On-line Differential Electrochemical Mass Spectrometry Research Articles

Porous lithiophilic Cu-Sn solid solution current collector for dendrite-free lithium metal batteries

Lithium metal batteries (LMBs) have high energy density but suffer from the formation of Li dendrites and unstable solid electrolyte interface. Herein, a three-dimensional porous Cu-Sn solid solution was designed as current collector for LMBs and was fabricated through the combination of vapor phase alloying with subsequent vapor phase dealloying. The effect of the Sn addition on electrochemical performances and Li plating/stripping behaviors was investigated using in-situ X-ray diffraction, ex-situ scanning electron microscopy, as well as density functional theory calculations. As benchmarked with porous Cu (3D-Cu), the addition of lithiophilic Sn can efficiently improve the Li plating/stripping performance, especially for the 1.5 at.% Sn addition (3D-Cu98.5Sn1.5). The 3D-Cu98.5Sn1.5 current collector maintains coulombic efficiency of 95 % up to 200 cycles at 1 mA cm−2. Moreover, the existence of Sn in solid solution exhibits a much lower binding energy (-3.223 eV) and nucleation overpotential (28.9 mV) compared with those of 3D-Cu, indicating that the metallic Li is extremely susceptible to nucleation and growth on the surface. Additionally, the gas evolution scenarios were probed by on-line differential electrochemical mass spectrometry. Our findings show that the 3D-Cu98.5Sn1.5 current collector effectively enhances the uniformity of Li plating and suppresses the generation of dendrites in LMBs.

Polymer‐Confined Pyrolysis Promotes the Formation of Ultrafine Single‐Phase High‐Entropy Alloys: A Promising Electrocatalyst for Oxidation of Nitrogen

AbstractHigh‐entropy alloys (HEAs) made up of multiple metallic elements have gained attention for their excellent electrocatalytic performance. However, their application in the field of nitrogen (N2) oxidation reaction (NOR) remains underexplored. In this study, a “pomegranate‐like” carbon embedded with ultrafine AuPdPtRhIr HEA (HEA@C) is synthesized using a polymer‐confined pyrolysis strategy. Molecular dynamics (MD) simulations show that small‐sized metal nanoparticles formed by the confinement of polyvinyl alcohol (PVA) during the hydrothermal process can easily form a single‐phase HEA through a thermodynamically‐driven solid‐phase diffusion process during subsequent pyrolysis. Additionally, a porous carbon layer which in situ converted from the PVA shell can effectively inhibit the agglomeration of HEA nanoparticles and confine the surrounding N2. Experimentally, the HEA@C nanohybrid demonstrates a satisfactory NO3− yield rate of 23.8 µg h−1 mgcat.−1 and a high Faraday efficiency of 13.8% for the NOR process. By using operando Fourier Transform Infrared spectroscopy, online differential electrochemical mass spectrometry (DEMS), and density functional theory calculations, potential efficient active sites (Rh–Ir–o) and pathways for the electrochemical conversion of inert N2 to NO3− are revealed. This research provides an effective strategy for producing highly dispersed ultrafine HEA nanoparticles, showing a wide range of applications in advanced electrocatalysis.

Atomically Dispersed Unsaturated Cu‐N3 Sites on High‐Curvature Hierarchically Porous Carbon Nanotube for Synergetic Enhanced Nitrate Electroreduction to Ammonia

