Selective Ammonia Electrooxidation on TiB₄ and VB₄ quantum dots: Theoretical insights into catalytic activity and OER suppression

Abstract

Ammonia (NH₃) has emerged as a promising carbon-free hydrogen carrier for sustainable energy applications. However, the development of cost-effective and efficient electrocatalysts for the ammonia oxidation reaction (AOR) remains a significant challenge. In this work, we employ density functional theory (DFT) calculations to investigate the structural stability, electronic properties, and catalytic performance of TiB₄ and VB₄ quantum dots (QDs) toward AOR. Structural optimizations, Mulliken charge analysis, and binding energy assessments confirm the thermodynamic stability of both QDs, with TiB₄ exhibiting slightly higher stability. Adsorption energy analysis reveals a strong affinity of both QDs for NH₃, with preferential binding at the transition metal centers. Reaction mechanisms were explored through both the Oswin–Salomon (OS) and Gerischer–Mauerer (G–M) pathways, and corresponding free energy diagrams highlight TiB₄–S1 as the most promising active site. It exhibits remarkably low overpotentials of 0.084 V and 0.655 V for the OS and G–M mechanisms, respectively—outperforming benchmark noble-metal catalysts such as Pt(100) and Fe/Pt(100). In contrast, VB₄ QDs suffer from high energy barriers and less favourable reaction energetics. Furthermore, comparative analysis with the competing oxygen evolution reaction (OER) confirms that TiB₄ QDs exhibit superior selectivity for AOR under anodic conditions. These findings position TiB₄ QDs as highly efficient, non-noble metal-based electrocatalysts for AOR, offering great potential for integration into next-generation fuel cells and green hydrogen technologies.