Electroreduction Method Research Articles

Efficient Electroreduction of Low Nitrate Concentration via Nitrate Self-Enrichment and Active Hydrogen Inducement on the Ce(IV)-Co3O4 Cathode.

Low concentrations of nitrate (NO3-) widely exist in wastewater, post-treated wastewater, and natural environments; its further disposal is a challenge but meaningful for its discharge goals. Electroreduction of NO3- is a promising method that allows to eliminate NO3- and even generate higher-value NH3. However, the massive side reaction of hydrogen evolution has raised great obstacles in the electroreduction of low concentrations of NO3-. Herein, we present an efficient electroreduction method for low or even ultralow concentrations of NO3- via NO3- self-enrichment and active hydrogen (H*) inducement on the Ce(IV)-Co3O4 cathode. The key mechanism is that the strong oxytropism of Ce(IV) in Co3O4 resulted in two changes in structures, including loose nanoporous structures with copious dual adsorption sites of Ce-Co showing strong self-enrichment of NO3- and abundant oxygen vacancies (Ovs) inducing substantial H*. Ultimately, the bifunctional role synergistically promoted the selective conversion of NH3 rather than H2. As a result, Ce(IV)-Co3O4 demonstrated a NO3- self-enrichment with a 4.3-fold up-adsorption, a 7.5-fold enhancement of NH3 Faradic efficiency, and a 93.1% diminution of energy consumption when compared to Co3O4, substantially exceeding other reported electroreduction cathodes for NO3- concentrations lower than 100 mg·L-1. This work provides an effective treatment method for low or even ultralow concentrations of NO3-.

Preparation of metallic lead from lead sulfide by bagged cathode solid-phase electroreduction in a low-temperature and weakly alkaline solution

Developing a method to recovering metallic lead from lead sulfide at lower temperatures without emitting lead dust and SOx gas holds significant importance in terms of environmental sustainability and economy efficiency. In this study, we employ a bagged cathode to directly produce metallic lead from lead sulfide in a low-cost weakly alkaline electrolyte (200 g/L Na2SO4 + 0.1 mol/L NaOH) at a temperature as low as 40 °C. The use of bagged cathode effectively immobilizes reactants and reduces cathodic polarization, thereby enabling the electro-reduction of lead sulfide under mild conditions. During the electroreduction process, the granular lead sulfide powders gradually undergo transformation into rod- or sheet-like metallic lead, achieving lead recovery ratio and desulfurization rate reaching 96.4 % and 97.9 %, respectively. Cyclic voltammetry analysis confirms that the oxidation reaction of S2− released from cathode is irreversible, thereby not interfering the cathodic electroreduction of lead sulfide. This bagged cathode direct electroreduction method utilizing a low-temperature, weakly alkaline aqueous solution exhibits the potential for application to other sulfides or oxides.

Multiwalled carbon nanotubes supported Fe nanostructured interfaces for electrochemical detection of uric acid

Uric acid (UA) levels in biological fluids are an important diagnostic and prognostic biomarker for various metabolic disorders. Therefore, a convenient, facile, one-step electroreduction method to develop Fe nanostructured (FeNS) interfaces for highly sensitive electrochemical detection of UA. The synthesis process was thoroughly investigated at various deposition potentials, pH of the electrochemical bath solutions, and growth durations to attain excellent electrochemical response towards UA detection. The morphology and elemental composition of the FeNS/MWCNT were analyzed using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDXS) techniques. We observed uniform deposition of FeNSs with sizes ranging from 100 − 120 nm on tubular nanostructures. The multiwalled carbon nanotubes supported Fe nanostructured interfaces (FeNS/MWCNT) generated at a potential of –1.1 V demonstrated excellent electrochemical response towards UA with a wide linear detection range of 5 to 500 µM with a sensitivity of 6.5605 µA µM−1 cm−2 and low detection limit of 3.26 µM. The excellent electrochemical response was attributed to the synergistic effect of MWCNTs, which facilitated FeNSs growth, leading to increased active sites for electrocatalysis and sensitive detection of UA. The convenience of the synthesis process, tunable electrochemical response, and reliability of the detection process make FeNS interfaces a potential option for developing electrochemical UA sensors.

Tuning of Interfacial Charge Transport in Organic Heterostructures via Aryl Electrografting for Efficient Gas Sensors.

