Electroreduction Of Oxide Research Articles

Electron-deficient Cuδ+ stabilized by interfacial Cu–O-Al bonding for accelerating electrocatalytic nitrate conversion

Electrocatalytic nitrate reduction to NH3 not only enables the recycling of nutrients from nitrate wastewater but can also lead to complete nitrogen elimination when paired with an NH3 oxidation reaction to achieve innocuous N2. Albeit electron-deficient copper (Cuδ+) is an active catalytic site for an electrocatalytic nitrate reduction reaction (ENRR), its stabilization under the reductive polarization potential of ENRR is challenging. Herein, we report the in-situ electroreduction of CuAl-mixed oxide to construct a Cu-Al2O3 interface with strong metal-support interactions (CuAl-LDO-r), which can form and stabilize Cuδ+via Cu–O-Al bonds. The batch ENRR tests revealed that Cu52Al48-LDO-r delivers an NH3-N selectivity of 97.4%, stable specific activity of 661.6 mg-N m-2h−1 for NH3-N production (faradaic current efficiency of 70.4%), and minimal Cu leaching when reducing 22.5 mg L-1 NO3–-N at −1.10 V vs. Ag/AgCl, outperforming most of the reported catalysts under similar reaction conditions. Combined in-situ spectrometric analyses and theoretical calculations demonstrate that the robust performance of Cuδ+ originates from its substantial affinity toward the N-intermediates, which promotes molecule activation and prevents intercoupling to dinitrogen species. For nitrate elimination, the ENRR was coupled with an anode-driven breakpoint chlorination reaction, and the designed system enabled complete conversion of NO3–-N (44.5 mg L-1) to N2 with an electrical consumption of 1.82 kwh molN-1.

Reduced Graphene Oxide/Poly(2-Aminopyridine) Modified Molecularly Imprinted Glassy Carbon Electrode (GCE) for the Determination of Kanamycin in Milk and Pork by Differential Pulse Voltammetry (DPV)

Kanamycin (KAN) is a widely used aminoglycoside antibiotic that has attracted attention due to its presence in food and the environment. In order to obtain a simple, rapid, and sensitive method for kanamycin, an electrochemical sensor was fabricated by successively modifying a glassy carbon electrode (GCE) with reduced graphene oxide (rGO), poly(2-aminopyridine) (pAP) film, and a KAN molecularly imprinted membrane (KAN-MIM) that was prepared by electroreduction of graphene oxide and the electropolymerization of 2-aminopyridine and dopamine. The morphology and electrochemical parameters were characterized for the sensor designated by KAN-MIM/pAP/rGO/GCE. As a result of the amplification of the modified electrode, excellent analytical performance was obtained on the bases of sensitivity, selectivity, repeatability, and stability. The linear range and limit of detection for kanamycin were from 0.02 to 250.0 μmol·L−1 and 7.0 nmol·L−1, respectively. The sensor was employed to determine KAN in pork and milk with recoveries from 89.2% to 109.0% and a relative standard deviation less than 6.0%.

Efficient nitric oxide electroreduction toward ambient ammonia synthesis catalyzed by a CoP nanoarray

A CoP nanoneedle array supported on Ti mesh acts as a high-active electrocatalyst with a low onset potential toward NO-to-NH3 conversion, achieving a faradaic efficiency of 88.3% and a yield of 47.22 μmol h−1 cm−2.

Insights from Operando and Identical Location (IL) Techniques on the Activation of Electrocatalysts for the Conversion of CO₂: A Mini-Review.

