Electrocatalytic Reduction Of Nitrite Research Articles

Enhanced electrocatalytic nitrite reduction to ammonia over P-doped TiO2 nanobelt array

P-doped TiO2 nanobelt array supported on titanium plate acts as a high efficiency electrocatalyst for NO2− reduction reaction, attaining a satisfactory faradaic efficiency of 90.6% and a large NH3 yield as high as 560.8 μmol h−1 cm−2.

Ni nanoparticle-decorated biomass carbon for efficient electrocatalytic nitrite reduction to ammonia.

Electrocatalytic nitrite (NO2-) reduction to ammonia (NH3) can not only synthesize value-added NH3, but also remove NO2- pollutants from the environment. However, the low efficiency of NO2--to-NH3 conversion hinders its applications. Here, Ni nanoparticle-decorated juncus-derived biomass carbon prepared at 800 °C (Ni@JBC-800) serves as an efficient catalyst for NH3 synthesis by selective electroreduction of NO2-. This catalyst shows a remarkable NH3 yield of 4117.3 μg h-1 mgcat.-1 and a large faradaic efficiency of 83.4% in an alkaline electrolyte. The catalytic mechanism is further investigated by theoretical calculations.

A Keggin-type polyoxomolybdate-based crystalline material formed by hydrothermal transformation: photo/electro-catalytic properties and mechanism study

This study constructs a POM-based crystalline material of [(SiMo12O40)Cu6(2,2′-bipy)6(Mo6O22)] (1). The photocatalytic MB degradation and electrocatalytic nitrite reduction properties of complex 1 are systematically studied for the first time.

Ambient ammonia production via electrocatalytic nitrite reduction catalyzed by a CoP nanoarray

Ambient ammonia production via electrocatalytic nitrite reduction catalyzed by a CoP nanoarray

Scalable Reactor Design for Electrocatalytic Nitrite Reduction with Minimal Mass Transfer Limitations

A parallel-plate thin-layer (PPTL) flow reactor with potential control and custom-made cathode of Pd–In modified activated carbon cloth was developed for electrocatalytic removal of nitrite from water; the effect of applied potential and flow rate were investigated. Compared to other reactors in the literature, rapid nitrite reduction (first-order rate constant is 0.38 L gPd–1 min–1), high current efficiency (CE, 51%), and low ammonium selectivity (5.4%) were observed at an applied potential of −0.60 V vs the Ag/AgCl reference electrode (RE) and a flow rate of 40 mL min–1 in a phosphate buffer solution of pH 6.5. Slightly faster kinetics were observed at more negative potentials (0.57 L gPd–1 min–1 at −1.0 V/RE), but then ammonium production (88%), H2 gas evolution (E0 = −0.61 V/RE), and current loss (CE < 10%) became problematic. Nitrite reduction was measured in the PPTL flow reactor for almost 50 2 h cycles over six months, with little apparent loss (30%) in activity. A reactive transport model was developed and used to simulate the kinetic data. The fitted intrinsic rate constant (kw) was 5.2 × 10–6 m s–1, and ratios of dimensionless Nusselt numbers to reaction rate constant values support the reactor being more reaction than mass transfer limited. Application of the parametrized model demonstrated how the PPTL reactor could be scaled (e.g., cathode dimensions, flow channel thickness), operated (i.e., flow rate), or modified (i.e., greater intrinsic catalyst activity) to most efficiently remove nitrite from larger flow streams.

Antioxidative metallic copper nanoparticles prepared by modified polyol method and their catalytic activities

In this study, antioxidant copper nanoparticles (CuNPs) were prepared by the modified polyol method using polyvinylpyrrolidone (PVP) and L-ascorbic acid as protective agents. The CuNPs with diameters of 61 ± 12 nm were coated with 8-nm-thick PVP coating and showed excellent resistance to chemical oxidation and coagulation for more than 160 days in ethylene glycol solution. The unique catalytic properties of CuNPs that do not appear in normal CuO or Cu2O nanoparticles are due to the properties of metallic copper elements. The CuNPs exhibited prolonged catalytic activity toward the chemical reduction of 4-nitrophenol as well as the excellent electrocatalytic reduction of nitrite (NO2−), suggesting an efficient electrochemical sensor for nitrite determination.

