Linear Scan Voltammetry Research Articles

(Invited) Highly Active Pt-Modified Catalyst for the Selective Electro-Oxidation of Saccharides

The increasing demand of energy and high value-added compounds, and the extinction of fossil resource reservoirs result in replacing fossil resources with biomass. Cellulose and hemicellulose represent 40 to 60 wt% of agriculture green wastes and can be considered as raw materials. After transformation of these biopolymers into saccharides, the latter can serve as platform molecules to produce chemicals with high value added and/or industrial interest. In that context carbohydrates need to be studied more deeply for obtaining every possible outcome. Focusing on environmental problems, electro-reforming can provide hydrogen together with a supplementary valuable industrial compound, but this last process must show very high selectivity and low cost to compete with classical biotechnological methods for sugar conversion.monosaccharides, disaccharides and oligosaccharides are complex molecules bearing several oxygenated functions (primary alcohol, secondary alcohol, anomeric group) that are potentially electrochemically reactive. Therefore, it is needed to develop catalysts displaying very high activity at low potentials and very high selectivity towards a given compound. For this purpose, the synthesis and characterization of Pt-based binary catalysts will be presented and their electrocatalytic behavior towards the oxidation of saccharides (glucose and cellobiose bearing a reductive anomeric function, and methylglucoside and trehalose with a protected anomeric function) will be first studied by linear scan voltammetry in a classical three-electrode cell to evaluate their activity and by in situ infrared spectroscopy to determine reaction intermediates and products as a function of the electrode potential. Best candidates will be used as anode catalysts to perform the electroreforming of saccharides in a two-electrode electrolysis cell with simultaneous production of hydrogen at the cathode. Reaction products will be analyzed by HPLC, MS, and 1H and 13C NMR to determine the selectivity and the efficiency of the system.From the electrochemical and analytical results, the high efficiency of the Pt9Bi1/C catalysts will be emphasized, the electro-reactivity of the different functions determined, and reaction mechanisms discussed.

Photocatalytic hydrogen generation via water splitting using ZIF-67 derived Co3O4@C/TiO2

Water splitting via photocatalysis using titanium dioxide (TiO2) holds great potential for hydrogen gas generation. Herein, zeolitic imidazolate framework (ZIF-67) was used as a sacrificial precursor for the synthesis of cobalt oxide embedded nitrogen doped carbon (Co3O4@C) that was used as a co-catalyst with TiO2 for the hydrogen generation via photocatalytic water splitting. The optimal loading of Co3O4@C (7 wt%) exhibited a photocatalytic hydrogen production rate (HGR) of 11,400 µmol g−1 h−1. It demonstrated a 75-fold and 110-fold increase for cumulative (5 h) and initial hydrogen generation rates, respectively. The electrochemical measurements such as cyclic voltammetry (CV), linear scan voltammetry (LSV), electrochemical independence spectroscopy (EIS) using Nyquist plots, and photocurrent response were conducted to evaluate the catalytic performance of Co3O4@C/TiO2. Transient photocurrent response showed significant enhancement (4-fold) in photocurrent density of TiO2. Co3O4@C promoted the photocatalytic performance of TiO2 and improved the HGR. The photocatalysis using Co3O4@C/TiO2 is recyclable for more than four cycles without significant loss of their performance. The results of our study may open the door for further exploration toward effective photocatalyst.

High-Performance Ru 2 P Anodic Catalyst for Alkaline Polymer Electrolyte Fuel Cells

High-Performance Ru ₂ P Anodic Catalyst for Alkaline Polymer Electrolyte Fuel Cells

Safe and flexible chitosan‐based polymer gel as an electrolyte for use in zinc‐alkaline based chemistries