Modulation of interfacial conductivity in organic heterostructures is a highly promising strategy to improve the performance of electronic devices. In this endeavor, the present work reports the fabrication of a bilayer heterojunction device, combining octafluoro copper phthalocyanine (CuF8Pc) and lutetium bis-phthalocyanine (LuPc2) and tunes the charge transport at the Cu(F8Pc)-(LuPc2) interface by aryl electrografting on the device electrode to improve the device NH3-sensing properties. Dimethoxybenzene (DMB) and tetrafluoro benzene (TFB) electrografted by an aryldiazonium electroreduction method form a few-nanometer-thick organic film on ITO. The conductivity of the heterojunction devices formed by coating a Cu(F8Pc)/LuPc2 bilayer over the aryl-grafted electrode strongly varies according to the electronic effects of the substituents in the aryl. Accordingly, DMB increases while TFB decreases the mobile charges accumulation at the Cu(F8Pc)-(LuPc2) interface. This is explained by the perfect alignment of the frontier molecular orbitals of DMB and Cu(F8Pc), facilitating charge injection into the Cu(F8Pc) layer. On the contrary, TFB behaves like a strong acceptor and reduces the mobile charges accumulation at the Cu(F8Pc)-(LuPc2) interface. Such interfacial conductivity variation influences the device NH3-sensing properties, which increase because of DMB grafting and decrease in the presence of TFB. DMB-based heterojunction devices contain four times higher active sites for NH3 adsorption and could detect NH3 down to 1 ppm with limited interference from humidity, making them suitable for real environment NH3 detection.

Electro-reduced copper on polymeric C3N4 for photocatalytic reduction of CO2

Coupling light absorber with an efficient cocatalyst is the most common way to fabricate composite photocatalyst. The light absorber supplies electrons and holes, while the cocatalyst domains chemical reactions. Inspired by the results from electrochemical CO2 reduction, Cu-based materials are the most promising cocatalysts for photocatalytic CO2 reduction. However, oxide-derived copper (OD-Cu) hasn't been introduced into photocatalytic systems yet, due to easily undergoing valence changes once exposed to air. Herein, we find that OD-Cu could be decorated on photocatalyst, polymeric C3N4 (PCN), by a self-designed in-situ electroreduction method. The as-prepared OD-Cu/PCN presents better visible light absorption than the one without in-situ electroreduction and prefers multi-carbon products. According to CO2RR measurements, the highest selectivity to C2H5OH is 58%. Density functional theory calculation further indicates that the unique structure between OD-Cu and PCN leads to a low energy barrier of C–C coupling due to the enhanced *CO dimerization and thus promotes the production of C2H5OH. Moreover, this optimized sample achieves a solar-to-fuel efficiency, of up to 0.94%, which is 1.69 times the pristine PCN.

Strategies for Nitrate and Nitrite Removal: Closing the Loop Using Membrane Electroreduction and Catalytic Reduction Processes

The excessive use of fertilizers is the primary cause of increasing contamination of surface water and groundwater by nitrate ions. To address this problem, this study explores an optimized electroreduction method using a current-voltage approach to reduce nitrate ions. The nitrate electroreduction process employed a copper cathode (Cu) and titanium coated with titanium and ruthenium oxides (Ti/70TiO230RuO2) anode. The use of a current density beyond the limiting one promoted a greater reduction of nitrate. A current density of 3.5 mA/cm2 produced 91% nitrate reduction, resulting in 85 mg/L of N-Nitrite. Subsequently, the research investigates the use of electroreduction and catalytic processes for the treatment of this nitrite brine, aiming at high selectivity for gaseous compounds. To this end, active carbon fiber containing a Pd catalyst was employed. The electroreduction of nitrite achieved 28% and 36% reduction, using a Ti/70TiO230RuO2 anode and Ti/70TiO230RuO2 or Cu cathodes, respectively, at a current density of 2.3 mA/cm2, producing only ammonium ions. On the other hand, the use of nitrite catalytic reduction allowed the complete reduction of N-Nitrites, with high selectivity to gaseous nitrogen (97%). The combined approach of electrochemical reduction, using a current density above the limiting one, and catalytic reduction, with Pd-based carbon fibers, offers several benefits, including selectivity, efficiency, versatility, and sustainability. As such, it represents a promising strategy for the removal of nitrates from water with high selectivity to gaseous compounds, addressing an urgent environmental challenge.

