Electrochemical Reduction Method Research Articles

Electrochemical identification and quantification of through‐plane proton channels in graphene oxide membranes

Stacked graphene oxide (GO) proton membranes are promising candidates for use in energy devices due to their proton conductivity. Identification of through‐plane channels in these membranes is critical but challenging due to their anisotropic nature. Here, we present an electrochemical reduction method for identifying and quantifying through‐plane proton channels in GO membranes. The simplicity lies in the operando optical observation of the change in contrast as GO is electrochemically reduced. Here, we find three proton‐dominated three‐phase interfaces, which are critical for the reduction reactions of GO membranes. Based on these findings, a method is proposed to identify and quantify through‐plane channels in stacked GO proton membranes using a simple three‐electrode device in combination with real‐time imaging of the membrane surface.

Electrochemical identification and quantification of through-plane proton channels in graphene oxide membranes.

Stacked graphene oxide (GO) proton membranes are promising candidates for use in energy devices due to their proton conductivity. Identification of through-plane channels in these membranes is critical but challenging due to their anisotropic nature. Here, we present an electrochemical reduction method for identifying and quantifying through-plane proton channels in GO membranes. The simplicity lies in the operando optical observation of the change in contrast as GO is electrochemically reduced. Here, we find three proton-dominated three-phase interfaces, which are critical for the reduction reactions of GO membranes. Based on these findings, a method is proposed to identify and quantify through-plane channels in stacked GO proton membranes using a simple three-electrode device in combination with real-time imaging of the membrane surface.

Shear‐Strained Pd Single‐Atom Electrocatalysts for Nitrate Reduction to Ammonia

AbstractElectrochemical nitrate reduction method (NitRR) is a low‐carbon, environmentally friendly, and efficient method for synthesizing ammonia, which has received widespread attention in recent years. Copper‐based catalysts have a leading edge in nitrate reduction due to their good adsorption of *NO3. However, the formation of active hydrogen (*H) on Cu surfaces is difficult and insufficient, resulting in a large amount of the by‐product NO2−. In this work, Pd single atoms suspended on the interlayer unsaturated bonds of CuO atoms formed due to dislocations (Pd−CuO) were prepared by low temperature treatment, and the Pd single atoms located on the dislocations were subjected to shear stress and the dynamic effect of support formation to promote the conversion of nitrate into ammonia. The catalysis had an ammonia yield of 4.2 mol. gcat−1. h−1, and a Faraday efficiency of 90 % for ammonia production at −0.5 V vs. RHE. Electrochemical in situ characterization and theoretical calculations indicate that the dynamic effects of Pd single atoms and carriers under shear stress obviously promote the production of active hydrogen, reduce the reaction energy barrier of the decision‐making step for nitrate conversion to ammonia, further promote ammonia generation.

Shear-Strained Pd Single-Atom Electrocatalysts for Nitrate Reduction to Ammonia.

Electrochemical nitrate reduction method (NitRR) is a low-carbon, environmentally friendly, and efficient method for synthesizing ammonia, which has received widespread attention in recent years. Copper-based catalysts have a leading edge in nitrate reduction due to their good adsorption of *NO3. However, the formation of active hydrogen (*H) on Cu surfaces is difficult and insufficient, resulting in a large amount of the by-product NO2 -. In this work, Pd single atoms suspended on the interlayer unsaturated bonds of CuO atoms formed due to dislocations (Pd-CuO) were prepared by low temperature treatment, and the Pd single atoms located on the dislocations were subjected to shear stress and the dynamic effect of support formation to promote the conversion of nitrate into ammonia. The catalysis had an ammonia yield of 4.2 mol. gcat -1. h-1, and a Faraday efficiency of 90 % for ammonia production at -0.5 V vs. RHE. Electrochemical in situ characterization and theoretical calculations indicate that the dynamic effects of Pd single atoms and carriers under shear stress obviously promote the production of active hydrogen, reduce the reaction energy barrier of the decision-making step for nitrate conversion to ammonia, further promote ammonia generation.