In this mini-review we compare two prototypical metal foam electrocatalysts applied to the transformation of CO₂ into value-added products (e.g. alcohols on Cu foams and formate on Bi foams). A substantial improvement in the catalyst performance is typically achieved through thermal annealing of the as-deposited foam materials, followed by the electro-reduction of the pre-formed oxidic precursors prior or during the actual CO₂ electrolysis. Utilizing highly insightful and sensitive complementary operando analytical techniques (XAS, XRD, and Raman spectroscopy) we demonstrate that this catalyst pre-activation process is entirely accomplished in case of the oxidized Cu foams prior to the formation of hydrocarbons and alcohols from the CO₂. The actually active catalyst is therefore the metallic Cu derived from the precursor by means of oxide electro-reduction. Conversely, in their oxidic form, the Cu-based foam catalysts are inactive towards the CO₂ reduction reaction (denoted ec-CO₂ RR). Oxidized Bi foams can be regarded as an excellent counter example to the above-mentioned Cu case as both metallic and the thermally derived oxidic Bi foams are highly active towards ec-CO₂ RR (formate production). Indeed, operando Raman spectroscopy reveals that CO₂ electrolysis occurs upon its embedment into the oxidic Bi₂O₃ foam precursor, which itself undergoes partial transformation into an active sub-carbonate phase. The potential-dependent transition of sub-carbonates/oxides into the corresponding metallic Bi foam dictates the characteristic changes of the ec-CO₂ RR pathway. Identical location (IL) microscopic inspection of the catalyst materials, e.g. by means of scanning electron microscopy, demonstrates substantial morphological alterations on the nm length scale on the material surface as consequence of the sub-carbonate formation and the potential-driven oxide reduction into the metallic Bi foam. The foam morphology on a mesoscopic length scale (macroporosity) remains, by contrast, fully unaffected by these phase transitions.

Associative vs. dissociative mechanism: Electrocatalysis of nitric oxide to ammonia

Nitric oxide reduction to ammonia by electrocatalysis is the potential application in the elimination of smog and energy conversion. In this work, the feasibility of the application of two-dimensional metal borides (MBenes) in nitric oxide electroreduction reaction (NOER) was investigated through density functional theory calculations. Including the geometry and electronic structure of five kinds of MBenes, the adsorption of NO on the surface of these substrates, the selective adsorption of hydrogen protons during the hydrogenation process, and the overpotential in the electrocatalytic ammonia synthesis process. As a result, MnB exhibited the most favorable catalytic performance according to the associative pathways, which is thermodynamically performed spontaneously, and WB has a minimum overpotential of 0.37 V vs. RHE in the process of ammonia production according to the dissociative pathway. Overall, our work is the first to explore the electrocatalytic NO through the dissociative mechanism to synthesize ammonia in-depth and proves that MBenes are efficient NO electrocatalytic ammonia synthesis catalysts. These research results provide a new direction for the development of electrocatalytic ammonia synthesis experimentally and theoretically.

NO Electroreduction by Transition Metal Dichalcogenides with Chalcogen Vacancies

AbstractNitric oxide electroreduction reaction (NOER) is one of the most attractive routes for ammonia synthesis and NOx‐related pollutant treatment. However, current research on NOER catalysts mainly focus on noble metals and single atom catalysts, while low‐cost transition metal dichalcogenides (TMDs) are rarely considered, let alone their product selectivity. Herein, using first‐principles calculations, we systematically investigate the performance of a series of single‐layer TMDs (MoS2, MoSe2, MoTe2, TaTe2 and WTe2) in the 1T’ phase as electrocatalysts for NOER. Our results reveal that defective 1T’‐MoS2 and 1T’‐MoSe2 monolayers (with the most common sulphur and selenium vacancies, respectively) exhibit excellent activity for NOER as well as high selectivity for ammonia, which can be correspondingly yielded at 0 and −0.06 V potentials, comparable to the best Pt‐based and single atom catalysts. Furthermore, these two catalysts efficiently suppress the competing hydrogen evolution reaction (HER). Thus, single‐layer TMDs synthesized with chalcogen vacancies may serve as efficient catalysts for electrochemical ammonia synthesis from pollutants and electrocatalytic denitrification.

Promoting nitric oxide electroreduction to ammonia over electron-rich Cu modulated by Ru doping

Promoting nitric oxide electroreduction to ammonia over electron-rich Cu modulated by Ru doping

Transition-Metal Borides (MBenes) as New High-Efficiency Catalysts for Nitric Oxide Electroreduction to Ammonia by a High-Throughput Approach.

