Tafel Analysis Research Articles

Carbon nanotubes/PANI composite as an efficient counter electrode material for dye sensitized solar cell

Counter electrodes of dye sensitized solar cells (DSSCs) mainly employed platinum (Pt) as a catalyst due to high catalytic activity toward triiodide reduction in their operating process. However, using Pt in DSSCs highly increases the cost, which became a challenge for practical applications from their economic feasibility point of view. Therefore, in this work, we have developed a cost-effective material carbon nanotubes (CNTs) to replace expensive Pt. CNTs based DSSC has been considered as a potential candidate for future practical applications. We prepared CNTs/Polyaniline (PANI) composite as a CE material for DSSCs by doctor blade technique. The DSSCs fabricated with CNTs-PANI composite CE show the best power conversion efficiency (PCE) of 6.67%, which is comparable to 7.70% of Pt CE. The modified CNTs-PANI counter electrode exhibited excellent electrocatalytic activity that facilitated higher electron transfer, suppressed charge recombination, enhanced electron life, and faster triiodide reduction are confirmed by several characterisation techniques such as impedance spectroscopy, cyclic voltammetry (CV), and tafel analysis. A comparative study of these electrodes reveal that effective surface roughness plays an essential role in improving the electrochemical properties of the devices.

Exploring the role of different morphologies of β–Ni(OH)2 for electrocatalytic urea oxidation and the effects of electrochemically active surface area

Ni(OH)2, as a multifunctional material, has found its applications in a great number of research areas. In particular, it is an efficient catalyst for urea oxidation reaction (UOR), which is an important alternative to oxygen evolution reaction in electrocatalytic water splitting. This work investigates the effect of materials morphology on the electrocatalytic UOR performance of β–Ni(OH)2, as well as the importance of characterising the catalysts’ surface by electrochemical active surface area. Three different morphologies (nanoflowers, nanocubes, and nanosheets) were prepared via a simple hydrothermal approach. The morphology and structure of the as-prepared samples were carefully examined by scanning electron microscopy, transmission electron microscopy, and powder X-ray diffraction.The UOR performance of β–Ni(OH)2was evaluated by means of cyclic voltammetry, linear sweep voltammetry, Tafel analysis, and electrochemical surface area. Nanosheet Ni(OH)2 electrocatalyst exhibits higher current density responses (28.3 mA cm−2ECSA at 1.6 V vs. RHE) and a lower slope in the Tafel plot (72.6 mV dec-1). Consequently, due to the exposure of more active sites to the reactants, the Ni(OH)2 electrode with nanosheet morphology displayed higher electrocatalytic performance during UOR compared to the nanoflower and nanocube samples.

Synthesis and Electrocatalytic Performance of TiO2 Supported on Carbon Nanoparticles Towards Positive Half-Cell Reaction of Hydrogen-1,4p-benzoquinone Flow-Battery

The Hydrogen- 1,4 p-Benzoquinone redox flow battery (H2—BQ RFB) is simple and economic to use with a cell potential of 0.714 V. Carbon-based electrodes are extensively used as electrode materials due to their comprehensive properties but possess poor hydrophilic nature and low electrochemical activity. It is essential to modify carbon-based materials before employing them in battery applications. Because of its low-cost and enhanced catalytic activity, Titanium dioxide (TiO2) is chosen to modify the carbon material. In the present work, TiO2 supported on carbon nanoparticles (TiO2@CNP) electrocatalyst was synthesized by using the ultra-sound assisted sol-gel method for the positive half-cell of H2—BQ RFB. The composition of the sol is optimized by using cyclic voltammetry (CV) analysis. Surface morphology TiO2@CNP coated on carbon paper was carried out using Scanning Electron Microscope (SEM). The TiO2 and carbon interaction bonds were identified using Fourier transform infrared spectroscopy (FTIR). The phase and crystalline nature were identified by using X-ray diffraction (XRD). The activity of the electrode was assessed by CV and Tafel analysis. The electrocatalyst was tested in H2—BQ RFB positive half-cell by galvanostatic charge-discharge and obtained energy efficiency up to 73%.