Manganese cobalt sulfide nanoparticles wrapped by reduced graphene oxide: a fascinating nanocomposite as an efficient electrochemical sensing platform for vanillin determination

In this work, a fascinating nanocomposite based on manganese-cobalt sulfide (MnS/Co3S4) wrapped by electrochemically reduced graphene oxide (ERGO) has been successfully synthesized on the surface of a glassy carbon electrode (GCE) by a facile hydrothermal assisted electrochemical reduction method. The modified electrode was fully characterized by scanning electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy. The morphological results illustrate that MnS/Co3S4 are embedded in the ERGO layers, resulting in a rough surface and three-dimensional (3D) microstructure. The as-synthesized MnS/Co3S4-ERGO/GCE displays distinctly enhanced electrocatalytic activity for vanillin oxidation in comparison with that of the ERGO/GCE and MnS/Co3S4/GCE. Therefore, the MnS/Co3S4-ERGO/GCE can be used as an effective electrochemical sensing platform for the sensitive determination of vanillin, and the fabricated sensor displays a wide linear range of 0.02−1.00 μmol/L and 1.0−40.0 μmol/L, low detection limit of 4.0 nmol/L and satisfactory recoveries between 98.0% and 102.8%.

Electrochemical reduction of nitrate to Ammonia: Recent progress and future directions

Ammonia (NH3) is essential for global food production as a key agricultural fertilizer and is increasingly recognized as a renewable energy carrier. The electrochemical nitrate reduction (eNO3RR) method stands out as a promising alternative to the traditional, energy-intensive and CO2-emitting Haber-Bosch process, capable of converting residual NO3– pollutants in water systems into valuable NH3 under ambient conditions. Advancing this process toward commercialization relies on the development of electrocatalysts that are highly active, durable, and cost-effective. This article reviews recent progress in electrocatalyst design aimed at improving the efficiency and selectivity of the NO3– to NH3 conversion. Through an exploration of innovative strategies, including doping, alloying, defect engineering, hybridization and single/dual-atom catalysts, this review details how these methods have markedly enhanced catalyst performance, offering avenues to surmount the challenges posed by traditional pure material-based electrocatalysts. Furthermore, the potential for scaling up these technologies for industrial applications is explored. The objective is to provide a comprehensive overview that not only addresses the scientific and technical challenges but also suggests future directions in the development of sustainable and efficient ammonia synthesis technologies, contributing to global efforts in sustainable energy and agricultural practices.

Activating MnO2 nanosheet arrays for accelerated water oxidation through the synergic effect of Ni loading and O vacancies

Birnessite (δ-MnO2), inspired by biological photosynthesis, holds promise as oxygen evolution reaction (OER) catalysts in water electrolysis for clean energy. Given that Mn3+ serves as the active sites, various strategies have been employed to increase the Mn3+ content to boost the OER activity. To surpass the limitations of the traditional adsorbate evolution mechanism (AEM), we have adopted an electrochemical reduction method to introduce metallic Ni and enrich oxygen vacancies onto δ-MnO2 nanosheets. The resulting Ni/MnO2v/CC exhibits exceptional OER performance, with a reduction in overpotential by 190 mV (from 478 mV to 289 mV) at 10 mA cm−2 and a Tafel slope as low as 45 mV dec-1, indicating accelerated catalytic activity. Experimental and theoretical analyses attribute this enhancement to a transition from the traditional AEM to lattice oxygen mechanism (LOM) mechanism. Moreover, the dual modification also enhances electronic conductivity, electrochemical surface area, and charge transfer ability of δ-MnO2. Our work offers a pathway to overcome conventional limitations in OER electrocatalysts, applicable not only to Mn-based catalysts but also to a range of other transition metal oxides.

Constructing surface concave defects on NiFe layered double hydroxides by electrochemical reduction for efficient oxygen evolution reaction

NiFe-LDH has been proved to be one of the most effective non-noble metals electrocatalysts for oxygen evolution reaction, but inadequate exposure of the active sites prevents its performance from being comparable to noble metal catalysts. Herein, we prepare 3D nanoflower-like NiFe-LDH composed of bumpy, thin nanosheets by hydrothermal combined with electrochemical reduction method. Various characterization results reveal that the nanosheets of NiFe-LDH are partial exfoliated and reduced by the atomic H* and H2 in the electrochemical reduction process, which results in the generation of surface oxygen vacancies (Vos), forming plenty concave defects in the surface of nanosheets. The optimized partially surface reduced NiFe-LDH exhibits an outstanding catalytic activity for OER with long-term stability. The overpotential is only 185 mV at 100 mA cm−2 with no obvious deterioration in 100 h operation process. The enhanced activity is attributed to the more exposure and the adjustment of electron density of metal active sites. This work provides a universality method to strip nanosheets and induce oxygen vacancies on oxygenated catalysts.

