Highly efficient iron and cobalt benzimidazole metal organic framework electrocatalysts for hydrogen evolution reaction

Abstract

Reported herein were two new electrocatalysts based on metal-organic frameworks (MOFs) that were easily crystallized into the pure 3D net. The cobalt (Co-MOF) and iron (Fe-MOF) metal bearing MOFs were prepared with the reaction of cobalt or iron cations with a benzimidazole linker in the mixture of dimethyl formamide (DMF), ethanol, and water using a solvothermal synthesis method. Without any further post-treatments, Co-MOF and Fe-MOF were directly used as promising electrocatalysts for facilitating hydrogen evolution reactions (HER). Remarkably, the high HER catalytic activity was provided through practical measurements with incredible achievement by utilizing Co-MOF and Fe-MOF. The experimental studies showed that both Co-MOF and Fe-MOF coordinated with water molecules and opened access to the metal cation site which facilitated the electrocatalytic activity of them with the lattice water. Both MOFs exhibited superior HER activity including very low overpotentials, low Tafel slopes, high exchange current densities, and long-term stabilities. While the HER overpotential of the GCE/Co-MOF electrode decreased up to 50 mV at a current density of 10 mA/cm² with a Tafel slope of 38.57 $mV.{dec}^{-1}$, Fe-MOF also achieved another incredible overpotential reduction with 46 mV and a Tafel value of 46.71 $mV.{dec}^{-1}$, which were very close to the commercial Pt/C electrocatalyst having 42 mV of overpotential with a Tafel slope of about 34.32 $mV.{dec}^{-1}$. Additionally, these electrocatalysts showed great current stability with linear sweep voltammetry and good chronoamperometric stability of 86.7% with Fe-MOF and 67.7% with Co-MOF with 12 h tests under stirring for HER. Consequently, this research study represented one of the most successful studies that were done and managed to report one of the best electrocatalytic performances with two simple MOF structures since we managed to break off the limitation for finding available and inexpensive catalysts that were competitive with platinum catalysts that represented the major obstacles (being expensive and rare) that hampered the development of more sophisticated hydrogen production systems.