High NH3 Yield Rate Research Articles

Electrochemical Synthesis of Metasequoia-Like Reduced Graphene Oxide Coated Cobalt-Silver Catalyst for Stable and Efficient Electrocatalytic Nitrate Reduction to Ammonia.

Electrocatalytic nitrate (NO3 -) reduction to ammonia (NH3) is a green and efficient NH3synthesis technology. Metallic silver (Ag) is one of the well-known electrocatalysts for NO3 - reduction. However, under alkaline conditions, its poor water-splitting ability fails to provide sufficient protonic hydrogen required for NH3 synthesis, resulting in low NH3 selectivity. Additionally, metal catalysts are prone to leaching and oxidation during electrocatalysis, resulting in poor stability. Herein, cobalt (Co) into Ag (CoAg) catalyst is doped, which not only increases the NH3 selectivity by 34.4%, but also reduces the reduction potential by 0.1V. Meanwhile, reduced graphene oxide (rGO) as a protective "armor" is used to encapsulate the CoAg catalyst (rGO2.92@CoAg). The rGO2.92@CoAg catalyst shows excellent stability for over 300 hours (h) of continuous reaction. The Co and Ag contents in the rGO2.92@CoAg catalyst after continuous tests decreases by only 4.3% and 3.1%, respectively, which are much lower than those of the CoAg catalyst without the rGO (90.8%, 52.6%). Moreover, the rGO2.92@CoAg catalyst shows high Faradaic efficiency (99.3%) and NH3 yield rate (1.47mmol h-1 cm-2). Therefore, a high performance and strong stability rGO2.92@CoAg catalyst is obtained by Co doping and rGO coating, which provides theoretical basis for practical industrial application.

Iron and nickel based alloy nanoparticles anchored on phosphorus-modified carbon-nitrogen plane enhances electrochemical nitrate reduction to ammonia

The catalysts of iron and nickel nanoparticles anchored on carbon–nitrogen plane (FeNi-CN) are considered as the potential candidates for promising electrochemical nitrate reduction to ammonia (ENO3RR). However, the high d-orbital energy levels of iron and nickel sites coordinated with nitrogen atoms often lead to overly strong adsorption of reaction intermediates on active sites, severely limiting the improvement of catalytic performance. Herein, a catalyst FeNi3@P-NC consisting FeNi3 alloy nanoparticles confined in phosphorus (P)-modified carbon–nitrogen plane is successfully fabricated, where the electron withdrawal effect induced by P on the carbon–nitrogen plane decreases the d-orbital energy, and optimizes the d-band center of FeNi alloy, thus weakening the overly strong adsorption of intermediates at the metal-N sites and thereby improving NO3RR activity. The prepared FeNi3@P-NC catalyst exhibits exceptional NO3RR performance with a 93 ± 4.5 % Faradaic efficiency of NH3 production (FENH3) and a high NH3 yield rate (YNH3) of 9633 ± 227.3 μg h−1 cm−2 at −0.7 V versus Reversible Hydrogen Electrode (vs. RHE) under alkaline medium. Importantly, FeNi3@P-NC also demonstrates superior catalytic stability and durability, which maintains stability over twenty-five successive electrochemical cycles and for 50 h of continuous electrolysis at 100 mA cm−2.

Modulating Nitrogen Adsorption Mode and Microenvironment of Active Sites for Boosting Electrochemical Nitrogen Reduction.

