Electrocatalytic Reduction Of Nitrate Research Articles

MOF‐on‐MOF Heterostructured Electrocatalysts for Efficient Nitrate Reduction to Ammonia

AbstractElectrocatalytic nitrate reduction reaction (NO3−RR) is an important route for sustainable NH3 synthesis and environmental remediation. Metal–organic frameworks (MOFs) are one family of promising NO3−RR electrocatalysts, however, there is plenty of room to improve in their performance, calling for new design principles. Herein, a MOF‐on‐MOF heterostructured electrocatalyst with interfacial dual active sites and build‐in electric field is fabricated for efficient NO3−RR to NH3 production. By growing Co‐HHTP (HHTP=2,3,6,7,10,11‐hexahydroxytriphenylene) nanorods on Ni‐BDC (BDC=1,4‐benzenedicarboxylate) nanosheets, experimental and theoretical investigations demonstrate the formation of Ni−O−Co bonds at the interface of MOF‐on‐MOF heterostructure, leading to dual active sites tailed for NO3−RR. The Ni sites facilitate the adsorption and activation of NO3−, while the Co sites boost the H2O decomposition to supply active hydrogen (Hads) for N‐containing intermediates hydrogenation on adjacent Ni sites, cooperatively reducing the energy barriers of NO3−RR process. Together with the accelerated electron transfer enabled by built‐in electric field, remarkable NO3−RR performance is achieved with an NH3 yield rate of 11.46 mg h−1 cm−2 and a Faradaic efficiency of 98.4 %, outperforming most reported MOF‐based electrocatalysts. This work provides new insights into the design of high‐performance NO3−RR electrocatalysts.

MOF-on-MOF Heterostructured Electrocatalysts for Efficient Nitrate Reduction to Ammonia.

Electrocatalytic nitrate reduction reaction (NO3 -RR) is an important route for sustainable NH3 synthesis and environmental remediation. Metal-organic frameworks (MOFs) are one family of promising NO3 -RR electrocatalysts, however, there is plenty of room to improve in their performance, calling for new design principles. Herein, a MOF-on-MOF heterostructured electrocatalyst with interfacial dual active sites and build-in electric field is fabricated for efficient NO3 -RR to NH3 production. By growing Co-HHTP (HHTP=2,3,6,7,10,11-hexahydroxytriphenylene) nanorods on Ni-BDC (BDC=1,4-benzenedicarboxylate) nanosheets, experimental and theoretical investigations demonstrate the formation of Ni-O-Co bonds at the interface of MOF-on-MOF heterostructure, leading to dual active sites tailed for NO3 -RR. The Ni sites facilitate the adsorption and activation of NO3 -, while the Co sites boost the H2O decomposition to supply active hydrogen (Hads) for N-containing intermediates hydrogenation on adjacent Ni sites, cooperatively reducing the energy barriers of NO3 -RR process. Together with the accelerated electron transfer enabled by built-in electric field, remarkable NO3 -RR performance is achieved with an NH3 yield rate of 11.46 mg h-1 cm-2 and a Faradaic efficiency of 98.4 %, outperforming most reported MOF-based electrocatalysts. This work provides new insights into the design of high-performance NO3 -RR electrocatalysts.

Unveiling Ionized Interfacial Water-Induced Localized H* Enrichment for Electrocatalytic Nitrate Reduction.

Electrocatalytic nitrate reduction reaction (NO3RR) is a process that requires the participation of eight electrons and nine protons. The regulation of active hydrogen (H*) supply and a deep understanding of related processes are necessary for improving the ammonia yield rate and Faradaic efficiency (FE). Herein, we synthesized a series of atomically precise copper-halide clusters Cu2X2(BINAP)2 (X = Cl, Br, I), among which the Cu2Cl2(BINAP)2 cluster shows the optimal ammonia FE of 94.0% and an ammonia yield rate of 373 μmol h-1 cm-2. In situ experiments and theoretical calculations reveal that halogen atoms, especially Cl in Cu2Cl2(BIANP)2, can significantly affect the distance of alkali metal-ionized water on the catalyst surface, which can promote the water dissociation to enhance the localized H* enrichment for the continues hydrogenation of nitrate to ammonia. This work explains the role of H* in the hydrogenation process of NO3RR and the importance of localized H* enrichment strategy for improving the FEs.

