Cyclic Voltammetry Cycling Research Articles

Electrochemically Derived Crystalline CuO from Covellite CuS Nanoplates: A Multifunctional Anode Material.

In the present era, electrochemical water splitting has been showcased as a reliable solution for alternative and sustainable energy development. The development of a cheap, albeit active, catalyst to split water at a substantial overpotential with long durability is a perdurable challenge. Moreover, understanding the nature of surface-active species under electrochemical conditions remains fundamentally important. A facile hydrothermal approach is herein adapted to prepare covellite (hexagonal) phase CuS nanoplates. In the covellite CuS lattice, copper is present in a mixed-valent state, supported by two different binding energy values (932.10 eV for CuI and 933.65 eV for CuII) found in X-ray photoelectron spectroscopy analysis, and adopted two different geometries, that is, trigonal planar preferably for CuI and tetrahedral preferably for CuII. The as-synthesized covellite CuS behaves as an efficient electro(pre)catalyst for alkaline water oxidation while deposited on a glassy carbon and nickel foam (NF) electrodes. Under cyclic voltammetry cycles, covellite CuS electrochemically and irreversibly oxidized to CuO, indicated by a redox feature at 1.2 V (vs the reversible hydrogen electrode) and an ex situ Raman study. Electrochemically activated covellite CuS to the CuO phase (termed as CuSEA) behaves as a pure copper-based catalyst showing an overpotential (η) of only 349 (±5) mV at a current density of 20 mA cm-2, and the TOF value obtained at η349 (at 349 mV) is 1.1 × 10-3 s-1. A low Rct of 5.90 Ω and a moderate Tafel slope of 82 mV dec-1 confirm the fair activity of the CuSEA catalyst compared to the CuS precatalyst, reference CuO, and other reported copper catalysts. Notably, the CuSEA/NF anode can deliver a constant current of ca. 15 mA cm-2 over a period of 10 h and even a high current density of 100 mA cm-2 for 1 h. Post-oxygen evolution reaction (OER)-chronoamperometric characterization of the anode via several spectroscopic and microscopic tools firmly establishes the formation of crystalline CuO as the active material along with some amorphous Cu(OH)2 via bulk reconstruction of the covellite CuS under electrochemical conditions. Given the promising OER activity, the CuSEA/NF anode can be fabricated as a water electrolyzer, Pt(-)//(+)CuSEA/NF, that delivers a j of 10 mA cm-2 at a cell potential of 1.58 V. The same electrolyzer can further be used for electrochemical transformation of organic feedstocks like ethanol, furfural, and 5-hydroxymethylfurfural to their respective acids. The present study showcases that a highly active CuO/Cu(OH)2 heterostructure can be constructed in situ on NF from the covellite CuS nanoplate, which is not only a superior pure copper-based electrocatalyst active for OER and overall water splitting but also for the electro-oxidation of industrial feedstocks.

Sulfolane as a co-solvent for carbonate-electrolytes in lithium-ion batteries using a LiMn2O4 cathode

In this study, we aimed to evaluate the effect of sulfolane (SL) as a co-solvent in conventional carbonate-based electrolytes and its compatibility with a LiMn2O4 (LMO) cathode. The amount of SL was varied from 10 to 50 vol.% in an EC-DMC mixture (1:1 vol. ratio) within a 1.0-M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt. The thermal properties of the electrolytes were studied using thermogravimetric analysis (TGA). Solvent flammability was measured via self-extinguishing time (SET) and ignition time indexes while viscosity was gauged by the Ostwald method. Ionic conductivity was evaluated by electrochemical impedance spectroscopy (EIS). Electrochemical techniques such as cyclic voltammetry (CV) and galvanostatic cycling with potential limitation (GCPL) were carried out to evaluate battery performance with the selected electrolytes. The results indicated that an increasing proportion of SL leads to an enhancement of the thermal and oxidation stability of the electrolytes. At 20-vol.% SL and below, the as-synthesized electrolytes exhibited a high ionic conductivity of 7.45 mS.cm-1 (25oC) and enabled LMO to deliver a specific capacity of 103 mAh.g-1 with a capacity retention of 92% after 20 cycles at C/10 rate. Due to such favourable properties, SL can be used as a co-solvent in EC-DMC systems to enhance the safety of lithium-ion batteries under high voltage conditions.

