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

Abstract

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 of photocatalytic hydrogen evolution rates from 1260 to 3218 μmol 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 generate 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 higher proton conductivity than 1, thus promoting the usage rate of active metal sites in 2 for enhanced hydrogen evolution reaction kinetics.