AbstractA novel flexible, high performing chitosan‐based gel electrolyte with poly (vinyl alcohol) (PVA) and potassium hydroxide (KOH) additives is prepared, using an optimized energy and time efficient method. Incorporation of a gel‐based electrolyte in batteries aims to eliminate safety hazards present within conventional liquid‐based electrolyte constructions. The ionic conductivity values obtained at room temperature are in the range of 5.32–105 mS/cm depending on composition. Optical, scanning electron microscopy, X‐ray diffraction, and Fourier transform infrared spectra studies are conducted to understand morphological and structural changes in the films with additives. Thermogravimetric analysis, manual bending and tensile tests, linear scan and cyclic voltammetry analysis are also conducted to study the physical and electrochemical stability of the films. Also, the prepared electrolytes are incorporated to form Zn‐MnO2 batteries and tested. Results reveal no physical damage of the films under continuous bending over 250 cycles. Mechanical properties for CPK0.3 suggest a strong and ductile material well suited for the intended application. Additionally, the novel electrolyte exhibits excellent physical stability up to 50οC, electrochemical stability until 2 V for zinc electrodes and prove to successfully accommodate redox reactions involved in the Zn‐MnO2 alkaline system.

Synergetic electrocatalytic degradation of isophorone by active oxygen species generated in the gas diffusion electrode and PbO2 anode

Significant efforts have been made to achieve efficient H2O2 generation via oxygen reduction reaction (ORR). Here, the acetylene black (AB)-based gas diffusion electrodes (GDEs) modified by PTFE were fabricated and applied in a closed autoclave for H2O2 generation for the first time. The surface morphology, BET, XPS, cyclic voltammetry curves and linear scanning voltammetry curves of GDEs were all characterized. Additionally, the H2O2 generation experiments of GDEs and the relationship between H2O2 yield and BET surface area (SBET), double layer capacitance (Cdl) were all investigated. It could be found that the SBET and Cdl of GDEs kept a good linear relationship with H2O2 content, and 2#GDE (AB:PTFE = 1:3) possessed the optimal H2O2 generation capacity. Also, the effect of oxygen pressure and current density on H2O2 production was evaluated detailedly, indicating higher oxygen pressure was beneficial to the H2O2 generation and the preferable current density was 20 mA cm−2 due to the side reactions. And all the H2O2 electro-generation experiments exhibited a higher oxygen utilization efficiency (0.77%–2.93%). Finally, the efficient and synergetic electro-catalytic degradation of isophorone was achieved by self-made PbO2 anode and GDE.

Revised electrochemical etching system for a reproducible fabrication of ultra-sharp tungsten tips

This article proposes an improved version of the drop-off electrochemical etching technique, developed for a reproducible production of ultra-sharp metal tips. Firstly, a comprehensive survey of other mechanical and physicochemical procedures is made in order to individuate three issues commonly neglected: (i) the influence of external perturbations, (ii) the positions of the electrode (a W wire) and counter-electrode (a Pt ring) and (iii) the counter-electrode shape. These issues need to be carefully fixed, in an enclosed and geometrically well-defined configuration, to better control the opening angle, radius of curvature and aspect ratio. The quality of the tips produced is evaluated comparing their performances, in imaging a reference sample with scanning tunnelling microscopy, to those of commercial tips. Using established procedures and data reported in the literature, an optimal set of the parameters can be identified obtaining high-quality tips with an opening angle < 10° and a radius of curvature ~ 30 nm. Furthermore, achieving a higher reproducibility allows us to investigate the electrochemical process monitoring the time dependence of the current from the etching parameters, such as the wire immersion, electrolyte concentration and applied bias voltage. Thus, the current versus time curves can be analysed in terms of linear scan voltammetry and electrochemical impedance spectroscopy, in order to investigate the phenomena occurring during the wire etching. In particular, at the beginning of the electrochemical process, the replacement of the native W oxide with a thicker layer of WO3(H2O)x oxide is observed, in agreement with previous observations.

