Intrinsic Electrochemical Activity Research Articles

Nanoflower-like NiCoFe layered hydroxide by in-situ electrochemical corrosion as highly efficient electrocatalyst for water oxidation

Layered double hydroxides have been widely applied for oxygen evolution reaction (OER) in the alkaline water electrolysis. However, the issues of poor connection between the catalyst and nickel foam and the specific mechanisms for active sites has not been fully documented. In this study, the in-situ nickel foam etching in a mixed solution of ferric chloride and cobalt nitrate at low temperatures was adopted for NiCoFe layered ternary hydroxides (NiCoFe LTHs) synthesis with a better tight integration. Physicochemical characterization indicated that the NiCoFe LTHs could grow directly through corroding nickel foam with a nano-flower-like morphology and structures. That is favorable for electron transfer from the catalytic layer to the conductive substrate. With the transition metal ions interaction and the tight integration construction, NiCo1Fe4-LTH-T60/NF presented an enhanced electrolysis performance with the overpotential of 234 mV (1.464 V vs. RHE) at current density of 100 mA cm−2 in 1 M KOH electrolyte. The Tafel slope for NiCo1Fe4-LTH-T60/NF electrode was 36.19 mV dec−1 for an enhanced OER kinetics. Besides, it demonstrated faster interfacial charge transfer process, better intrinsic electrochemical activity and stability in large current stability testing. It was revealed that the synergistic effect of the transition metal ions interaction enhancement and the mechanism of oxygen evolution elementary reaction for NiCo1Fe4-LTH-T60/NF during the water electrolysis by the electrochemical and theoretical calculation. This work provides theoretical basis and experimental support for the design and synthesis of future OER catalyst and substrate, which is significant for hydrogen and oxygen generation from water electrolysis.

Conductive Polymer-Based Electrodes and Supercapacitors: Materials, Electrolytes, and Characterizations.

New materials and the interactions between them are the basis of novel energy storage devices such as supercapacitors and batteries. In recent years, because of the increasing demand for electricity as an energy source, the development of new energy storage materials is among the most actively studied topics. Conductive polymers (CPs), because of their intrinsic electrochemical activity and electrical conductivity, have also been intensively explored. While most of the high capacitance reported in the literature comes from hybrid materials, for example, conductive polymers composed of metal oxides and carbon materials, such as graphene and carbon nanotubes, new chemistry and the 3D structure of conductive polymers remain critical. This comprehensive review focuses on the basic properties of three popular conductive polymers and their composites with carbon materials and metal oxides that have been actively explored as energy storage materials, i.e., polypyrrole (PPy), polyaniline (PANi), and polythiophene (PTh), and various types of electrolytes, including aqueous, organic, quasi-solid, and self-healing electrolytes. Important experimental parameters affecting material property and morphology are also discussed. Electrochemical and analytical techniques frequently employed in material and supercapacitor research are presented. In particular, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) are discussed in detail, including how to extract data from spectra to calculate key parameters. Pros and cons of CP-based supercapacitors are discussed together with their potential applications.

Room-temperature synthesis of VO(OH)2 as a high capacity cathode material for aqueous zinc ion batteries

The development of satisfactory cathodes plays a key role in the widespread utilization of aqueous zinc ion batteries. Cathode materials with high specific capacity and long cycling life are still urgently needed for aqueous zinc ion batteries. Herein, a new cathode material VO(OH)2 is synthesized by a facile room-temperature precipitation approach, and its electrochemical characteristics and structural evolution process are investigated. Benefiting from its intrinsic electrochemical activity, the VO(OH)2 cathode exhibits a remarkable specific capacity of 488 mAh g−1 at 0.1 A g−1, retains a high capacity of 219.1 mAh g−1 at the increased current density of 10 A g−1, and provides a maximum energy density of 439.2 Wh kg−1. In addition, when subjected to a 12,000 cycles charge/discharge test at 10 A g−1, the cathode retains a capacity of 185.8 mAh g−1, highlighting durable cycling performance. The structural evolution analysis reveals that of VO(OH)2 cathode may be in-situ transformed to an amorphous vanadium oxide V2O5-x in the first charging process, which could reversibly intercalate/deintercalate zinc ions. This research supplies a promising cathode material for aqueous zinc ion batteries and enhances understanding of vanadium oxyhydroxide in metal ion storage.