Enhanced Performance of Carbon-Selenide Composite with La0.9Ce0.1NiO3 Perovskite Oxide for Outstanding Counter Electrodes in Platinum-Free Dye-Sensitized Solar Cells.

For large-scale applications, dye-sensitized solar cells (DSSCs) require the replacement of the scarce platinum (Pt)-based counter electrode (CE) with efficient and cheap alternatives. In this respect, low-cost perovskite oxides (ABO3) have been introduced as promising additives to composite-based CEs in Pt-free DSSCs. Herein, we synthesized composites from La0.9Ce0.1NiO3 (L) perovskite oxide and functionalized-multiwall-carbon-nanotubes wrapped in selenides derived from metal-organic-frameworks (f-MWCNT-ZnSe-CoSe2, “F”). L and F were then mixed with carbon black (CB) in different mass ratios to prepare L@CB, F@CB, and L@F@CB composites. The electrochemical analysis revealed that the L@F@CB composite with a mass ratio of 1.5:3:1.5 exhibits better electrocatalytic activity than Pt. In addition, the related DSSC reached a better PCE of 7.49% compared to its Pt-based counterpart (7.09%). This improved performance is the result of the increase in the oxygen vacancy by L due to the replacement of La with Ce in its structure, leading to more active sites in the L@F@CB composites. Moreover, the F@CB composite favors the contribution to the high electrical conductivity of the hybrid carbon nanotube–carbon black, which also offers good stability to the L@F@CB CE by not showing any obvious change in morphology and peak-to-peak separation even after 100 cyclic voltammetry cycles. Consequently, the corresponding L@F@CB-based device achieved enhanced stability. Our work demonstrates that L@F@CB composites with a low cost are excellent alternatives to Pt CE in DSSCs.

Nitrogen-doped carbon black supported synergistic palladium single atoms and nanoparticles for electrocatalytic oxidation of methanol

For commercially viable direct methanol fuel cells, electrocatalysts play a crucial role in motivating the sluggish methanol oxidation reaction (MOR) over anode. Unfortunately, the large-scale applications of current MOR catalysts are hampered by their poor tolerance to poisoning and fast activity degradation. Herein, a unique composite catalyst comprised of partial Pd nanoparticles and partial Pd single atoms (PdNPs/Pd-Nx@C) is developed. The as-fabricated catalyst exhibits remarkable activity of 9.45 mA·cm−2 towards MOR in alkaline solution, which is 7.05 and 3.92 times that of commercial Pd/C and nanoparticle type (PdNPs@C) electrocatalysts, respectively. Impressively, the PdNPs/Pd-Nx@C shows the highest long-time stability with 90.38% and 89.8% of the initial activity retained after 3600 s chronoamperometry (CA) test and 2000 cycles of cyclic voltammetry (CV) measurements with accelerated durability test (ADT), respectively. Combined with high-angle annular darkfield scanning transmission electron microscopy (HAADF-STEM), X-ray adsorption fine structure (XAFS) spectra and X-ray photoelectron spectroscopy (XPS) analyses, the superior performance of PdNPs/Pd-Nx@C can be ascribed to the synergistic effect from the Pd single atoms, N-doped carbon supports and Pd nanoparticles. Notably, the embedded Pd single atoms are liable to transfer electrons to the substrate due to the electronic metal-support interactions (EMSI) and the charge transfer between Pd nanoparticles and carbon supports is suppressed, inducing a weak adsorption strength of poisonous carbonous intermediate species on active Pd nanoparticles and improved poisoning tolerance in MOR process, which is verified by density functional theory (DFT) calculations as well as CO-stripping voltammetry experiments. This work not only contributes the first example of a synergistic catalyst between nanoparticles and single atoms for MOR but also deepens the knowledge on the metal-support interaction.