Syntheses, Crystal Structure, Electrocatalytic, and Magnetic Properties of the Monolanthanide-Containing Germanotungstates [Ln(H2O) n GeW11O39]5- (Ln = Dy, Er, n = 4,3).

Two monolanthanide-containing polyanions based on monolacunary Keggin germanotungstates [Ln(H2O)nGeW11O39]5– (Ln = Dy, Er, n = 4,3) have been synthesized in simple one-pot synthetic procedure and compositionally characterized in solid state by single-crystal X-ray diffraction, powder X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, and elemental analysis. Electronic absorption and emission spectra of the title compounds in solution were also studied. The [DyIII(H2O)4GeW11O39]5– Keggin POM exhibits a slow relaxation of magnetization. The cyclic voltammetry measurements and mass spectrometry were carried out to check the stability of the compounds in solution. Both polyanions prove efficient in the electrocatalytic reduction of nitrite. To our knowledge, this observation establishes the first example of electrocatalysis of nitrite reduction by all inorganic monolanthanide-containing germanotungstates family.

Proton-Coupled-Electron Transfer Enhances the Electrocatalytic Reduction of Nitrite to NO in a Bioinspired Copper Complex

The selective and efficient electrocatalytic reduction of nitrite to nitric oxide (NO) is of tremendous importance, both for the development of NO-release systems for biomedical applications and for the removal of nitrogen oxide pollutants from the environment. In nature, this transformation is mediated by (amongst others) enzymes known as the copper-containing nitrite reductases. The development of synthetic copper complexes that can reduce nitrite to NO has therefore attracted considerable interest. However, there are no studies describing the crucial role of proton-coupled-electron transfer during nitrite reduction when using such synthetic complexes. In this talk, I will describe a system for the electrocatalytic reduction of nitrite to NO in which the role of proton-relaying units in the secondary coordination sphere of the metal can be probed for the first time (ACS Catal. 2018, 8, 5070–5084). Our results suggest that positioning a pendant carboxylate group in close proximity to the copper centre gives an electrocatalyst that is twice as effective for nitrite reduction than the analogous compound that lacks such a proton-relaying moiety. These results highlight the critical role of proton-coupled-electron transfer in the reduction of nitrite to NO and have important implications for the design of biomimetic catalysts for the selective interconversions of the nitrogen oxides. Figure 1

Nitric Oxide Generation On Demand for Biomedical Applications via Electrocatalytic Nitrite Reduction by Copper BMPA- and BEPA-Carboxylate Complexes.

Intravascular (IV) catheters are essential devices in the hospital that are used to monitor a patient's blood and for administering drugs or nutrients. However, IV catheters are also prone to blood clotting at the point of insertion and infection by formation of robust bacterial biofilms on their surface. Nitric oxide (NO) is ideally suited to counteract both of these problems, due to its antimicrobial properties and its ability to inhibit platelet activation/aggregation. One way to equip catheters with NO releasing properties is by electrocatalytic nitrite reduction to NO by copper complexes in a multi-lumen configuration. In this work, we systematically investigate six closely related Cu(II) BMPA- and BEPA-carboxylate complexes (BMPA = bis-(2-methylpyridyl)amine); BEPA = bis-(2-ethylpyridyl)amine), using carboxylate groups of different chain lengths. The corresponding Cu(II) complexes were characterized using UV-Vis, EPR spectroscopy, and X-ray crystallography. Using detailed cyclic voltammetry (CV) and bulk electrocatalyic studies (with real-time NO quantification), in aqueous buffer, pH 7.4, we are able to derive clear reactivity relations between the ligand structures of the complexes, their Faradaic efficiencies for NO generation, their turnover frequencies (TOFs), and their redox potentials. Our results show that the complex [Cu(BEPA-Bu)](OAc) is the best catalyst with a high Faradaic efficiency over large nitrite concentration ranges and the expected best tolerance to oxygen levels. For this species, the more positive redox potential suppresses NO disproportionation, which is a major Achilles heel of the (faster) catalysts with the more negative reduction potentials.