Fabrication of Zr-Ti-Si glassy metallic overlay on 3D printed Ti-6Al4V implant prototypes for enhanced biocompatibility

Implantable materials with enhanced corrosion resistance and bioactivity are highly desired for biomedical application. A 3D metal printed prototype surface was coated with amorphous alloy components of elements Zr, Ti and Si (Zr54Ti35 Si11) as a novel biomedical grade ternary system for the implants. A DC magnetron sputtering technique was used to sputter the films on Ti-6Al-4 V implant prototypes, exhibiting a smooth and denser coating with root means square surface roughness of 1.4 nm. Surface morphology and structural integrity of the thin film metallic glass (TFMG) was studied from electron microscopic techniques and X-ray diffraction analysis. The TFMG is thermally stable with a large supercooled liquid region (∆Tx) of 81.2 °C. Mechanical characteristics of the coatings were studied using the nanoindentation method to correlate the hardness and modulus of the implant materials. Under the simulated body fluid condition, Ti-6Al-4 V implant with 500 nm thickness coatings (Zr54Ti35Si11) exhibited the superior corrosion resistance rate 1 × 10−6 mpy with a charge transfer resistance of 34 kΩ promising for practical application. Electrochemical impedance spectra and Tafel analysis revealed that the corrosion resistance was prominent in the 500 nm thickness TFMG system than the 250 nm and uncoated bare counterparts. The in-vitro biocompatibility and cytotoxicity studies of the as-coated 3D printed implants were studied using the human osteoblast and L929 fibroblast cell lines, respectively. A hemocompatibility study on the implant materials revealed that erythrocytes remain biconcave without aggregation, platelet activation and thrombogenesis, supporting the biocompatibility of the implants. The integration of such unique properties makes these TFMG system ideal candidates for biomedical implants.

Coupling covariance matrix adaptation with continuum modeling for determination of kinetic parameters associated with electrochemical CO2 reduction

Coupling covariance matrix adaptation with continuum modeling for determination of kinetic parameters associated with electrochemical CO2 reduction

Determination and Comparison of Parameters from Cyclic Voltammetry of LaCl3 in Eutectic LiCl-KCl

Electrochemical measurements of LaCl3 were obtained in eutectic LiCl-KCl at 773 K. Cyclic voltammetry data were acquired using a tungsten electrode LaCl3 amounts in the molten salt in the range of 0.5 to 3.0 wt%. Both cyclic voltammetry and Tafel analyses of the data resulted in calculation of values for the charge transfer coefficient (0.262), diffusion coefficient (1.67 × 10-5 cm2 s-1), exchange current density (0.0148 to 0.0473 A cm-2), and charge transfer resistance (0.404 to 1.99 Ω) related to lanthanum ions in the molten salt. Calculated values were compared to those available in the literature. The values of parameters found in literature varied significantly in comparison to those in the present study due to dissimilar experimental conditions, e.g., electrode material, temperature, and LaCl3 concentration.

Critical influence of phase transition on the hydrogen evolution reaction activity of Heusler alloys

Unraveling structure-property relationships is of critical importance for designing superior catalysts. Heusler alloys are a family of materials whose atomic packing structure may change with a change in the external field, for example, temperature, magnetic field, and/or stress, and are ideal models for studying the structure-property relationship. In this study, a series of Ni–Mn–Sn–Co Heusler alloys with controlled phases and compositions, including the tetragonal martensite phase (Ni46Mn36Sn11Co7, labeled Co7), cubic austenite phase (Ni42Mn43Sn10Co5, labeled Co5), and tetragonal/cubic mixing phase (Ni46Mn38Sn12Co4, labeled Co4) were investigated. The alloys with the martensitic phase exhibited superior catalytic activity toward hydrogen evolution reaction (HER) than those with the austenitic phase. At an overpotential of 350 mV, the HER current density of the martensite phase of the Co7 sample was almost 2 times higher than that of the austenite phase of the Co5 sample. In-situ temperature-dependent catalytic measurements for the Co4 alloy suggest that the catalytic activity decreases significantly when phase transformation from martensite to austenite occurs. The efficient electron transfer kinetics and low electron work function are responsible for the high activity of the martensite phase, according to Tafel and work function analyses. These results provide a promising strategy for the development of high-performance Heusler alloys by controlling their phase structures and phase transitions.

Characterization of Octyl Hydroxamic Acid as Inhibitor on Cu Chemical Mechanical Polishing

As an inhibitor for copper (Cu), Octyl hydroxamic acid (OHA) has been extensively studied through a combination of density functional theory (DFT) and experiments. Our findings indicate that using a concentration of 3 mM OHA as an inhibitor can lead to a remarkable removal rate (RR) and surface quality when the pH is at 10. Tafel analysis of potentiodynamic polarization plots was performed to demonstrate that OHA can lower the corrosion current. Further insight into the adsorption behavior of OHA on the Cu surface was obtained through a comprehensive study combining X-ray photoelectron spectroscopy (XPS), DFT calculations, and adsorption isotherm model analysis.