Method of developing Thermo–Kinetic diagrams: The Cu–H2O–acetate and the Cu-H2O systems

A method to develop thermo-kinetic (TK) diagrams for the Cu−H2O−acetate and Cu−H2O systems is described. Conventional Eh-pH diagrams, also known as Pourbaix diagrams, are developed based on the thermodynamic stability of component species, typically in aqueous media. TK diagrams are an improvement on Eh-pH diagrams as they also describe the kinetics of electrochemical processes. These diagrams are developed by using data from linear scan voltammetry of Cu rotating disk electrodes exposed to aqueous media of different pH. By applying the same procedure, the TK diagrams can be developed for other metals or mineral systems exposed to aqueous media containing ligands. To ensure reproducibility and reconstruction of the TK diagrams for other metal/mineral/electrolyte systems, some important experimental considerations are highlighted in this study. These TK diagrams are useful to evaluate the corrosion of metals, the leaching performance of minerals and to predict the suitable conditions for metal recycling processes.Briefly, this article explains:•Important experimental considerations that could affect the kinetics of electrochemical processes.•A method to construct TK diagrams with examples of the Cu−H2O−acetate and Cu−H2O systems.•With overlaid Eh-pH diagrams, TK diagrams explain both the thermodynamic stability of component species and the kinetics of the electrochemical processes.

Evaluation of voltammetric method for the determination of electrodeposited copper in citrate medium validated by ICP-OES

Copper (Cu) is a toxic pollutant and its presence in wastewater, even at low concentrations, can have a significant environmental impact. In this work, a method for the determination of Cu was developed using a voltammetric technique involving a platinum electrode in citrate medium. Cu at a ppb level was determined by both chronoamperometry (CA) and anodic linear scanning voltammetry (ALSV), and the results were compared to those from inductively coupled plasma optical emission spectroscopy (ICP-OES). The results obtained were similar, having a deviation of 2.56%. The least squares method was used to evaluate the correlation between the ALSV and ICP-OES results. Statistical analyses showed a 95% confidence interval.

Lowering the Energy Consumption of Zinc Electrowinning By Electrocatalysis of the Oxygen Evolution Reaction Using Manganese Oxides

Zinc has a wide range of commercial applications including but not limited to galvanizing iron and steel and production of various metal alloys such as brass and bronze. In hydrometallurgical processes, zinc electrowinning from sulfate-based electrolytes is the last step of zinc extraction in which high purity metallic zinc is electrodeposited from a highly acidic solution on an aluminum cathode. The electrowinning stage is very energy-intensive and responsible for approximately 80% of the power requirement of a zinc refinery (1). Thus, improving the energy efficiency and lowering the operating costs of zinc electrowinning are of primary significance. The oxygen evolution reaction (OER) overpotential on conventional lead-silver (Pb-Ag) anodes contributes to nearly 25% of the total electrowinning cell potential (2). Therefore, the high anodic OER overpotential places a heavy financial burden on zinc refining plants.The present study aims to evaluate novel anodic electrocatalysts incorporating MnO x in order to lower the anodic OER overpotential of the zinc electrowinning process. Anodically electrodeposited MnO x catalysts on Pb-Ag electrodes were prepared using galvanostatic and potentiodynamic polarizations. The OER catalytic activity and stability of MnOx electrodeposited Pb-Ag electrodes were evaluated in 160 g/L sulphuric acid solution with 3 g/L of manganese (II) and in the absence and presence of 0.3 g/L of chloride ion at 35°C, using a standard three-electrode setup. The electrolyte composition and operating conditions were selected such that to be directly applicable to the industrial zinc electrowinning process. The OER activity of the MnOx electrodeposited electrodes was investigated through potentiodynamic polarization and 72-hour galvanostatic electrolysis at 50 mA/cm2 superficial current density. Finally, the activity of MnOx electrodeposited Pb-Ag electrodes was explored in a full zinc electrowinning cell through 24-hour galvanostatic electrolysis at 50 mA/cm2 superficial current density.The OER potential variations of the bare Pb-Ag and MnO x electrodeposited Pb-Ag anodes during the 72-hour galvanostatic polarization are shown in Fig. 1. In the absence and presence of chloride ions, the three MnO x electrodeposited Pb-Ag electrodes are observed to reduce the anodic potential by maximum of 150 mV and 80 mV, respectively. Investigation of these novel electrodes in the full-cell zinc electrowinning operation corroborated the half-cell experiments, revealing a maximum of 130 mV reduction in cell potential at 50 mA/cm2 superficial current density and in the presence of 0.3 g/L of chloride ion. Thus, this work demonstrates that MnO x electrodeposited Pb-Ag anodes have great capacity to lower the power consumption of the zinc electrowinning process.Fig. 1. OER activity and stability comparison under galvanostatic polarization for four anodes: bare Pb-Ag (baseline) and three MnOx electrodeposited Pb-Ag anodes prepared via linear scan voltammetry (LSV), constant current density (CCD), and cyclic voltammetry (CV). Superficial current density: 50 mA/cm2. Electrolyte:160 g/L H2SO4 with 3 g/L Mn2+ and 0.3 g/L Cl- at 35°C.References A. C. Scott, R. M. Pitbaldo, G.W. Barton, A. R. Ault, J. Appl Electrochem, 18, 120–127 (1988). Schmachtel, M. Toiminen, K. Kontturi, O. Forsen, M. H. Barker, J. Appl Electrochem, 39, 1835–1848 (2009). Figure 1

