Electrochemical Redox Research Articles

Direct electrochemical reduction of graphene oxide thin film for aptamer-based selective and highly sensitive detection of matrix metalloproteinase 2

Simple and low-cost biosensing solutions are suitable for point-of-care applications aiming to overcome the gap between scientific concepts and technological production. To compete with sensitivity and selectivity of golden standards, such as liquid chromatography, the functionalization of biosensors is continuously optimized to enhance the signal and improve their performance, often leading to complex chemical assay development. In this research, the efforts are made on optimizing the methodology for electrochemical reduction of graphene oxide to produce thin film-modified gold electrodes. Under the employed specific conditions, 20 cycles of cyclic voltammetry (CV) are shown to be optimal for superior electrical activation of graphene oxide into electrochemically reduced graphene oxide (ERGO). This platform is further used to develop a matrix metalloproteinase 2 (MMP-2) biosensor, where specific anti-MMP2 aptamers are utilized as a biorecognition element. MMP-2 is a protein which is typically overexpressed in tumor tissues, with important roles in tumor invasion, metastasis as well as in tumor angiogenesis. Based on impedimetric measurements, we were able to detect as low as 3.32 pg mL−1 of MMP-2 in PBS with a dynamic range of 10 pg mL−1 – 10 ng mL−1. Further experiments with real blood samples revealed a promising potential of the developed sensor for direct measurement of MMP-2 in complex media. High specificity of detection is demonstrated – even to the closely related enzyme MMP-9. Finally, the potential of reuse was demonstrated by signal restoration after experimental detection of MMP-2.

3D hierarchical flowerball-like CoSe2/MnSe nanosheet arrays as a novel electrode for electrochemical sensing of hydrazine

Hydrazine (N2H4) is considered to be a highly toxic substance harmful to human body and environment, and has received much attention in the field of electrochemical detection in recent years. In this study, 3D hierarchical flowerball-like CoSe2/MnSe nanosheet arrays (CoSe2/MnSe FNSAs) were obtained using CoMn-LDH as precursor and cobalt glycerate spheres as the sacrificial template by simple hydrothermal reaction and selenization method. Bimetal selenides have more active electrochemical activity and more abundant electrochemical redox reactions. The unique hierarchical flowerball-like nanosheet array heterostructure can accelerate ionic diffusion kinetics and improve electron transfer. As a hydrazine electrochemical sensor, CoSe2/MnSe FNSAs exhibits excellent electrocatalytic performance with a wide detection range of 0.001–7.45 mM and a low detection limit of 0.4 μM. This strategy provides a new choice for the detection of environmental organic pollutants.

Electrochemical redox of arsenic (III) and Cu (II) mixtures with ultraflat Au(111) thin films in water

The ability to detect trace concentrations of arsenite, As (III), in real water solutions is impacted by co-contamination of other metals and co-occurring ions. The presence of copper (II) ions are the most likely co-contaminant in natural waters to interfere with electrochemical As (III) detection, due to the close oxidation potentials of Cu (II) and As (III). The use of well-oriented ultraflat Au(111) thin film electrodes provided increased peak separation and sensitivity for electrochemical deposition and oxidation of Cu (II) and As (III) in 0.5 M sulfuric acid compared to an Au wire electrode. However, mixtures of Cu (II) and As (III) altered the oxidation peak positions during both cyclic voltammetry (CV) and linear stripping voltammetry (LSV) analysis. Calibration curves using the standard additions method in trace concentrations were conducted for Cu, As, and Cu & As solutions. Sweeping the potential at 10 mV s−1 during CV in Cu & As mixtures resulted in a sequential deposition condition where a layer of Cu inhibited co-deposition of As to the electrode. In contrast, the rapid potential stepping of LSV to a potential where Cu and As reduction simultaneously occurs produced a peak profile different from Cu or As alone. A larger oxidation peak during LSV was also observed when both Cu and As were present. X-ray photoelectron spectroscopy indicates a Cu-As alloy is formed on the surface after LSV deposition.SYNOPSIS: Analysis of Cu (II), As (III) and Cu (II) & As (III) mixtures suggests that a Cu3As intermetallic phase is formed during LSV which impacts trace As detection even in trace Cu conditions. This has important implications for the ability to determine As concentrations near the MCL of 10 µg L−1 in natural water systems which may contain Cu (II) and other co-contaminants.

