Abstract
Synthesis of ammonia at ambient conditions is very demanding yet challenging to achieve due to the production of ammonia fuel, which is considered to be a future fuel for sustainable energy. In this context, computational studies on the catalytic activity of the edge sites of boron nitride nanomaterials for possible nitrogen reduction into ammonia have been investigated. Geometrical and electronic properties of zigzag and armchair B-open edges of BN sheet (BOE) models have been unraveled to substantiate their catalytic nature. Results reveal that BOE sites exhibit very high potential determining steps (PDS) of 2.0 eV. Doping of carbon (C) at the nitrogen center, which is vicinal to the BOE site reduces the PDS of the N2 reduction reaction (NRR) (to 1.18–1.33 eV) due to the regulation of charge distribution around the active BOE site. Further, the NRR at the C doped at various edge sites of a boron nitride sheet (BNS) has also been studied in detail. Among the 12 new C-doped defective BNS models, 9 model catalysts are useful for nitrogen activation through either chemisorption or physisorption. Among these, ZC N , AC N , and ZC BV models are efficient in catalyzing NRR with lower PDS of 0.86, 0.88, and 0.86 eV, respectively. The effect of carbon doping in tuning the potential requirements of NRR has been analyzed by comparing the relative stability of intermediates on the catalyst with and without carbon doping. Results reveal that C-doping destabilizes the intermediates compared to non-doped systems, thereby reducing the possibility of catalyst poisoning. However, their interactions with catalysts are good enough so that the NRR activity of the catalyst does not decrease due to C-doping.
Highlights
A century ago, ammonia was the savior of the world in the form of fertilizer which grew crops faster when food crises arrived due to the growing population (Aber et al, 1989; Bogaard et al, 2013; Galloway et al, 2017)
2) Carbon doping significantly enhances the catalytic activity of B-open edge sites by modulating charge density distribution and reducing the limiting potential
3) Carbon doping effectively decreases the interactions between catalysts and N2 reduction reaction (NRR) intermediates and concomitant reduction in the poisoning of the model catalyst reducing the catalytic activity of edges towards nitrogen fixation
Summary
A century ago, ammonia was the savior of the world in the form of fertilizer which grew crops faster when food crises arrived due to the growing population (Aber et al, 1989; Bogaard et al, 2013; Galloway et al, 2017). Carbon-free energy storage is one of the major targets for sustainable energy and environment (Spatzal et al, 2014; McEnaney et al, 2017; Guo et al, 2018) In this context, ammonia is believed to be a future fuel owing to its advantages (Chehade and Dincer, 2021). Doping of carbon at either the boron or nitrogen site of h-BN exhibits magnetism (Okada and Oshiyama, 2001; Li et al, 2009) It is well known from previous studies that boron-based catalysts have a high potential for the nitrogen reduction reaction (Zhao and Chen, 2017; Zhang et al, 2019). The role of edge sites in catalyzing NRR has been investigated systematically using density functional theory (DFT)-based methods. Both zigzag and armchair edges have been considered for evaluation. The model involves the calculation using the formula as given in Eq 2
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