(55b) A Systematic DFT Study of Defects in Sb?MoO? for Efficient Nitrogen Reduction to Ammonia

Ammonia is a critical component of synthetic fertilizers and has been industrially produced for over a century through the Haber-Bosch process. While effective, this method is highly energy-intensive, requiring nitrogen separation from air, hydrogen generation via steam methane reforming (a fossil fuel-dependent process), and operation under high temperature and pressure with a catalyst. As a result, the Haber-Bosch process accounts for approximately 1% of global energy consumption. With the global demand for food and fertilizers continuing to rise, there is an urgent need for sustainable alternatives to ammonia production.

Photocatalytic nitrogen fixation has emerged as a promising green alternative, offering the potential to convert nitrogen (N₂) to ammonia (NH₃) under ambient conditions using solar energy. This approach circumvents the harsh requirements of Haber-Bosch by leveraging semiconductor photocatalysts that harness light to generate electron–hole pairs, driving redox reactions on their surfaces. Despite significant research efforts, the practical application of photocatalytic nitrogen reduction reactions (NRR) has been limited by the low activity of photocatalysts, often due to rapid recombination of charge carriers and a scarcity of active sites.

To address these limitations, defect engineering has been explored as a strategy to enhance photocatalytic performance. In this study, we investigate antimony molybdate (Sb₂MoO₆) as a potential photocatalyst for green ammonia synthesis using density functional theory (DFT). Specifically, we examine the role of structural defects, such as oxygen vacancies (OVs), in creating active sites for nitrogen fixation. We further explore how the incorporation of transition metal dopants, such as Fe and Co, influences the formation and behavior of these vacancies. Building on this knowledge, we present a systematic investigation into how defects influence the reaction mechanisms and energetics of the NRR. Our goal is to develop rational defect-engineering strategies to enhance the photocatalytic activity and selectivity of Sb₂MoO₆ for sustainable nitrogen fixation.