Synthesis of Alkoxy-TEMPO Aminoxyl Radicals and Electrochemical Characterization in Acetonitrile for Energy Storage Applications

In this paper, we describe the synthesis and characterization of alkoxylated TEMPO, (2,2,6,6-tetramethylpiperidin-1-yl)oxyl, radicals with potential application in organic non-aqueous redox flow batteries. The behavior of a series of TEMPO derivatives with varying lengths of alkoxy chain is analyzed in acetonitrile solutions using electrochemical techniques, electron paramagnetic resonance (EPR) spectroscopy, and measurements of permeability through three different membranes. Electrochemical redox potentials are only weakly dependent on the substituent, but, in contrast, exchange current densities derived from the data do depend on the substitution. EPR lends further insight into these properties via the determination of hyperfine splitting constant and rotational correlation time. There is a negligible effect of the substituents on those parameters among the modified TEMPO radicals. Finally, permeation rates of modified TEMPO derivatives through membranes depend significantly on both the membrane and the substitution of TEMPO, providing insights into capacity fade measurements in the literature.

Lithiophilic Li-Si alloy-solid electrolyte interface enabled by high-concentration dual salt-reinforced quasi-solid-state electrolyte

Solid polymer electrolytes (SPEs) are urgently required to achieve practical solid-state lithium metal batteries (LMBs) and lithium-ion batteries (LIBs). Herein, we proposed a mechanism for modulating interfacial conduction and anode interfaces in high-concentration SPEs by LiDFBOP. Optimized electrolyte exhibits superior ionic conductivity and remarkable interface compatibility with salt-rich clusters: (1) polymer-plastic crystal electrolyte (P-PCE, TPU-SN matrix) dissociates ion pairs to facilitate Li+ transport in the electrolyte and regulates Li+ diffusion in the SEI. The crosslinking structure of the matrix compensates for the loss of mechanical strength at high-salt concentrations; (2) dual-anion TFSI–n-DFBOP–m in the Li+ solvation sheath facilitates facile Li+ desolvation and formation of salt-rich clusters and is conducive to the formation of Li conductive segments of TPU-SN matrix; (3) theoretical calculations indicate that the decomposition products of LiDFBOP form SEI with lower binding energy with LiF in the SN system, thereby enhancing the interfacial electrochemical redox kinetics of SPE and creating a solid interface SEI layer rich in LiF. As a result, the optimized electrolyte exhibits an excellent ionic conductivity of 9.31 × 10−4 S cm−1 at 30 °C and a broadened electrochemical stability up to 4.73 V. The designed electrolyte effectively prevents the formation of Li dendrites in Li symmetric cells for over 6500 h at 0.1 mA cm−2. The specific Li-Si alloy-solid state half-cell capacity shows 711.6 mAh g−1 after 60 cycles at 0.3 A g−1. Excellent rate performance and cycling stability are achieved for these solid-state batteries with Li-Si alloy anodes and NCM 811 cathodes. NCM 811|| Prelithiated silicon-based anode solid-state cell delivers a discharge capacity of 195.55 mAh g−1 and a capacity retention of 97.8% after 120 cycles. NCM 811||Li solid-state cell also delivers capacity retention of 84.2% after 450 cycles.

