Electrochemical Synthesis of Ammonium from Nitrates via Surface Engineering in Cu₂O(100) Facets

Abstract

Revealing the reactivity of different exposed facets is crucial for designing highly effective electrocatalysts to selectively reduce nitrate (NO 3 − ) to ammonia (NH 4 + ). Herein, two dominant exposures of Cu 2 O(100) and Cu 2 O(111) facets are designed to explore the effects of interfaces on properties. Cu 2 O(100) achieved a relatively high NH 4 + yield rate of 743 μg h −1 mg cat.−1 associated with a Faradic efficiency of 82.3% at −0.6 V vs the reversible hydrogen electrode (RHE), attributed to a relatively lower energy barrier (0.18 eV) for NH 3 production than the Cu 2 O( 111) surface (1.43 eV). In addition, 15 N isotope-labeling experiments were used to quantitatively analyze the yield rate of NH 4 + and further confirmed the reliability of nitrogen sources. This work provides reliable evidence to improve the selectivity of NO 3 − to NH 4 + by crystal facet engineering.

Nitrate electrochemical reduction to ammonia on Cu2O catalysts

“…The authors supported that the difference in FE lies in the lower energy barrier for NH3 production on Cu2O (100) based on the different electronic properties of the Cu species on the Cu2O (100) and (111) surfaces. [28] However, our experiments were performed at a significantly higher pH, which is known to play an essential role in NO3 -RR. [16,29] Another contribution to the observed differences might be the presence of Cu 0 species.…”

“…Density functional theory calculations by Hu et al [30] showed that for a polycrystalline Cu catalyst, Cu (111) is more efficient for NO3 -RR to NH3 production in alkaline media than Cu (100). Since in the work of Ye et al [28] the catalyst structure and composition during or post-reaction were not investigated, the active phase of the catalyst is still unclear.…”

Why copper catalyzes electrochemical reduction of nitrate to ammonia

“…Data extracted from ref. 20,21,[42][43][44][45][46][47][32][33][34][35][36][39][40][41] To unravel the reasons behind such high activity and selectivity for NO 3 RR to ammonia on Cubased catalysts, we need to establish an understanding about the NO 3 RR mechanism to ammonia on transition metals. Several efforts have already been made in the literature to understand the NO 3 RR mechanism.…”

Mesoporous PdN Alloy Nanocubes for Efficient Electrochemical Nitrate Reduction to Ammonia

“…[ 5 ] Electrochemical reduction of NO 3 − to NH 3 (NO 3 − ‐to‐NH 3 ) involves a complicated eight‐electron reaction pathway (1.20 V vs the reversible hydrogen electrode (vs RHE)), which remarkably lowers the overall kinetic rate. [ 5a,6 ] Competitively, a five‐electron transfer pathway, NO 3 − ‐to‐N 2 , only requires a slightly higher reaction potential of 1.25 V, unavoidably decreasing the NH 3 Faradaic efficiency (FE NH3 ) and the energy efficiency for NITRR electrocatalysis. [ 6b,7 ] Besides, undesired consumption of electron donors by H 2 generation with HER in an aqueous solution also disfavors the NO 3 − ‐to‐NH 3 electrocatalysis.…”