AbstractCu‐based single‐atom catalysts (SACs) are regarded as promising candidates for electrocatalytic reduction of nitrate to ammonia (NO3RR) owing to the appropriate intrinsic activity and the merits of SACs. However, most reported Cu SACs are based on 4N saturated coordination and supported on planer carbon substrate, and their performances are unsatisfactory. Herein, low‐coordinated Cu‐N3 SACs are designed and constructed on high‐curvature hierarchically porous N‐doped carbon nanotube (NCNT) via a stepwise polymerization–surface modification–electrostatic adsorption–carbonization strategy. The Cu‐N3 SACs/NCNT exhibits outstanding NO3RR performance with maximal Faradaic efficiency of 89.64% and NH3 yield rate of up to 30.09 mg mgcat−1 h−1 (70.8 mol gCu−1 h−1), superior to most reported SACs and Cu‐based catalysts. The results integrated from potassium thiocyanide poisoning experiments, online differential electrochemical mass spectrometry, in situ Fourier transform infrared spectroscopy, and density functional theory calculations demonstrate: 1) unsaturated Cu is active site; 2) Cu‐N3 SACs/NCNT possesses NO*‐HNO*‐H2NO*‐H2NOH* pathway; 3) low‐coordinated Cu‐N3 sites and high‐curvature carbon support synergetic promote reaction dynamics and reduce rate‐determining step barrier. This study inspires a synergetic enhancement catalysis strategy of creating unsaturated coordination environment and regulating support structure.

Mechanistic Aspects and Side Reactions during Reversible Mg Deposition and Oxygen Reduction on a Pt Film Electrode in BMP‐TFSI‐Based Electrolytes: A DEMS Study

AbstractReversible Mg deposition/stripping and O2 reduction/evolution on a Pt film electrode in neat and O2‐saturated 1‐butyl‐1‐methylpyrrolidinium bis(trifluoromethylsulfonyl) imide (BMP‐TFSI) electrolytes, containing Mg(TFSI)2 and/or Mg(BH4)2 as Mg source as well as Mg(BH4)2 and/or the crown ether 18‐c‐6 as additive, were investigated by online differential electrochemical mass spectrometry (DEMS) and by scanning electron microscopy/energy dispersed X‐ray spectroscopy. Combined cyclic voltammetry and DEMS measurements reveal a complex network of partial reactions, including borohydride electro‐oxidation by reaction with water or O2, chemical bulk reaction of these components, as well as electro‐oxidation of H2, and electrolyte decomposition, in addition to the primary reactions Mg deposition/stripping and ORR/OER. They provide detailed insights into the potential dependent reactions occurring under these conditions, demonstrating that also the additive 18‐c‐6 undergoes decomposition upon reduction of Mg2+. Contributions from chemical bulk reactions are resolved by DEMS measurements in borohydride containing solution without a Pt electrode. Electrocatalytic borohydride oxidation, explored by similar measurements with a Pt electrode, can lead to H2 or H+ formation. Under open circuit potential conditions, charge compensation by the ORR results in the formation of a mixed potential. Consequences of these findings for applications in Mg‐air batteries are discussed.

Selective electroreduction of nitrate wastewater to ammonia fertilizer via highly dispersed ruthenium nanocluster catalyst

Electrochemical reduction of nitrate (NO3-) wastewater to ammonia (NH3) offers a promising but challenging approach for wastewater treatment of nitrate pollutants and resource recovery of ammonia fertilizer. However, the low catalytic activities and selective efficiency have limited their development and application. Herein, we report a facile chemical reduction method for the successful preparation of Ru nanoclusters (NCs) on ultrathin MoO2 nanosheet substrates (Ru NCs/MoO2 NSs). The Ru NCs/MoO2 NSs electrocatalyst exhibits superior activity and selectivity for NO3- electroreduction to NH3, with an NH3 yield rate of 50.9 mg·h−1·g−1cat. at − 0.4 V and a faradaic efficiency of 83.5 % at − 0.3 V versus reversible hydrogen electrode. Operando electrochemical impedance spectroscopy further indicates the faster reaction kinetics of the Ru SCs/MoO2 NSs at the electrode-electrolyte interfaces compared with MoO2 NSs. In situ spectroscopic studies and on-line differential electrochemical mass spectrometry reveal the proposed reaction pathway for the conversion of NO3- to NH3, namely, deoxygenation reactions *NO3-→*NO2-→*NO and hydrogenation steps *NO→*NOH→*NH2OH→*NH3. Density functional theory calculations further verify the effective N-end NOH pathway with the conversion of *NO to *NOH as the rate-determining step requiring a low energy barrier of 0.44 eV, which is lower than that of the O-end ONH pathway (1.17 eV).