Investigation of polypyrrole/TiO2 and poypyrrole/WO3 nanocomposites as anode modifier in salt bridge microbial fuel cell using municipal wastewater

Developing nanocomposite materials based on conducting polymers (CPs) and metal-oxide nanoparticles, which combine redox electrochemistry of CPs with intrinsic properties of nano-scale semiconducting materials, may offer improved microbial fuel cells (MFCs) performances. Polypyrrole (PPY) based nanocomposites were synthesized by chemical oxidative polymerization method and were further used as an anode modifier in salt bridge MFCs. The PPY-based nanocomposites were characterized by X-ray diffraction, Fourier-Transform Infrared (FTIR) spectroscopy, and Scanning Electron Microscopy (SEM). The maximum power density of 16.7 mW/m2, 20.1 mW/m2, and 22.5 mW/m2 were obtained for MFC2-PPY, MFC3-PPY/TiO2 and MFC4-PPY/WO3 respectively, suggesting that modification of the anode with PPY- based nanocomposites is beneficial in the electricity generation of the MFC, and have superior performance as compared to the controller MFC1-CC (11.6 mW/m2).

Electrochemical synthesis of donor-acceptor triazine based polymers with halochromic and electrochromic properties

Two triazine monomers substituted with aromatic α,β unsaturated ketones (chalcones) as connecting arms, holding triphenylamine or carbazole ending groups, were by the first time synthesized using commercial and inexpensive starting materials in just two steps. Triphenylamine and carbazole groups were strategically introduced in order to allow electrochemical polymerization and redox activity of the obtained films. The chalcone, together with the triphenylamine or carbazole outer groups, give rise to the formation of a donor-acceptor systems, allowing the generation of photoinduced intramolecular charge transfer (ICT) electronic transitions and providing basic sites for protonation. Because of the star-like chemical structure of the used triazine, electrochemical polymerization of these monomers conducted to the formation of hyperbranched structures. The polymeric materials exhibited not only electrochromic properties but also showed a halochromic behavior. Spectroelectrochemical studies of the films showed different colorations in the three redox states (neutral, semioxidized and fully oxidized). The color changes are fast and easily detected by the naked eye. Electrochemical parameters such as optical contrast, coloration efficiency, optical memory, and long-term stability for both films were obtained and compared. A quasi-solid window-type electrochromic device was assembled using the electrogenerated polymer with the best electrochromic performance and stability. Moreover, the triphenylamine based polymer showed reversible color changes upon acid-base vapor exposure cycles, demonstrating that this polymer can be used not only in electrochromic devices but also in acid vapor sensors.

Redox behaviour of boron subphthalocyanine carbon nanotube composites

Organic redox-active carbon composites can be used as sustainable electrode materials in electrochemical energy storage systems. Among numerous redox active species, peripherally dodecafluorinated boron subphthalocyanines (F12BsubPcs) have shown electrochemical redox activities in the solution phase. Nonetheless, the electrochemical properties of solid F12BsubPcs when compositing with nano carbon warrants further investigation for potential applications in energy storage. In this work, nanometer scale axially brominated F12BsubPcs (Br-F12BsubPcs) were coated onto bare graphitized multiwalled carbon nanotubes (GCNT) and COOH-functionalized GCNT (COOH-GCNT) by a facile dip coating method to produce two composites and to compare the effects of the surface functional group interactions with Br-F12BsubPcs. While the surface chemical and morphological characterizations confirmed the presence of Br-F12BsubPc coating on both bare and COOH-GCNTs, the coverage on the latter was higher. Cyclic voltammetric studies in acidic electrolyte revealed a highly reversible redox couple on both composites with Br-F12BsubPc coated COOH-GCNT demonstrating up to c.a. 70% higher redox peak currents than with Br-F12BsubPc coated GCNT. Further analyses of the coated COOH-GCNT suggested a 2-electron transfer process. The charge transfer has fast-kinetics and a strong dependence on the proton concentration. The composites produced in this work demonstrate potential for future application in energy storage and can provide a strategy for developing BsubPc-based carbon composites.