Intramolecular Hydrogen Bonding Facilitates Electrocatalytic Reduction of Nitrite in Aqueous Solutions.

This work reports a combined experimental and computational mechanistic investigation into the electrocatalytic reduction of nitrite to ammonia by a cobalt macrocycle in an aqueous solution. In the presence of a nitrite substrate, the Co(III) precatalyst, [Co(DIM)(NO2)2]+ (DIM = 2,3-dimethyl-1,4,8,11-tetraazacyclotetradeca-1,3-diene), is formed in situ. Cyclic voltammetry and density functional theory (DFT) calculations show that this complex is reduced by two electrons, the first of which is coupled with nitrite ligand loss, to provide the active catalyst. Experimental observations suggest that the key N-O bond cleavage step is facilitated by intramolecular proton transfer from an amine group of the macrocycle to a nitro ligand, as supported by modeling several potential reaction pathways with DFT. These results provide insights into how the combination of a redox active ligand and first-row transition metal can facilitate the multiproton/electron process of nitrite reduction.

Synthesis, Crystal Structure, Electrochemistry and Electro-Catalytic Properties of the Manganese-Containing Polyoxotungstate, [(Mn(H2O)3)2(H2W12O42)]6−

We present the synthesis and structural characterization of the manganese-containing polyoxotungstate, [(Mn(H2O)3)2(H2W12O42)]6− (1), obtained by reaction of MnCl2 with six equivalents of Na2WO4 in the presence of Zn(CH3COO)2 in acetate medium (pH 4.7). This has been assessed by various techniques (FTIR, TGA, UV-Visible, XPS, elemental analysis, single crystal X-ray and electrochemistry). Single-crystal X-ray analyses showed that, in the solid state, 1 forms a 2-D network in which [H2W12O42]10− fragments are linked in pairs via Mn2+ ions, leading to linear chains of the form [(Mn(H2O)3)2(H2W12O42)]n6n−. The connection between chains occurs also via Mn2+ ions which bind [H2W12O42]10− fragments belonging to two adjacent chains, forming an infinite 2-D network. A complete electrochemical study was done in aqueous solution where 1 is stable in the pH range 1 to 6. This complex undergoes multiple electron-transfer processes that lead to the electro-generation of manganese high oxidation state species that catalyse water electro-oxidation. 1 is also effective in the electro-catalytic reduction of nitrite and dioxygen.

Bifunctional Electro-Catalysts Stemmed from Ln-Substituted Monovacant/Saturated Keggin Polyoxotungstates and Cu-Terpyridine Chlorides