Electrochemical reduction of N2(NRR) offers a sustainable approach for ammonia (NH3) synthesis, serving as a complementary to the traditional emission- and energy-intensive Haber-Bosch process. However, it faces challenges in N2 activation and competing with pronounced hydrogen evolution reaction (HER). Herein an efficient electrocatalyst comprised of ultrafine Ru nanoclusters (NCs) confined by a hydrophobic molecular layer is developed on the surface of 2D Ti3C2Tx for NRR. These experimental and theoretical calculation results demonstrate that 1) ultrafine Ru NCs dispersed on the Ti3C2Tx surface form paired active sites for N2 chemisorption in a unique tilted configuration with low-energy activation 2) the hydrophobic molecular layer modulates the local microenvironment surrounding catalytically active sites, enabling efficient N2 accumulation while repelling H2O diffusion to the active sites on the Ti3C2Tx surface, thereby leading to an increased N2 concentration and suppressed HER. As a result, an exceptionally high NH3 yield rate of 33.5µg h-1mg-1cat and Faradaic efficiency of 65.3% are obtained at -0.25V versus reversible hydrogen electrode (RHE) in 0.1m Na2SO4, outperforming those previously reported Ti3C2Tx-derived electrocatalysts. This work provides a valuable strategy for the rational design of advanced electrocatalysts by manipulating active sites and local microenvironments for efficient electrocatalysis.

Coherent NiS2@SnS2nanosheet for accelerating electrocatalytic nitrate reduction to ammonia.

The development of an effective and selective catalyst is the key to improving the multi-electron transfer nitrate reduction reaction (NO3-RR) to ammonia. Here, we synthesized a coherent NiS2@SnS2nanosheet catalyst loaded on carbon cloth via one-step solvothermal method. Experimental data reveals that the integration of NiS2and SnS2can enhance the NO3-RR performance in terms of high NH3yield rate of 408.2μg h-1cm-2and Faradaic efficiency of 89.61%, as well as satisfying cycling and long-time stability.

Promoted Two-Step Ammonia Synthesis with CoOOH/Co foam at Ampere-Level Current Density and Nearly 100% Faraday Efficiency from Air and Water.

Ammonia (NH3) is regarded as an essential hydrogen storage material in the new energy field, and plasma-electrocatalytic synthesis of NH3 (PESA) is an alternative to the traditional Haber-Bosch process. Here, a bifunctional catalyst CoOOH/CF is proposed to enhance the PESA process. Benefiting from the efficient activation of O2 by CoOOH/CF, NOx - yield rate can reach the highest value of 171.90mmol h-1 to date. Additionally, CoOOH holds a more negative d-band center, thereby exhibiting weaker adsorption toward NO*, lowering the energy barrier for the rate determining step, resulting in a high NH3 yield rate (302.55mg h-1 cm-2 at -0.8V) with ampere-level NH3 current density (2.86 A cm-2 at -0.8V) and nearly 100% Faraday efficiency (FE, 99.8% at -0.6V). Moreover, CoOOH/CF achieves an excellent 4.54g h-1 NH3 yield rate with 97.9% FE in an enlarged electrolyzer, demonstrating the feasibility of PESA on a large scale.

Electrocatalytic nitrite conversion to ammonia over Mn single atoms anchored on MoO3-x

Electrocatalytic reduction of NO2 to NH3 (NO2RR) offers a promising route to attain harmful NO2– removal and valuable NH3 production. Herein, Mn single atoms anchored on oxygen vacancy-rich MoO3-x (Mn1/MoO3-x) are developed as a high-performance catalyst for the NO2RR. Atom characterizations unravel that the isolated Mn atoms exist as Mn1-O5 moieties on MoO3-x. Theoretical calculations and in situ electrochemical spectroscopic measurements unveil that Mn1/MoO3-x follows a Langmuir-Hinshelwood mechanism to drive the NO2RR process, in which Mn1-O5 site facilitates the adsorption and activation of NO2– to form the intermediates, while MoO3-x substrate dissociates H2O to yield *H. The generated *H is then transferred from MoO3-x substrate to Mn1-O5 site which promotes the intermediate protonation to produce NH3. Remarkably, Mn1/MoO3-x in flow cell reaches the high NH3 yield rate of 546.25 μmol h−1 cm−2 and NH3-Faraday efficiency of 92.6 %, outperforming most reported NO2RR catalysts.

Cu/CuxO/Graphdiyne Tandem Catalyst for Efficient Electrocatalytic Nitrate Reduction to Ammonia.