Here, the authors performed density functional theory calculations to study the catalytic performance of the nitric oxide reduction reaction (NORR) via a series of transition metal borides (MBenes). This work screened the M2 B2 type MBenes from the IVB to V transition metals from the periodic table and systematically probed the catalytic activity and selectivity for the NORR process. It has been reported that Fe2 B2 , Mn2 B2 , and Rh2 B2 can be high-performance catalysts for converting NO to NH3 with smaller limiting potentials than other MBenes, and Nb2 B2 and Hf2 B2 have low limiting potentials of -0.11 V and -0.17 V for the NO production of NH3 . The binding energy of ΔG*N can be a good descriptor of catalytic performance and is determined by the volcano plot of the rate-determining step. The reaction mechanisms for NO reduction to NH3 , N2 , and N2 O have been studied in detail, atomic *N can interact with another *N or one *NO molecule to form N2 and N2 O via two successive hydrogenations. In this regard, *NO hydrogenation to *NOH has a lower formation energy than *HNO, and the MBenes have high selectivity for promoting the NORR and suppressing the hydrogen evolution reaction competition process.

Electro-reduced graphene oxide nanosheets coupled with RuAu bimetallic nanoparticles for efficient hydrogen evolution electrocatalysis

• One-step electroreduction method was used for RuAu-RGO catalyst preparation. • Homogeneously anchored RuAu nanoparticle on RGO sheets show excellent HER activity. • Catalyst showed strong electronic coupling interaction between Ru, Au, and RGO. • In Zn-CO 2 cell system, catalyst showed low overpotential. Electrocatalytic Hydrogen Evolution Reaction (HER) in water electrolysis holds a great promise for sustainable hydrogen production but the preparation of an efficient and stable catalyst is remained challenging. Herein, a simple one-step simultaneous electro-reduction of graphene oxide, ruthenium chloride, and gold chloride precursors without involving any pre-/or post- mechanical, hydrothermal, or carbonization step, is reported to prepare homogeneously anchored ruthenium (Ru) and gold (Au) nanoparticles on reduced graphene oxide (RGO) as an efficient electrocatalyst for HER. The highly dispersed RuAu bimetallic nanoparticles on RGO sheets induce faster reaction kinetics with high turnover frequency, associating with strong electronic coupling interaction between RGO, Ru, and Au nanoparticles which improve the intrinsic HER activity of the catalyst as revealed by combined experimental and theoretical results. The as prepared RuAu-RGO catalyst demonstrates excellent HER activity with an overpotential of 56 mV at the current density of 10 mA cm −2 outperforming the monometallic Ru-RGO and Au-RGO catalysts in 1 M KOH solution. The RuAu-RGO catalyst exhibits utmost stability in the practical water splitting, far surpassing the benchmark Pt/C-IrO 2 system. Furthermore, the catalyst was employed as a cathode coupling with zinc (Zn) anode in an aqueous Zn-CO 2 system to generate hydrogen, it demonstrated positive shift in the onset potential of HER by 0.24 V than for HER in typical three-electrode testing configuration broadening its applicability.

Vacancy-triggered and dopant-assisted NO electrocatalytic reduction over MoS2.

Nitric oxide electroreduction reaction (NOER) is an efficient method for NH3 synthesis and NOx-related pollutant treatment. However, current research on NOER catalysts mainly focuses on noble metals and single atom catalysts, while low-cost transition metal dichalcogenides (TMDCs) are rarely considered. Herein, by applying density functional theory (DFT) calculations, we study the catalytic performance of NOER over 2H-MoS2 monolayers with the most common S vacancies and some Mo atoms substituted by transition metal atoms (denoted as TM-MoS2@VS). Our results show that an S vacancy and a heteroatom substitution tend to form a first nearest neighbour (1NN) pair, which greatly improves the NOER catalytic performance of 2H-MoS2. The S vacancy site can trigger NOER by strongly adsorbing a NO molecule and elongating the NO bond, while the heteroatom dopant can assist NOER by tuning the electron donating capability of 2H-MoS2 which breaks the linear scaling relations among key reaction intermediates. At low NO coverage, NH3 can be correspondingly yielded at -0.06 and -0.38 V onset potentials over the Pt- and Au-doped MoS2 catalysts with S vacancies (Pt-MoS2@VS and Au-MoS2@VS). At high NO coverage, N2O/N2 is thermodynamically favored. Meanwhile, the competing hydrogen evolution reaction (HER) is suppressed. Thus, the Pt-MoS2@VS catalysts are promising candidates for NOER. In addition, coupling the substitutional doping of Mo atoms to S vacancies presents great potential in improving the catalytic activity and selectivity of MoS2 for other reactions. In general, the strategy of coupling hetero-metal doping and chalcogen vacancy can be extended to enhance the catalytic activity of other TMDCs.