Silver-π Interaction: A Diverse Approach to Hybrid Material and Its Efficacy in Electrocatalytic Reduction of Nitrate to Ammonia.

Inspired by the intriguing nature of the metal-π interaction in organometallic chemistry, a novel 1D hybrid material has been designed. Herein, a functionalized tellurium allyl macrocycle (TAM) acts as a molecular building block and is knit together via silver-π interaction to obtain Ag-TAM. Ag is coordinated to two allyl groups and a phenyl ring in η2 mode. Instead of the conventional polymerization strategy, a metal-π interaction is employed to interlink macrocycles. TAM and Ag-TAM showed electrocatalytic capability for the conversion of nitrate to ammonia. Ag-TAM showed an NH3 yield rate 2-fold greater than TAM with a high faradaic efficiency of 94.6% with good durability, proving that interlinking of macrocycles via metal-π interaction improves the catalytic activity. Detailed periodic density functional theory (DFT) calculations unveil novel mechanistic insights, suggesting cooperative catalysis between neighboring Ag sites and contributing to the enhanced efficiency.

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.

High efficiency conversion of low concentration nitrate boosted with amorphous Cu0 nanorods prepared via in-situ reconstruction

Electrocatalytic nitrate reduction reaction (NO3−RR) is a green and competitive method for removing nitrate from water, requiring highly active and long-term stable electrocatalysts. In this work, we report a Cu0 nanorod catalyst with disordered structure (re-Cu NRs), prepared by electrochemical in situ reconfiguration of copper-based nitrides (Cu3N NRs). The amorphous structure allows the exposure of abundant active sites to enhance the electrocatalytic activity because of the disordered atomic arrangement. At a potential of −1.2V vs. Ag/AgCl, the re-Cu NRs catalyst achieved nearly 100% nitrate conversion within 120 min at a low nitrate concentration (50 mg/L), without the accumulation of nitrite. In-situ DEMS detection reveals that the NO3−RR on re-Cu NRs followed the pathway of *NO3− → *NO2− → *NO → *N → *NH → *NH2 → *NH3. Furthermore, combining this proposed pathway with electrochlorination could efficiently transform ammonia into harmless N2 (∼99.41%). Theoretical calculations confirm that the amorphous structure on the surface of re-Cu NRs catalysts can facilitate strongly adsorbed nitrate, weaken the rate-determining step of *NH3 → NH3, and suppress Hydrogen evolution reaction (HER). This study provides a new approach for designing efficient and stable amorphous catalysts for electrocatalytic nitrate reduction.

Electroreduction of nitrate to ammonia on graphyne-based single-atom catalysts by combined density functional theory and machine learning study

Nitrate pollution has emerged as a significant global issue, prompting increased interests in electrocatalytic reduction of nitrate to ammonia (NO3RR). This study explores the use of graphyne as the substrate to anchor single transition metal (TM) atoms from the 3d and 4d series on acetylene corners, creating single-atom catalysts (SAC) for the NO3RR reaction. Two catalysts, CrGY and MoGY, were finally identified as promising catalysts for NO3RR with low limiting potential and high selectivity for NH3. To further investigate the origin of catalyst activity, in addition to traditional electronic structrue analysis, machine learning models of the least solution shrinkage and selection operator (LASSO), the sure independence screening and sparsifying operator (SISSO) and the gradient boosting regression (GBR) algorithm are adopt to reveal the intrinsic properties of catalysts that determine the NO3RR performance. After preliminary evaluation of the 13 prepared features with LASSO algorithm, GBR models revealed that the nitrate adsorption free energy ΔGNO3- and the NO bond length are the two most important descriptors for NO3RR performance. A general equation for the relationship between the limiting potential and the characteristics of the catalysts are obtained by SISSO model. Finally, with the assitance of combined density functional calculations and machine learning, this study provides new enlightening insights into practical application of graphyne as SACs for NO3RR.