Nitrogen-doped carbon nanotube encapsulated Co9S8 composite cathode for high-selective capacitive extraction of uranium (VI) from radioactive wastewater

Selective extraction of uranium [U(VI)] from uranium containing nuclear wastewater is of great significance in alleviating the uranium resources shortages and eliminating the radioactive radiation. Benefited by the merits of cost-effectiveness and environment-friendliness, capacitive deionization (CDI) shows a great promise towards selective removal of U(VI). However, exploring novel electrode materials with high intrinsic affinity rather than the excessive assistance of external means faces challenges. Herein, a nitrogen-doped carbon tube encapsulated Co9S8 composite (CS-NCNT) was developed as a Faradic cathode for selective electrosorption of U(VI) from radioactive wastewater. This work mainly emphasized on these following results: (i) The electrochemical redox activity and high surface-controlled ratios endowed the optimized CS-NCNT-2 electrode a maximum electrosorption capacity (189 mg g−1) towards U(VI). (ii) Except that CS-NCNT-2 exhibited excellent selective electrosorption performance in U(VI)-containing spiked real seawater, an ultrahigh selectivity coefficient of 707 (UO22+ over Na+) was also achieved at a Na+: UO22+ molar ratio of 200. (iii) The valence state analysis and molecular dynamic simulation revealed the essence of the reversible electrosorption-desorption process and the preferable extraction towards UO22+ compared with Na+ ions, respectively. Overall, this work can be potentially expanded to other metal chalcogenides-based electrode materials for selective removal of UO22+ even other radionuclide in U(VI)-containing radioactive wastewater.

On the formation of dendritic iron from alkaline electrochemical reduction of iron oxide prepared for metal fuel applications

Low-temperature electrochemical reduction (electroreduction) of iron oxides is a promising alternative to the conventional methods for iron production due to its CO2-free operation and relatively low energy consumption. In this work, we demonstrate a novel approach for electrochemical iron production by promoting the formation of dendritic structures during iron electrodeposition, which facilitates the easy harvesting of deposits in powder form. Experiments were conducted using a single pair of parallel plate electrodes, immersed in a mixture of hematite (Fe2O3) powder and aqueous alkaline (NaOH) slurry. The effects of current density, Fe2O3 mass fraction, temperature, and powder size on current efficiency and deposit morphology are investigated. A large quantity of dendritic iron structures is observed when experiments are carried out without stirring and/or applying heat from a heating plate. This condition suggests temperature and (ion/species) concentration gradients in the system. The dendrites are mainly deposited on the cathode's sides, corners, and edges. Different deposits and dendritic structures (compact layer deposit, moss-like deposit, deposit with whisker-like dendrites, and deposit with crystal-like dendrites) are observed as operating conditions change. Overall, a cathodic deposition of metallic iron with a high Faradaic efficiency (≥90 %) is successfully accomplished. The present findings provide new insights into the production of electrolytic iron powder and its future use as a carbon neutral and sustainable fuel/energy carrier.

P-NP mineralization, total nitrogen removal and toxicity reduction using an alternating-electroreduction-electrooxidation system

Electrochemical degradation has emerged as a sustainable technology for treating p-Nitrophenol (p-NP). However, most studies have focused only on electrochemical oxidation or electrochemical reduction, and limited research on alternating-electroreduction-electrooxidation system (AEES). The process of p-NP degradation in AEES system has not been understood. In this work, the effect of AEES on p-NP treatment was investigated by regulating the reduction and oxidation time ratios as well as the alternating cycles. The results indicated that the different modes had a significant effect on p-NP degradation rate and TN removal, while the effect on mineralization was limited. Obviously, the sequential reduction–oxidation system performed better than the sequential oxidation–reduction system, with p-NP degradation rates increasing by 34.2 % and 147.9 % over the oxidation and reduction modes alone, respectively. Moreover, an increase in the number of alternating cycles (R60O120 × 1 to R10O20 × 6) results in the improved mineralization from 84.4 % ± 2.1 % to 88.7 % ± 1.7 % and TN removal from 35.1 % ± 1.9 % to 46.6 % ± 2.1 %. The increased mineralization, decreased nitrogen compounds, and reduced complex by-products also contributed to 10.0 % ± 1.4 % reduction of acute toxicity. On the basis of intermediates identification, a degradation pathway for AEES including free radical substitution and ring opening process were proposed.