Three inorganic–organic hybrids based on monovacant/saturated polyoxotungstates and 3d-4f metal chlorides: [Cu2(tpy)2][Sm(H2O)3K(α-HSiW11O39)]Cl·2H2O (1), [Cu2(tpy)2][Eu(H2O)3K(α-HSiW11O39)]Cl·2H2O (2), Cu4Cl4(tpy)4(α-SiW12O40)]·2H2O (3), (tpy = 2,2′:6′,2″-terpyridine), were fabricated in the same POW/Ln/Cu-tpy reaction systems by adjusting pH. Compounds 1 and 2 display 1D circle-connecting-circle chain structure featured by {Ln–α–SiW11} polyoxoanion clusters and {Cu/tpy} units. Compound 3 with 3D supramolecular structure consists of saturated α-SiW12 clusters and [Cu2Cl2(tpy)2]2+ motifs. Compounds 1–3 exhibit bifunctional electro-catalytic behaviors for not merely reduction of nitrite but also oxidation of ascorbic acid. Electrocatalytic tests make clear that Sm-substituted hybrid based on POWs exhibits better activity than that for Eu-substitued/statured Keggin hybrids for electrocatalytic reduction of nitrite, statured Keggin hybrid shows better electro-catalytic performance for oxidations of ascorbic acid than those for Ln-substituted hybrids. The differences of electro-catalytic performances among three hybrids should be attributing to the distinctions of structures and electrochemical properties. Three inorganic-organic hybrids based on monovacant/saturated polyoxotungstates and 3d–4f metal chlorides were fabricated in the same POM/Ln/Cu-tpy reaction systems by adjusting pH. Compounds 1 and 2 display 1D circle-connecting-circle chain structure featured by {Ln–α–SiW11} polyxoanion clusters and {Cu/tpy} units, Compound 3 with 3D supramolecular structure consists of saturated α-SiW12 clusters and [Cu2Cl2(tpy)2]2+ motifs. Cyclic voltammetries of n-CPEs (n = 1–3) displayed bifunctional electrocatalytic activities toward reduction of nitrite and oxidation of ascorbic acid.

Proton-Coupled Electron Transfer Enhances the Electrocatalytic Reduction of Nitrite to NO in a Bioinspired Copper Complex

The selective and efficient electrocatalytic reduction of nitrite to nitric oxide (NO) is of tremendous importance, both for the development of NO-release systems for biomedical applications and for the removal of nitrogen oxide pollutants from the environment. In nature, this transformation is mediated by (among others) enzymes known as the copper-containing nitrite reductases. The development of synthetic copper complexes that can reduce nitrite to NO has therefore attracted considerable interest. However, there are no studies describing the crucial role of proton-coupled electron transfer during nitrite reduction when such synthetic complexes are used. Herein, we describe the synthesis and characterization of two previously unreported Cu complexes (3 and 4) for the electrocatalytic reduction of nitrite to NO, in which the role of proton-relaying units in the secondary coordination sphere of the metal can be probed. Complex 4 bears a pendant carboxylate group in close proximity to the copper center, whi...

Selective Electrocatalytic Reduction of Nitrite to Dinitrogen Based on Decoupled Proton-Electron Transfer.

The development of denitrification catalysts which can reduce nitrate and nitrite to dinitrogen is critical for sustaining the nitrogen cycle. However, regulating the selectivity has proven to be a challenge, due to the difficulty of controlling complex multielectron/proton reactions. Here we report that utilizing sequential proton-electron transfer (SPET) pathways is a viable strategy to enhance the selectivity of electrochemical reactions. The selectivity of an oxo-molybdenum sulfide electrocatalyst toward nitrite reduction to dinitrogen exhibited a volcano-type pH dependence with a maximum at pH 5. The pH-dependent formation of the intermediate species (distorted Mo(V) oxo species) identified using operando electron paramagnetic resonance (EPR) and Raman spectroscopy was in accord with a mathematical prediction that the pKa of the reaction intermediates determines the pH-dependence of the SPET-derived product. By utilizing this acute pH dependence, we achieved a Faradaic efficiency of 13.5% for nitrite reduction to dinitrogen, which is the highest value reported to date under neutral conditions.

Organic–inorganic hybrids based on polyoxometalates and copper coordination complexes

Two new hybrids based on Keggin polyoxometalates have been hydrothermally synthesized and characterized by elemental analysis, IR spectroscopy, TG analysis, and single-crystal X-ray diffraction. The crystal structure analyses reveal that complex 1 has an infinite 1D chain structure, constructed from [Cu(2,2′-bpy)(4,4′-bpy)(H2O)] fragments and [H2PMo11VO40]2− building blocks. Complex 2 has a 2D molecular ladder structure, with a basic structural unit composed of one bis(µ-OH) dicopper(II) [Cu2(OH)2(H2O)2(4,4′-bpy)3] fragment, one [HPMo12O40], and four water molecules. The [Cu2(OH)2(H2O)2(4,4′-bpy)3] units connect alternately to form edge rails. The [HPMo12O40] clusters act as rungs of the ladder, linking pairs of Cu atoms from the two adjacent edge rails. The electrochemical behavior of the complexes in modified carbon paste electrodes and their electrocatalytic reduction of nitrite were investigated.

