DFT study of Al-doped In2O3 with surface frustrated Lewis pair sites for enhanced nitrogen reduction efficiency

Abstract

Ammonia (NH₃) is a pivotal energy carrier and chemical feedstock. However, its conventional synthesis via the Haber–Bosch process suffers from high energy demand and CO₂ emissions. Developing efficient electrocatalysts for the nitrogen reduction reaction (NRR) under mild conditions remains a critical challenge, particularly because of the competing hydrogen evolution reaction (HER) and inert nature of N₂. Herein, we propose a novel strategy for engineering surface frustrated Lewis pairs (SFLPs) on metal-doped In₂O₃ to synergistically activate N₂ and suppress the HER. Through density functional theory (DFT) screening of 15 dopants, Al-doped In₂O₃ (Al@In₂O₃) emerged as the optimal catalyst, in which Al and adjacent In atoms functioned as spatially separated Lewis acid and base sites, respectively. This unique SFLPs configuration enables a “donation-acceptance” mechanism: Al accepts π-electrons from N₂ via unoccupied 3p orbitals, while In donates electrons to polarize N₂, collectively weakening the N≡N bond. The Al@In₂O₃ exhibited a low limiting potential of − 0.560 V for the NRR and a high HER barrier (ΔG_HER = 0.936 eV), outperforming pristine In₂O₃ and other doped counterparts. Mechanistic analysis revealed that Al doping redistributes surface charges, creating electron-deficient Al sites and electron-rich In regions, which not only stabilize N₂ adsorption but also disrupt proton adsorption for HER suppression. Furthermore, orbital-resolved studies demonstrated that H⁺ adsorption during the rate-determining step (ΔG_RDS = 0.61 eV) modifies the hybridization of the N orbitals, facilitating subsequent hydrogenation. This study provides theoretical evidence of SFLPs-mediated N₂ activation on oxide catalysts, offering a universal design principle for high-selectivity NRR systems by leveraging p-block element synergies.