Metal Organic Frameworks Derived Layered Double Hydroxide Nanosheets for Electrochemical Energy Storage and Conversion

AbstractPorous materials are promising for energy applications and MOF‐derived layered double hydroxide (LDH) nanosheets vertically align on the conductive substrates showed an ultrathin porous morphology with tunable coordination environments for the metallic sites. This unique structure provides larger surface area, better intrinsic electrochemical activity than conventional LDH nanosheets. Herein, the synthetic strategies of MOF‐derived LDHs and their promising applications in electrochemistry are reviewed, presenting the significant potential and challenges of MOFs‐derived LDH nanosheets in advanced energy storage and conversion applications, providing an effective platform for efficient and sustainable MOFs‐based systems in future.

Engineered oxidation states in NiCo2O4@CeO2 nanourchin architectures with abundant oxygen vacancies for enhanced oxygen evolution reaction performance

Sluggish oxygen evolution reaction (OER) as the half reaction of water electrolysis hindered the production of clean hydrogen, necessitates a cost-effective electrocatalyst. Spinel nickel cobaltite (NiCo2O4), characterized by its lower cost, flexibility in oxidation states of cations, and stable spinel structure, holds promise as an OER electrocatalyst. However, there is still room for improvement in terms of its intrinsic electrochemical activity, conductivity, and active surface area. Inspired by the flexible valence states of Ni and Co, in this study, CeO2 was introduced into NiCo2O4 for further electronic structure adjustment. The result was the synthesis of an urchin-like NiCo2O4@CeO2 (NCOC), and the elucidation of its formation mechanisms, expressed conclusively through reaction formulas. NCOC, characterized by an open architecture and a rough surface, ensures rapid mass transportation and charge diffusion. Within NCOC, numerous oxophilic Ce3+ sites with oxygen vacancies construct electron transport pathways, accelerating charge-transfer. This simultaneously induces an increase in the oxidation states and proportions of Ni3+ and Co3+ in NCOC, reinforcing the covalence of Ni–O and Co–O bonds, expediting the ad/desorption of intermediates during OER. The electronic structure variations of NCOC were further verified through density functional theory (DFT) analyses, revealing alterations in adsorption configurations of intermediates and a decrease in adsorption free energies for intermediates on NCOC during OER. In practical terms, NCOC demonstrated a low overpotential of 228 mV at a current density of 10 mA cm−2 under 1 M KOH, maintaining long-term electrochemical stability for 100 h. Overall, this study provides a universal approach for designing highly cost-efficient electrocatalysts for OER.

Breaking the Ru-O-Ru Symmetry of a RuO2 Catalyst for Sustainable Acidic Water Oxidation.

Proton exchange membrane water electrolysis is a highly promising hydrogen production technique for sustainable energy supply, however, achieving a highly active and durable catalyst for acidic water oxidation still remains a formidable challenge. Herein, we propose a local microenvironment regulation strategy for precisely tuning In-RuO2 /graphene (In-RuO2 /G) catalyst with intrinsic electrochemical activity and stability to boost acidic water oxidation. The In-RuO2 /G displays robust acid oxygen evolution reaction performance with a mass activity of 671 A gcat -1 at 1.5 V, an overpotential of 187 mV at 10 mA cm-2 , and long-lasting stability of 350 h at 100 mA cm-2 , which arises from the asymmetric Ru-O-In local structure interactions. Further, it is unraveled theoretically that the asymmetric Ru-O-In structure breaks the thermodynamic activity limit of the traditional adsorption evolution mechanism which significantly weakens the formation energy barrier of OOH*, thus inducing a new rate-determining step of OH* absorption. Therefore, this strategy showcases the immense potential for constructing high-performance acidic catalysts for water electrolyzers.