Regioselective Doping into Atomically Aligned Core–Shell Structures for Electrocatalytic Reduction of Nitrate to Ammonia

AbstractThe electrochemical nitrate reduction reaction (NO3−RR) presents an environmentally friendly approach for efficient NO3− pollutant removal and ammonia (NH3) production, compared to the conventional Haber–Bosch approach. While core/shell engineering has demonstrated its potential in enhancing NO3−RR performance, significant synthetic challenges and limited shell layer modification capabilities impede the exploration of high‐performance NO3−RR core/shell catalysts. Herein, CuCoO/Co(OH)2 core/shell structure via in situ electrochemical activation is synthesized. The catalyst delivers a maximum NH3 Faradaic efficiency (FE) of 94.7% at −0.5 VRHE with excellent durability and selectivity for NH3 over a wide range of potentials in NO3−RR, surpassing the electrocatalytic performance of both undoped shell and core components. The outstanding performance Cu─CoO/Co(OH)2 is ascribed to the enhanced charge transfer, stabilization of key reaction intermediates, and regulation of hydrogen adsorption over Cu‐doped core/shell structure. Furthermore, the assembled Zn−NO3− battery device attains a peak current density exceeding 32 mA cm−2 and an NH3 yield of up to 145.4 µmol h−1 cm−2. The work offers a novel core/shell engineering strategy in electrocatalytic NO3−RR and sheds light on the doping effects on the electrochemical NH3 synthesis.

Atomic-Dispersed Cu Catalysts for Electrochemical Nitrate Reduction: Coordination Engineering and Fundamental Insights.

The development of Cu-based atomic dispersed catalysts with tailored coordination environments represents a significant step forward in enhancing the electrocatalytic reduction of nitrate to ammonia. By precisely modulating the electronic structures of Cu active centers, the binding strength of the *NO3 intermediates is successfully tuned, thereby substantially improving the catalytic activity toward electrochemical nitrate reduction reaction (eNO3RR). This study reveals that the N4-coordinated Cu single-atom catalyst (Cu-SAC) exhibits superior performance due to its robust interaction with coordinating atoms. Notably, this optimized catalyst achieves a low limiting potential of -0.38V, while the dual-atom system further reduces this value to -0.32V, demonstrating exceptional activity. Detailed electronic structure analysis, including the examination of d-band centers, Bader charges, and projected density of states (PDOS), provides a comprehensive understanding of the origin of this high activity. Specifically, the high and concentrated density of states near the Fermi level plays a crucial role in facilitating the electrocatalytic nitrate reduction process. This work not only offers crucial insights into the underlying mechanisms of eNO3RR but also provides valuable guidelines for the rational design of highly efficient electrocatalysts for this important reaction.

CoNi layered double hydroxides grown on Ag nanowires for high-efficient nitrate-to-ammonia conversion

Electrocatalytic reduction of nitrate to ammonia is a promising technology. The sluggish rate of the nitrate-to-nitrite reduction is the core issue. By reducing the energy barrier of this step, the reactivity can be greatly promoted. Here, we have documented Co2Ni1 layered double hydroxide (LDH) on Ag nanowire (NW) that demonstrates efficient catalytic activity in electro-reducing nitrate to ammonia under a diverse set of application conditions. It achieves a high ammonia yield (2.50 mmol h−l cm−2) and Faradaic efficiency (99.6 %) at −0.7 V versus a reversible hydrogen electrode (VRHE). Through comparative experiments, it has been proven that the selective reduction of nitrate to nitrite on Ag NW is the key. This series of Ag NW heterostructure electrodes provides new insights into the design principles of high-performance and high-durability nitrate reduction electrodes under environmentally relevant wastewater conditions.

