First, both POMOFs and inner Keggin

First, both POMOFs and inner Keggin POMs are prepared under acidic synthetic conditions.Therefore, the obtained POMOFs may be stable in the acidic electrolyte solution during electrochemical measurements. TheFT-IR spectrum images of compounds 1−3 also further verify the good stability in the acidic solution.Second, both the high connected number of POMs and the encapsulation structure of the whole framework are beneficial to the stability of compounds, so compound-1−3-basedelectrode materials are all stable. The connected number of POMs and the connected modes between guest POMs and host MOFs are summarized in Table S2. On the one hand, the connected number of POMs and Ag for 2 and 3 is higher than that of 1. Meanwhile, compound 1 shows an open framework, whereas both 2 and 3 are both closed nanocage frameworks.So both 2 and 3 are more stable than 1. On the other hand, SiW12 POMs are wholly encapsulated into unprecedentedly closed Ag32 nanocage framework in 2, whereas discrete BW12 POMs act as exotemplates and are partially encapsulated into the open windows of the closed Ag24 nanocage framework in 3. Thus the stability for three POMOFs is 2 > 3 > 1.