Breaking the Ru−O−Ru Symmetry of a RuO2 Catalyst for Sustainable Acidic Water Oxidation

AbstractProton exchange membrane water electrolysis is a highly promising hydrogen production technique for sustainable energy supply, however, achieving a highly active and durable catalyst for acidic water oxidation still remains a formidable challenge. Herein, we propose a local microenvironment regulation strategy for precisely tuning In−RuO2/graphene (In−RuO2/G) catalyst with intrinsic electrochemical activity and stability to boost acidic water oxidation. The In−RuO2/G displays robust acid oxygen evolution reaction performance with a mass activity of 671 A gcat−1 at 1.5 V, an overpotential of 187 mV at 10 mA cm−2, and long‐lasting stability of 350 h at 100 mA cm−2, which arises from the asymmetric Ru−O−In local structure interactions. Further, it is unraveled theoretically that the asymmetric Ru−O−In structure breaks the thermodynamic activity limit of the traditional adsorption evolution mechanism which significantly weakens the formation energy barrier of OOH*, thus inducing a new rate‐determining step of OH* absorption. Therefore, this strategy showcases the immense potential for constructing high‐performance acidic catalysts for water electrolyzers.

Graphdiyne and Nitrogen-Doped Graphdiyne Nanotubes as Highly Efficient Electrocatalysts for Oxygen Reduction Reaction

Electrocatalysts with high efficiency and low cost are always urgently needed for oxygen reduction reaction (ORR). As a new carbon allotrope, graphdiyne (GDY) has received much attention due to its unique chemical structure containing sp- and sp2-hybridized carbons, and intrinsic electrochemical activity ascribed to its inherent conductivity. Herein, we prepared two graphdiyne materials named GDY nanotube and nitrogen-doped GDY (NGDY) nanotube via cross-coupling reactions on the surface of Cu nanowires. As metal-free catalysts, their electrocatalytic activities for ORR were demonstrated. The results showed that the NGDY nanotube presents more excellent electrochemical performance than that of the GDY nanotube, including more positive potential and faster kinetics and charge transfer process. The improvement can be ascribed to the greater number of structural electrocatalytic active sites from nitrogen atoms as well as the hollow nanotube morphology, which is beneficial to the adsorption of oxygen and acceleration of the catalytic reaction. This work helps develop high-quality graphdiyne-based electrocatalysts with well-defined chemical structures and morphologies for various electrochemical reactions.

Efficient charge transfer at the donor-bridge-acceptor interface for excellent supercapacitors

The intrinsic electrochemical activity and active sites of the battery-like electrode in supercapacitors originate from efficient charge transfer at the interface. A seamless all-carbon graphdiyne layer on CoNi2S4 yolk-shell spheres (CoNi2S4/GDY YSSs) provides a unique structure of a flawless “donor–bridge–acceptor” interface, where Ni atoms and Co atoms serve as electron donors and acceptors, respectively, connected by the sp-C–Ni and sp-C–Co bonds as bridges. Importantly, this particular can facilitate effective electron transfer from the Ni atoms to the Co atoms, resulting in more interfacial Co2+ active sites and reversible redox coupling of Co-S/Co-S-OH and Co-S-OH/Co-S-O to increase the specific capacitance. Additionally, the seamless all-carbon graphdiyne layer greatly enhances the structural and interfacial stability of CoNi2S4 yolk-shell spheres, effectively avoiding structural deterioration to enhance cycling stability performance. Profiting from its structural merits, the CoNi2S4/GDY YSSs electrode delivers a considerable capacitance of 856C/g at 1 A/g, along with exceptional rate capability (61.9 % for 50-fold current density increase). Furthermore, an asymmetric supercapacitor with the CoNi2S4/GDY YSSs electrode cathode achieves a remarkable maximum energy density of 91.7 Wh/kg at a power density of 793 W/kg. Furthermore, the strategy proposed in this study has the potential to open up new pathways for the battery-like electrode design with realistic supercapacitor applications.

One-Pot Graphene Supported Pt3Cu Nanoparticles—From Theory towards an Effective Molecular Oxygen Reduction Reaction Catalyst