Role of OH Intermediates during the Au Oxide Electro-Reduction at Low pH Elucidated by Electrochemical Surface-Enhanced Raman Spectroscopy and Implicit Solvent Density Functional Theory.

Molecular understanding of the electrochemical oxidation of metals and the electro-reduction of metal oxides is of pivotal importance for the rational design of catalyst-based devices where metal(oxide) electrodes play a crucial role. Operando monitoring and reliable identification of reacting species, however, are challenging tasks because they require surface-molecular sensitive and specific experiments under reaction conditions and sophisticated theoretical calculations. The lack of molecular insight under operating conditions is largely due to the limited availability of operando tools and to date still hinders a quick technological advancement of electrocatalytic devices. Here, we present a combination of advanced density functional theory (DFT) calculations considering implicit solvent contributions and time-resolved electrochemical surface-enhanced Raman spectroscopy (EC-SERS) to identify short-lived reaction intermediates during the showcase electro-reduction of Au oxide (AuOx) in sulfuric acid over several tens of seconds. The EC-SER spectra provide evidence for temporary Au-OH formation and for the asynchronous adsorption of (bi)sulfate ions at the surface during the reduction process. Spectral intensity fluctuations indicate an OH/(bi)sulfate turnover period of 4 s. As such, the presented EC-SERS potential jump approach combined with implicit solvent DFT simulations allows us to propose a reaction mechanism and prove that short-lived Au-OH intermediates also play an active role during the AuOx electro-reduction in acidic media, implying their potential relevance also for other electrocatalytic systems operating at low pH, like metal corrosion, the oxidation of CO, HCOOH, and other small organic molecules, and the oxygen evolution reaction.

Bilirubin oxidase oriented on novel type three-dimensional biocathodes with reduced graphene aggregation for biocathode

Aggregation of reduced graphene oxide (RGO) due to π-π stacking is a recurrent problem in graphene-based electrochemistry, decreasing the effective working area and therefore the performance of the RGO electrodes. Dispersing RGO on three-dimensional (3D) carbon paper electrodes is one strategy towards overcoming this challenge, with partial relief aggregation. In this report, we describe the grafting of negatively charged 4-aminobenzoic acid (4-ABA) onto a graphene functionalized carbon paper electrode surface. 4-ABA functionalization induces separation of the RGO layers, at the same time leading to favorable orientation of the blue multi-copper enzyme Myrothecium verrucaria bilirubin oxidase (MvBOD) for direct electron transfer (DET) in the dioxygen reduction reaction (ORR) at neutral pH. Simultaneous electroreduction of graphene oxide to RGO and covalent attachment of 4-ABA are achieved by applying alternating cathodic and anodic electrochemical potential pulses, leading to a high catalytic current density (Δjcat:193 ± 4 μA cm−2) under static conditions. Electrochemically grafted 4-ABA not only leads to a favorable orientation of BOD as validated by fitting a kinetic model to the electrocatalytic data, but also acts to alleviate RGO aggregation as disclosed by scanning electron microscopy, most likely due to the electrostatic repulsion between 4-ABA-grafted graphene layers. With a half-lifetime of 55 h, the bioelectrode also shows the highest operational stability for DET-type MvBOD-based bioelectrodes reported to date. The bioelectrode was finally shown to work well as a biocathode of a membrane-less glucose/O2 enzymatic biofuel cell with a maximum power density of 22 μW cm−2 and an open circuit voltage of 0.51 V.