Methods of Extracting TiO2 and Other Related Compounds from Ilmenite

Although ilmenite and rutile are extensively used to extract TiO2 at the industrial level, through the sulphate and chloride processes, they can also be recognized to possess the potential to be employed as the raw material to synthesize other titanium compounds as well. The Pulmoddai mineral sand deposit in Sri Lanka is considered as a valuable resource containing pure ilmenite and can be used as a very good source of both titanium and iron. Because of the lower TiO2 content compared to rutile, processes, such as the Becher process, Laporte process and Kataoka process, have been developed to upgrade ilmenite into higher grade synthetic rutile. Additionally, research studies have been carried out to develop methods, such as the hydrochloride process, H3PO4/NH3 process, alkaline roasting process, aluminothermic reduction method, alkaline decomposition method, molten salt electroreduction method and magnesiothermic reduction method, to synthesize TiO2 and other related titanium compounds, such as titanium and iron oxides, composites and alloys, from naturally occurring ilmenite where these methods possess both rewards as well as drawbacks over the others.

Lewis Acidic Support Boosts C-C Coupling in the Pulsed Electrochemical CO2 Reaction.

Copper-oxide electrocatalysts have been demonstrated to effectively perform the electrochemical CO2 reduction reaction (CO2RR) toward C2+ products, yet preserving the reactive high-valent CuOx has remained elusive. Herein, we demonstrate a model system of Lewis acidic supported Cu electrocatalyst with a pulsed electroreduction method to achieve enhanced performance for C2+ products, in which an optimized electrocatalyst could reach ∼76% Faradaic efficiency for C2+ products (FEC2+) at ∼-0.99 V versus reversible hydrogen electrode, and the corresponding mass activity can be enhanced by ∼2 times as compared to that of conventional CuOx. In situ time-resolved X-ray absorption spectroscopy investigating the dynamic chemical/physical nature of Cu during CO2RR discloses that an activation process induced by the KOH electrolyte during pulsed electroreduction greatly enriched the Cuδ+O/Znδ+O interfaces, which further reveals that the presence of Znδ+O species under the cathodic potential could effectively serve as a Lewis acidic support for preserving the Cuδ+O species to facilitate the formation of C2+ products, and the catalyst structure-property relationship of Cuδ+O/Znδ+O interfaces can be evidently realized. More importantly, we find a universality of stabilizing Cuδ+O species for various metal oxide supports and to provide a general concept of appropriate electrocatalyst-Lewis acidic support interaction for promoting C2+ products.

Fabrication of U-Ti alloy through direct electro-reduction from U3O8 and TiO2 mixtures in LiCl molten salt

U-Ti alloys have attracted much attention for its excellent mechanical performance and corrosion resistance. The conventional method to fabricate U-Ti alloy by melting U and Ti metals shows great disadvantages in high energy consumption, excessive impurity content, low security and compositional segregation. Hereby, direct electro-reduction method was employed to fabricate U-Ti alloy from U3O8 and TiO2 mixtures in LiCl molten salt. The co-reduction route and process were also analyzed in detail, which are helpful to comprehend the effects of alloying elements on electro-reduction of uranium oxides, further promoting the application of this technique on nuclear fuel recycling.

Strengthening adhesion of polycarbazole films on ITO surface by covalent electrografting of monomer

Strong adhesion of a functional polymer coating to a solid support is a key requirement to achieve its robustness and high performance in different application areas. Herein, a novel carbazole derivative, 9-methyl-9H-carbazole-3,6-diamine (m-Cz-diamine), is synthesized and covalently grafted onto an ITO surface through the diazonium electroreduction method. The functionalization of the ITO surface is confirmed by XPS spectroscopy, water contact angle measurements and cyclic voltammetry analysis, revealing the covalent anchoring of an organic film (m-Cz-ITO). The functionalized ITO surface is then studied for oxidative electropolymerization of m-Cz-diamine and carbazole, showing clear advantages over a bare ITO substrate in terms of polymer film adhesion. The polymer films electrodeposited onto an electrografted ITO surface demonstrate very strong adhesion, as they do not delaminate, either by a scotch tape pulling, storing in air, or immersing under water for two months. On the other hand, the polymer films grown on a bare ITO substrate peel off easily in all the aforementioned stability tests. Therefore, electrografting an organic film onto the ITO surface clearly improves the adhesion of the polymer films on top of it. Moreover, it is interesting to note that the physicochemical properties of the polymer films deposited on the functionalized ITO substrate remain unchanged.