S-vacancy-rich NiFe-S nanosheets based on a fully electrochemical strategy for large-scale and quasi-industrial OER catalysts

The oxygen evolution reaction (OER) is regarded as a critical component in the water splitting system. Creating vacancies, increasing active surface area, and optimizing electronic structure would improve electrocatalytic performance. Herein, a facile electrochemical reduction method is used to generate sulfur vacancies in nickel iron sulfide (NiFe-S) with a large geometry area of 15 × 16 cm2, which is synthesized using an electrodeposition process assisted with the ion exchange (IOE) method. The X-ray absorption spectroscopies (XAS) are applied for atomic-level structural analysis, verifying that electrochemical desulfurization generates abundant S vacancies. The NiFe-S with abundant sulfur vacancies (NiFe-S-Vs) exhibits a low overpotential (252 mV at 100 mA cm−2), and long stability for 260 h at 500 mA cm−2. More importantly, the NiFe-S-Vs catalyst also delivers a small overpotential (235 mV at 1000 mA cm−2) and high alkaline tolerance (140 h at 500 mA cm−2) in 6 M KOH at 60 °C), implying a potentially significant industrial application prospect. Finally, theory calculation further illustrates the high performance of as-prepared vacancies-rich catalyst.

Formation of Sn seeds on indium-free TCO for plating metallization of silicon heterojunction solar cells

The cost-prohibitive ITO and low-temperature silver paste pose significant challenges in the manufacture of SHJ solar cells. The SnO2-based TCO (indium-free) and Cu electroplating are promising solutions to address these issues. The key point of Cu electroplating is the seed layer for achieving good adhesion and low contact resistivity to the TCO. In this study, we report the electrochemical reduction method for the Sn seeds on FTO films, offering an alternative to the costly vacuum deposition process. We reveal that the electrochemical reduction process is dominated by the breaking of lower-energy bonds during electrons injection, resulting in the formation of tin nanoparticles which serve as the excellent seeds for the subsequent electroplating of a nickel metal layer on the FTO film. A tightly binding interface without any pores between the FTO film and Ni was observed, confirming its effectiveness. Our calculation results using the DFT method manifest that the binding energies of Sn/Ni interface are significantly lower than SnO2/Ni, indicating that Sn seeds present a lower energy barrier for deposition, which promotes Ni deposition kinetics. The integration of indium-free TCO, seeds preparation of electrochemical reduction, and copper electroplating is expected to boost SHJ solar cells in near future.

Silver-impregnated zeolitized tuffs for environmental degradation of ozone

The natural zeolites were ultrasonically treated and impregnated with silver nanoparticles. The surface stabilized silver nanoparticles dispersion was obtained using an effective electrochemical reduction method. The phase and elemental composition, structure of the Ag-impregnated zeolites (clinoptilolite and mordenite) was studied by various methods such as powder X-ray diffraction, X-ray fluorescence analyses and Fourier-transform infrared spectroscopy. The Ag-impregnated clinoptilolite and mordenite natural zeolite materials with 1.20 wt %, 0.97 wt %, 0.83 wt % and 1.18 wt % silver content were established by XRF analysis. As initial materials were used three types clinoptilolite from Beli Plast, Most, Golobradovo (Kardzhali, Bulgaria) deposits and mordenite from Lyaskovets deposit in Eastern Rhodopes, Bulgaria. The catalytic ability of Ag-mordenite and Ag-clinoptilolites was investigated in the ecologically important reaction of ozone decomposition. The Ag-loaded mordenite demonstrates the higher conversion degree of ozone more than 40% in comparison with Ag-clinoptilolite materials at room temperature.

One-step solvothermal synthesis of MoS2@Ti cathode for electrochemical reduction of Hg2+ and predicting BP neural network model

Although mercury is one of the heavy metal pollutants that endanger human health and the environment, it is also an essential raw material needed for industrial development. We try to use electrochemical reduction method to realize the resource utilization of mercury. MoS2@Ti electrodes were prepared using a one-step solvothermal method, and XRD, XPS, SEM and EDS were used to analyze the MoS2 powder. The prepared highly reactive MoS2@Ti electrode was used as a cathode to electrochemically reduce the mercury-containing solution. After a series of single-factor experiments, under the conditions of stirring rate of 400 r/min, electrode spacing of 20 mm, constant potential of 2 V and electrolytic time of 2 h, the removal efficiency of Hg2+ in 10 ∼ 50 mg/L HgSO4-10 % H2SO4 solution reached 94.5 % or above. The reaction mechanism of MoS2@Ti was investigated mainly by using the indirect reaction of superoxide radicals and hydrogen radicals to achieve the reduction of Hg2+. And the MoS2@Ti electrode can still reach 80.0 % removal efficiency after five times of repeated use. A neural network model was used to predict the efficiency of Hg2+ reduction in this system with a high accuracy of RMSE 1.3049 and R2 0.9511. The above study contributes to the realization of the resource utilization of mercury.

