxide catalysts either emphasizes the role of bimetallic interactions or focuses on the role of oxygen vacancies (OVs), resulting in a lack of thoroughness. Herein, a Bi-Co bimetallic oxide (BCO) was constructed for NO 3 RR, illustrating 1.5∼7.8 folds higher NH 3 yield rate than those of commercial single metal oxide (Bi 2 O 3 , Co 3 O 4 ). The NO 3 RR pathway by BCO was explored according to H* capture test, DEMS, and isotope labeling experiment. An in-situ Raman test showed the structure evolution of BCO during NO 3 RR, and therefore the catalytic sites of BCO were further identified according to physical characteristics before and after NO 3 RR. Results suggest that Bi 0 , OVs and amorphous Co oxide as the real active sites play a vital role in nitrate electroreduction. Furthermore, research on 25 articles also indicates the presence of multiple catalytic sites in bimetallic oxides for NO 3 RR. This study provides a new and comprehensive insight into the active sites identification for the type of bimetallic oxide NO 3 RR electrocatalysts.