The electrocatalytic reduction reaction of nitrate (NO3 -) to ammonia (NH3) is a feasible way to achieve artificial nitrogen cycle. However, the low yield rate and poor selectivity toward NH3 product is a technical challenge. Here a graphdiyne (GDY)-based tandem catalyst featuring Cu/CuxO nanoparticles anchored to GDY support (termed Cu/CuxO/GDY) for efficient electrocatalytic NO3 - reduction is presented. A high NH3 yield rate of 25.4mg h-1 mgcat. -1 (25.4mg h-1 cm-2) with a Faradaic efficiency of 99.8% at an applied potential of -0.8V versus RHE using the designed catalyst is achieved. These performance metrics outperform most reported NO3 - to NH3 catalysts in the alkaline media. Electrochemical measurements and density functional theory reveal that the NO3 - preferentially attacks Cu/CuxO, and the GDY can effectively catalyze the reduction of NO2 - to NH3. This work highlights the efficacy of GDY as a new class of tandem catalysts for the artificial nitrogen cycle and provides powerful guidelines for the design of tandem electrocatalysts.

Spatially Separated Cu/Ru on Ordered Mesoporous Carbon for Superior Ammonia Electrosynthesis from Nitrate over a Wide Potential Window.

Nitrate (NO3-) in wastewater poses a serious threat to human health and the ecological environment. The electrocatalytic NO3- reduction to ammonia (NH3) reaction (NO3-RR) emerges as a promising carbon-free energy route for enabling NO3- removal and sustainable NH3 synthesis. However, it remains a challenge to achieve high Faraday efficiencies at a wide potential window due to the complex multiple-electron reduction process. Herein, spatially separated dual-metal tandem electrocatalysts made of a nitrogen-doped ordered mesoporous carbon support with ultrasmall and high-content Cu nanoparticles encapsulated inside and large and low-content Ru nanoparticles dispersed on the external surface (denoted as Ru/Cu@NOMC) are designed. In electrocatalytic NO3-RR, the Cu sites can quickly convert NO3- to adsorbed NO2- (*NO2-), while the Ru sites can efficiently produce active hydrogen (*H) to enhance the kinetics of converting *NO2- to NH3 on the Cu sites. Due to the synergistic effect between the Cu and Ru sites, Ru/Cu@NOMC exhibits a maximum NH3 Faradaic efficiency (FENH3) of approximately 100% at -0.1 V vs reversible hydrogen electrode (RHE) and a high NH3 yield rate of 1267 mmol gcat-1 h-1 at -0.5 V vs RHE. Finite element method (FEM) simulation and electrochemical in situ Raman spectroscopy revealed that the mesoporous framework can enhance the intermediate concentration due to the in situ confinement effect. Thanks to the Cu-Ru synergistic effect and the mesopore confinement effect, a wide potential window of approximately 500 mV for FENH3 over 90% and a superior stability for NH3 production over 156 h can be achieved on the Ru/Cu@NOMC catalyst.

A high-performance electrocatalyst for sustainable ammonia synthesis via single-atom Ru-embedded Fe2O3 nitrogen-DOPED carbon

Ammonia (NH3) is an important industrial chemical, but the production of NH3 by the conventional Haber-Bosch process consumes large amounts of energy and has a serious environmental impact. Electrochemical nitrogen reduction reaction (NRR) offers a promising green alternative, but challenges remain in developing efficient catalysts. Here, we report the synthesis of single-atom Ru-embedded metal–organic framework-derived Fe2O3 nitrogen-doped carbon (Ru/Fe2O3-NC) materials via plasma-enhanced chemical vapour deposition. Under ambient conditions, the Ru/Fe2O3-NC catalyst exhibited a high NH3 yield rate of 141.18 μg h−1 mgcat.−1 in 0.1 M K2SO4 with a Faraday efficiency (FE) of 48.89 %, which was superior to the pristine Fe2O3-NC catalyst. Online differential electrochemical mass spectrometry (DEMS) analysis confirmed the selective generation of NH3 and no by-product N2H4 was detected. The Ru/Fe2O3-NC catalyst also showed remarkable stability during prolonged electrolysis. This work demonstrates the synergistic effect of incorporating single-atomic Ru in the Fe2O3-NC framework and provides a new platform for the development of advanced catalysts for the efficient and sustainable electrochemical synthesis of NH3.