Promoting active hydrogen supply for kinetically matched tandem electrocatalytic nitrate reduction to ammonia

Electrocatalytic nitrate reduction (NO3RR) shows admirable potential for environmental remediation and producing valuable NH3. However, the catalyst is restricted by the kinetic mismatch between NO3--to-NO2- and NO2--to-NH3, which results in excess NO2- and poor NH3 selectivity. Herein, a kinetically matched tandem electrocatalytic strategy with tunable active hydrogen(*H) supply is designed. The combination of Cu2O and Co11(HPO3)8(OH)6 (CoPO) playing key roles in NO3RR by i) on-demand supply of *H from CoPO; ii) the electronically coupled interface between Cu2O and CoPO enhance *H transfer kinetics. The Cu2O-CoPO-2 exhibits high NH3 yield of 22 mg cm−2 h−1 with Faradaic efficiency of 95 % at −0.37 V vs. RHE. In situ characterizations indicate the dynamic equilibrium between *H production and consumption contributes to high NO3RR performance. The techno-economic analyses reveal the system is economically viable compared to Haber-Bosch (H-B) process, which benefits from industrial current densities and superior energy efficiency at low potentials.

Homogeneously Mixed Cu-Co Bimetallic Catalyst Derived from Hydroxy Double Salt for Industrial-Level High-Rate Nitrate-to-Ammonia Electrosynthesis.

Electrocatalytic nitrate reduction reaction (NO3RR) presents an innovative approach for sustainable NH3 production. However, selective NH3 production is hindered by the multiple intermediates involved in the NO3RR process and the competitive hydrogen evolution reaction. Hence, the development of highly efficient NO3RR catalysts is paramount. Herein, we report highly efficient bimetallic catalysts derived from hydroxy double salt (HDS). Under NO3RR conditions, Cu1Co1-HDS undergoes in situ reconstruction, forming nanocomposites of homogeneously distributed metallic Cu0 and Co(OH)2. Reconstruction-induced Cu0 rapidly converts NO3- to NO2-, which is further hydrogenated to NH3 by Co(OH)2. Homogeneously mixed Cu and Co species maximize this synergistic effect, achieving outstanding NO3RR performance including the highest NH3 yield rate (4.625 mmol h-1 cm-2) reported for powder-type NO3RR catalysts. Integration of Cu1Co1-HDS with a commercial Si solar cell attained 4.53% solar-to-ammonia efficiency from industrial wastewater-level concentrations of NO3- (2000 ppm), demonstrating practical application potential for solar-driven NH3 production. This study provides a strategy for enhancing the NH3 yield rate by optimizing the compositions and distributions of Cu and Co.

A bioinspired Fe/Mo bimetallic nitride catalyst for efficient electrochemical ammonia synthesis and Zn-nitrate battery

The electrocatalytic nitrate reduction reaction to ammonia (NRA) offers a promising alternative to traditional ammonia synthesis methods. In nature, enzymes containing molybdenum and iron sites catalyze the reduction of nitrate and nitrite ions. Drawing inspiration from these enzymes, we synthesized a carbon-coated nano-octahedra of FeMo-based nitride (FeMoN@C NO) by pyrolyzing phosphomolybdic acid hydrate (POM) doped Fe-NH2-MIL-101 to catalyze NRA. Experimental results demonstrate that in an alkaline environment, FeMoN@C NO exhibits a suitable hydrogen evolution reaction (HER) capacity, and the protons or hydroxyls produced effectively facilitate the hydrogenation reaction in the ammonia synthesis process. Additionally, the introduction of Mo increases the number of active sites and effectively reduces the thermodynamic barrier in NRA, thereby enhancing the rate of ammonia synthesis. As a result, FeMoN@C NO displays outstanding NH3 Faradaic efficiency (FE) of 98.2 % and an NH3 yield of 434.16 µmol/h cm−2. Building upon the excellent electrocatalytic properties of FeMoN@C NO, a new Zn-nitrate battery system is assembled in this work, which exhibits an outstanding peak power density of 3.23 mW cm−2 and an FE of 91.58 % for NH3 production. This work provides a new perspective for designing enzyme-mimicking nitrate reduction catalysts and broadens the application of Zn-based batteries.