A Spectroscopic Study on Nitrogen Electrooxidation to Nitrate

AbstractAs a potential substitute technique for conventional nitrate production, electrocatalytic nitrogen oxidation reaction (NOR) is gaining more and more attention. But, the pathway of this reaction is still unknown owing to the lack of understanding on key reaction intermediates. Herein, electrochemical in situ attenuated total reflection surface‐enhanced infrared absorption spectroscopy (ATR‐SEIRAS) and isotope‐labeled online differential electrochemical mass spectrometry (DEMS) are employed to study the NOR mechanism over a Rh catalyst. Based on the detected asymmetric NO2− bending, NO3− vibration, N=O stretching, and N−N stretching as well as isotope‐labeled mass signals of N2O and NO, it can be deduced that the NOR undergoes an associative mechanism (distal approach) and the strong N≡N bond in N2 prefers to break concurrently with the hydroxyl addition in distal N.

A Spectroscopic Study on Nitrogen Electrooxidation to Nitrate.

As a potential substitute technique for conventional nitrate production, electrocatalytic nitrogen oxidation reaction (NOR) is gaining more and more attention. But, the pathway of this reaction is still unknown owing to the lack of understanding on key reaction intermediates. Herein, electrochemical in situ attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) and isotope-labeled online differential electrochemical mass spectrometry (DEMS) are employed to study the NOR mechanism over a Rh catalyst. Based on the detected asymmetric NO2- bending, NO3- vibration, N=O stretching, and N-N stretching as well as isotope-labeled mass signals of N2O and NO, it can be deduced that the NOR undergoes an associative mechanism (distal approach) and the strong N≡N bond in N2 prefers to break concurrently with the hydroxyl addition in distal N.

Electrochemical nitrate reduction to high-value ammonia on two-dimensional molybdenum carbide nanosheets for nitrate-containing wastewater upcycling

Electrochemical conversion of nitrate wastewater into high-value ammonia fertilizer has attracted extensive attention in wastewater treatment and resource recovery, but presents great challenges due to complicated reaction pathways and competing side reactions. Herein, we report a feasible method for the successful fabrication of Mo2C nanosheets (Mo2C NSs) as electrocatalyst for the electroreduction of nitrate to ammonia. Compared to Mo2C nanoparticles, the Mo2C NSs exhibited superior activity and selectivity in NH3 electrosynthesis with an NH3 yield rate of 25.2 mg·h−1·mg−1cat. at −0.4 V and a Faradaic efficiency of 81.4 % at −0.3 V versus reversible hydrogen electrode. The X-ray diffraction and transmission electron microscopy characterization verifted the controllable conversion of 2D MoO2 NSs into 2D Mo2C NSs. In situ spectroscopic studies and on-line differential electrochemical mass spectrometry revealed the proposed reaction pathway of NO3− to NH3 conversion, *NO3− → *NO2− → *NO→*NOH → *NH2OH → *NH3. Density functional theory calculations further verified the effective N-end NOH pathway with the conversion of *NH2OH to *NH2 as the rate-determining step requiring a low energy barrier of 0.58 eV. Importantly, the key hydrogenation of *NO to form *NOH species underwent a lower energy barrier of 0.39 eV compared with the formation of *ONH species (1.06 eV).

Electrocatalytic Reduction of Nitrate to Ammonia via a Au/Cu Single Atom Alloy Catalyst.

Electrocatalytic ammonia (NH3) synthesis from the reduction of nitrate (NO3-) is one of the effective and mild methods to treat nitrogen-containing wastewater from stationary sources and to obtain NH3 readily compared with the Haber-Bosch process. However, the low efficiency of electrocatalytic NO3- reduction to NH3 on traditional Cu-based catalysts hinders their practical application. Here, we prepare a Au/Cu single atom (SA) alloy (Au/Cu SAA) that shows a high performance of NH3 synthesis with 99.69% Faradaic efficiency at -0.80 V vs RHE. The structures of Au SAs and alloyed Au/Cu are confirmed by the detailed characterizations. Online differential electrochemical mass spectrometry confirms the occurrence of key reaction intermediates (*NO2, *NO, and *NH3). Density functional theory calculations demonstrate that Au SAs efficiently reduce the adsorption energy of *NO3-, and the newly formed Au-Cu bonds boost the reduction process of *NO2 to *NO. Meanwhile, Au/Cu SAAs produce significantly less N2 and N2O byproducts due to the prohibition of N-N coupling on single atoms, which finally leads to excellent Faradaic efficiency and NH3 selectivity.

