Potential Dependence of Ammonia Selectivity of Electrochemical Nitrate Reduction on Copper Oxide

Abstract

Nitrate electrochemical reduction (eNO 3 RR) has been considered as an alternative strategy for decentralized ammonia production, while there are two critical issues regarding high overpotential and poor selectivity because of nitrite production at low overpotentials. Therefore, it is significant to understand the reaction mechanism of ammonia and nitrite selectivity. In addition, it was found that hydrogen evolution reaction (HER) can become notable and drastically affects the Faradaic efficiency. In this work, taking copper oxide as an example, we have combined density functional theory (DFT) calculations and microkinetic modeling (MKM) to understand the products selectivity and Faradaic efficiency of eNO 3 RR to NH 3 at varying potentials. Our models are consistent qualitatively with the experimental results, describing well the competition of ammonia, nitrite, and hydrogen. As the charge transfer coefficient (β) for *NO 2 protonation (*NO 2 to HNO 2 (g)) is smaller than that of *NO hydrogenation (*NO to *NHO), ammonia production becomes more favorable gradually. As the larger charge transfer coefficient (β) for HER compared to *NO hydrogenation (*NO to *NHO), ammonia production becomes less preferable at high overpotentials. The present mechanistic insights can provide design principles of eNO 3 RR activity and selectivity over ammonia, nitrite, and hydrogen.

Recent Advances in Electrocatalysts for Efficient Nitrate Reduction to Ammonia

“…carried a throughout thermodynamic and kinetic study on the factors, including facets, applied potentials, and exposed surfaces, to reveal the e‐NO 3 RR reaction mechanisms of perfect and defective Cu 2 O surface. [ 134 ] The (110) and (111) facets of defective Cu 2 O exhibited better catalytic performance than pure Cu facets, consistent with the results from the hybrid Cu/Cu 2 O nanowire arrays. Differently, by dividing the 8‐electrons direct nitrate‐to‐ammonia conversion to [2+6] staged pathway, Jiang and co‐workers found that Cu° could has a high ammonia FE under ultra‐low staged potentials ( Figure a,d), which was more superior to Cu/Cu 2 O.…”

Work Function-Tailored Nitrogenase-like Fe Double-Atom Catalysts on Transition Metal Dichalcogenides for Nitrogen Fixation

“…To address this, Xiao et al. developed the constant potential simulation method and the microkinetic model combined with DFT calculations, and successfully interpreted the complex U -dependent selectivity of the electrochemical nitrogen oxides reduction reactions. − Due to the U -independence, *NN adsorption on Fe 2 /MX 2 systems could be regarded as a thermochemical behavior without obvious proton and electron transfer, and consequently the competition between HER and NRR at varying U can be interpreted by the *NN and *H coverages, which are determined by the Δ G values under different U . Thus, it is reasonable to explore the U -dependent selectivity of Fe 2 /MX 2 systems using the CHE model.…”

Activity Trend and Selectivity of Electrochemical Ammonia Synthesis in Reverse Artificial Nitrogen Cycle

“…In short summary, the ammonia selectivity at low overpotentials is still low. It can be attributed to the diverse adsorption structure of NO 2 /HNO 2 , [15b] while all weak adsorbed NO 2 /HNO 2 species prefer to desorb, instead of being reduced to ammonia. A high ammonia selectivity at large overpotential is benefited from the small charge transfer coefficient for the chemical desorption of HNO 2 production.…”