A General Strategy Based on Hetero‐Charge Coupling Effect for Constructing Single‐Atom Sites

AbstractSingle‐atom catalysts have emerged as cutting‐edge hotspots in the field of material science owing to their excellent catalytic performance brought about by well‐defined metal single‐atom sites (M SASs). However, huge challenges still lie in achieving the rational design and precise synthesis of M SASs. Herein, we report a novel synthesis strategy based on the hetero‐charge coupling effect (HCCE) to prepare M SASs loaded on N and S co‐doped porous carbon (M1/NSC). The proposed strategy was widely applied to prepare 17 types of M1/NSC composed of single or multi‐metal with the integrated regulation of the coordination environment and electronic structure, exhibiting good universality and flexible adjustability. Furthermore, this strategy provided a low‐cost method of efficiently synthesizing M1/NSC with high yields, that can produce more than 50 g catalyst at one time, which is key to large‐scale production. Among various as‐prepared unary M1/NSC (M can be Fe, Co, Ni, V, Cr, Mn, Mo, Pd, W, Re, Ir, Pt, or Bi) catalysts, Fe1/NSC delivered excellent performance for electrocatalytic nitrate reduction to NH3 with high NH3 Faradaic efficiency of 86.6 % and high NH3 yield rate of 1.50 mg h−1 mgcat.−1 at −0.6 V vs. RHE. Even using Fe1/NSC as a cathode in a Zn‐nitrate battery, it exhibited a high open circuit voltage of 1.756 V and high energy density of 4.42 mW cm−2 with good cycling stability.

A General Strategy Based on Hetero-Charge Coupling Effect for Constructing Single-Atom Sites.

Single-atom catalysts have emerged as cutting-edge hotspots in the field of material science owing to their excellent catalytic performance brought about by well-defined metal single-atom sites (M SASs). However, huge challenges still lie in achieving the rational design and precise synthesis of M SASs. Herein, we report a novel synthesis strategy based on the hetero-charge coupling effect (HCCE) to prepare M SASs loaded on N and S co-doped porous carbon (M1/NSC). The proposed strategy was widely applied to prepare 17 types of M1/NSC composed of single or multi-metal with the integrated regulation of the coordination environment and electronic structure, exhibiting good universality and flexible adjustability. Furthermore, this strategy provided a low-cost method of efficiently synthesizing M1/NSC with high yields, that can produce more than 50 g catalyst at one time, which is key to large-scale production. Among various as-prepared unary M1/NSC (M can be Fe, Co, Ni, V, Cr, Mn, Mo, Pd, W, Re, Ir, Pt, or Bi) catalysts, Fe1/NSC delivered excellent performance for electrocatalytic nitrate reduction to NH3 with high NH3 Faradaic efficiency of 86.6 % and high NH3 yield rate of 1.50 mg h-1 mgcat. -1 at -0.6 V vs. RHE. Even using Fe1/NSC as a cathode in a Zn-nitrate battery, it exhibited a high open circuit voltage of 1.756 V and high energy density of 4.42 mW cm-2 with good cycling stability.

Polynuclear Cobalt Cluster-Based Coordination Polymers for Efficient Nitrate-to-Ammonia Electroreduction.