A selective and efficient precious metal-free electrocatalyst for chlorine evolution reaction: An experimental and computational study

Chlor-Alkali (CA) process benefits from chlorine evolution reaction (ClER) over various precious metal oxides electrocatalysts. This study introduces a novel precious metal-free Ti 0:35 V 0:35 Sn 0:25 Sb 0.05 -oxide electrocatalyst which selectively conducts the reaction pathway towards ClER with a high faradaic current efficiency of ~88%. The electrocatalyst and its electrochemical activity were scrutinized by various techniques such as field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and linear scanning voltammetry (LSV). A decent overpotential difference (DE) between oxygen evolution reaction (OER) and chlorine evolution reactions (ClER) was attributed to the reasonable design of the electrocatalyst composite. Namely, the geometric structure and surface properties of the synthesized electrocatalyst, as well as the associated electrochemical selectivity was tuned by incorporation of vanadium pentoxide, antimony and tin oxide in the electrocatalyst material. In addition, the electronic properties of the synthesized electrocatalysts including band structure and the corresponding electron density were studied by density functional theory (DFT) calculations. • A cost-effective Ti 0:35 V 0:35 Sn 0:25 Sb 0.05 -oxide electrocatalyst was synthesized. • The developed electrocatalyst was tuned towards chlorine evolution reaction. • Preferred chlorine evolution was resulted rather than oxygen evolution reaction. • The electronic structure of the developed electrocatalysts was explored by DFT. • The presence of vanadium oxide could lower the band gap of the electrocatalyst.

Phyto-mediated semiconducting n-type electrode nanomaterial: structural, compositional, and supercapacitor investigations

Sustainable fabrication of efficient electrode is highly demandable in the present time particularly for supercapacitors. In the present work, we have functionalized zinc oxide nanoparticles (ZnO-NPs) using foliar constituents for the first time. Leaves aqueous extract of Euphorbia cognata Boiss was used as organic fuel to synthesize ZnO-NPs. The leaves extract was reacted with zinc acetate (Zn(O2CCH3)2 (H2O)2) hydro complex to obtain phyto-organic functional groups, and subsequent formation of ZnO-NPs was accomplished by thermal treatment. The X rays diffractions and energy dispersive X ray spectroscopy identified pure ZnO phase while field emission scanning electron microscopy showed spherical ZnO-NPs with particle size range of 40–65 nm. The phyto synthesized ZnO-NPs revealed direct band gap value of 3 eV via Tauc plot. The biosynthesized ZnO-NPs were, for the first time, integrated into thin film electrode by physical vapor deposition (PVD) and were subjected to cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and linear scan voltammetry (LSV). The fabricated ZnO thin film (ZnO-TFs) electrode exhibited the capacitance of 336.12 Fg−1 at 10 mVs−1 by CV. However, pseudocapacitive behavior was well demonstrated by LSV and CV at different scan rates. The EIS analysis illustrated very minor semi-circle arc with lower Rct and Warburg impedance by Nyquist plot indicating good electrochemical conductivity of ZnO-TFs. Overall, the results of the current study revealed that phyto-synthesized ZnO has a considerable potential for supercapacitor.

