Intrinsic facet-dependent electrochemical activities of BiOBr nanosheets for Br- exchange in electrochemically switched ion exchange process

Creating surface atomic arrangement and coordination of BiOBr with a special highly-exposed crystal facet could significantly alter its performance. Although many efforts have been made to explore the relationship between the exposed facet and photo-reactivity, little has been done to investigate Br- exchange activity on the specific facet during an electrochemically switched ion exchange (ESIX) process. In this study, BiOBr nanosheets with highly exposed (001) and (010) facets (named as BOB-001 and BOB-001, respectively) were synthesized, and the effect of exposed crystal facet on ESIX activity was investigated for the first time. The electrochemical investigation suggested that the BOB-010 had better ESIX performance for Br- recovery than the BOB-001. Due to the difference in the surface state as well as the property, the Bi-O bond of the exposed [Bi2O2] layer in the BOB -001 could be broken at a higher potential for the exchange of Br-. While for the BOB-010, Br- could easily pass through the open channel between the [Bi2O2] layers for ion exchange. Furthermore, the photo-assisted elec-trochemically switched ion exchange (P-ESIX) performances of BOB-001 and BOB-010 were investigated. It is found that the real photo-assisted performance of BOB-010 was remarkably higher than that of BOB-001 because of its better photo-response characteristics. This study gives a better insight into the facet-dependent electro-chemical ion-exchange performance of BiOBr.