Roles of Heterojunction and Cu Vacancies in the Au@Cu_2–xSe for the Enhancement of Electrochemical Nitrogen Reduction Performance

Abstract

The utilization of hydrogen (H 2 ) as a fuel source is hindered by the limited infrastructure and storage requirements. In contrast, ammonia (NH 3 ) offers a promising solution as a hydrogen carrier due to its high energy density, liquid storage capacity, low cost, and sustainable manufacturing. NH 3 has garnered significant attention as a key component in the development of next-generation refueling stations, aligning with the goal of a carbon-free economy. The electrochemical nitrogen reduction reaction (ENRR) enables the production of NH 3 from nitrogen (N 2 ) under ambient conditions. However, the low efficiency of the ENRR is limited by challenges such as the electron-stealing hydrogen evolution reaction (HER) and the breaking of the stable N 2 triple bond. To address these limitations and enhance ENRR performance, we prepared Au@ Cu 2−x Se electrocatalysts with a core@shell structure using a seed-mediated growth method and a facile hot-injection method. The catalytic activity was evaluated using both an aqueous electrolyte of KOH solution and a nonaqueous electrolyte consisting of tetrahydrofuran (THF) solvent with lithium perchlorate and ethanol as proton donors. ENRR in both aqueous and nonaqueous electrolytes was facilitated by the synergistic interaction between Au and Cu 2−x Se (copper selenide), forming an Ohmic junction between the metal and p-type semiconductor that effectively suppressed the HER. Furthermore, in nonaqueous conditions, the Cu vacancies in the Cu 2−x Se layer of Au@Cu 2−x Se promoted the formation of lithium nitride (Li 3 N), leading to improved NH 3 production. The synergistic effect of Ohmic junctions and Cu vacancies in Au@Cu 2−x Se led to significantly higher ammonia yield and faradaic efficiency (FE) in nonaqueous systems compared to those in aqueous conditions. The maximum NH 3 yields were approximately 1.10 and 3.64 μg h −1 cm −2 , with the corresponding FE of 2.24 and 67.52% for aqueous and nonaqueous electrolytes, respectively. This study demonstrates an attractive strategy for designing catalysts with increased ENRR activity by effectively engineering vacancies and heterojunctions in Cu-based electrocatalysts in both aqueous and nonaqueous media.

Solar Self-Driven Electrocatalytic Reduction of N2 Directly to CO2-Free Generation of Ammonia on a Coupled Ce-Mediated Cu/Porous Carbon Electrode

“…The Cu 2p spectra of Cu 0.10 -PC and Cu x Ce y -PC in Figure c exhibit four characteristic peaks as V 0 , V 1 , U 0 , and U 1 . Among the main peaks, V 0 and U 0 belong to Cu 2p 3/2 and Cu 2p 1/2 orbits of Cu 0/+ (in Cu 0.10 -PC) and Cu + (in Cu x Ce y -PC), respectively . The other peaks, V 1 and U 1 , are attributed to Cu 2p 3/2 and Cu 2p 1/2 orbitals of Cu 2+ species, , respectively.…”

Thiol Ligand-Modified Au for Highly Efficient Electroreduction of Nitrate to Ammonia

“…The TEM image and XRD pattern of para-Au/C after cyclic electrolysis displayed no obvious change, representing the structural robustness of para-Au/C (Figure S10). In addition, a 15 N isotope-labeling experiment was conducted to further quantify the product (Figure S11). The FE for NH 3 at −0.6 V vs RHE determined by 1 H NMR was approximated to the results detected via the UV−vis method (Figure S12).…”

“…As one of the most fundamental industrial products, ammonia (NH 3 ) is not only an indispensable chemical in fertilizer, medicine, dye, and other industries but also an important carbon-free energy storage medium. − Currently, the predominant method of NH 3 synthesis, the Haber–Bosch process, requires extreme reaction conditions of high temperature (400–500 °C) and high pressure (150–300 bar) with only 10–20% conversion efficiency. − It is reported that the annual energy consumption for NH 3 synthesis accounts for 1–2% of the total global energy supply accompanied by about 1.5% of the global carbon emissions, leading to significant damage to the natural environment. − Therefore, a clean and economical route for NH 3 production is urgently needed in pursuit of a sustainable chemical industry. − …”

Boosting the Faraday Efficiency of Electrochemical Ammonia Synthesis via the Strain Effect Induced by Interfacial Hybrid Formation between BN and Carbon Nanotubes

“…For example, it provides active sites for N 2 adsorption and activation to improve the eNRR performance of the catalyst; the electronic structure can be modified by defect engineering to change the reaction thermodynamics and kinetics. These defects include vacancies, structure effect, heterostructure, and so on. − …”