In this work, recent research progresses in the formation of Pt3Cu nanoparticles onto the surface of graphene are described, and the obtained results are contrasted with previously published theoretical studies. To form these nanoparticles, tetrabutylammonium hexachloroplatinate, and copper acetylacetonate are used as platinum and copper precursors, respectively. Oleylamine is used as a reductor and a solvent. The obtained catalyst is characterized via X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and energy dispersive spectroscopy X-ray (EDS). To assess the catalytic activity, the graphene-supported Pt3Cu material is tested with cyclic voltammetry, “CO stripping”, and oxygen reduction reaction potentiodynamic curves to find the nature and the intrinsic electrochemical activity of the material. It can be observed that the tetrabutylammonium cation plays a critical role in anchoring and supporting nanoparticles over graphene, from which a broad discussion about the true nature of the anchoring mechanism was derived. The growth mechanism of the nanoparticles on the surface of graphene was observed, supporting the conducted theoretical models. With this study, a reliable, versatile, and efficient synthesis of nanocatalysts is presented, demonstrating the potentiality of Pt3Cu/graphene as an effective cathode catalyst. This study demonstrates the importance of reliable ab inito theoretical results as a useful source of information for the synthesis of the Pt3Cu alloy system.

Enhancement of the intrinsic Ni/GDC activity under rSOC operation by means of Fe–Au doping: An electro-kinetic study

The investigation dealt with the effect of Fe and Au wt.% concentrations on the enhanced performance and stability of Ni/GDC under rSOC operation. Moreover, it focused on the comparison of the intrinsic electro-kinetics between the best performing Fe–Au-modified cell and Ni/GDC under SOE operation. The rSOC performance and stability of all cells was examined in the temperature range of 900–800 °C. The electro-kinetic measurements took place at 900 °C by varying the pH2O. All Fe–Au–Ni/GDC electrodes exhibited enhanced activity, compared to the SoA Ni/GDC, with variations in their stability after three rSOC cycles. Specifically, the fuel electrode with the lowest wt.% concentration in Fe and Au (0.5Fe–1Au–Ni/GDC) exhibited the highest activity and stability under rSOC operation. By increasing the wt.% loadings to 2 wt% Fe and 3 wt% Au, there was rapid degradation of the initially high performance, mainly due to increase of the ohmic resistance. SEM analysis showed higher macro-porosity on the reduced state of the modified electrodes, which in the case of the best performing 0.5Fe–1Au–Ni/GDC was the least affected after rSOC operation. Interestingly, the SOE performance of the examined Fe–Au-modified electrodes was not similarly inhibited by the decrease of temperature, compared to Ni/GDC. This was further clarified through electro-kinetic measurements, aiming to verify the effect from the Fe–Au doping on the intrinsic electrochemical activity of Ni/GDC for the H2O electrolysis reaction. Comparison between the SoA and the best performing 0.5Fe–1Au–Ni/GDC showed an enhancing effect on the intrinsic electro-kinetics of the modified electrode. Specifically, the dependence of the polarization resistance on the pH2O was found to be strongly positive, resulting in a higher apparent reaction order, compared to Ni/GDC.

Intrinsic electrochemical activity modulation of MOF-derived C/N-NiCoMn-LDH/Ag electrode for low temperature hybrid supercapacitors

Layered double hydroxides (LDHs) are promising electrode candidates for supercapacitors. However, limitations like inferior cycling stability and unsatisfactory charge storage capability at low temperatures have exerted negative effects on their applications. Herein, a novel synthetic process has been elaborately designed and provided to have the composition and structure of the C/N-NiCoMn-LDH/Ag (C/N-CNMA) delicately regulated. Both the experimental and theoretical researches unveil that the incorporated manganese species and elemental silver could dramatically modulate the bandgap, crystallinity and surface electron structure of the LDH, leading to the remarkable improvement in its conductivity, exposed active sites and intrinsic electrochemical activity, and thus the OH* and O* adsorption free energy could be remarkably optimized, even at low temperatures. In addition, the low crystallinity C/N-CNMA is of great electrochemical compatibility with both the KOH aqueous electrolyte and the isobutyl alcohol (IPA) modulated organohydrogel electrolyte. By means of adjusting the solvation and hydrogen bonding in the electrolytes, the assembled hybrid supercapacitors deliver excellent energy density, power density and cycling stability in the temperature range of -30 to 25 °C. Specifically, the gel electrolyte with IPA as the anti-freezing functional additive displays high flexibility and ionic conductivity at low temperatures.