Direct and Scalable Electroreduction of Triphenylphosphine Oxide to Triphenylphosphine

The direct and scalable electroreduction of triphenylphosphine oxide (TPPO)-the stoichiometric byproduct of some of the most common synthetic organic reactions-to triphenylphosphine (TPP) remains an unmet challenge that would dramatically reduce the cost and waste associated with performing desirable reactions that are mediated by TPP on a large scale. This report details an electrochemical methodology for the single-step reduction of TPPO to TPP using an aluminum anode in combination with a supporting electrolyte that continuously regenerates a Lewis acid from the products of anodic oxidation. The resulting Lewis acid activates TPPO for reduction at mild potentials and promotes P-O over P-C bond cleavage to selectively form TPP over other byproducts. Finally, this robust methodology is applied to (i) the reduction of synthetically useful classes of phosphine oxides, (ii) the one-pot recycling of TPPO generated from a Wittig reaction, and (iii) the gram-scale reduction of TPPO at high concentration (1 M) with continuous product extraction and in flow at high current density.

Cu@g-C3N4: An Efficient Single-Atom Electrocatalyst for NO Electrochemical Reduction with Suppressed Hydrogen Evolution

Nitric oxide electroreduction reaction (NOER) is one of the most attractive routes for ammonia synthesis and pollutant treatment. However, the current research efforts toward the NOER mainly focus ...

Electrochemical Deposition of Gold Nanoparticles on Reduced Graphene Oxide by Fast Scan Cyclic Voltammetry for the Sensitive Determination of As(III).

In this study, a stable, sensitive electrochemical sensor was fabricated by the electrochemical codeposition of reduced graphene oxide (rGO) and gold nanoparticles on a glassy carbon electrode (rGO-Aunano/GCE) using cyclic voltammetry (CV), which enabled a simple and controllable electrode modification strategy for the determination of trace As(III) by square wave anodic stripping voltammetry (SWASV). SWASV, CV, electrochemical impedance spectroscopy (EIS), X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the electrochemical properties and morphology of the proposed sensing platform. The number of sweep segments, the deposition potential and the deposition time were optimized to obtain ideal sensitivity. The presence of rGO from the electroreduction of graphene oxide on the sensing interface effectively enlarged the specific surface area and consequently improved the preconcentration capacity for As(III). The rGO-Aunano/GCE sensor exhibited outstanding detection performance for As(III) due to the combined effect of Aunano and rGO formed during the electroreduction process. Under the optimized conditions, a linear range from 13.375 × 10−9 to 668.75 × 10−9 mol/L (1.0 to 50.0 μg/L) was obtained with a detection limit of 1.07 × 10−9 mol/L (0.08 μg/L) (S/N = 3). The reproducibility and reliability of the rGO-Aunano/GCE sensor were also verified by performing 8 repetitive measurements. Finally, the rGO-Aunano/GCE sensor was used for the analysis of real samples with satisfactory results.

In situ Electroreduction of Graphene Oxide: Increased Sensitivity for the Determination of NADH

AbstractA novel and useful method to catalyze the electro‐oxidation of nicotinamide adenine dinucleotide (NADH) over a glassy carbon electrode (GCE) modified with graphene oxide (GO) is presented. Based on the presence of oxygen moieties in GO, which can be easily reduced, an in situ electrochemical generation of reduced graphene oxide (denoted as erGO) applying a sufficient negative potential. A potential of −1.000 V was selected to generate the erGO/GCE as a pretreatment potential before the detection of NADH. The in situ generated erGO/GCE system produces a decrease in the overpotential of NADH oxidation from +0.720 V to +0.230 V compared with GCE. The process also produced an important increase in current signals. The modified electrode was characterized by scanning electron (SEM) and electrochemical microscopies (SECM), cyclic voltammetry and by Raman spectroscopy. Amperometric detection of NADH via this straightforward electrocatalytic method provides a wide linear range between 10 and 100 μM, a lower detection limit of 0.36 μM and an excellent sensitivity of (1.47±0.09) μA mM−1.

Three-Dimensional Graphene Matrix-Supported and Thylakoid Membrane-Based High-Performance Bioelectrochemical Solar Cell

A combination of thylakoid membranes (TMs) as photobiocatalysts with high-surface-area electroactive materials could hold great potential for sustainable “green” solar energy conversion. We have studied the orientated immobilization of TMs on high-surface-area graphene electrodes, which were fabricated by electroreduction of graphene oxide and simultaneous electrodeposition with further aminoaryl functionalization. We have achieved the highest performance to date under direct electron transfer conditions through a biocompatible “wiring” of TMs to graphene sheets. The photobiocurrent density generated by the optimized mediator-free TM-based bioanodes yielded up to 5.24 ± 0.50 μA cm–2. The photobioelectrochemical cell integrating the photobioanode in combination with an oxygen reducing enzymatic biocathode delivered a maximum power output of 1.79 ± 0.19 μW cm–2. Our approach ensures a simplified cell design, a greater load of photosynthetic units, a minimized overpotential loss, and an enhanced overall performance.