Dissolution of nanoprecipitate on aluminum-alloy anode for high discharging performance in Al battery applications

Use of aluminum alloy anodes as metal fuel in electrochemical batteries has specific advantages in numerous applications. In this paper, we report novel Al alloy anodes obtained by adding In and Bi to a reported Al ternary-element alloy, Al-Zn-Sn. An electron probe microanalyzer is used to obtain the elemental composition of Al-5Zn-0.1Sn, Al-5Z-0.1Sn-0.1In, and Al-5Zn-0.1Sn-0.1In-0.1Bi. Tafel analysis, electrochemical impedance spectroscopy, and constant-current chronopotentiometry are performed for electrochemical analysis. In addition, the self-corrosion of the alloys is examined to determine the hydrogen evolution and anode discharge stability. These results indicate that Al-5Zn-0.1Sn-0.1In-0.1Bi has the highest anode performance. On the basis of the scanning electron microscopy and transmission electron microscopy microstructure analysis, we propose that the dissolution and sedimentation process induced by Bi nanoprecipitates may activate a passive Al surface, significantly enhancing the discharge efficiency.

Fly ash boosted electrocatalytic properties of PEDOT:PSS counter electrodes for the triiodide reduction in dye-sensitized solar cells

Fly ash solid waste from a power plant was applied in a solar cell application for the first time. A doctor blade was used to coat FTO-glass with a composite film of mixed fly ash and PEDOT:PSS (FP). XRD, FTIR, SEM, EDX, and BET analyses were used to elucidate the crystal structure, morphology, and functional groups of fly ash in the current research. A significantly high efficiency solar cell was fabricated utilizing fly ash. CV, Tafel, and EIS analyses indicated a decrease in charge transfer resistance and an increased catalytic activity in the counter electrodes. The performance of DSSCs made from FP counter electrodes varied depending on the percentage of fly ash particles present. Fly ash mixed with PEDOT:PSS in a concentration ratio of 2:5 g/mL showed a high efficiency of 4.23%, which is comparable to Pt DSSC's (4.84%). Moreover, FP-2:5 presented a more highly efficient electrode than counter electrodes made from PEDOT:PSS mixed with MoO (3.08%) and CoO (3.65%). This suitability of this low-cost CE material for use in DSSCs has been established.

Electrochemical Kinetics Study of Ultrasound-Assisted Chalcopyrite Oxidation

Ultrasound-assisted chalcopyrite leaching has been reported previously, showing a noticeable improvement in leaching kinetics. However, the effect of ultrasound on the chalcopyrite oxidation kinetics from an electrochemical perspective has not been addressed. This study examines the ultrasonic enhancement of chalcopyrite oxidation kinetics in sulfuric acid solution from both conventional leaching and electrochemistry aspects. Electrochemical techniques, including linear sweep voltammetry (LSV) and chronoamperometry (CA), were used to illustrate the kinetics of chalcopyrite ultrasound-assisted leaching. Tafel analysis by LSV showed that 20% amplitude ultrasound power had increased the chalcopyrite electrochemical dissolution rate by about 20% in both Fe3+-free and 10 mM Fe3+-containing 0.5 M sulfuric acid solution. The CA tests indicated a drastic increase in the Fe3+ reduction reaction when ultrasound was applied (20% amplitude). At 0.5 V, the Fe3+ to Fe2+ reduction current density at 30 min drastically increased from − 65.54 without ultrasound to − 1165.84 µA cm−2 with ultrasound.Graphical

Electrodeposited Ni–Mo coatings as electrocatalytic materials for green hydrogen production

In this work, nanocrystalline nickel and nickel-molybdenum alloys were electrodeposited from electrolytes based on deep eutectic solvents. Eutectic mixtures of choline chloride with ethylene glycol (ethaline) and urea (reline) were used as typical representatives of deep eutectic solvents. The deposited Ni and Ni–Mo films were evaluated as potential electrocatalytic materials for green hydrogen production via electrolysis of alkaline aqueous solutions. The electrodeposited samples were characterized by XRD, SEM and EDX techniques, and the electrochemical behavior was evaluated by means of linear voltammetry and Tafel analysis. It was shown that the deposition of nickel (without molybdenum) from the electrolytes based on ethaline provides a higher electrocatalytic activity of the material with respect to the hydrogen evolution reaction than the material deposited from the reline-based electrolytes. The reline-based plating electrolytes contribute to a greater inclusion of molybdenum in the fabricated Ni–Mo alloys and therefore ensure increased electrocatalytic activity as compared with the ethaline-based electrolytes. The electrocatalytic behavior well correlates with the molybdenum content in the coatings. Ni and Ni–Mo electrodeposits produced from the deep eutectic solvent-mediated plating baths exhibit improved electrocatalytic performance and can be considered as promising catalytic materials for water electrolysis in green hydrogen energy.