Ion exchange synthesis of Fe-doped clustered CoP nanowires as superior electrocatalyst for hydrogen evolution reaction

Green hydrogen production from electrochemical water splitting currently suffers from the key issues of high energy consumption and cost. Herein, we demonstrated the synthesis of highly efficient and stable clustered CoP nanowires electrocatalysts on nickel foam. Moreover, an ion exchange strategy was proposed to precisely control the doping content of iron to further modify the intrinsic electrochemical activity of CoP nanowires. The introduction of iron effectively alters the surface atomic configuration and electronic structure of CoP and increases the active sites, thus accelerating the overall reaction rate and enhancing the catalytic performance. It has been demonstrated that the CoFeP-30-30/NF electrode exhibits platinum-like catalytic activity with only an overpotential of 29.8 mV at 10 mA·cm−2 and outstanding stability toward hydrogen evolution reaction. The synthetic strategy of CoFeP/NF electrode proposed in this work will significantly promote the development of highly efficient transition metal phosphides electrocatalysts with lower overpotential and better stability.

Free and bound histidine in reactions at mercury electrode

The intrinsic electrochemical activity of some amino acids as well as their residues in peptides and proteins at mercury electrodes can be utilized for fundamental research purposes and for the development of label-free reagentless analytical methods. Here we present a new concept of how to investigate free histidine (His) and how to detect its residues within the more complex structures of some peptides and proteins at a hanging mercury drop electrode. The approach is based on the ability of the deprotonated His imidazole group to oxidize the electrode mercury at potentials less positive than those of the electrolytic (anodic) dissolution of mercury. Using cyclic voltammetry, we found that in a weakly alkaline solution of free His or bound in His homohexapeptide, the oxidative formation and the reductive cleavage of the bond between the imidazole group and the electrode mercury are reversible and take place in an adsorbed state. In addition to free His and His homohexapeptide, also more complex heteropeptide samples such as angiotensin peptides, a modified fragment of amyloid β peptide, and His-tagged mutant protein α-synuclein A53T were investigated by constant-current chronopotentiometry in neutral solution. The proposed methodology could be further applied for the investigation of the acid-base and metal chelating properties of His-containing peptides or proteins, and for the study of their structural changes and interactions with other substances.

Intrinsic electrochemical activity of Ni in Ni3Sn4 anode accommodating high capacity and mechanical stability for fast-charging lithium-ion batteries

Fast interfacial kinetics derived from bicontinuous three-dimensional (3D) architecture is a strategic feature for achieving fast-charging lithium-ion batteries (LIBs). One of the main reasons is its large active surface and short diffusion path. Yet, understanding of unusual electrochemical properties still remain great challenge due to its complexity. In this study, we proposed a nickel–tin compound (Ni3Sn4) supported by 3D Nickel scaffolds as main frame because the Ni3Sn4 clearly offers a higher reversible capacity and stable cycling performance than bare tin (Sn). In order to verify the role of Ni, atomic-scale simulation based on density functional theory systematically addressed to the reaction mechanism and structural evolution of Ni3Sn4 during the lithiation process. Our findings are that Ni enables Ni3Sn4 to possess higher mechanical stability in terms of reactive flow stress, subsequently lead to improve Li storage capability. This study elucidates an understanding of the lithiation mechanism of Ni3Sn4 and provides a new perspective for the design of high-capacity and high-power 3D anodes for fast-charging LIBs.

Ru-incorporated oxygen-vacancy-enriched MoO2 electrocatalysts for hydrogen evolution reaction

Designing highly efficient Pt-free electrocatalysts with low overpotential for the alkaline hydrogen evolution reaction (HER) remains a significant challenge. In this paper, we successfully construct Ru-incorporated oxygen-vacancy-enriched MoO2 nanosheets (Ru/MoO2−x) for the HER through a “one stone two birds” strategy. This strategy can solve two urgent problems simultaneously, the intrinsic electrochemical activity of original MoO2 is far from satisfactory and the H2O adsorption/dissociation abilities of Ru are weak. Specifically, the oxygen-vacancy-enriched MoO3 serves as an excellent platform for anchoring and trapping Ru ions. In-depth analyses indicate that the incorporation of Ru nanoclusters induces transition from MoO3 to MoO2, generates oxygen vacancies, and creates Ru-O-Mo sites. The synergistic effect of Ru nanoclusters, Ru-O-Mo sites and oxygen-vacancy-enriched MoO2 will endow the obtained catalyst excellent electrocatalytic activity. In particular, the optimal Ru/MoO2−x electrocatalyst delivered a low overpotential of 29 mV at 10 mA cm−2 in a basic electrolyte.