Unlocking long-chain hydrocarbons (C2–7) via direct electrochemical CO2 and CO reduction on balanced Au/Ni electrodes

Electrochemical (EC) CO2 reduction method has been widely used as a green energy and environmental solution strategy. The use of Au/Ni electrodes was introduced to showcase a new concept of the direct EC Fischer-Tropsch (dEC F-T) synthesis pathway. This pathway involves the combination of electrodes that produce H2 and CO (syngas) during electrochemical CO2 reduction. The introduction of Au on the Ni electrode surface led to an increase in CO production and a gradual decrease in H2 production. When the interface was balanced, a pronounced F-T synthesis pathway was observed, resulting in the production of a series of hydrocarbons (CnH2n and CnH2n+2, n = 2–7). The dEC F-T synthesis was evaluated under different conditions, including electrolytes, concentrations, metal supports (Co and Fe), various overlayer metals (Ag and Cu), light irradiation, and isotope effects. The process was elucidated through surface C−C coupling polymerization reactions based on Anderson-Schulz-Flory weight distribution analysis. Additionally, the F-T synthesis was demonstrated through EC CO reduction via direct CO and H adsorption. The dEC F-T path provides a novel strategy for energy and environment by producing high-value long-chain hydrocarbons.

Ultrasensitive Electrochemical Platform for Dopamine Detection Based on CoNi-MOF@ERGO Composite.

An electrochemical sensor applied for dopamine (DA) detection was constructed. An easy static way was used to synthesize bimetallic CoNi-MOF. Next, it was mixed with graphene oxide (GO) under ultrasound to get a uniform suspension. Subsequently, the solution was coated on the glassy carbon electrode (GCE) to form CoNi-MOF@ERGO/GCE by the electrochemical reduction method. The interaction between CoNi-MOF and electrochemically reduced graphene oxide (ERGO) enhances the electrocatalytic performance for DA detection. CoNi-MOF@ERGO/GCE has a wider linear range (0.1-400 μM) and a lower detection limit (0.086 μM) under optimum conditions. Furthermore, it has been applied to test DA in human serum samples. The results reveal that the DA sensor shows excellent performance, which will provide a novel idea for more sensitive and quicker DA detection.

(Invited) A Review of Electrochemical Methods for Extraction of Oxygen From Regolith

The surface of many planetary bodies, including the Moon and Mars, is composed primarily of metal oxides. A number of competing technologies have been proposed to extract oxygen from the dust on the surface. These methods include reduction of the iron- and silicon-containing species by hydrogen or by electrons. The direct electrochemical reduction methods run at different temperatures, from approximately room temperature to over the melting point of iron. Some of these methods produce liquid metal, and others solid metal powders. The latter can optionally extend the electrolysis to recover oxygen from aluminum and titanium species, although at an energetic cost. This talk will review recent progress and current capabilities for these processes.

The determination of dimethyl sulfoxide in natural waters using electrochemical reduction

AbstractA highly specific electrochemical reduction method has been developed that enables the trace level measurement of dimethyl sulfoxide (DMSO) concentration in natural waters. Following the sparging of native dimethyl sulfide (DMS) from the sample, DMSO is reduced to DMS using a novel electrochemical workflow that relies upon CuSO4 as a redox mediator. The DMS produced through DMSO reduction is collected, concentrated, and detected using a previously described Purge & Trap‐Atmospheric Pressure Chemical Ionization‐Tandem Mass Spectrometry (P&T‐APCI‐MS/MS) analytical workflow. The method provides a 0.5 pM detection limit for the analysis of DMSO in 10 mL sample volumes, with a demonstrated method precision of 5.4% for the analysis of consecutive 10 nM aqueous standards. The method selectivity for DMSO was evaluated using a range of commonly observed marine organosulfur compounds, none of which were found to interfere with the analysis at a reduction potential of 4 V. Method intercomparison confirmed that the electrochemical reduction provides results that are equivalent (at the 95% confidence level) to an established TiCl3 reduction protocol for the analysis of both freshwater and seawater samples. Relative to established methods of DMSO reduction, the electrochemical method provides excellent selectivity and reproducibility, and offers the potential for automated, high‐throughput analysis. In addition, the new electrochemical method does not require expensive, difficult to procure enzymes or hazardous, corrosive chemical reagents. Depth profile measurements of DMSO, DMS, and dimethylsulfoniopropionate (DMSP) for unfiltered seawater samples collected in Saanich Inlet, a coastal fjord in British Columbia, demonstrate the effectiveness of the DMSO reduction method in an oceanographic context.