Nonwoven Ni–NiO/carbon fibers for electrochemical water oxidation

The development of technologically efficient anodes for water oxidation is crucial to improve hydrogen production via water splitting. Electrodes based on metallic active sites dispersed in carbon matrices have been shown to be an attractive way to attain this goal. However, challenges remain to prevent catalyst agglomeration that otherwise can result in a decrease of performance over time.In this work, we report an alternative and efficient method to produce nickel-nickel oxide nanoparticles-embedded in carbon nanofibers (Ni–NiO/C), by the solution blow spinning (SBS) process. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses show the carbon nanofibrillar matrix as a robust support, with well-dispersed nickel nanoparticles on the surface. The responses of the linear scanning voltammetry, cyclic voltammetry and electrochemical impedance spectroscopy demonstrate how a small fraction of nickel on the fiber surface (≈1.2–5.3%) is enough to promote substantial improvement in performance (η = 278 and 309 mV vs RHE for 10 mA cm−2) and a significant turnover frequency (TOF) values of 1.38 (η = 278) and 1.30 s−1 (η = 309). These promising results are correlated with a large amount of Ni3+ present on the fiber surfaces, as identified by X-ray Photoelectron Spectroscopy (XPS). This work provides a low-cost and rapid preparation technique that can be extended for the manufacture of a wide variety of electrodes based on metals supported on carbon nanofibers.

Enhanced Electrocatalytic Activity of Stainless Steel Substrate by Nickel Sulfides for Efficient Hydrogen Evolution

Water splitting is one of the efficient ways to produce hydrogen with zero carbon dioxide emission. Thus far, Pt has been regarded as a highly reactive catalyst for the hydrogen evolution reaction (HER); however, the high cost and rarity of Pt significantly hinder its commercial use. Herein, we successfully developed an HER catalyst composed of NiSx (x = 1 or 2) on stainless steel (NiSx/SUS) using electrodeposition and sulfurization techniques. Notably, the electrochemical active surface area(ECSA) of NiSx/SUS was improved more than two orders of magnitude, resulting in a considerable improvement in the electrochemical charge transfer and HER activity in comparison with stainless steel (SUS). The long-term HER examination by linear scan voltammetry (LSV) confirmed that NiSx/SUS was stable up to 2000 cycles.

Proposing an unbiased oxygen reduction reaction onset potential determination by using a Savitzky-Golay differentiation procedure

For proper and fair comparison of the performance of Oxygen reduction reaction (ORR) electrocatalysts an un-biased method to determine an onset potential value is needed. Here we report an easy mathematical approach based on the second derivative of linear sweep voltammetry curves, referred to as a second order discrete differentiation method (SODDM) that allows to accurately provide the onset potential. Analysis of the published results showed that the reported values might be affected by an intrinsic human error associated with the application of the most common approaches addressed as a tangent method or those relaying on a visual estimation of the onset potential based on the shape of a linear scan voltammetry (LSV) curve. We have also demonstrated that by using SODDM, electrochemical data collected on different instruments by different researchers leads to comparable results in terms of the ORR onset potential values.