Enhancing sensitivity of hemoglobin-based electrochemical biosensor by using protein conformational intermediate

Redox proteins-based electrochemical biosensors possess high selectivity and biological compatibility but suffer from the low voltammetric response because of the deep bury of heme groups in proteins. Herein, conformational intermediate based on accurately modulating three-dimensional structure of hemoglobin (Hb) was proposed to construct an electrochemical biosensor for improving the response sensitivity. Hb was entrapped in dimethyldidodecylammonium bromide (DDAB) film to modify glassy carbon electrode (DDAB/Hb/GCE). The unfolding processes of Hb were then monitored by UV–vis spectroscopy, fluorescence, circular dichroism, and electrochemistry to obtain the appropriate conditions for maintaining intermediate. Under the optimized conditions, the sensor exhibited accelerated direct electron transfer and high sensitivity for sensing hydrogen peroxide (H2O2) and nitrite (NaNO2). The sensitivities for detecting H2O2 and NaNO2 were improved as 2.3 and 4.4 times higher than those on the native DDAB/Hb/GCE. The electrocatalytic reduction of nitrite showed a wider linear range from 0 to 225.0μM with a high sensitivity of 0.4731μAμM−1 and a low limit of detection of 0.069μM. The unfolded Hb-based sensor possesses the advantages of excellent stability, good reproducibility, and satisfactory recovery. The results provide a new strategy to utilize the unique properties of proteins intermediate in the development of electrochemical biosensors.

Synthesis, characterization, magnetic and electrochemical properties of a new 3D hexa-copper-substituted germanotungstate

An inorganic–organic hybrid hexa-copper-substituted germanotungstate Na{sub 2}[Cu(dap){sub 2}]{sub 2}[Cu(dap){sub 2}] ([Cu{sub 6}(H{sub 2}O){sub 2}(dap){sub 2}][B-α-GeW{sub 9}O{sub 34}]{sub 2})·4H{sub 2}O (1) (dap=1,2-diaminopropane) has been hydrothermally prepared and characterized by elemental analyses, inductively coupled plasma atomic emission spectrometry (ICP–AES) analyses, IR spectra, powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA) and single-crystal X-ray diffraction. 1 displays the six-connected 3D network with the long topological (O′Keefe) vertex symbol is 4·4·6{sub 4}·4·4·4·4·6{sub 4}·4·4·4·6{sub 4}·4·4·4 and the short vertex (Schlafli) symbol of 4{sup 12}6{sup 3}. Magnetic measurements indicate that there are the overall ferromagnetic exchange interactions in the belt-like hexa-Cu{sup II} cluster in 1. Furthermore, the electrochemical behavior and electrocatalysis of 1 modified carbon paste electrode (1-CPE) have been studied. The reductions of nitrite, bromate and hydrogen peroxide are principally mediated by the W{sup VI}-based wave. - Graphical abstract: A hexa-Cu{sup II} sandwiched germanotungstate has been synthesized and structurally characterized. The magnetic, solid-state electrochemical and electrocatalytic properties have been investigated. Display Omitted - Highlights: • Transition-metal substituted polyoxometalates. • Hexa-copper-substituted germanotungstate. • Six-connected 3D network. • Electrocatalytic reduction of nitrite, bromate and hydrogen peroxide.