The electrocatalytic nitrate reduction reaction (NITRR) holds great promise for purifying wastewater and producing valuable ammonia (NH3). However, the lack of efficient electrocatalysts has impeded the achievement of highly selective NH3 synthesis from the NITRR. In this study, we report the design and synthesis of two polynuclear Co-cluster-based coordination polymers, {[Co2(TCPPDA)(H2O)5]·(H2O)9(DMF)} and {Co1.5(TCPPDA)[(CH3)2NH2]·(H2O)6(DMF)2} (namely, NJUZ-2 and NJUZ-3), which possess distinct coordination motifs with well-defined porosity, high-density catalytic sites, accessible mass transfer channels, and nanoconfined chemical environments. Benefitting from their intriguing multicore metal-organic coordination framework structures, NJUZ-2 and NJUZ-3 exhibit remarkable catalytic activities for the NITRR. At a potential of -0.8 V (vs. RHE) in an H-type cell, they achieve an optimal Faradaic efficiency of approximately 98.5% and high long-term durability for selective NH3 production. Furthermore, the electrocatalytic performance is well maintained even under strongly acidic conditions. When operated under an industrially relevant current density of 469.9 mA cm-2 in a flow cell, a high NH3 yield rate of up to 3370.6 mmol h-1 g-1cat. was observed at -0.5 V (vs. RHE), which is 20.1-fold higher than that obtained in H-type cells under the same conditions. Extensive experimental analyses, in combination with theoretical computations, reveal that the great enhancement of the NITRR activity is attributed to the preferential adsorption of NO3- and the reduction in energy input required for the hydrogenation of *NO3 and *NO2 intermediates.

Vacancy engineering of BiFeO3 perovskite for low-barrier electrochemical nitrogen fixation

Because of its environmental and intrinsic benefits, the nitrogen reduction reaction (NRR) using electrocatalysts has garnered significant attention. Engineering on the surface is commonly utilized to improve electrocatalytic activity by introducing atomic defects. In this study, we have developed a successful strategy to promote nitrogen activation by introducing oxygen vacancies into BiFeO3 perovskite. BiFeO3 with oxygen vacancies (denoted as VO-BiFeO3) possesses a high NH3 yield rate (89.3 μg h−1 mgcat−1) and Faradaic efficiency (FE) (13.5 %) at −0.40 V versus the reversible hydrogen electrode (RHE). According to density functional theory (DFT) calculations, the introduction of oxygen vacancies increases the binding capacity for nitrogen immobilization and reduces the energy barrier for the rate-determining step of NRR. Moreover, the analysis of the thermodynamic limiting potentials towards N2 reduction and H2 evolution demonstrates that VO-BiFeO3 has a higher selectivity for NRR than pristine BiFeO3.

Construction of frustrated lewis pairs in ZnO surface for boosting electrocatalytic NO reduction to NH3: Theoretical prediction and experimental validation

Herein, we reported the design of unique FLPs for electrocatalytic reduction of nitric oxide (NOER) through anion doping on the ZnO (100) surface. The results demonstrated that the introduced dopant and its adjacent non−bonding Zn site function as a Lewis base and Lewis acid, respectively, to synergistically activate NO molecules. Using density functional theory for material screening, P−doped ZnO is predicted to exhibit rather high NOER activity with an ultralow limiting potential (−0.04 V), accompanied by the excellent suppression effect on the competitive side reactions to guarantee its high selectivity for NH3 production. Motivated by the theoretical prediction, the synthesized P−doped ZnO catalyst showed a high NH3 yield rate (218.2 μmol h−1cm−2 at −0.7 V) and a high Faradaic efficiency (91.4 %), as confirmed by our experimental measurements. This work not only suggests a high−performance catalyst for NO reduction but also expands upon the potential applications of FLPs in electrocatalysis.

Enhanced nitrite electroreduction to ammonia via interfacial dual-site adsorption

The nitrite (NO2−) to ammonia (NH3) electroreduction reaction (NO2−RR) would be impeded by sluggish proton-coupled electron transfer kinetics and competitive hydrogen evolution reaction (HER). A key to improving the NH3 selectivity is to facilitate adsorption and activation of NO2−, which is generally undesirable in unitary species. In this work, an efficient NO2−RR catalyst is constructed by cooperating Pd with In2O3, in which NO2− could adsorb on interfacial dual-site through “Pd–N–O–In” linkage, leading to strengthened NO2− adsorption and easier N=O bond cleavage than that on unitary Pd or In2O3. Moreover, the Pd/In2O3 composite exhibits moderate H* adsorption, which may facilitate protonation kinetics while inhibiting competitive HER. As a result, it exhibits a fairly high NH3 yield rate of 622.76 mmol h−1 g−1cat with a Faradaic efficiency (FE) of 95.72%, good selectivity of 91.96%, and cycling stability towards the NO2−RR, surpassing unitary In2O3 and Pd/C electrocatalysts. Besides, computed results indicate that NH3 production on Pd/In2O3 follows the deoxidation to hydrogenation pathway. This work highlights the significance of H* and NO2− adsorption modulation and N=O activation in NO2−RR electrochemistry by creating synergy between a mediocre catalyst with an appropriate cooperator.