Why standard electrokinetic analysis often fails for nanostructured electrodes - Reviewing inhomogeneous electroactivity

The advancement of electrocatalysis from fundamental research to application is a process that requires researchers from different fields to co-work seamlessly to be effective. In this mini review, we highlight common problems that are faced when the complexity of novel electrode assemblies, consisting of nanostructured materials are moved from a fundamental view towards an evaluation for application. When the classical kinetic descriptors such as Butler-Volmer kinetics are applied to complex electrode assemblies, a clear distinction and attribution of material properties versus electrode performance becomes challenging. We emphasize recent advancements to discern and analyse electrocatalysis at composite or nanostructured electrodes. We discuss the origins of inhomogeneities in the electrocatalytic activity of three-dimensional electrodes, how these can be detected and which necessary changes from the classical methods, such as Tafel analysis, can be performed to ensure a sound data acquisition and evaluation.

Lead as an effective facilitator for ethanol electrooxidation on Rh catalyst in alkaline media: RhPb/C vs RhRu/C

Rh-based catalysts have attracted much attention due to their ability to efficiently break CC bonds in ethanol oxidation reaction(EOR), while pure Rh catalyst have low EOR activity. It is important to improve the EOR activity of Rh-based catalyst. Herein, we have been successfully synthesized carbon supported Rh, Rh-Pb, and Rh-Ru alloy catalysts. The catalytic activity of RhPb/C for ethanol oxidation is 0.96 mA/cm2, which is 8 times than that of Rh/C. The steady-state current density of RhPb/C at 0.5 V is 17 and 20 times higher than that of RhRu/C and Rh/C, respectively. The results show that adding a small portion of lead significantly enhanced the Rh-based catalyst activity, stability, and anti-poisoning ability during EOR in alkaline media. Moreover, the Tafel slope of RhPb/C catalyst for EOR is 118 mVdec−1, which is similar with that of Pt/C(116 mVdec−1), while the Tafel slope of RhRu/C is 77 mVdec−1, similar to that of Rh/C(87 mVdec−1). The CO-stripping potential of RhRu/C, Rh/C and RhPb/C is 0.535 V, 0.573 V and 0.601 V, respectively. Combined with the cyclic voltammetry, chronoamperometry, CO-stripping and Tafel analysis, it is concluded that for RhRu/C catalyst, the improvement of EOR is mainly attributed to the bifunctional mechanism, while for RhPb/C catalyst, the ensemble effect and the electronic effect of Pb is essential to the improvement of EOR.

Graphite/β-PbO2 Composite Inert Anode Synthesis Using Electrochemical Methods

The anode material is one of the determining factors for the success of the electrowinning process. This study aims to coat the graphite substrate with β-PbO2 to produce an inert graphite/β-PbO2 composite material with low cost and good quality. The graphite/β-PbO2 synthesis is expected to be used as an anode for inert composites for electrowinning processes. The β-PbO2 deposition layer was prepared on the surface of the graphite substrate by an electrodeposition process using a sulfuric acid electrolyte. The effect of electrolyte concentration and voltage on graphite/β-PbO2 synthesis was investigated using a potentiodynamic polarization test through Tafel analysis. Experimental data have shown that there is an increase in the current density value at the beginning of the process and then a decrease due to passivation; this is due to anodic polarization in the graphite/β-PbO2 synthesis process. Suitable conditions can effectively increase the rate of formation of β-PbO2. The results of scanning electron microscopy with energy-dispersive X-ray spectroscopic analysis of the formed crystal structure showed that the β-PbO2 deposition layer obtained had a well-formed tetragonal structure at a voltage of 9 V.

Investigation on corrosion inhibitors for zinc batteries: Sodium sulphate

To store energy rechargeable batteries had developed widely. Over the concern of safety and cost-efficient, rechargeable aqueous metal-ion batteries are mostly favored. Various studies have been performed on different aqueous metal-ion batteries. Out of them, zinc-ion batteries have some unique and outstanding benefits. The aqueous electrolytes give assurance against exploding by their non-flammable nature. The zinc anodes are being used as it benefits the stability and redox reversibility. Zinc anodes have a higher theoretical capacity (820 mAh g−1) and low redox potential [−0.76 V vs. SHE (standard hydrogen electrode)]. As a measure to increase corrosion resistance, sodium sulphate is being used as an inhibitor. The zinc anode is being analyzed at different concentrations of the inhibitor and the best concentration is being identified for the battery applications. Potentiostatic EIS (Electrochemical Impedance Spectroscopy) and Tafel analysis are done to determine the corrosion behavior of the zinc with the addition of the inhibitor.

