Cu/2D-CuO_x Nanocomposites with Abundant Oxygen Vacancy Defects for Enhancing Ammonia Selectivity of Electrocatalytic Nitrate Reduction

Abstract

At present, a variety of catalysts have been studied and used for the electrocatalytic reduction of nitrate. However, it is still a great challenge to improve the selectivity of the electrocatalytic nitrate reduction reaction (NO3 –RR) catalyst for ammonia and reduce the activity of the competitive reaction. Herein, two-dimensional CuO x nanosheets with abundant oxygen vacancy defects were in situ grown on Cu nanoparticles to construct Cu/2D-CuO x composite nanomaterials as nitrate reduction electrocatalysts. The two-dimensional (2D) nanosheet morphology facilitated the exposure of active sites and promoted the mass/charge transfer process during electrocatalysis. As a result, the synergistic effect of abundant oxygen vacancy defects and the 2D nanosheet-like structure on the surface of the catalyst endows the Cu/2D-CuO x with superior performance for the nitrate reduction reaction, achieving high ammonia selectivity (97.56%) and NH4 + yield (1476 μg h–1 mg–1).

Modulation of Reactive Hydrogen Adsorbed on Dual-Active Site NiMoO4 Nanocubes for Reduction of Nitrate to Ammonia

“…Undoubtedly, a proper catalyst design is essential for the high efficiency and selectivity of the electrocatalytic NO 3 – RR to NH 3 . Nonprecious monometallic catalysts, such as iron, , cobalt, , and copper, − are the main choices for NO 3 – RR owing to their high cost-effectiveness, but their catalytic activity and selectivity are inadequate to meet the growing demand of NH 3 synthesis. Furthermore, other materials, nickel, have rarely been investigated because they are generally considered unsuitable for NO 3 – RR as the HER is their main competing reaction. − However, the nitrate reduction process heavily relies on *H, which is produced via H 2 O splitting. − To address this issue, a strategy has been proposed to use new material design ideas to ensure that sufficient *H is obtained to achieve a high NH 3 conversion rate and inhibit the HER. , The main challenge facing this strategy is how to prevent the formation of hydrogen from *H.…”

Boron Regulated Fe Single-Atom Structures for Electrocatalytic Nitrate Reduction to Ammonia

“…However, NO 3 RR is accomplished through multiple electron and proton transfers, − while there are also intense side reactions such as the hydrogen evolution reaction (HER), − which can decrease the yield and Faradaic efficiency of NH 3 . Therefore, an efficient catalyst is needed to enhance the selectivity and stability of the NO 3 RR.…”

Electroreduction from Nitrite to Ammonia over Cobalt Sulfide Nanorods on Nickel

“…Ammonia (NH 3 ) is widely employed in a multitude of fields, including agriculture, energy, and industrial production, due to its high energy density (4.3 kWh kg –1 ) and hydrogen content (17.6 wt %). − Currently, the industrial production of ammonia heavily relies on the Haber–Bosch process, which employs ferrite catalysts to catalyze the reaction of nitrogen (N 2 ) and hydrogen (H 2 ) under extreme environments (350–550 °C, 150–350 atm). − This process contributes to 2% of world energy consumption and 1.4% of global carbon dioxide (CO 2 ) emissions annually. − The chemical industry urgently needs new NH 3 synthesis technologies to alleviate the consumption caused by the inherent Haber–Bosch process, which is in line with the environmental goals of the Paris Climate Agreement and the persistent shift from mineral fuels to renewable energy. − The electrochemical nitrogen reduction reaction (NRR) is a sustainable approach for synthesizing NH 3 by converting N 2 to NH 3 using clean energy under environmental conditions. − However, the higher bond energy of the NN triple bond (941 kJ mol –1 ) and the lower solubility of N 2 in water lead to inefficiency, which renders the effective decomposition of N 2 extremely difficult. , In contrast, the electrochemical nitrite reduction reaction (NO 2 RR) represents a more efficient strategy for synthesizing NH 3 , due to its lower NO dissociation energy (204 kJ mol –1 ) and higher water solubility, as well as the possibility of utilizing NO 2 – as a nitrogen source for NH 3 synthesis. − Meanwhile, NO 2 – , which is highly detrimental to human health and ecosystems, is accumulating in water resources due to the rapid development of industrialization and urbanization. − Therefore, NO 2 RR can achieve both the removal of harmful NO 2 – and the production of NH 3 , which represents a feasible strategy for the substitution of the Haber–Bosch process. − …”