Recent advances in carbon-based catalysts for electrocatalytic nitrate reduction to ammonia

Recent advances in carbon-based catalysts for electrocatalytic nitrate reduction to ammonia

The electrocatalytic reduction of nitrate to ammonia (NARR) using MOF-808 enhanced by the transition metal Fe (III) and H2PO4−/HPO42−

The combustion of fossil fuels has led to a surge in global CO2 emissions, causing environmental pollution and climate change issues that cannot be ignored. Ammonia, a green and carbon-free hydrogen energy, is emerging as a promising contender for new renewable fuels. Electrocatalytic nitrate-to-ammonia reduction reaction (NARR) is an emerging green synthesis method compared to the Haber-Bosch approach, and its performance is mainly controlled by selective hydrogenation. In this work, we report an efficient Fe@MOF-808-H2PO4−/HPO42− electrocatalyst (donated as Fe@MOF-808-P) for the electrocatalytic reduction of nitrate-to-ammonia. The results showed that the highest Faraday efficiency of NH3 (FENH3) is 90.8 ± 0.5 % at −0.9 V versus reversible hydrogen electrode (vs. RHE) in a 0.5 M potassium sulfate (K2SO4) solution containing nitrite (NO3−), the corresponding NH3 yield and specific activity are 420.4 ± 18.1 μmol h−1 cm−2 and 1035.9 ± 20.1 mgNH3 h−1 mgFe, respectively.Furthermore, a comparative analysis of the catalytic performance of Fe@MOF-808-H2O, MOF-808, MOF-808-P, and carbon cloth (CC) revealed that introducing P could accelerate the hydrogenation process of NO3− in the NARR process, confirming that Fe is the primary active center. Additionally, the cyclic electrolysis experiment demonstrated that the catalyst showed excellent stability. The results highlighted the promising potential of ammonia for future applications in renewable energy systems.

Single-, double-, and triple-atom catalysts on PC6 for nitrate reduction to ammonia: A computational screening

Single-atom catalysts (SACs) exhibit higher atomic utilization, while double-atom catalysts (DACs) and triple-atom catalysts (TACs) have an advantage due to the synergistic effect of multiple atomic centers. However, the current research on the mechanism of multiple-atom catalysts in electrocatalytic nitrate reduction to ammonia (NRA) remains insufficient. Herein, we investigated a series of homonuclear single-, double-, and triple-atom catalysts on carbon phosphide (PC6) monolayers (TMn@PC6, where TM = non-noble transition metals; n = 1, 2, or 3). The NRA activity of these catalysts was assessed by the density functional theory calculations, Co3@PC6 and Ru3@PC6 exhibit superior limiting potentials of −0.34 V and −0.36 V, respectively. Their capability to produce *H with optimal free energy on their surface enhances the electrochemical potential-determining step of *NO to *NOH while simultaneously inhibiting the hydrogen evolution reaction. The movement of the d-band center, induced by metal atom doping, regulates the adsorption strength of *NO, thus achieving a lower barrier for the hydrogenation step. This work provides theoretical guidance for the development of highly efficient multiple-atom catalysts for NRA.

Nickel-cobalt alloy nanosheet-decorated three-dimensional titanium dioxide nanobelts electrodeposited on titanium meshes for boosting selective nitrate electroreduction to ammonia

Electrocatalytic nitrate reduction reaction presents a promising avenue for environmentally friendly ammonia (NH3) synthesis and wastewater treatment. An essential aspect to consider is the meticulous design of electrocatalysts. This study explores the utilization of a Ni-Co alloy nanosheet-decorated three-dimensional titanium dioxide (3D-TiO2) nanobelts electrodeposited on titanium meshes (NixCoy@TiO2/TM) for efficient electrocatalytic NH3 production. The optimized Ni1Co3@TiO2/TM electrode achieves a significant NH3 yield of 676.3 ± 27.1 umol h−1 cm−2 with an impressive Faradaic efficiency (FE) of 95.1 % ± 2.1 % in a 0.1 M KOH solution containing 0.1 M NO3− at −0.4 V versus the reversible hydrogen electrode. Additionally, the electrode demonstrates exceptional electrochemical activity for NH3 synthesis in simulated wastewater, delivering an outstanding NH3 yield of 751.6 ± 44.3 umol h−1 cm−2 with a FE of 96.8 % ± 0.4 % at the same potential of −0.4 V. Moreover, the electrode exhibits minimal variation in current density, NH3 yields and FEs throughout the 24-h stability test and the 20-cycle test, demonstrating its excellent stability and durability. This study offers a straightforward electrodeposited approach for the development of 3D-nanostructured alloys as catalysts for NH3 electrosynthesis from nitrates at room temperature.

