A post synthetically modified metal–organic framework as an efficient hydrogen evolution reaction catalyst in all pH conditions

Abstract

Transition-metal-based metal–organic frameworks (MOFs) have received great interest for the development of low cost, platinum-free, non-precious water splitting electrocatalysts for hydrogen generation to resolve the energy crisis. Recent studies are mainly concerned with the use of MOFs as a self-sacrificing template for the synthesis of carbon-based electrocatalysts encapsulating metallic sites. However, the process often produces undesired metal nanoparticles, lowering the catalytic activity of the materials. This report explores a novel strategy to improve the intrinsic electrocatalytic activity of MOFs by a ligand substitution method. Ligands with different electron donating capacity have been used for the substitution process and the hydrogen evolution activity has been found to be greatly affected by the presence of different donor ligands. The MOF used in this work is designed with Ni as a metal center with 5-azido isophthalic acid as the primary linker. Subsequently, the MOF is functionalized with different organic moieties, i.e., N,N-dimethylethylenediamine (DMEDA) and 4-aminotetrafluoropyridine (4-ATFP) with rich non-metal catalytic active sites by means of post synthetic modification. A comparative study has been performed which shows the 4-ATFP functionalized MOF to have the best electrocatalytic activity among the three with significant performance in all three media, i.e. neutral, acidic and alkaline. Furthermore, theoretical approaches have been employed for the analysis of these experimental observations.