Morphology-Tuned Electrochemical Immunosensing of a Breast Cancer Biomarker Using Hierarchical Palladium Nanostructured Interfaces.

Metallic nanostructures are considered attractive candidates for designing novel biosensors due to their enormously significant surface area, accelerated kinetics, and improved affinity. Controllable morphological tuning of metallic nanostructures on sensing interfaces is crucial for attaining clinically relevant sensitivity and exquisite selectivity in a complex biological environment. Therefore, a facile, convenient, and robust one-step electroreduction method was employed to develop different morphological variants of palladium (Pd) nanostructures supported onto oxidized carbon nanotubes to facilitate label-free electrochemical immunosensing of HER2. The morphological and structural attributes of the synthesized Pd nanostructures were thoroughly investigated using scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and atomic force microscopy techniques. In-depth electrochemical investigations revealed an intimate correlation between the nanostructured sensor and electrochemical response, suggesting the suitability of hierarchical palladium nanostructures supported onto carbon nanotubes [Pd(−0.1 V)/CNT] for sensitive detection of HER2. The high surface area of hierarchical Pd nanostructures enabled an ultrasensitive electrochemical response toward HER2 (detection limit: 1 ng/mL) with a wide detection range of 10 to 100 ng/mL. The ease of surface modification, sensitivity, and reliable electrochemical response in human plasma samples suggested the enormous potential of Pd nanostructuring for chip-level point-of-care screening of HER2-positive breast cancer patients.

Electrocatalytic Removal of Low-Concentration Uranium Using TiO2 Nanotube Arrays/Ti Mesh Electrodes.

Groundwater containing naturally occurring uranium is a conventional drinking water source in many countries. Removal of low concentrations of uranium complexes in groundwater is a challenging task. Here, we demonstrated that the TiO2 nanotube arrays/Ti (TNTAs/Ti) mesh electrode could break through the concentration limit and efficiently remove low concentrations of uranium complexes from both simulated and real groundwater. U(VI) complexes in groundwater were electro-reduced to UO2 and deposited on the TNTAs/Ti mesh electrode surface. The adsorption rate and electron transfer rate of the anatase TNTAs/Ti mesh electrode were twice that of the rutile TNTAs/Ti mesh electrode. Therefore, the anatase TNTAs/Ti mesh electrode exhibited excellent electrocatalytic activity toward the electrochemical removal of U(VI), which could work at a higher potential and significantly reduce the energy consumption of U(VI) removal. The U(VI) adsorption capacity on the anatase TNTAs/Ti mesh electrode was limited due to the low U(VI) concentration. However, the anatase TNTAs/Ti mesh electrode displayed a huge U(VI) removal capacity using the electroreduction method, where adsorption and reduction of U(VI) were mutually promoted and induced continuous accumulation of UO2 on the electrode. The accumulated UO2 can be easily recovered in dilute HNO3, and the electrode can be used repeatedly.

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

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

Preparation of stoichiometric uranium dioxide (UO2.000) via electro-reduction method in LiCl molten salt

Preparation of stoichiometric uranium dioxide (UO2.000) via electro-reduction method in LiCl molten salt

Introducing oxygen vacancies to NiFe LDH through electrochemical reduction to promote the oxygen evolution reaction.

The transition metal hydroxide NiFe LDH is a promising oxygen evolution reaction (OER) catalyst. Surface engineering, such as the introduction of oxygen vacancies into NiFe LDH, has been reported to further improve the OER performance; however, searching a facile approach remains an issue. In this work, we report a novel and efficient electrochemical reduction method for in situ introduction of oxygen vacancies into NiFe LDH laminates by applying a constant negative voltage. The results show that the reduced NiFe LDH (denoted as r-NiFe LDH) exhibits enhanced OER performance versus its counterpart NiFe due to the increase of oxygen vacancy density, the electrochemically active surface area, wetting ability, and the significant electron transfer rate. In 1 M KOH, the r-NiFe LDH shows a high current density of 110 mA cm-2 at 1.60 V (vs. RHE), which is 2.8 times the current density of NiFe LDH (40 mA cm-2), as well as the long-term stability of 100 h. This electroreduction method is also applicable to other LDH materials loaded by different current substrates or synthesized by various methods, demonstrating its universality for the enhancement of the OER activity of LDH electrocatalysts.