Surface oxidation of cobalt carbonate and oxide nanowires by electrocatalytic oxygen evolution reaction in alkaline solution

The electrocatalytic water electrolysis is the most eco-friendly technique for hydrogen generation, which is governed by the electrode reaction kinetics involving cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER) in common alkaline electrolytes. Cobalt oxide (Co3O4) and related compounds are the most efficient OER catalysts, replacing the noble metals. In this work, the surface oxidations of the cobalt carbonate (Co(CO3)0.5OH·0.11H2O) and Co3O4 nanowires during the OER are carefully investigated by contrasting the polarization curves, Tafel plots, and x-ray photoelectron spectroscopy (XPS) spectra, before and after the 1000th cyclic voltammetry (CV) cycling in 1 M KOH alkaline solution. The overpotentials required to reach a current density (j) of 20 mA cm−2 (η 20) are estimated to be 313 mV for the 300 °C-calcined Co3O4, 350 mV for the 400 °C-calcined Co3O4, 365 mV for the 500 °C-calcined Co3O4, and 373 mV for the cobalt carbonate (Co(CO3)0.5OH·0.11H2O). The Tafel slope of cobalt carbonate (Co(CO3)0.5OH·0.11H2O) nanowires is the highest at 93 mV dec−1, while it is measured to be 57 mV dec−1 for the 300 °C-calcined Co3O4, 47 mV dec−1 for the 400 °C-calcined Co3O4, and 79 mV dec−1 for the 500 °C-calcined Co3O4. As a result, the oxidation from Co2+ to Co3+ within Co3O4 during the OER is detected, which improves the OER activity. On the other hand, the formation of cobalt hydoxide is found on the surface of the Co3O4 nanowires during the OER in alkaline solution, which decreases the OER activity. For the surface oxidation of the cobalt carbonate (Co(CO3)0.5OH·0.11H2O) nanowires, the increase in the amounts of Co3+ and oxygen vacancy and the formation of O-C-O and carbonates are found, which highly enhance the OER activity. These findings indicate that the surface redox kinetics during the electrocatalytic reactions should be considered important in order to enhance the electrocatalytic activity, and furthermore can provide insight into future challenges in designing advanced electrocatalysts.

Composition engineered ternary copper chalcogenide alloyed counter electrodes for high-performance and stable quantum dot-sensitized solar cells

The rational design and development of economical, high-performance, and stable counter electrodes (CE) are critical to bringing the quantum dot-sensitized solar cell (QDSSCs) from the laboratory to a practical application. In this respect, we used a two-step approach to fabricate ternary copper chalcogenide (Cu 2−x S y Se 1−y ) alloyed semiconductors onto fluorine-doped tin oxide (FTO). In the first step, the binary copper chalcogenides CuS nanostructures that are synthesized using the microwave-irradiation technique are screen-printed onto the FTO substrate and annealed in a nitrogen atmosphere to obtain Cu 2−x S CE. In the second step, ternary Cu 2−x S y Se 1−y alloyed electrocatalyst is obtained through a composition engineering approach in which the elemental Se was incorporated on the surface of as-synthesized Cu 2−x S nanostructures using the drop-casting method. Compared to the pristine Cu 2−x S CE, the as-synthesized Cu 2−x S y Se 1−y CE has exhibited tunable crystal structures, compositions, morphologies. The electrochemical analysis revealed that the optimized Cu 2−x S y Se 1−y CE has exhibited low charge transfer resistance (R ct ), and excellent reduction activity to S n 2− species of the polysulfide electrolyte. Accordingly, QDSSCs assembled with Cu 2−x S y Se 1−y CE have delivered conversion efficiencies of 8.02%, which are higher than those of pristine Cu 2−x S CE (7.24%). Noticeably, Cu 2−x S y Se 1−y CE has demonstrated outstanding electrochemical stability in polysulfide redox couple , exhibiting no substantial fluctuations in either the current density or shape of the curve even after 200 continuous cyclic voltammetry (CV) cycles. Moreover, the best cell devices constructed using Cu 2−x S y Se 1−y CE validated remarkable stability under open-air conditions, retaining <60% of the original performance after 120 h of illumination. Overall, the ease of synthesis, low cost, time efficiency, and excellent electrocatalytic characteristics of the Cu 2−x S y Se 1−y alloyed semiconductors film demonstrated in this work make it an encouraging applicant for use as a CE material in photovoltaic applications. The two-step synthesis procedure of the ternary copper chalcogenide counter electrode. • Ternary copper chalcogenide (Cu 2−x S y Se 1−y ) alloyed electrocatalyst developed. • Cu 2−x S y Se 1−y exhibited compositions dependent tuneable crystal structures and surface morphologies. • Cu 2−x S y Se 1−y served as an efficient and stable counter electrode in the QDSSCs.