Efficient electrocatalytic reduction of nitrite species on zeolite modified electrode with Cu-ZSM-5

The electrocatalytic reduction of nitrite has been studied on the surface of zeolite modified electrode using exchanged ZSM-5 with copper (ME/Cu-ZSM-5). The process of reduction and kinetics studies were investigated through cyclic voltammetry and chronoamperometry techniques. The i-E characteristics of ME/Cu-ZSM-5 presented the faradic process associated to redox couple Cu2+/Cu+ with a ΔE=0.064V/SCE. On the other hand, voltammetric studies showed that in presence of nitrite, the cathodic peak current of ME/Cu-ZSM-5 increases followed by a decrease in the corresponding anodic current. This indicated that nitrite species were reduced by a cooperative effect of the acidic properties of zeolite and copper that acts as a redox mediator being immobilized on the electrode surface via an electrocatalytic mechanism. Further experiments showed that electrocatalytic activity increases as Si/Al ratio decreases, the electrocatalytic activity was improved when the material Cu-ZSM-5 was calcined prior to electrode preparation. The values of the rate constant of the catalytic reduction of nitrite and the detection limit obtained were 5.9×102cm3mol−1s−1 and 1.4×10−5molL−1, respectively.

A novel and simple electrochemical sensor for electrocatalytic reduction of nitrite and oxidation of phenylhydrazine based on poly (o-anisidine) film using ionic liquid carbon paste electrode

In this study, nitrite electroreduction and phenylhydrazine electrooxidation were investigated on poly(o-anisidine) formed by cyclic voltammetry at the surface of ionic liquid carbon paste electrode. The films were characterized by cyclic voltammetry and scanning electron microscopy (SEM) and were contrasted with poly(o-anisidine) prepared under identical conditions in the absence of ionic liquid in carbon paste electrode. This carbon paste modified electrode exhibits a good electrocatalytic capability (via an EC’ mechanism) for both electrooxidation and electroreduction of some important molecules. The obtained results showed that the catalytic oxidation peak currents of phenylhydrazine and catalytic reduction peak currents of nitrite at the surface of this simple (unfunctionalized) polymeric electrode were linearly dependent on their concentrations. Electrode was successfully applied for determination of nitrite and phenylhydrazine in real samples.

A new Wells-Dawson polyoxometalate-based metal-organic hybrid decorated by the flexible bis-pyridyl-bis-amide ligand

A new Wells-Dawson polyoxometalate-based compound, H[Cu(L) 2 (P 2 W 18 O 62 ) 0.5 ]·~ 3H 2 O ( 1 ) (L = N,N′-bis(3-pyridinecarboxamide)-1,6- hexane), has been hydrothermally synthesized. Compound 1 is a 2D network based on [P 2 W 18 O 62 ] 6 − polyanion and nonparallel 1D Cu(L) 2 polymer chain constructed from two types of bi-nuclear circles alternately arraying with the dihedral angle of 34.75°. Compound 1 represents the first example of 2D Wells-Dawson POM-based compound constructed from the flexible bis-pyridyl-bis-amide ligand. Moreover, the electrochemical behavior, luminescent property and photocatalytic activity of 1 have been investigated. By introducing the N,N′-bis(3-pyridinecarboxamide)-1,6-hexane (L) in Wells-Dawson type polyoxometalate system, a new 2D inorganic–organic hybrid H[Cu(L) 2 (P 2 W 18 O 62 ) 0.5 ]·~ 3H 2 O was obtained, which represents the first example by combining the Wells-Dawson polyoxometalate with the flexible bis-pyridyl-bis-amide ligand. The title compound shows excellent activity in electrocatalytic reduction of nitrite and photocatalytic degradation of MB. ► Flexible bis-pyridyl-bis-amide was first introduced into the Wells-Dawson POM system. ► A new 2D inorganic–organic hybrid was constructed from [P 2 W 18 O 62 ] 6 − and 1D Cu(L) 2 chain. ► The 1D Cu(L) 2 chain is formed by the alternate arrangement of two types of bi-nuclear circles. ► The compound shows excellent electrocatalytic and photocatalytic activities.