Interfacial engineering of CoMn2O4/NC induced electronic delocalization boosts electrocatalytic nitrogen oxyanions reduction to ammonia

Electrocatalytic nitrate (NO3−) reduction reaction (NO3−RR) is a promising avenue for wastewater treatment and value-added ammonia (NH3) generation. Herein, cobalt manganese spinel nanoparticles embedded in multichannel carbon fibers (CoMn2O4/NC) to obtain optimal NH3 Faradaic efficiency is 92.4% with a yield rate of 144.5 mmol h−1 g−1 at − 0.7 V versus reversible hydrogen electrode (vs. RHE). The interfacial between CoMn2O4 and NC induces the 3d orbital electrons of Co and Mn in less localized states, which promotes *NH3 desorption. Electrochemical in situ Raman spectra and online differential electrochemical mass spectrometry (DEMS) identified the intermediates and products. The theoretical calculation demonstrates that the existence of NC could reduce the free energy difference of the rate-determining step (RDS, 0.42 eV) of NO3−RR, suppressing hydrogen evolution reaction (HER) by enhancing the interaction of *H. Coupled benzyl alcohol oxidation reaction (BOR) with NO2−RR to obtain lower reduction voltage and high value-added anode products.

Selective electroreduction of nitrate to ammonia via NbWO6 perovskite nanosheets with oxygen vacancy

Electrocatalytic nitrate reduction to ammonia (NRA) under ambient conditions is significant for carbon-neutral synthetic fuels. Nevertheless, the lack of efficient electrocatalysts with tunable nanostructure for NRA remains a grand challenge. Herein, NbWO6 nanosheets with oxygen vacancy (NbWO6-x) was demonstrated via thermal treatment and exfoliation with NH3 selectivity of 86.8% and Faradaic efficiency of 85.7% toward NRA. 1H nuclear magnetic resonance spectra coupled with 15N isotope labeling experiments proved that NH3 originated from NO3−. The function of oxygen vacancy was revealed by computational studies in NRA. Moreover, the reaction mechanism and pathway of NRA could be deduced based on the results of online differential electrochemical mass spectrometry (DEMS). This work provides a selective NH3 generation strategy to decarbonize the energy-chemical sector, bridging the gap between batteries and biofuels.

Oxide-Derived Core-Shell Cu@Zn Nanowires for Urea Electrosynthesis from Carbon Dioxide and Nitrate in Water.

Urea electrosynthesis provides an intriguing strategy to improve upon the conventional urea manufacturing technique, which is associated with high energy requirements and environmental pollution. However, the electrochemical coupling of NO3- and CO2 in H2O to prepare urea under ambient conditions is still a major challenge. Herein, self-supported core-shell Cu@Zn nanowires are constructed through an electroreduction method and exhibit superior performance toward urea electrosynthesis via CO2 and NO3- contaminants as feedstocks. Both 1H NMR spectra and liquid chromatography identify urea production. The optimized urea yield rate and Faradaic efficiency over Cu@Zn can reach 7.29 μmol cm-2 h-1 and 9.28% at -1.02 V vs RHE, respectively. The reaction pathway is revealed based on the intermediates detected through in situ attenuated total reflection Fourier transform infrared spectroscopy and online differential electrochemical mass spectrometry. The combined results of theoretical calculations and experiments prove that the electron transfer from the Zn shell to the Cu core can not only facilitate the formation of *CO and *NH2 intermediates but also promote the coupling of these intermediates to form C-N bonds, leading to a high faradaic efficiency and yield of the urea product.