The development of a gas-feeding CO2 fuel cell using direct hydrazine oxidation reaction

Electrochemical carbon dioxide (CO2) reduction has attracted attention for converting CO2 into value-added products at room temperature. Conventional electrochemical CO2 reduction methods require external energy because of the high overpotential of the oxygen evolution reaction (OER). To overcome the limitation of the OER, we propose a gaseous CO2 reduction system that uses an aqueous hydrazine (N2H4) oxidation reaction. In this study, the N2H4-CO2 fuel cell is proposed for the simultaneous generation of electricity with CO2 conversion. During the operation of the aqueous N2H4/gas-feeding CO2 fuel cell, a power density of 20.31 mW/cm2 was obtained and 49.20 % of CO2 was converted to CO at the Ag cathode. We also evaluated the correlation between the flow rate of the anolyte and the hydrophobicity of the Ag cathode in terms of cell performance.

Study on the photoelectrocatalytic activity of reduced TiO2 nanotube films for removal of methyl orange

Abstract The reduced TiO2 film on which a photoelectrocatalytic (PEC) process had occurred was created from TiO2 nanotube film electrodes by the electrochemical reduction method. The obtained samples’ structure and morphology were characterized using UV-Vis diffuse reflectance spectroscopy, scanning electron microscopy, high-resolution transmission electron microscopy, photoluminescence, and X-ray diffraction. Cyclic voltammetry, linear sweep voltammetry, electrochemical impedance spectroscopy, chronoamperometry, UV-Vis absorbance spectroscopy, and Mott–Schottky plots were employed to examine the electrochemical and photoelectrochemical activities of the prepared electrodes. The results showed that the optimal conditions of cathodic polarization were a potential of −1.4 V for 60 min. The reduced TiO2 nanotube film electrode had better photoelectrochemical activities than pristine TiO2 under UV light due to the higher photocurrent density (13.7 mA‧cm−2) at 1.5 V (vs Ag/AgCl, sat. KCl reference electrode) compared to pristine TiO2 achieving 7.3 mA‧cm−2, indicating more effective charge separation and transport. The degradation of methyl orange (MO) on pristine TiO2 and reduced TiO2 electrodes was carried out in electrocatalytic (EC) and PEC conditions. The PEC process on the reduced TiO2 electrode had the highest MO processing efficiency (98.4%), and the EC process for MO removal on reduced TiO2 had higher efficiency (95.1%) than the PEC process on pristine TiO2 (89.2%).

Singlet Oxygen Generation via an Electrochemical Reduction Method Assisted by a Ruthenium(II) Complex.

In this work, singlet oxygen (1O2) is unprecedently recorded in the electrochemical reduction of tris(2,2'-bipyridine)ruthenium(II) [Ru(bpy)32+] in an acetonitrile solution with dissolved oxygen, which is well characterized by the specific probe of Singlet Oxygen Sensor Greens and the technique of electron-spin resonance in this work. Importantly, this new electrochemical method to produce 1O2 shows higher efficiency than the conventional photodriven method. Furthermore, taken together with the inherent advantages of electrochemical techniques compared with the photochemical/chemical-driven method, this electrochemical method would inevitably show great promise in reactive-oxygen-species-related studies in the future.

Comparison of Thermal and Laser-Reduced Graphene Oxide Production for Energy Storage Applications.

A way to obtain graphene-based materials on a large-scale level is by means of chemical methods for the oxidation of graphite to obtain graphene oxide (GO), in combination with thermal, laser, chemical and electrochemical reduction methods to produce reduced graphene oxide (rGO). Among these methods, thermal and laser-based reduction processes are attractive, due to their fast and low-cost characteristics. In this study, first a modified Hummer's method was applied to obtain graphite oxide (GrO)/graphene oxide. Subsequently, an electrical furnace, a fusion instrument, a tubular reactor, a heating plate, and a microwave oven were used for the thermal reduction, and UV and CO2 lasers were used for the photothermal and/or photochemical reduction. The chemical and structural characterizations of the fabricated rGO samples were performed by Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), scanning electron microscope (SEM) and Raman spectroscopy measurements. The analysis and comparison of the results revealed that the strongest feature of the thermal reduction methods is the production of high specific surface area, fundamental for volumetric energy applications such as hydrogen storage, whereas in the case of the laser reduction methods, a highly localized reduction is achieved, ideal for microsupercapacitors in flexible electronics.