Synthesis of ZnO Nanorods and Its Application in Zinc-Silver Secondary Batteries

In this paper, ZnO nanorods were synthesized by the hydrothermal method and used as anodes for zinc-silver batteries. The Tafel and EIS curve analysis results show that ZnO nanorods have better anti-corrosion and charge transport properties than ZnO powders. At 0.1 C discharge conditions, the ZnO electrode exhibits more stable cycle efficiency than the powder electrode; after 25 cycles, the capacity is higher by 95%. The superior electrochemical performance is due to the ZnO nanorods having the ability to conduct electrons and increase the surface area. Therefore, the possible growth mechanism of ZnO nanorods has been investigated.

Co supported on N and S dual-doped reduced graphene oxide as highly active oxygen-reduction catalyst for direct ethanol fuel cells

Oxygen reduction reaction (ORR) is one of the key features for the efficient functioning of several energy conversion devices such as fuel cells, appearing the necessity of development of new low-cost catalyst materials. Heteroatom-doped carbon materials have attracted attention in this field due to its physicochemical and electronic properties. In this work, a nitrogen and sulfur doped material with anchored Co3O4 nanoparticles (Co/SN-rGO) is proposed as cathode catalyst for direct ethanol fuel cells (DEFCs) and results are compared with different doped graphene nanomaterials (GMs). The effect of the heteroatoms and cobalt oxide nanoparticles in the final efficiency was studied. Synthesized materials were characterized and the activity of Co/SN-rGO and GMs for the ORR was studied. Co/SN-rGO presents high ORR performance in terms of onset potential (Eonset), 0.86 V (vs RHE) and half-wave potential (E1/2) 0.72 V (vs RHE). Tafel analysis shows 60 mV dec-1 at low overpotential for potential dependent ORR mechanism. Besides, when Co/SN-rGO performance is evaluated in a DEFC using a fuel cell test station, main results indicate higher catalytic activity, stability, and ethanol tolerance of Co/SN-rGO in comparison to a carbon-supported Pt catalyst.

How Acid Washing Nickel Foam Substrates Improves the Efficiency of the Alkaline Hydrogen Evolution Reaction

Nickel foam substrates are frequently utilised as porous 3D substrates for renewable energy applications. The preparation of these substrates usually includes an acid-washing step, but the degree to which this step affects the final electrochemical performance after spray-coating a catalyst ink is unreported. Herein, we report the effects of acid washing through physicochemical and electrochemical characterisation. The electrochemical performance was determined through repeated measurements of catalyst-coated nickel foam substrates both with and without the initial step of acid washing. It was found that acid washing increased the current density by 17.9% for the acid-treated MoS2-coated nickel foam electrode. This increment was affiliated with an electrochemically active surface area that increased by 11.2%, and a Tafel analysis indicated that the acid-treated MoS2-coated electrodes facilitated the initial water dissociation step of the hydrogen evolution reaction with greater ease. Similar effects were also discovered for acid-treated PtIr(1:3)/C-coated nickel foam substrates. The stability was also improved; the degradation rate was reduced by 18.9% for the acid-treated MoS2-coated electrodes. This demonstrates the utility of acid washing nickel foam electrodes.

Synthesis of 3D Porous Cu Nanostructures on Ag Thin Film Using Dynamic Hydrogen Bubble Template for Electrochemical Conversion of CO2 to Ethanol.

Cu-based nanomaterials have been widely considered to be promising electrocatalysts for the direct conversion of CO2 to high-value hydrocarbons. However, poor selectivity and slow kinetics have hindered the use of Cu-based catalysts for large-scale industrial applications. In this work, we report on a tunable Cu-based synthesis strategy using a dynamic hydrogen bubble template (DHBT) coupled with a sputtered Ag thin film for the electrochemical reduction of CO2 to ethanol. Remarkably, the introduction of Ag into the base of the three-dimensional (3D) Cu nanostructure induced changes in the CO2 reduction reaction (CO2RR) pathway, which resulted in the generation of ethanol with high Faradaic Efficiency (FE). This observation was further investigated through Tafel and electrochemical impedance spectroscopic analyses. The rational design of the electrocatalyst was shown to promote the spillover of formed CO intermediates from the Ag sites to the 3D porous Cu nanostructure for further reduction to C2 products. Finally, challenges toward the development of multi-metallic electrocatalysts for the direct catalysis of CO2 to hydrocarbons were elucidated, and future perspectives were highlighted.