Ruthenium Complex of sp2 Carbon-Conjugated Covalent Organic Frameworks as an Efficient Electrocatalyst for Hydrogen Evolution.

It is still a great challenge to explore hydrogen evolution reaction (HER) electrocatalysts with both lower overpotential and higher stability in acidic electrolytes. In this work, an efficient HER catalyst, Ru@COF-1, is prepared by complexation of triazine-cored sp2 carbon-conjugated covalent organic frameworks (COFs) with ruthenium ion. Ru@COF-1 possesses high crystallinity and porosity, which are beneficial for electrocatalysis. The large specific surface area and regular porous channels of Ru@COF-1 facilitate full contact between reactants and catalytic sites. The nitrogen atoms of triazines are protonated in the acidic media, which greatly improve the conductivity of Ru@COF-1. This synergistic effect makes the overpotential of Ru@COF-1 about 200mV at 10mAcm-2 , which is lower than other reported COFs-based electrocatalysts. Moreover, Ru@COF-1 exhibits exceptionally electrocatalytic durability in the acidic electrolytes. It is particularly stable and remains highly active after 1000 cyclic voltammetry cycles. Density functional theory calculations demonstrate that tetracoordinated Ru-N2 Cl2 moieties are the major contributors to the outstanding HER performance. This work provides a new idea for developing protonated HER electrocatalysts in acidic media.

CoTe nanorods based electrochemical sensor for quantitative detection of albumin from chronic kidney disease patients

• Highly selective electrochemical sensing of albumin by CoTe nanorods. • LOD and LOQ of CoTe-GCE for albumin is 0.09 nM and 0.003 nM, respectively. • Stability of CoTe-GCE upto 100 cycles of cyclic voltammetry. • CoTe-GCE quantifies albumin from urine samples of chronic kidney disease (CKD) patients. • Statistical modelling of urine albumin reveals positive relation with ACR and negative with urine creatinine. Electrochemical sensing monitors the levels of biomolecules and is specific, rapid, low cost, and automated. An electrical stimulus given to biological system helps in detecting electrical response through oxidation–reduction peaks in a cyclic voltammogram (CV). Herein, an electrochemical sensor based on CoTe nanorods is developed for albumin sensing. Sensing parameters such as scan rate, pH, concentration, and effect of interferences are optimized. Linearity, detection and quantification limits for CoTe modified glassy carbon electrode (CoTe-GCE) are 0.961 nM, 0.09 nM and 0.003 nM respectively. The stability of designed sensor is measured by running 100 cycles of CV. CoTe-GCE quantifies albumin from urine samples of chronic kidney disease (CKD) patients. Normal distribution of data (albumin, albumin to creatinine ratio (ACR), and creatinine) is found out by Shapiro-Wilk test. The correlation of urine albumin by Pearson’s correlation analysis reveals positive relation with ACR (P = 0.000, r = 0.043*) and negative with urine creatinine (p = 0.003, r = -0.141*). Using CoTe-GCE electrochemical sensor, albumin and creatinine levels in urine can be used as prognostic factors in CKD patients before disease progresses to end-stage renal disease (ESRD).