A Bioinspired Iron-Centered Electrocatalyst for Selective Catalytic Reduction of Nitrate to Ammonia

Nitrate has been commonly used in fertilizers, synthetic materials, and explosives; however, its irregular release leads to extensive contaminants in many sources of drinking water because of its high solubility and mobility. Unfortunately, efficient nitrate removal at low concentrations has been challenging for a long time. Inspired by nitrate reductase with iron as the active center in plants, we constructed a novel nanozyme catalyst, FeNPs@MXene, and proved that the confinement effect of Cl size facilitates the formation of FeOOH nanoshuttles. The FeNPs@MXene electrocatalyst can achieve selective catalytic reduction of nitrate to ammonia, including up to 97.8% conversion of nitrate and high selectivity toward ammonia (76.8%). By precisely analyzing in situ electrochemical online differential electrochemical mass spectrometry (DEMS) and 15N isotope labeling experiments, the electroreduction of nitrate to ammonia was clearly proven. Using density functional theory (DFT) calculations and conductive atomic force microscopy (C-AFM), the built-in electric field formed between FeOOH and MXene is proven to be beneficial to nitrate adsorption and can lower the reaction barrier of key intermediates. This design of iron-based nanozymes offers new illuminating insight into the NO3RR.

Electrocatalytic selective oxidation of ethylene glycol: A concise review of catalyst development and reaction mechanism with comparison to thermocatalytic oxidation process

As an important water and seawater degradable plastic monomer, glycolic acid can be synthesized by selective oxidation of ethylene glycol. This review recapitulates recent advances in electrocatalytic ethylene glycol oxidation reaction (EGOR) from the aspects of catalytic performance and reaction mechanism. For catalytic performance evaluation, target product yield and space-time yield are correlated and analyzed for electrocatalytic and thermocatalytic EGOR systems. To elucidate the rationale behind the electrocatalytic selective oxidation of ethylene glycol, previous works using in situ Fourier transform infrared spectroscopy, online differential electrochemical mass spectrometry, ion chromatography, and theoretical calculations to investigate EGOR are systematically reviewed. Finally, the advantages of electrocatalytic EGOR are summarized by comparing electrocatalytic and thermocatalytic processes.

Selective electrocatalytic reduction of nitrate to dinitrogen by Cu2O nanowires with mixed oxidation-state

• CuO/Cu 2 O NWs contains switchable oxidation states of Cu (I/II to 0/I). • N 2 selectivity is 99.8% over Cu/Cu 2 O NWs, the highest reported so far. • Cu/Cu 2 O NWs provides active sites for hydrogen/oxygen-adsorbing simultaneously. • Cu/Cu 2 O NWs yields sufficient H* and limit hydrogen bubbles negative effect. • N 2 production based on NO 3 RR is proceeded by H*-mediated route. Selective electrocatalytic nitrate reduction reaction to dinitrogen is a promising water treatment technology to manage nitrate. While, a lack of efficient electrode remains the primary hurdle for achieving the goal. For non-noble electrode, the strong adsorption of oxygen atoms on Cu resulted in low selectivity and inducing nitrite accumulation during the long-term operation. Herein, it is found that Cu 2 O nanowires with mixed oxidation-state can selective reduction of nitrate to dinitrogen. CuO-coated Cu 2 O nanowires (CuO/Cu 2 O NWs) was electrochemically converted into Cu/Cu 2 O NWs for hydrogen/oxygen-adsorbing which was verified by In-situ infrared spectro-electrochemical experiments. H 2 split and H*-adsorbing of Cu/Cu 2 O are desired to yield sufficient H* and limit hydrogen bubbles negative effect. Online differential electrochemical mass spectrometry confirmed dinitrogen generation over Cu/Cu 2 O NWs with over 99.8% selectivity. Computational studies suggest that active Cu/Cu 2 O NWs reduces the free energy changes associated with both nitrate activation and N − N coupling. Energetically favorable pathways for dinitrogen production based on nitrate reduction are proposed herein and the origin of this selective dinitrogen formation is clarified.