In‐situ formation of an efficient trimetallic (CuZnAg) electrocatalyst for water oxidation

There is a need to develop highly efficient electrocatalysts based on non-noble metals which can be used for water splitting. Thus, to realize an acceptable oxygen evolution reaction (OER) performance, a combination of non-noble metals was used to improve the architecture and conducive to a facile OER. For this purpose, a binder-free and non-noble metal-based trimetallic (CuZnAg) composite OER a electrocatalyst was grown at the surface of fluorine-doped tin oxide by a facile one step in-situ electrodeposition method using chronoamperometry. The formation and performance of the catalyst were ensured from XRD, SEM, EDX, chronoamperometry, and linear scan voltammetry. The trimetallic composite showed good results toward OER in 1 M KOH electrolyte at pH 13 at a current density of 1 mA/cm2 with an overpotential of 303 mV at a scan rate of 10 mV/sec. The results revealed robust electrochemical durability under alkaline conditions and the electrocatalyst holds great promise for OER.

Electrochemical Discrimination of Dihydroxybenzene Isomer at Different Thiols Self-Assembled Monolayers on Gold and Simultaneous Determination of Catechol and Hydroquinone

The discrimination effect of dihydroxybenzene isomer including catechol (CAT), hydroquinone (HQ) and resorcinol (RE) on bare gold, and a series of thiols self-assembled monolayers (SAMs) including mercaptohexanol (MCH), 6-mercaptohexanoic acid (MHA), mercaptoethylamine (MEA), thiol-modified double-stranded DNA (ds-DNA), single-stranded DNA (ss-DNA) is first investigated by cyclic voltammetry (CV) and linear scan voltammetry (LSV). Results show that CAT, HQ and RE can not be electrochemically discriminated simultaneously by bare gold or thiols SAMs based on their oxidation or reduction peaks. Furthermore, RE has a big interference on the electrochemical response of CAT and HQ. At acidic solution (pH 4.4), in presence of RE, CAT and HQ can not be discriminated on bare gold, ds-DNA or ss-DNA SAMs. However, CAT and HQ can be discriminated well at MCH, MHA, and MEA SAMs on gold based on the difference of reduction peak potentials (ΔE pc) as 219, 212 and 165 mV respectively. MCH SAMs is chosen to study simultaneous determination of CAT and HQ due to bigger ΔE pc and current response. We fix the potential at 0.7 V for 60 s to enrich the oxidation products of CAT and HQ, then investigated the relationships of reduction peak current (i pc) with the concentrations of CAT and HQ. The i pc values are linear with the concentrations of CAT and HQ in the range of 7.0 × 10−6∼1.04 × 10−3 M. The limit of detection (LOD) is calculated to be 5.9 × 10−7 M for CAT and 8.3 × 10−7 M for HQ (S/N = 3). The MCH SAMs on gold is applied to the simultaneous determination of CAT and HQ in lake water sample and satisfactory result is obtained.

Trace Ti3+- and N-codoped TiO2 nanotube array anode for significantly enhanced electrocatalytic degradation of tetracycline and metronidazole

A trace Ti3+- and N-codoped TiO2 nanotube array (TiON) anode is fabricated by electrochemical reduction after introducing nitrogen into the TiON. The TiON anode material is characterized by scanning electron microscopy, X-ray diffraction, Raman spectra and X-ray photoelectron spectroscopy. Electrochemical analyses of TiON, including cyclic voltammetry, electrochemical impedance spectroscopy and linear scan voltammetry, are conducted to confirm that the electrochemical performance could be significantly improved by electrochemical reduction and N doping. The achieved TiON anode is applied to the electrocatalytic oxidation of tetracycline (TC) and metronidazole (MNZ). The effect of applied current density, initial solution pH and initial TC/MNZ concentration on the reaction kinetics is systematically evaluated to obtain the optimal conditions. The degradation processes follow an apparent first-order kinetic model in all conditions. After 240 min of reaction time, the TC removal efficiency, chemical oxygen demand (COD) removal rate and total organic carbon (TOC) removal rate are >99%, 92.86% and 74.98%, respectively. The MNZ removal efficiency, COD and TOC removal rate achieved are >99%, 93.03% and 79.30%, respectively, after 240 min of degradation. The excellent removal efficiency of TC and MNZ indicates that this TiON anode is a promising material in the practical application of removing antibiotics from water.

