Controllable proton conducting pathways via situating polyoxometalates in targeting pores of a metal-organic framework
Proton conductivity is traditionally affected by proton concentration, mobility, hopping sites, etc. in metal-organic frameworks (MOFs). The influence of proton conducting pathways’ profile has not been demonstrated owing to lacking suitable model. MIL-101 contains two types of tunnels with zigzag and linear profiles constructed by the cages with different sizes. However, it is hard to build up an exclusive proton-conducting pathway with only one profile in MIL-101, because the introduced carriers usually locate without targeting. Keggin-type H3PW12O40 (HPW) has a unique nano size which is between the window sizes of the cages in MIL-101, coupling with its strong acidity, good stability and abundant proton-hopping sites. Two types of hydrogen bond networks are constructed by situating HPWs in targeting pores of MIL-101, respectively. Linear pathways provide faster proton diffusion rate comparing with its zigzag counterpart about 2.1-fold. Further modification of HPW-impregnated MIL-101 with flexible polyamine results a conductivity of 1.52×10-2 S cm-1.