Comparing B3LYP and B97 Dispersion-corrected Functionals for Studying Adsorption and Vibrational Spectra in Nitrogen...

Area of Science:

• Computational Chemistry
• Materials Science
• Electrochemistry

Background:

• Electrochemical ammonia synthesis is a sustainable alternative to the energy-intensive Haber-Bosch process.
• Platinum-Iridium (Pt-Ir) alloys have shown potential as catalysts, prompting investigation into pure iridium.
• Accurate modeling of nitrogen (N2) adsorption is crucial for understanding ammonia synthesis mechanisms.

Purpose of the Study:

• To investigate pure iridium as a catalyst for electrochemical ammonia synthesis.
• To characterize the adsorption of nitrogen and its intermediates (N, NH, NH2, NH3) on iridium surfaces.
• To evaluate the performance of different dispersion-corrected density functional theory (DFT) methods for modeling N2 adsorption.

Main Methods:

• Employed dispersion-corrected density functional theory (DFT) methods, including B3LYP, B3LYP-D3, and B97-D3.
• Calculated key molecular characteristics: bond energies, bond lengths, spin densities, and vibrational frequencies.
• Compared adsorption on two iridium surfaces: (111) and (100).

Main Results:

• Adsorption energies were found to be stronger on the (100) iridium surface compared to the (111) surface.
• The trend in adsorption energies across the tested DFT methods was E_B3LYP > E_B3LYP-D3 > E_B97-D3 on both surfaces.
• The B97-D3 method showed potential for reduced computational time while maintaining accuracy in vibrational analysis.

Conclusions:

• Pure iridium is a viable catalyst candidate for electrochemical ammonia synthesis.
• Dispersion-corrected DFT methods, particularly B97-D3, are effective for modeling N2 adsorption on transition metal catalysts.
• Surface structure significantly influences catalyst performance, with the (100) surface showing stronger adsorption.