What question did this study set out to answer?

This work aims to enhance electrocatalytic ammonia synthesis by modifying the ligand structure of CALF-20.

April 12, 2026

In Silico Imine-Based Ligand Engineering of CALF-20 for Electrocatalytic Ammonia Production

Key Points

This work aims to enhance electrocatalytic ammonia synthesis by modifying the ligand structure of CALF-20.
In silico modeling using PBE + D3 calculations
Spectroscopic and ab initio molecular dynamics analyses
Investigating bonding configurations of transition metals with CALF-20
Fe-bound CALF-20 configuration is the most stable among tested metals
Shift of the d-band center indicates changes in electronic properties
Enhanced adsorption of N2 and NO2 confirmed by spectroscopic measurements
MFe-CALF-20 shows favorable performance in ammonia synthesis with low activation energies

Abstract

Electrocatalytic ammonia synthesis is emerging as a globally compelling, sustainable alternative to the Haber-Bosch process under ambient conditions. As a result, active-site engineering has taken center stage in the development of stable and effective electrocatalysts. In this work, we report how the introduction of an imine group in the ligand backbone of CALF-20, a Zn-based, moisture-stable MOF with high surface area, results in the formation of an N4 macrocycle for transition-metal anchoring. PBE + D3 calculations, supported by spectroscopic, ab initio molecular dynamics, and electronic analyses, identify Fe-bound modified CALF-20 as the most stable configuration among the Mn-, Fe-, Co-, Ni-, Cu-, Ru-, Rh-, Ag-, and Au-anchored within the modified CALF-20 framework. Upon modification, the d-band center shifts from −5.08 to −4.44 eV in MFe-CALF-20. Adsorption studies confirm activation of both N2 and NO2, reflected by bond elongation and red-shifted IR peaks. Mechanistic studies show that MFe-CALF-20 selectively facilitates NH3 formation, exhibiting PDS values of 0.69 and 0.62 eV for the NRR and NO2RR, respectively, while a competitive adsorption shows a clear preference over HER. Our study illustrates how functionalization tunes CALF-20 for dual application as an adsorbent and as an electrocatalyst for NH3 synthesis and storage.

Mark Helpful

Bookmark

Relay