Iron vacancies engineering of Fe x C@NC hybrids toward enhanced lithium-ion storage properties

Defect engineering have profound influence on the energy storage properties of electrode hybrids by adjusting their intrinsic electronic characteristics. For iron carbide based materials, however, the effect of defect (especially cation vacancies) toward their electrochemical performance are still unclear. Herein, the feasible and scalable synthesis of Fe x C@NC with 3D honeycomb-like carbon architecture and abundant Fe vacancies via template etching is reported. Such structure enable outstanding lithium-ion storage properties owing to hierarchical pores, improved intrinsic electrochemical activity, as well as the introduction of more active sites. As a result, the Fe x C@NC-2 presents a high reversible specific capacity of 1079 mAh g−1 after 1000 cycles. Moreover, an excellent cycling stability can be achieved via maintaining a high-capacity retention (689 mAh g−1, 98.4%) over 1000 cycles at 5 A g−1. This study provides a feasible strategy for developing high-performance hybrids with hierarchical pore and rich defects structures.

Fabrication of Ni–Mo-based Electrocatalysts by Modified Zn Phosphating for Hydrogen Evolution Reaction

The preparation of low-cost, simple, and scalable electrodes is crucial for the commercialization of water electrolyzers for H2 production. Herein, we demonstrate the fabrication of cathodes through Mo-modified Zn phosphating of Ni foam (NiF) for water electrolysis, which has been largely utilized in surface coating industry. In situ growth of electrocatalytically active layers in the hydrogen evolution reaction (HER) was occurred after 1 min of phosphating to form ZnNiMoPi, and subseque activation resulted in the formation of ZnNiMoPOxHy. ZnNiMoPOxHy exhibited superior HER performance than NiF, primarily because of the increased electrochemically active surface area of ZnNiMoPOxHy compared to that of bare NiF. Although further investigations to improve the intrinsic electrochemical activity toward the HER and detailed mechanistic studies are required, these results suggest that phosphating is a promising coating method and will possibly advance the fabrication procedure of electrodes for water electrolyzers with better practical applications.

Recent Progress in Prussian Blue/Prussian Blue Analogue-Derived Metallic Compounds

Abstract Prussian blue (PB) and its analogues (PBAs) are promising coordination polymers (CPs) with an adjustable composition and open framework. Nonetheless, their intrinsic electrochemical activity and electrical conductivity are poor, which hinder their applications in energy conversion and storage. In catalytic applications, metal compounds derived from PB/PBAs have a lot of advantages, such as outstanding stability, selectivity, and electrical conductivity. Furthermore, they can be used as electrode materials for electrochemical energy storage and conversion, while having preferable electronic conductivity, sufficient catalytic active sites, as well as a larger specific surface area and tunable size to achieve an optimized performance. This review summarizes the current achievements of PB/PBA-derived metallic nanomaterials, as well as the existing limitations, urgent challenges and future development.

Redox-active water-soluble carbon nanomaterials generated from graphite

The cyclic voltammetric response of the anolyte generated under strong polarization of graphite electrodes in a phosphate solution was investigated to evaluate the intrinsic electrochemical activity of water-soluble carbon-based nanomaterials contained in it. Two electroreducible oxygen-containing functional groups were identified: quinone and epoxide. Since the nanomaterial was found to be surface-bounded to the electrode, the surface coverage of quinone and epoxide groups was quantified to appraise the effect of synthesis experimental conditions on the relative amounts of the two functionalization groups. The synthesis conditions were investigated in terms of the electrolytic solution composition (ionic strength and pH) and duration of the graphite polarization under galvanostatic polarization. Most appropriate experimental conditions to generate quinone rather than epoxide moieties (Γ quin /Γ ep = 2.5) were found when the nanomaterial was generated in a 3 h-assay using a neutral pH phosphate solution with low ionic strength (I = 0.1). These results may be taken as a guideline to modulate the redox-active water-soluble carbon nanomaterial functionalization, opening new perspectives to its application in sensing, energy storage, and nanomedicine.