Synergistic effect of oxygen defects and hetero-phase junctions of TiO2 for selective nitrate electroreduction to ammonia

Electrocatalytic nitrate reduction to ammonia (NH3) has been received increasing attention due to the potential of both decontaminating nitrogen oxide (NOx) from industrial exhaust gas and providing an option for NH3 synthesis. However, their related catalytic process and mechanism dominated by the active phase structure and active sites of nitrate to ammonia electrocatalyst still remain unclear. To this end, in this study TiO2 nanomaterials with constructed hetero-phase junctions and oxygen defects were used to study the catalytic mechanism and make a clear of the function of hetero-phase junctions and defects. Combined with EPR and FT-IR methods, oxygen defects acted as the adsorption sites of NO3- are experimentally confirmed. Systematic characterizations further demonstrate that enhanced performance with the highest NH3 Faradaic efficiency (78.0%) and selectivity (81.9%) for NITRR can be attributed to the Ti3+- Odef pairs and hetero-phase junctions induced strong interface interactions between anatase and rutile phases. The online differential electrochemical mass spectrometry (DEMS) and density functional theory (DFT) calculations demonstrate that both Ti3+ - Odef pairs and hetero-phase junctions lead to the decrease of adsorption energy of NO3- and promote the formation of *NOH intermediates, revealing the reaction mechanism for NH3 synthesis from NO3-.

Metal-organic framework derived carbon-supported bimetallic copper-nickel alloy electrocatalysts for highly selective nitrate reduction to ammonia

Developing electrocatalysts for efficient reduction of nitrate contaminant to value-added ammonia as energy carrier is a pivotal part for restoring the nitrogen cycle. However, the selectivity of ammonia is far from satisfaction, often suffering from accumulation of toxic nitrite byproduct. Herein, a series of CuNi alloy nanoparticles embedded in nitrogen-doped carbon matrix (CuNi/NC) with hierarchical pores were fabricated by pyrolysis of bimetallic metal–organic frameworks (MOFs). The catalysts exhibited excellent selectivity (94.4%) and faradaic efficiency (79.6%) for nitrate reduction to ammonia, greatly outperforming the performance of monometallic Cu/NC (selectivity of 60.8% and faradaic efficiency of 60.6%). Impressively, the introduction of nickel distinctly suppressed the production of toxic byproduct of nitrite. Online differential electrochemical mass spectrometry (DEMS) and in situ surface-enhanced infrared absorption spectroscopy (SEIRAS) tests were utilized to reveal the key intermediates and the reaction pathway. Density functional theory (DFT) calculations demonstrated that the introducing of nickel into copper lattice modified both the electronic and geometric structures of the catalysts. The copper and nickel sites in the CuNi alloy catalysts operate synergistically to facilitate the hydrogenation of NO2* to HNO2* and suppress the hydrogen evolution reaction, boosting the selective formation of ammonia. This work could provide a new synthetic route for bimetallic catalysts and mechanistic understanding for nitrate to ammonia reaction.

New insight on electroreduction of nitrate to ammonia driven by oxygen vacancies-induced strong interface interactions

Ammonia (NH3) synthesis from electrochemical conversion of nitrate (NO3−) can efficiently reduce the emission of nitrogen oxide. However, the complex reaction pathways of nitrate reduction to NH3 are not fully revealed by previous reports. Here we point out that Ag/Cu2O hybrids prepared with the assistance of oxygen vacancies (OV) have very competitive activity (selectivity: 96.85%, Faradaic efficiency: 96.45%) for NH3 synthesis from NO3−. Detailed characterizations demonstrate that this high performance of Ag/Cu2O hybrids derives from the strong interface interactions owing to the formation of strong AgCu bonds. Both online differential electrochemical mass spectrometry (DEMS) and density functional theory (DFT) calculations demonstrate that the strong interface interactions between Ag nanoparticles (NPs) and Cu2O can efficiently boost the adsorption of NO3− and facilitate the formation of *N intermediates in NH3 synthesis.