Efficient ammonia synthesis from the air using tandem non-thermal plasma and electrocatalysis at ambient conditions

While electrochemical N2 reduction presents a sustainable approach to NH3 synthesis, addressing the emission- and energy-intensive limitations of the Haber-Bosch process, it grapples with challenges in N2 activation and competing with pronounced hydrogen evolution reaction. Here we present a tandem air-NOx-NOx−-NH3 system that combines non-thermal plasma-enabled N2 oxidation with Ni(OH)x/Cu-catalyzed electrochemical NOx− reduction. It delivers a high NH3 yield rate of 3 mmol h−1 cm−2 and a corresponding Faradaic efficiency of 92% at −0.25 V versus reversible hydrogen electrode in batch experiments, outperforming previously reported ones. Furthermore, in a flow mode concurrently operating the non-thermal plasma and the NOx− electrolyzer, a stable NH3 yield rate of approximately 1.25 mmol h−1 cm−2 is sustained over 100 h using pure air as the intake. Mechanistic studies indicate that amorphous Ni(OH)x on Cu interacts with hydrated K+ in the double layer through noncovalent interactions and accelerates the activation of water, enriching adsorbed hydrogen species that can readily react with N-containing intermediates. In situ spectroscopies and density functional theory (DFT) results reveal that NOx− adsorption and their hydrogenation process are optimized over the Ni(OH)x/Cu surface. This work provides new insights into electricity-driven distributed NH3 production using natural air at ambient conditions.

Fe induced geometric/electronic structure engineering in YSZ nanosheets for enhanced electrocatalytic nitrogen reduction reactions

Constructing 2D geometric structure and optimize electronic structure of transition metal oxide have been demonstrated to be effective strategy to reinforce its electrochemical dinitrogen reduction reaction (NRR) performances. But combining these two advantages into metal oxide based electrocatalyst simultaneously to achieve synergic effects remains one technological challenge but very significant. Here, a self-sacrificing template coupling with Fe doped strategy were proposed to optimize the geometric and electronic structure of Zr-based electrocatalyst. Experimental results revealed that the optimal sample 2Fe-YSZ was endowed with uniform 2D heterostructures, rich oxygen vacancy and increased electronic density, which induced by the framework Fe element. These traits thus confer the 2Fe-YSZ produced through extensive exposure to extra active sites, significantly boosting the absorption and activation of N2 molecules. And the DFT calculation further validates the promotive effect of framework Fe. As expected, in the electrocatalytic NRR test, 2Fe-YSZ demonstrated high Faradaic efficiency (38.89 %) and NH3 yield rate (19.58 μg h−1 mg−1) at − 0.5 V in 0.1 M HCl, comparable to most Zr-based electrocatalytic materials for ambient NRR. This geometric/electronic structure engineering strategy could provide an idea the rational design of efficient NRR catalysts.

