Unveiling the lattice distortion and electron-donating effects in methoxy-functionalized MOF photocatalysts for H2O2 production

Semiconducting metal-organic frameworks (MOFs) are emerging photocatalysts for H2O2 production via the two-electron oxygen reduction (2e-ORR) process. Whether and how the functional groups on MOF nodes affect the 2e-ORR mechanism and performance remain largely unexplored. Herein, we report that partial replacement of formate (-COO-) by methoxy (-OMe) coordinated Zr-oxo cluster in UIO-66-NH2 significantly enhances the H2O2 production. The introduction of -OMe groups induces lattice distortion in UIO-66-NH2, resulting in the change of proton donor for the protonation of OOH* intermediate from -COOH to -NH3+ with a lowered kinetic energy barrier. The -OMe groups with electron-donating effect contribute to promoted light harvesting and charge separation. The 2e-ORR selectivity of -OMe functionalized UIO-66-NH2 is also enhanced, evidenced by rotating ring-disk electrode test and theoretical calculation. As a result, an improved photocatalytic ability is achieved with an H2O2 yield of 312.9 mM g(-1) h(-1), similar to 4.7 times higher than that of the original UIO-66-NH2.

Automated summary

This study found that partial replacement of formate by methoxy in UIO-66-NH2 can significantly enhance the production of H2O2. The introduction of methoxy induces lattice distortion and changes the proton donor for the protonation of OOH* intermediate, lowering the kinetic energy barrier. Methoxy groups also have an electron-donating effect, contributing to enhanced light harvesting and charge separation. The selectivity of the methoxy-functionalized UIO-66-NH2 for 2e-ORR is also improved.