Direct electrolytic preparation of chromium metal in CaCl 2 –NaCl eutectic salt

Abstract The electro-reduction of chromium oxide (Cr2O3) was investigated in an equimolar mixture of CaCl2–NaCl molten salt at 800 °C for developing a more efficient process for chromium preparation. Cyclic voltammetry and potentiostatic electrolysis were used to study the electro-reduction of the Cr2O3-loaded metallic cavity electrode. In addition, a number of parameters affecting the rate and extent of Cr2O3 electrolysis were considered to better understand the electrolysis process. The results demonstrate that CaCl2–NaCl molten salt is applicable for preparing Cr directly from Cr2O3 and the electrolysis parameters exert great influence on the cathode product. Under optimal experimental conditions, nodular Cr with an oxygen content of 0.5% (mass fraction) was obtained without any chromium carbides detected by XRD. Furthermore, the relatively high solubility of CaO and quite rapid crystal growth result in the formation of large platelet CaCr2O4, and the addition of NaCl to CaCl2 results in several variations on the electrolysis process and the product morphology from pure CaCl2 molten salt.

One-step coelectrodeposition-assisted layer-by-layer assembly of gold nanoparticles and reduced graphene oxide and its self-healing three-dimensional nanohybrid for an ultrasensitive DNA sensor.

A layer-by-layer (LBL) assembly was employed for preparing multilayer thin films with a controlled architecture and composition. In this study, we report the one-step coelectrodeposition-assisted LBL assembly of both gold nanoparticles (AuNPs) and reduced graphene oxide (rGO) on the surface of a glassy carbon electrode (GCE) for the ultrasensitive electrochemical impedance sensing of DNA hybridization. A self-healable nanohybrid thin film with a three-dimensional (3D) alternate-layered nanoarchitecture was obtained by the one-step simultaneous electro-reduction of both graphene oxide and gold chloride in a high acidic medium of H2SO4 using cyclic voltammetry and was confirmed by different characterization techniques. The DNA bioelectrode was prepared by immobilizing the capture DNA onto the surface of the as-obtained self-healable AuNP/rGO/AuNP/GCE with a 3D LBL nanoarchitecture via gold-thiol interactions, which then served as an impedance sensing platform for the label-free ultrasensitive electrochemical detection of DNA hybridization over a wide range from 1.0 × 10-9 to 1.0 × 10-13 g ml-1, a low limit of detection of 3.9 × 10-14 g ml-1 (S/N = 3), ultrahigh sensitivity, and excellent selectivity. This study presents a promising electrochemical sensing platform for the label-free ultrasensitive detection of DNA hybridization with potential application in cancer diagnostics and the preparation of a self-healable nanohybrid thin film with a 3D alternate-layered nanoarchitecture via a one-step coelectrodeposition-assisted LBL assembly.

Performance of Fe-N/C Oxygen Reduction Electrocatalysts toward NO2-, NO, and NH2OH Electroreduction: From Fundamental Insights into the Active Center to a New Method for Environmental Nitrite Destruction.

Although major progress has recently been achieved through ex situ methods, there is still a lack of understanding of the behavior of the active center in non-precious metal Fe-N/C catalysts under operating conditions. Utilizing nitrite, nitric oxide, and hydroxylamine as molecular probes, we show that the active site for the oxygen reduction reaction (ORR) is different under acidic and alkaline conditions. An in-depth investigation of the ORR in acid reveals a behavior which is similar to that of iron macrocyclic complexes and suggests a contribution of the metal center in the catalytic cycle. We also show that this catalyst is highly active toward nitrite and nitric oxide electroreduction under various pH values with ammonia as a significant byproduct. This study offers fundamental insight into the chemical behavior of the active site and demonstrates a possible use of these materials for nitrite and nitric oxide sensing applications or environmental nitrite destruction.