Effect of Pt-Ni deposition sequence on the bimetal-modified boron-doped diamond on catalytic performance for glucose oxidation in neutral media

• The PtNi modified boron-doped diamond were fabricated to detect glucose at neutral pH. • Electrodeposition sequences effect on electrocatalytic properties of Pt-Ni bimetals. • The PtNi biemetal prepared by co-deposition had the highest stability and sensitivity. The growing number of people with diabetes has gained extensive attention over the past decades, driving the need to develop sensitive glucose sensors to monitor glucose levels under physiological pH conditions. Bi-metal (Pt-Ni) modified boron-doped diamond (BDD) electrodes were reported to allow a continuous and stable response measurement of glucose under neutral pH conditions. Effects of the electrochemical deposition sequence on the morphology and electrocatalytic properties of the Pt-Ni bimetal were systematically investigated. Electrochemical tests showed that the Pt-Ni bimetal clusters prepared by the co-deposition (one step) method had higher stability and sensitivity for the glucose detection than those prepared by the two-step deposition method. The PtNi-BDD increased around 19% of the initial signal after 200 consecutive cyclic voltammetry cycles for 2400 s, while as a comparison, Ni/Pt-BDD and Pt-BDD increased 44% and 40% for 2400 s, respectively. In addition, the sensitivity of PtNi-BDD was obtained to be 110.4 μA cm −1 mm −1 in the range of 2–12 mM glucose concentration, around 6.1, 15.5, and 6.0 times higher than that of Pt/Ni-BDD, Ni/Pt-BDD, and single metal Pt, respectively.

Fabrication, Microstructure, Mechanical, and Electrochemical Properties of NiMnFeCu High Entropy Alloy from Elemental Powders

Transition metal based high entropy alloys (HEAs) are often used in electrocatalytic (water electrolysis) applications due to the synergistic effect operating among its constituent elements and unpaired electrons in d orbitals of the concerned metal. In this study, a low cost NiMnFeCu high entropy alloy was successfully synthesised using the combined techniques of mechanical milling (MA) and vacuum sintering. X-ray diffraction was used to analyse the phase composition, optical microscopy, and scanning electron microscopy were used to characterise the fabricated material’s microstructure and chemical homogeneity, thermal, and mechanical properties were tested using the differential scanning calorimetry method and a universal testing machine, respectively. Electrochemical workstation was used to carry out preliminary electrochemical studies such as linear sweep voltammetry (LSV), cyclic voltammetry (CV) and chronoamperometry. The results showed that the as- sintered NiMnFeCu HEA possessed a single- phase FCC structure. The HEA NiMnFeCu sintered at 1050 °C (S4) and 1000 °C (S2) with a holding time of 2 h showed a yield strength of 516.3 MPa and 389.8 MPa, respectively, and the micro-hardness values were measured to be 233.45 ± 9 HV and 198.7 ± 8 HV, respectively. Preliminary electrochemical studies proved that the alloy sintered at 1000 °C (S2) with a holding time of 2 h exhibited excellent electrocatalytic properties with a measured overpotential of 322 mV at 10 mA cm−2 at 100 cycles of CV and good stability for 10 h when compared to state-of-the-art electrocatalytic materials IrO2 and RuO2. This suggested that the HEA NiMnFeCu fabricated under the condition S2 could potentially be used for industrial-scale water electrolysis as it possesses permissible mechanical and good electrochemical properties.

Electro-deposited copper nanoclusters on leaf-shaped cobalt phosphide for boosting hydrogen evolution reaction