A novel electrochemical strategy to detect hydrogen peroxide by utilizing peroxidase-mimicking activity of cerium oxide/graphene oxide nanocomposites

We herein describe a novel electrochemical strategy to detect hydrogen peroxide (H2O2) by utilizing the peroxidase-mimicking activity of cerium oxide nanoparticles (CeO2 NP) and reduced graphene oxide (rGO). Particularly, CeO2 NP/rGO nanocomposites were deposited on the commercial electrode by a very convenient and direct electrochemical reduction of graphene oxide. Due to the peroxidase-mimicking activity of CeO2 NP and the outstanding electrochemical properties of reduced graphene oxide, the reduction current of H2O2 was greatly enhanced. Based on this strategy, we reliably determined H2O2 down to 1.67 μM with excellent specificity and further validated its practical capabilities by robustly detecting H2O2 present in heterogeneous human serum samples. We believe that this work could serve as a new facile platform for H2O2 detection.

Improving nitric oxide reduction reaction through surface doping on superstructures

Electrochemical nitric oxide reduction reaction (NORR) combining the production of NH3 with the removal of atmospheric pollutant NO is regarded as a promising strategy for producing important chemicals and reducing environmental pollution. However, existing NORR electrocatalysts such as Cu(111) have disadvantages of low activity and selectivity. In this work, the Cu2Si/Cu(111) and Cu2Si/Si(111) superstructures are proposed as NORR electrocatalysts with high stability, activity and selectivity. The results indicate that doping p-block element Si on Cu(111) and transition metal Cu on Si(111) changes the surface chemical environment and local physical properties, optimizing NO adsorption energy and successfully getting rid of the energy barriers of 0.15 and 1.56 eV on Cu(111) and Si(111), respectively. It is of great interest to find that the interfacial effect suppresses the competitive hydrogen evolution reaction (HER) by improving the interlayer charge transfer and modulating Si-3pz orbital, thus ensuring the high NORR selectivity. This theoretical work paves a new way to help design better NORR electrocatalysts for producing renewable fuels from pollutant NO.

Cost-effective layered double hydroxides/conductive polymer nanocomposites for electrochemical detection of wastewater pollutants

There is an urgent need to develop multifunctional cost-effective nanomaterials and nanocomposites that can be used in numerous applications while showing high efficiency and cheaper implementation compared to conventional techniques and/or materials. In this work, zinc/iron layered double hydroxide (LDH) and polyaniline (PANI) were synthesized as a model LDH/conductive polymer nanocomposite, which is a promising family of cheap multifunctional materials. This electrochemical properties of this nanocomposite was investigated for detection of heavy metal (HM) ions in water streams, using lead as a model HM. In the present work, zinc/iron LDH and PANI was assigned as carbon paste electrode modifier. The composite was fully characterized using various characterization techniques including X-ray diffraction (XRD), scanning electron microscope (SEM), and Fourier transform InfraRed (FTIR). The electrochemical redox reactions of lead (II) ions at the modified electrode interface were investigated using cyclic voltammetry (CV), differential pulse voltammetry (DPV), Accordingly, a linear relation of Pb2+ ions was achieved in the concentration range 1–80 µM with limit of detection (LOD) was 167.8 nM and limit of quantification (LOQ) was 559.4 nM. Furthermore, the cost of using such material for lead removal using a typical adsorption study was compared to using conventional inductively coupled plasma (ICP) or atomic absorption spectrometry (AAS) equipment for tracking HM removal during the adsorption process. Cost analysis revealed that the final overall cost of the modified carbon paste electrode is estimated as 1.25 USD. This cost represents less than 0.1% of the total cost required to conduct the same adsorption study using a typical ICP or AAS equipment. This composite can pave the road towards portable measurements for onsite detection of wastewater pollutants using cheap disposable-electrodes as compared to massive expensive off site equipment such as ICP and AAS.

