Sustainability has gained momentum due to climate change and environmental pollution. Mankind is trying to look for safer fuels to meet the energy demands and conserve the world for future...

In this work, we employ density functional theory (DFT) to investigate the edge atomic structures and atomic boundaries in graphitic carbon nitride (g-C 3 N 4 ) nanoribbons to explore their role on structural stability and electronic and photocatalytic properties. Interestingly, the nanoribbon structures with mirror twin boundaries (MTBs) have higher structural stability than the conventional nanoribbon structures due to the C−C bond formations at the MTB region. Irrespective of their edge atomic structure, the curved and corrugated nanoribbons with direct band gap are thermodynamically more stable than the planar nanoribbons with indirect band gap. In addition, the distinct electronic structures of nanoribbons with and without MTB are calculated to understand their influence on the band gap and band edge positions of the nanoribbons. Very importantly, unlike the other nanostructures of g-C 3 N 4 , nanoribbons are shown to possess unique electronic structures that facilitate the tunable spatial separation of valence and conduction band states. This enhances the lifetime of excited charge carriers in nanoribbon morphology. To garner deep insights into the photocatalytic properties of the g-C 3 N 4 monolayer and nanoribbons, the Gibbs free energies (ΔG) of hydrogen and oxygen evolution reaction intermediates are studied to identify the active sites. To this end, our DFT studies predict enhanced photocatalytic activity of g-C 3 N 4 nanoribbons over the monolayer while providing new insights into the geometry, electronic structure, and photocatalytic properties of the nanoribbons, guiding the plausible development of g-C 3 N 4 nanoribbons.

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Ammonia is a potential carbon-free carrier for the on-site delivery of hydrogen and is critical in the development of a hydrogen economy. Designing a noble metal-free catalyst for the lowtemperature decomposition of NH 3 is a challenging task in this route. We conducted first-principles studies to have a comprehensive understanding of the ammonia decomposition mechanism on the molybdenum-doped iron nitride (Fe 3 N) surface. The results indicate that when Mo is doped on the surface of Fe 3 N(111) it donates electrons to the surface and alters the overall electronic structure of the catalyst. The activation energy for the intermediate steps of ammonia decomposition is substantially reduced on the Mo-doped Fe 3 N surface compared to undoped Fe 3 N. NH 3 adsorbs preferably on Mo sites over Mo-doped Fe 3 N(111). However, subsequent intermediate species NH 2 and NH prefer Fe sites for adsorption. The activation barrier for the recombination and desorption of nitrogen adatoms is highest compared to the other elementary steps in the breakdown of NH 3 on Mo-doped Fe 3 N(111) and therefore limits the overall rate of the decomposition reaction of ammonia. The Bader charge, density of state (DOS), and crystal orbital Hamiltonian population (COHP) calculations elucidate the electronic properties of the catalyst.

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