Exploring structural regulation of transition metal phosphides (TMPs) by incorporating suitable foreign components to increase hydrogen evolution reaction (HER) performance presents considerable development for electrocatalytic water-splitting technology. Herein, we reported an original construction strategy of thin-leaf-shaped cobalt phosphide coupled with copper nanoclusters supported on nickel foam (NF) for HER. A simple electrochemical deposition technique is used to obtain the interface-engineered Co2P@Cu nanostructure. The resultant nanocomposite with a vertically staggered structure shows the enhanced electrochemical characteristics derived from the Schottky junction at the interface between Co2P and Cu, which has a large of active sites and low charge-transfer resistance. The Schottky effect promotes charge distribution, accelerates adsorption of hydrogen intermediates, and facilitates electron transfer in the Co2P. As a result, the Co2P@Cu composite drives the current densities of 10 and 100 mA cm−2 for the alkaline HER to reach the lower overpotentials of 99.7 and 303.2 mV, respectively, and a smaller Tafel slope of 48.8 mV dec−1 compared to the bare Co2P electrocatalyst. Moreover, the proposed electrode exhibits good HER durability with almost no loss of Cu based on 2000 cycles of cyclic voltammetry sweeps and 24 h of chronoamperometry test. This work offers a perspective for the additive engineering of non-noble metals to metal phosphides toward efficient HER.

Synthesis and Characterization of Plant Derived Copper Oxide Nanoparticles and Their Application towards Oxygen Reduction Reaction

AbstractIn this work copper oxide nanoparticles (CuONPs) are prepared from precursor CuSO4.5H2O using plant leaves extract (PEE) of Eranthemum pulchellum(E. pulchellum).The synthesized CuONPs are characterized by ultraviolet visible (UV‐vis) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, X‐ray diffraction (XRD) and transmission electron microscopy (TEM). CuONPs are distorted spherical in shape, with the sizes ranging from 5 to 17 nm. PEE and CuONPs are coated on glassy carbon (GC) electrode and abbreviated as GC/PEE and GC/CuONPs, respectively. The modified electrodes GC/PEE and GC/CuONPs are characterized with cyclic voltammetry (CV) techniques. The modified electrode GC/CuONPs exhibits good electrocatalytic activity for oxygen reduction reaction (ORR). GC/CuONPs also shows excellent operational stability up to 1000 CV cycles.

Boosting the Oxygen Reduction Reaction in Zn–Air Batteries via a Uniform Trace N-Doped Carbon-Based Pore Structure

Zn–air batteries (ZABs) have attracted significant research interest due to their low cost, high safety, and large energy density. The oxygen reduction reaction (ORR) in ZABs can be boosted by employing an effective catalyst. The construction of an ORR catalyst comparable to commercial Pt/C remains a considerable challenge without introducing metal atoms due to the sluggish reaction kinetics. Herein, a nitrogen-doped carbon-based material with a uniform porous structure was constructed by the ingenious cooperation of urea and sodium chloride. The obtained catalyst (USPC) exhibited an onset potential of 0.939 V, a half-wave potential of 0.849 V, and a limiting current of 5.72 mA cm–2 in a 0.1 M KOH electrolyte. After 5000 cyclic voltammetry cycles, the limiting current density of the USPC decreased by 0.16 mA cm–2, and there was no negative shift in the half-wave potential. The assembled ZAB displayed a maximum power density of 167 mW cm–2, with an excellent specific capacity of 782 mA h g–1 at 10 mA cm–2 and good galvanostatic discharge–charge cycling durability, which were significantly improved compared to those of Pt/C. The pore size, chemical composition, and nitrogen content were not the controlling factors for the USPC in improving the ORR performance. Doping trace amounts of nitrogen could significantly promote the onset potential (vs RHE), and the uniform and fine nanopores could effectively increase the limiting current, that is, an improvement in ORR activity. This work illustrates the importance of the origin of the catalytic activity and promotes the development of high-performance ZABs.

Highly Dispersed Pt Clusters on F-Doped Tin(IV) Oxide Aerogel Matrix: An Ultra-Robust Hybrid Catalyst for Enhanced Hydrogen Evolution.