Structural, photophysical, and electrochemical redox properties of meso-tetrakis(pentafluorophenyl)porphyrins

This study delineates the synthesis and comprehensive characterization of metal complexes of meso-tetrakis(pentafluorophenyl)porphyrin (H2TPF[Formula: see text]P, 1) with first-row transition metal ions (M = Mn(III) 2, Fe(III) 3, Co(II) 4, Ni(II) 5, Cu(II) 6, and Zn(II) 7) to elucidate their structural, electronic spectral, and electrochemical redox properties. Co, Ni, Cu and Zn Complexes exhibit planar structure ([Formula: see text]24 = 0.003-0.021 Å and [Formula: see text]C[Formula: see text] = 0.004−0.041 Å) which is also confirmed by the single crystal data of complex ZnTPF[Formula: see text]P, 7 shows the planar geometry, while Fe and Mn complexes show the slightly nonplanar structure ([Formula: see text]24 = 0.101–0.143 Å and [Formula: see text]C[Formula: see text] = 0.080–0.112 Å), which are distorted due to their occupied axial sites by −Cl ligand as revealed by density functional theory (DFT) calculations. Furthermore, electronic spectroscopy revealed a gradual bathochromic shift following the order of NiTPF[Formula: see text]P < CoTPF[Formula: see text]P < CuTPF[Formula: see text]PCl < H2TPF[Formula: see text]P = FeTPF[Formula: see text]PCl < ZnTPF[Formula: see text]P < MnTPF[Formula: see text]PCl by appending different metal ions in the porphyrin core. MnTPF[Formula: see text]PCl exhibited the most significant bathochromic shift ([Formula: see text] = 63 nm) in the Soret band compared to H2TPF[Formula: see text]P. Also, MnTPF[Formula: see text]PCl and FeTPF[Formula: see text]PCl show a unique pattern of split Soret band at around 364 and 345 nm due to the interaction between the metal [Formula: see text]-orbitals and the surrounding ligands. The electrochemical redox potentials of the filled 3d orbital of Zn endow ZnTPF[Formula: see text]P (ring centered) with the lowest oxidation potential.

Static Three-Chamber ZnI2 Redox Batteries and Analyzed Electrochemically

Static three-chamber ZnI2 redox batteries are designed and analyzed electrochemically. The reversibility of the zinc plating/stripping process is evaluated by monitoring the cathodic/anodic peaks in the cyclic voltammograms. The electrochemical redox process of iodide on the cathode is analyzed based on the impedance spectra. The reversibility of zinc plating/stripping is related to I2 adsorption and improving performance of three-chamber ZnI2 redox battery could be attributed to the isolation of redox ions. The multi-electrolyte battery limits the influence of I2 adsorption and delivers better performance including of the high discharging voltage and power density.

Optically Imaging In Situ Effects of Electrochemical Cycling on Single Nanoparticle Electrocatalysis.

Single-nanoparticle studies often need one or a series of nanoparticle populations that are designed with differences in a nominally particular structural parameter to clarify the structure-activity relationship (SAR). However, the heterogeneity of various properties within any population would make it rather difficult to approach an ideal one-parameter control. In situ modification ensures the same nanoparticle to be investigated and also avoids complicating effects from the otherwise often needed ex situ operations. Herein, we apply electrochemical cycling to single platinum nanoparticles and optically examine their SAR. An electrocatalytic fluorescent microscopic method is established to evaluate the apparent catalytic activity of a number of single nanoparticles toward the oxygen reduction reaction. Meanwhile, dark-field microscopy with the substrate electrode under a cyclic potential control is found to be able to assess the electrochemically active surface area (ECSA) of single nanoparticles via induced chloride redox electrochemistry. Consequently, nanoparticles with drastically increased catalytic activity are discovered to have larger ECSAs upon potential regulation, and interestingly, there are also a few particles with decreased activity, as opposed to the overall trend, that all develop a smaller ECSA in the process. The deactivated nanoparticles against the overall enhancement effects of potential cycling are revealed for the first time. As such, the SAR of single nanoparticles when subjected to an in situ structural control is optically demonstrated.

In Situ Creation of Surface Defects on Pd@NiPd with Core-shell Hierarchical Structure Toward Boosting Electrocatalytic Activity.