Determination of Uric Acid in Biological Fluids by Ceria Nanoparticles Doped Reduced Graphene Oxide Nanocomposite Voltammetric Sensor

High levels of uric acid (UA) in the human body usually cause diabetes, hypertension and atherosclerosis, kidney diseases, and neurological diseases. Hence, it is important to develop sensitive methods for UA determination. In this paper, nanocomposite composed of ceria nanoparticles and reduced graphene was successfully modified on the surface of glassy carbon electrode (ceria NPs-rGO/GCE) by a simple electroreduction method. The morphology, structure and property of the ceria NPs-rGO/GCE was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The electrocatalytic activity of the ceria NPs-rGO/GCE for uric acid (UA) oxidation was studied in detail. The results showed that the ceria NPs-rGO/GCE exhibited excellent selectivity and high sensitivity for UA detection. In 0.05 M H2SO4 solution, a linear range of 0.02–20 μM and a low detection limit of 8.0 nM of UA were obtained on the ceria NPs-rGO/GCE. This developed method was successfully applied for the detection of UA in human serum and urine samples, and its recoveries reached 95.8%-105.0%.

Highly selective electrocatalytic reduction of CO2 to HCOOH over an in situ derived hydrocerussite thin film on a Pb substrate

A metal oxide electrode has been developed for the electrochemical CO2 reduction reaction (eCO2RR). It exhibits superior activity and product selectivity towards eCO2RR by circumventing the previously encountered problem of self-reduction with high-valence metals. Specifically, a hydrocerussite [Pb3(CO3)2(OH)2] thin film has been synthesized in situ on a Pb substrate (denoted as ER-HC) by an electroreduction method using a lead-based metal–organic framework (Pb-MOF) as a precursor. The ER-HC electrode exhibits a high selectivity of 96.8% towards HCOOH production with a partial current density of 1.9 mA cm−2 at −0.88 V vs. the reversible hydrogen electrode (RHE). A higher HCOOH partial current density of 7.3 mA cm−2 has been achieved at −0.98 V vs. RHE. Physicochemical and electrochemical characterization results demonstrate that the defective hydrocerussite surface exhibits appropriate adsorption free energy of formate (HCOO−) and a lower reaction free energy for HCOOH production from CO2, which greatly boosts the eCO2RR activity and HCOOH production selectivity. The structure and eCO2RR performance of the hydrocerussite thin film remain stable in 0.1 M KHCO3 as electrolyte, ensuring its durability. Overall, this work not only provides a metal oxide electrode (metal hydroxide, to be more precise) with excellent eCO2RR performance, but also expands the in situ electrochemical derivatization strategy for the fabrication of metal oxide electrodes.

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.

Electrosynthesis of urea from nitrite and CO2 over oxygen vacancy-rich ZnO porous nanosheets

Summary Urea electrosynthesis under mild conditions shows great potential to conquer the conventional manufacturing industry with huge energy consumption. Here, self-supported oxygen vacancy-rich ZnO (ZnO-V) porous nanosheets are prepared using the electroreduction method and adopted as an efficient catalyst for aqueous urea electrosynthesis by using CO2 and nitrite contaminants as feedstocks. The urea Faradaic efficiency of ZnO-V achieves 23.26% at −0.79 V versus the reversible hydrogen electrode (RHE), which is almost 3 times as high as that of ZnO (8.10%). Liquid chromatography is developed for quantitative analysis of urea. The combined results of online differential electrochemical mass spectrometry (DEMS) and in situ diffuse reflectance infrared Fourier transform spectroscopy unveil a possible coupling pathway of NH2∗ and COOH∗ intermediates for urea formation. Our work opens an avenue for rational construction of efficient electrocatalysts for urea electrosynthesis and broadens the scope of products available from nitrite and CO2 reduction.

Atomic defects in pothole-rich two-dimensional copper nanoplates triggering enhanced electrocatalytic selective nitrate-to-ammonia transformation

Defect-rich copper nanoplates were synthesized by an in situ electroreduction method and exhibited enhanced activity for selective electroreduction of nitrate to ammonia.