Dispersing the minuscule mass loading without hampering the high catalytic activity and long-term stability of a noble metal catalyst results in its ultimate efficacy for the electrochemical hydrogen evolution reaction (HER). Despite being the most efficient HER catalyst, the use of Pt is curtailed due to its scarcity and tendency to leach out in the harsh electrochemical reaction environment. In this study, we combined F-doped tin(IV) oxide (F-SnO2) aerogel with Pt catalyst to prevent metallic corrosion and to achieve abundant Pt active sites (approximately 5 nm clusters) with large specific surface area (321 cm2·g-1). With nanoscopic Pt loading inside the SnO2 aerogel matrix, the as-synthesized hybrid F-SnO2@Pt possesses a large specific surface area and high porosity and, thus, exhibits efficient experimental and intrinsic HER activity (a low overpotential of 42 mV at 10 mA·cm-2 in 0.5 M sulfuric acid), a 22-times larger turnover frequency (11.2 H2·s-1) than that of Pt/C at 50 mV, and excellent robustness over 10,000 cyclic voltammetry cycles. The existing metal support interaction and strong intermolecular forces between Pt and F-SnO2 account for the catalytic superiority and persistence against corrosion of F-SnO2@Pt compared to commercially used Pt/C. Density functional theory analysis suggests that hybridization between the Pt and F-SnO2 orbitals enhances intermediate hydrogen atom (H*) adsorption at their interface, which improves the reaction kinetics.

Electrochemical H2 Production using Polypyrazole based Zinc(II) Complex in Alkaline Medium

A zinc(II) complex of polypyazole containing ligand namely, [Tp*ZnCl] (Zn1) {Tp* = tris(3,5-dimethylpyrazolyl)borate}, along with its zinc(II) bound hydroxo complex [Tp*Zn–OH] (Zn2) were synthesized and characterized by FT-IR, Raman, 1H NMR techniques and elemental analysis. In alkaline solution (0.1 M KOH), the Zn2 modified glassy carbon (GC), namely GC–Zn2, was investigated as a molecular electrocatalyst for the hydrogen evolution reaction (HER). Different quantities (ca. 0.1–0.5 mg cm–2) of Zn2 were loaded on GC electrodes to make various GC–Zn2 electrodes. These electrodes were utilized as cathodes in 0.1 M KOH to produce H2 using linear sweep voltammetry (LSV) measurements. The HER electrocatalytic activity of the GC–Zn2 catalyst was found to be quite high and it increased with the catalyst loading density. The top performing electrocatalyst, GC–Zn2 (0.5 mg cm–2), demonstrated considerable HER catalytic performance with a low HER onset potential (EHER) of –33 mV vs. RHE and a high exchange current density of 0.59 mA cm–2. Moreover, the top performing electrocatalyst had a Tafel slope of –152 mV dec–1 and consumed an overpotential of 135 mV to generate a current density of 10 mA cm–2. Under the same operating conditions, these HER electrochemical kinetic parameters were found to be not remarkably far from those determined for commercial Pt/C (–10 mV vs. RHE, 0.88 mA cm–2, 108 mV dec–1 and 110 mV to yield a current density of 10 mA cm–2). In addition, the most active molecular electro-catalysts for H2 production from aqueous alkaline electrolytes were found to be comparable to the HER electrochemical kinetic parameters reported here for the GC–Zn2 electrocatalyst. Using 5000 cycles of repetitive cyclic voltammetry and 48 h of chronoamperometry measurements, the best electrocatalyst’s stability and long term durability were tested. It exhibited high stability for the HER catalytic activity.

Highly Dispersive Metal Atoms Anchored on Carbon Matrix Obtained by Direct Rapid Pyrolysis of Metal Complexes

Highly Dispersive Metal Atoms Anchored on Carbon Matrix Obtained by Direct Rapid Pyrolysis of Metal Complexes

MoO2/mesoporous carbon and MoO2/reduced graphene oxide composite electrodes for supercapacitor applications

The electrochemical properties of MoO2/mesoporous carbon and MoO2/reduced graphene oxide (rGO) materials have been investigated. Composite materials have been obtained by ultrasound dispersion of hydrothermally synthesized MoO2 and carbon or rGO (mass ratio of 1:1 and 1:2). The samples have been tested using XRD, SEM, and low-temperature nitrogen adsorption–desorption. The electrochemical performance was investigated by cyclic voltammetry and galvanostatic cycling methods. The maximal specific capacitance values for MoO2/carbon (1:1) and MoO2/carbon (1:2) materials are 225 and 120 F/g, respectively. It is the evidence that increase in carbon content causes specific capacitance decreasing. For the case of MoO2/reduced graphene oxide (1:1) material the maximal value of the specific capacitance is 52 F/g that is less than one for pure MoO2. An increase in reduced graphene oxide content causes the increase in specific capacitance value up to 232 F/g that corresponds to the decrease in MoO2 average particle sizes and contribution of reduced graphene oxide component to pseudocapacitance response.