A deep insight into surface structural evolution of the catalyst is a challenging issue to reveal the structure-activity relationship. In this contribution, based on a surface alloying strategy, the dual-functional Pd@NiPd catalyst with a unique core-shell hierarchical structure is developed through selective crystal growth, surface cocrystallization, directional self-assembly, and reduction process. The surface defects are created in situ on the outer NiPd alloy layer in the electrochemical redox processes, which endow the Pd@NiPd catalyst with excellent electrocatalytic activity of hydrogen generation reaction (HER) and oxygen generation reaction (OER) in alkaline media. The optimal Pd@NiPd-2 catalyst requires an overpotential of only 18 mV that is far lower than Pt/C benchmark (43 mV) at the current density of 10 mA cm-2 for the HER, and 210 mV that is far lower than RuO2 benchmark (430 mV) at 50 mA cm-2 for the OER. Density functional theory (DFT) calculations reveal that the outstanding electrocatalytic activity is originated from the creation of surface defect structure that induces a significant reduction in the adsorption and dissociation energy barriers of H2O molecules in the HER and a decrease in the conversion energy from O* to OOH* that resulted from the synergy of two adjacent Pd sites by forming O-bridge. This work affords a typical paradigm for exploiting efficient catalysts and investigating the dependence of electrocatalytic activity on the surface structural evolution.

Improving charge transfer via nickel–nickel oxide/molybdenum dioxide heterostructure for advanced supercapacitor electrode

Currently, asymmetric supercapacitors (ASCs), as significant energy storage devices, have gained tremendous attention for alleviating the ever-increasing demands of carbon-free energy. Herein, metallic nickel decorated nickel oxide/molybdenum dioxide nanorods are directly anchored on porous nickel foam (Ni-NiO/MoO2/NF) by a hydrothermal method and subsequent reduction engineering under H2/Ar aura. The H2-reduction induced oxygen vacancies, multi-phase configurations, and rich interfaces synergistically enchace the electrochemical energy storage capabilities of the Ni-NiO/MoO2/NF. Notably, the density functional theory (DFT) results indicate that the generated interfaces of both Ni/NiO and Ni/MoO2 facilitate the metallic characteristic and thus enhance the electrochemical redox activity. Consequently, the Ni-NiO/MoO2/NF shows a specific capacity of 256.8 C g–1 at 1 A g–1 and 159.9 C g–1 at 20 A g–1, as well as a good cycling durability (remains 90.7% capacity after 8000 cycles) in 2.0 M of KOH media. In addition, an ASC with a voltage window of 1.4 V is constructed by employing the Ni-NiO/MoO2/NF and activated carbon (AC) as positive electrode and negative electrode, respectively, which exhibits an energy density as 28.8 Wh kg−1 at 777.8 W kg−1 and 80.2% capacity retention after 8000 charge/discharge operation. Further, a home-made ASC is assembled and exhibits potential application to power an electric fan. This work provides an efficiently way to construct multi-component electrodes with abundant heterostructures for applications in portable devices.

Electrochemical Redox Conversion of Formate to CO via Coupling Fe-Co Layered Double Hydroxides and Au Catalysts.

Formate has been considered an inactive molecule and thus cannot be further reduced under CO2 reduction conditions, which limits its widespread application as feedstock. Here we present an electrochemical redox conversion of formate to CO through the potential-dependent generation of carbon dioxide radical anions (CO2 ⋅- ) on Fe-Co layered double hydroxides (Fe-Co LDHs) and the subsequent reduction of CO2 ⋅- to CO on Au catalysts. We present an electrodeposition protocol for the synthesis of Fe-Co LDHs with precise composition control and find that Fe1 Co4 exhibits a promising potential window for CO2 ⋅- formation between 1.14 and 1.4 V and an optimized potential at 1.24 V at a neutral pH condition. We further determined the formation of CO2 ⋅- at 1.24 V via electron paramagnetic resonance and CO2 at >1.4 V through differential electrochemical mass spectrometry. This work provides a redox chemistry route for converting formate into CO through a coupled slit parallel-plate electrode system.