Arrangement of Ordered D-A Components in a Metal-Organic Framework for Cocatalyst-Free Photocatalytic Hydrogen Evolution with Efficient Proton Conduction

The arrangement of donor-acceptor (D-A) components in order at a molecular level provides a means to achieve efficient electron-hole separation for promoting the activity of photocatalysts. Herein, we report the coordination assembly of D-A molecules with desired staggered energy levels in two isostructural metal-organic frameworks (MOFs) 1 and 2, which exhibit high photocatalytic hydrogen evolution activity without using any cocatalysts and photosensitizers. The modulation of active metal sites of the D-A MOFs leads to an increase in photocatalytic hydrogen evolution rates from 1260 to 3218 mu mol h-1 g-1. A detailed mechanism study revealed that the energy bond defined by the D-A components assisted with metal centers is the key to efficiently generating photogenerated charge carriers, and 2 has an appropriate affinity to proton to reduce the energy barrier for hydrogen evolution. Besides, the enhanced proton transport kinetics based on the arrayed free carboxyl groups in the hydrogen-bonded network endows 2 with higher proton conductivity than 1, thus promoting the usage rate of active metal sites in 2 for enhanced hydrogen evolution reaction kinetics.