The extensive fertilizer production intensifies the nitrogen cycle and results in high concentrations of nitrogen in groundwater. Balancing the nitrogen cycle is a great engineering challenge; this includes the conversion between various molecules such as nitrate, nitrite, nitric oxide, dinitrogen and ammonia. Within conversion of nitrogen-containing compounds, NO is the key intermediate, and its conversion can provide insight for nitrogen removal from water. Transition metal embedded in nitrogen-doped graphene has been shown as as a promising and efficient electrocatalyst for its conversion. Here we report density functional theory calculations, through which we show that lanthanum (as a prototype in lanthanide series) doped graphene is potentially active for electrocatalytic reduction of NO. We compared its activity with Co-based catalyst, the latter of which has been reported in the literature. We find that La adsorbs over the graphene surface due to its larger atomic radius. The spin-polarized results show distinct magnetic properties of the Co and La when interacting with the unpaired electron of NO. Furthermore, we show a free energy profile based on the computational hydrogen electrode model to help illustrate the potential-determining step on both catalysts. In addition, we find that presence of water strongly perturbs the free energy profile. Water can compete for adsorption sites and promote hydrogenation through hydrogen transfer between water and NO. The role of water is particularly pronounced on La-doped graphene due to its high level of hydration. This work thus shows the potential application of La-doped carbon materials for NO reduction.

Investigating the role of water in electrocatalytic reduction of NO over a La-doped carbon material through a DFT study

ACS Spring Meeting 2021

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