Matched Kinetics Process Over Fe2O3‐Co/NiO Heterostructure Enables Highly Efficient Nitrate Electroreduction to Ammonia

AbstractTandem nitrate electroreduction reaction (NO3−RR) is a promising method for green ammonia (NH3) synthesis. However, the mismatched kinetics processes between NO3−‐to‐NO2− and NO2−‐to‐NH3 results in poor selectivity for NH3 and excess NO2− evolution in electrolyte solution. Herein, a Ni2+ substitution strategy for developing oxide heterostructure in Co/Fe layered double oxides (LDOs) was designed and employed as tandem electrocataltysts for NO3−RR. (Co0.83Ni0.16)2Fe exhibited a high NH3 yield rate of 50.4 mg ⋅ cm−2 ⋅ h−1 with a Faradaic efficiency of 97.8 % at −0.42 V vs. reversible hydrogen electrode (RHE) in a pulsed electrolysis test. By combining with in situ/operando characterization technologies and theoretical calculations, we observed the strong selectivity of NH3 evolution over (Co0.83Ni0.16)2Fe, with Ni playing a dual role in NO3−RR by i) modifying the electronic behavior of Co, and ii) serving as complementary site for active hydrogen (*H) supply. Therefore, the adsorption capacity of *NO2 and its subsequent hydrogenation on the Co sites became more thermodynamically feasible. This study shows that Ni substitution promotes the kinetics of the NO3−RR and provides insights into the design of tandem electrocatalysts for NH3 evolution.

Matched Kinetics Process Over Fe2O3-Co/NiO Heterostructure Enables Highly Efficient Nitrate Electroreduction to Ammonia.

Tandem nitrate electroreduction reaction (NO3 -RR) is a promising method for green ammonia (NH3) synthesis. However, the mismatched kinetics processes between NO3 --to-NO2 - and NO2 --to-NH3 results in poor selectivity for NH3 and excess NO2 - evolution in electrolyte solution. Herein, a Ni2+ substitution strategy for developing oxide heterostructure in Co/Fe layered double oxides (LDOs) was designed and employed as tandem electrocataltysts for NO3 -RR. (Co0.83Ni0.16)2Fe exhibited a high NH3 yield rate of 50.4 mg ⋅ cm-2 ⋅ h-1 with a Faradaic efficiency of 97.8 % at -0.42 V vs. reversible hydrogen electrode (RHE) in a pulsed electrolysis test. By combining with in situ/operando characterization technologies and theoretical calculations, we observed the strong selectivity of NH3 evolution over (Co0.83Ni0.16)2Fe, with Ni playing a dual role in NO3 -RR by i) modifying the electronic behavior of Co, and ii) serving as complementary site for active hydrogen (*H) supply. Therefore, the adsorption capacity of *NO2 and its subsequent hydrogenation on the Co sites became more thermodynamically feasible. This study shows that Ni substitution promotes the kinetics of the NO3 -RR and provides insights into the design of tandem electrocatalysts for NH3 evolution.

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

Electroreduction of nitrate (NO3 -) to ammonia (NH3) is an environmentally friendly route for NH3 production, serving as an appealing alternative to the Haber-Bosch process. Recently, various noble metal-based electrocatalysts have been reported for electroreduction of NO3 -. However, the application of pure metal electrocatalysts is still limited by unsatisfactory performance, owing to the weak adsorption of nitrogen-containing intermediates on the surface of pure metal electrocatalysts. In this work, we report thiol ligand-modified Au nanoparticles as the effective electrocatalysts toward electroreduction of NO3 -. Specifically, three mercaptobenzoic acid (MBA) isomers, thiosalicylic acid (ortho-MBA), 3-mercaptobenzoic acid (meta-MBA), and 4-mercaptobenzoic acid (para-MBA), were employed to modify the surface of the Au nanocatalyst. During the NO3 - electroreduction, para-MBA modified Au (denoted as para-Au/C) displayed the highest catalytic activity among these Au-based catalysts. At -1.0 V versus reversible hydrogen electrode (vs RHE), para-Au/C exhibited a partial current density for NH3 of 472.2 mA cm-2, which was 1.7 times that of the pristine Au catalyst. Meanwhile, the Faradaic efficiency (FE) for NH3 reached 98.7% at -1.0 V vs RHE for para-Au/C. The modification of para-MBA significantly improved the intrinsic activity of the Au/C catalyst, thus accelerating the kinetics of NO3 - reduction and giving rise to a high NH3 yield rate of para-Au/C.