Enhanced rate performance of nanoporous nickel-antimony anode for sodium ion batteries

Engineering Sb-based anode materials is the key to enhance their electrochemical performance for sodium ion batteries (SIBs) by solving the issues of the rapid capacity decay and poor rate capability. In this work, a nanoporous NiSb alloy (np-NiSb) with a three-dimensionally interconnected ligament-channel structure was synthesized by a facile dealloying strategy. As an anode for SIBs, the np-NiSb alloy exhibits excellent cycling performance, rate capability and stability with a reversible capacity of 334.6 mAh g − 1 at 0.2 A g − 1 after 100 cycles, 155.6 mAh g − 1 at 20 A g − 1 and a capacity retention rate of 97% after 100 cycles at 1 A g − 1. The nanoporous structure and the introduction of inactive Ni effectively tolerate the dramatic volume changes during the charge/discharge processes, restraining the pulverization of np-NiSb. The unique ligament-channel network structure with an average size of about 30 nm significantly shortens the ion transmission distance, ensuring the fast charge transfer at high rates. Operando X-ray diffraction reveals the sodiation/desodiation mechanism of the np-NiSb anode during the discharge/charge processes. In addition, on-line differential electrochemical mass spectrometry further explores the reaction mechanism of np-NiSb. This work highlights constructing nanoporous Sb-based alloys as an effective strategy to improve the performance of SIBs.

Alloying effect-induced electron polarization drives nitrate electroreduction to ammonia

Electrocatalytic conversion of nitrate (NO 3 − ) to ammonia (NH 3 ) holds significant potential in the control of nitrogen oxide (NO x ) from stationary sources. However, previous studies on reaction intermediates remain unclear. Here we report that PdCu/Cu 2 O hybrids with mesoporous hollow sphere structure show high selectivity (96.70%) and Faradaic efficiency (94.32%) for NH 3 synthesis from NO 3 − . Detailed characterizations demonstrate that (1) Pd enables electron transfer (Pd 3d → Cu 3d) and causes the polarization of Cu 3d orbitals by forming partial PdCu alloys, which makes Pd electron deficient but offers empty orbits to adsorb NO 3 − , and (2) electron-rich Cu is more conducive to the occurrence of NO 3 − reduction. The mutual confirmation of online differential electrochemical mass spectrometry and density functional theory calculations demonstrates that PdCu alloys block the generation of ∗NOH intermediate and facilitate the formation of ∗N, providing a new mechanism for NH 3 synthesis from NO 3 − reduction reactions. • PdCu/Cu 2 O hybrids with alloying effect for electrocatalytic NH 3 synthesis • Pd causes the polarization of Cu 3d orbitals by forming partial PdCu alloys • PdCu alloys facilitate the formation of ∗N intermediates for better NH 3 synthesis The reduction treatment of NO x by traditional methods is conducted at high temperature (>400°C), and this process requires considerable energy. Our approach is to convert NO x into NO 3 − in solution by an oxidation and leaching absorption process and subsequently effectively convert NO 3 − into value-added NH 3 (a hydrogen source and a fertilizer). Electrocatalytic reduction of NO 3 − to NH 3 holds important potential in the control of NO x . However, previous studies have not been involved in the regulation of intermediates. By depositing Pd species on Cu 2 O, we achieved significantly improved NH 3 synthesis performance. Pd species make Cu 3d orbitals easier to polarize and act as new adsorption sites instead of Cu 2 O. Detailed characterizations demonstrate that highly dispersed PdCu alloys formed by the deposition of Pd 0 on Cu 2 O can tune the original NH 3 synthesis path of Cu 2 O by facilitating the formation of the ∗N intermediate, ultimately leading to a higher selectivity and Faradaic efficiency. PdCu/Cu 2 O hybrids with a mesoporous hollow sphere structure can efficiently synthesize NH 3 . Pd species make Cu 3d orbitals easier to polarize and act as new adsorption sites of NO 3 − instead of Cu 2 O. The highly dispersed PdCu alloys can efficiently facilitate the formation of ∗N and block the generation of the ∗NOH intermediate, leading to a remarkable selectivity toward NH 3 and Faradaic efficiency. This work highlights a promising route to design Cu 2 O hybrids for selective electrocatalytic NH 3 synthesis to control NO x emission.