General synthesis of high-entropy single-atom nanocages for electrosynthesis of ammonia from nitrate

Given the growing emphasis on energy efficiency, environmental sustainability, and agricultural demand, there’s a pressing need for decentralized and scalable ammonia production. Converting nitrate ions electrochemically, which are commonly found in industrial wastewater and polluted groundwater, into ammonia offers a viable approach for both wastewater treatment and ammonia production yet limited by low producibility and scalability. Here we report a versatile and scalable solution-phase synthesis of high-entropy single-atom nanocages (HESA NCs) in which Fe and other five metals-Co, Cu, Zn, Cd, and In-are isolated via cyano-bridges and coordinated with C and N, respectively. Incorporating and isolating the five metals into the matrix of Fe resulted in Fe-C5 active sites with a minimized symmetry of lattice as well as facilitated water dissociation and thus hydrogenation process. As a result, the Fe-HESA NCs exhibited a high selectivity toward NH3 from the electrocatalytic reduction of nitrate with a Faradaic efficiency of 93.4% while maintaining a high yield rate of 81.4 mg h−1 mg−1.

Electrofiltration-Enabled Nitrate Reduction Reactivity of Carbon Nanotube Electrified Membrane for Drinking Water Treatment

Electrocatalytic nitrate reduction could enable nitrate removal in drinking water without generating concentrated waste streams. However, current processes heavily rely upon metal catalysts with high activity to achieve sufficient nitrate removal, which increases treatment costs and can inevitably lead to leaching of metals into treated water. In this study, we elucidate how electrified filtration enables sufficient nitrate conversion to meet drinking water standards in metal-free defective CNTs by tunable matching of mass transport and reaction timescales. The metal-free carbon nanotube (CNT)-based electrified membrane (EM) was employed as a porous flow-through cathode to decrease the diffusion boundary layer. Computational fluid dynamics simulations revealed that the flow-through mode mitigates diffusion limitations to enhance overall reaction activity, as compared to the conventional flow-by mode at the same flow rate. Additionally, the nitrate reduction rate could be tuned by controlling the nitrate advection rate using permeate flux (0 to 60 L h-1 m-2). A maximum removal efficiency of 86.9% was reached when the mass transport rate matched the reaction rate across a range of applied potentials. Furthermore, defects in CNTs were identified as the catalytic active sites. We employed density functional theory and molecular dynamics simulations to gain insight into CNT defect-catalyzed nitrate reduction under electrofiltration. Finally, the long-term stability, tolerance of environmental interferences, and sufficient nitrate removal and N2 selectivity to meet drinking water standards were demonstrated in synthetic surface water, suggesting that the CNT-EM and flow-through reactor may provide a promising solution for decentralized nitrate destruction in drinking water.

Mitigating Side Reactions in Electrocatalytic Ammonia Synthesis by Nitrate Reduction

Electrocatalytic nitrate reduction holds significant promise for generating green ammonia and mitigating pollution, reducing energy input, and exhibiting zero-carbon emissions. However, the intricate multiple electron and proton transfer processes complicate the pathways from nitrate to ammonia, hindering the development of electrocatalysts with high activity and selectivity for practical use. The primary side reactions, such as the conversion of nitrate to gaseous nitrogen species and the hydrogen reduction reaction, limit the Faradaic efficiency of nitrate-to-ammonia conversion. In this work, we have developed a controllable methodology for preparing highly active Cu-based nanocatalysts. These nanocatalysts exhibit remarkable activity and selectivity in the electrochemical nitrate reduction reaction within a flow-cell device, with a high ammonia yield and high Faradaic efficiency.