A polymer sulfur-based electrode for high energy Li batteries. Influence of the materials of current collector and electrode design on the performance of lithium-sulfur batteries

Various compositions and types of materials based on the sulfur are used for the cathode of Li–S batteries with the aim to improve the performance of this system. In the present study, we investigated Li batteries with cathode based on polymer sulfur. Our development and evaluation confirm that the performance of Li–S batteries is also heavily dependent on the electrode technology, some extraneous materials like current collector, and the design of electrodes. The modification of the aluminum current collector of the sulfur electrode dramatically decreases the interface resistance of interface between sulfur cathode and current collector. Total impedance of Li-S batteries decreases, and the operating power increases. The modification of the design of electrodes results in increasing the energy of Li-S battery and stabilizing the battery parameters during cycling. In our article, these effects are confirmed by the results of Li-S battery testing with the polymer sulfur-based cathode: impedance spectroscopy, cyclic voltammetry, and galvanostatic cycling.

Pt/C Decorated with N-Doped Carbon Layers as a Highly Durable Electrocatalyst for the Oxygen Reduction Reaction

Exploiting advanced electrocatalysts for the sluggish oxygen reduction reaction (ORR) of the cathode is greatly crucial for proton-exchange membrane fuel cell (PEMFC) commercial application but still exhibit a significant challenge, especially the stability issues that have drawn attractive attention. Therefore, we introduced a nitrogen-doped carbon layer into the Pt/C surface, which not only prevents aggregation of Pt nanoparticles but also endows the electrocatalyst with enhanced performance without hiding the internal Pt active sites. The accelerated durability tests show an ignorable ORR activity loss (10 mV) in the as-prepared Pt/C@NC-0.06 sample compared to the pristine Pt/C catalyst (37 mV) after 5000 cyclic voltammetry cycles. Furthermore, in comparison to the pristine Pt/C catalyst (0.28 mA cm–2), the as-obtained Pt/C@NC-0.06 sample exhibits 2.32-fold improvement for the specific activity. The enhanced ORR properties of the Pt/C@NC-X catalyst in this work supplies a promising way to facilitate the electrocatalytic performance of catalysts in PEMFCs.

Facile Synthesis of Amorphous MoCo Lamellar Hydroxide for Alkaline Water Oxidation.

To find an oxygen evolution reaction (OER) catalyst with satisfactory catalytic performance and affordable cost is of great importance to the development of many new energy devices. In this work, a simple and effective strategy was developed to synthesize a series of amorphous MoCo lamellar hydroxide through one-step chemical co-precipitation. Systematic investigations showed that different functional agents (2-methylimidazole, NaOH, NH4 OH) in the fabrication process resulted in different micromorphology of the catalyst, thus influencing its electrocatalytic performance. Also, adding various amounts of Mo could influence the intrinsic catalytic properties. Samples synthesized with appropriate functional agent addition and optimized Mo addition exhibited amorphous nature and bent nanosheet morphology, as well as highest intrinsic catalytic activity, showing a low overpotential of 290 mV at 10 mA cm-2 and a small Tafel slope of 55 mV dec-1 in 1 m KOH solution. Additionally, the catalytic performance of the sample showed just small decay after 50 h chronopotentiometry test and 3000 cyclic voltammetry cycles, exhibiting the ultra-stable catalytic activity of the catalyst. This work provides a possible large-scale commercial production strategy of OER catalysts with promising performance and low fabrication cost.