Carbon-Supported Mo2C for Oxygen Reduction Reaction Electrocatalysis.

Molybdenum carbide (Mo2C)-based electrocatalysts were prepared using two different carbon supports, commercial carbon nanotubes (CNTs) and synthesised carbon xerogel (CXG), to be studied from the point of view of both capacitive and electrocatalytic properties. Cation type (K+ or Na+) in the alkaline electrolyte solution did not affect the rate of formation of the electrical double layer at a low scan rate of 10 mV s−1. Conversely, the different mobility of these cations through the electrolyte was found to be crucial for the rate of double-layer formation at higher scan rates. Molybdenum carbide supported on carbon xerogel (Mo2C/CXG) showed ca. 3 times higher double-layer capacity amounting to 75 mF cm−2 compared to molybdenum carbide supported on carbon nanotubes (Mo2C/CNT) with a value of 23 mF cm−2 due to having more than double the surface area size. The electrocatalytic properties of carbon-supported molybdenum carbides for the oxygen reduction reaction in alkaline media were evaluated using linear scan voltammetry with a rotating disk electrode. The studied materials demonstrated good electrocatalytic performance with Mo2C/CXG delivering higher current densities at more positive onset and half-wave potential. The number of electrons exchanged during oxygen reduction reaction (ORR) was calculated to be 3, suggesting a combination of four- and two-electron mechanism.

Non-precious and accessible nanocomposite of iron oxide on PDDA-Modified graphene for catalyzing oxygen reduction reaction

Abstract Nanocomposite catalysts composed of non-precious nanoparticles anchored by modified graphene for oxygen reduction reactions (ORRs) are the emphasis of research nowadays for wide application in electrocatalyst systems. Herein, an endeavor is made to report on a one-pot synthesis method to produce a catalyst for Fe3O4 and Ni–NiO nanoparticles on Polydiallyldimethylammonium chloride-modified graphenes (PDDA-G). The nanocomposite is characterized by spectral measurements, using scanning electron spectroscopy (SEM), transmitting electron spectroscopy (TEM), x-ray diffractometer (XRD) and Raman spectroscopy to reveal its microstructure. Through a layer-by-layer PDDA-G investigation, a significant anchoring of nanoparticles and maintenance of the graphene with good electron transporting properties and spatial distance in nanoscale by PDDA is achieved. Additionally, the electrochemical properties of Fe3O4@PDDA-G and Ni–NiO@PDDA-G are demonstrated by linear scan voltammetry (LSV) with rotation disk electrode (RDE). Fe3O4@PDDA-G displays prominent ORR activity in 2-electron and 4-electron pathways, and better ORR mass activities than Ni–NiO@PDDA-G and commercial Pt/C. The results of this study provide a new strategy to develop material design approaches for high-performance electrocatalysts to be employed in fuel cells.

Quantifying Electrocatalytic Reduction of CO2 on Twin Boundaries

Summary A protocol relying on the use of silver nanostructures with well-defined dimensions and morphologies (e.g., nanocubes and nanowires) has been developed to differentiate and quantitatively determine the atom-specific activities of different surface atoms toward catalyzing electrochemical CO2 reduction reaction (CO2RR). The atom-specific activity of the twin-boundary edges (TBEs) is comparable to (or slightly higher than) that of the single-crystal edges (SCEs) formed from the crossing of two {100} surfaces, and it is on the order of ∼16 attoampere/atom (aA/atom) toward electrochemical CO2RR. This value is more than two orders higher than the atom-specific activity of the {100} surface atoms, i.e., ∼0.1 aA/atom. The high catalytic activity of the TBEs, which represent a class of commonly existing surface defects in stable metal nanostructures with face-centered cubic lattices, is consistent with the DFT calculations, in which the bridge-type binding configuration of COOH∗ at the TBEs stabilizes this intermediate to promote overall CO2RR.