Tafel Analysis Research Articles

Morphology-Dependent Corrosion Inhibition and Self-Healing Properties of Polypyrrole and Indigo Carmine Composites on Carbon Steel 1018 in a Saline Environment.

The aim of this research is to explore the effectiveness of epoxy-resin@polypyrole composites as a corrosion inhibitor when applied as a coating on carbon steel 1018 in a 3.5 wt % sodium chloride electrolyte solution. The anticorrosion properties of these composite coatings can be optimized by manipulating their morphology. To investigate how modifications in the structure of epoxy resin coatings impact their ability to inhibit corrosion, three distinct forms of polypyrrole nanoparticles/indigo carmine structures, including granular, rod-shaped, and spiral rods, were synthesized and incorporated into epoxy resin coatings for analysis. Various characterization techniques, including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), Brunauer-Emmett-Teller (BET), Fourier transform infrared spectroscopy (FT-IR), and vibrating-sample magnetometer (VSM) analysis, were utilized to examine the structures of polymer nanoparticles. The FESEM images displayed that the indigo carmine concentration changes during micellar polymerization led to morphological changes in the polymer nanoparticles. Furthermore, electrochemical assessment methods such as Tafel analysis and electrochemical impedance spectroscopy (EIS) verified a reduction in corrosion current and enhancement in resistance due to the transformation of polymer nanoparticles from granular to spiral rods, leading to 99.99% corrosion inhibition. The corrosion rate of polymer nanoparticles varies significantly with their structure, exhibiting a rate of 1.9 × 10-6 for granular forms, 4.08 × 10-7 for rod-shaped structures, and 3.45 × 10-10 for spiral rods. In the next step, the self-healing properties of the scratched coating loaded by the spiral rod polymer nanoparticles were investigated by FESEM, UV-vis microscope images, energy-dispersive X-ray spectroscopy (EDX), EIS, and Tafel tests. The ability of polypyrrole and indigo carmine to inhibit corrosion, physically adhere to the metal surface, and create iron-indigo carmine complexes allows for the creation of a protective coating on carbon steel surfaces.

Ru-doped Aurivillius phase perovskites Bi4Ti3O12 for boosting photo-redox of N2 in photocatalytic nitrogen fixation

In this study, we prepared layered Aurivillius phase bismuth titanate perovskite oxide (Bi4Ti3O12, BT) using the sol–gel method and doped them with various amounts of Ru (BT-Rux, x = 0.05, 0.1, 0.25, and 0.5 % w/w) for photocatalytic nitrogen fixation in the absence of a sacrificial reagent. Among the prepared photocatalysts, BT-Ru0.25 showed the highest NH4+ formation rate of 119 μmolgcat−1 h−1, which is a 3.21-fold higher than BT. The Rietveld refinement X-ray diffraction results suggest that the expansion of the a and b lattice parameters of BT occurs with adding Ru, which correlates with the photocatalytic NH4+ production performance. This is because the expansion of a and b lattices of BT via Ru doping contributed to the increase in oxygen vacancies and the altered surface charge density in the Bi and Ti of BT, creating an asymmetric coordination environment that could induce the polarization of N2. Photoluminescence and Time-resolved photoluminescence analyses showed that the doping of Ru on BT reduced the recombination efficiency of the photogenerated electron-hole pairs and prolonged the electron decay time. In linear sweep voltammetry and Tafel analyses showed that Ru doping of BT suppressed the HER and photocorrosion. In-situ surfaced enhanced Raman spectroscopy (SERS) analysis revealed that the doping of Ru in BT improved the N2 interaction on the Bi-O bonds, accelerating the surface nitrogen oxidation reaction (NOR) to form NO3– and further undergoing a nitrate reduction reaction (NORR) for NH4+ production. This study highlights the importance of incorporating Ru into perovskite oxides to improve the separation of photogenerated carriers in photocatalytic NH4+ production without sacrificial reagents.

Electrocatalytic Performance and Kinetic Behavior of Anion‐Intercalated Borate‐Based NiFe LDH in Alkaline OER

AbstractThe synthesis of hydrogen via water electrolysis is an important step towards resolving the energy crisis and impeding global warming, as hydrogen can be used as a green energy carrier. The oxygen evolution as one half‐cell reaction (OER) is currently limiting efficient water splitting due to kinetic inhibition as well as a complex mechanism, causing a large overpotential. Nickel‐iron layered double hydroxides (LDH) were found to be suitable OER catalysts, as they are cost effective, stable and highly active. This work focuses on the intercalation of different organic and inorganic borates into the LDH interlayers to study their influence on OER. Besides activity and stability measurements, three borate candidates were chosen for a kinetic study, including steady‐state Tafel analysis and reaction order plots. It was found that the Bockris pathway with the second step as rate‐determining step was predominant for all three catalysts. Of all candidates, the intercalation of borate resulted in the highest performance, which was associated with a high reducibility affecting the active metal sites.

Electrokinetics of Nitrite to Ammonia Conversion in the Neutral Medium Over A Platinum Surface.

Polycrystalline Pt electrode was employed to selectively convert nitrite ions ( ) into useful nitrogenous compound through electrochemical reduction reaction in neutral medium. According to adsorptive stripping analysis, the reduction process produced nitric oxide (NO) on the surface of Pt electrode. The spectroscopic test and gas chromatographic studies discovered the presence of ammonia (NH3) in the electrolyzed solution, suggesting the transformation of adsorbed NO into NH3 during the reverse scan. Scan rate dependent investigation was performed to elucidate kinetic information relating to this reaction on Pt surface. From Ep vs scan rate (υ) and jp vs υ (logarithmic plot), it was found that the conversion of ion into NO is an irreversible reaction which relies on the diffusion of ions to electrode surface. The Tafel analysis unveiled that the first electron transfer sets the overall reaction rate, having formal reduction potential, E0'=-0.46 V and standard heterogeneous rate constant, k0= cm s-1. Reductive transfer coefficient (α) is another kinetics parameter, which was found to be approximate 0.77 from the difference between Ep and Ep/2 of the voltammograms obtained over scan rate range 0.005 V s-1 to 0.250 V s-1, indicating a stepwise process. According to temperature-dependent voltammograms, the nitrite reduction reaction on Pt had a calculated activation energy of about 19.8 kJ mol-1 and a pre-exponential factor of about 8.39×103 mA cm-2.

Electro-Co-Polymerisation of Polypyrrole-Polyaniline Composites in Ionic Liquids for Metal-Free Hydrogen Evolution Electrodes.

Pure organic films consisting of polypyrrole, polyaniline and a composite of polypyrrole and polyaniline electrodeposited in the ionic liquid EMIM-TFSI onto mesoporous carbon electrodes are tested for their hydrogen evolution reaction capabilities. The use of these intrinsically conducting polymers is seen as a way of stepping away from expensive and rare metallic catalysts. Co-polymerisation of polypyrrole and polyaniline in a 1 : 10 ratio in EMIM-TFSI was found to be doped with the TFSI- anion and be much more active to the hydrogen evolution reaction when compared to pure polymers. Tafel analysis of the composite gave a value of 144 mV/dec indicating that the Volmer step is the rate limiting step. However, stability tests showed an improvement in the composite's overpoential performance for the hydrogen evolution reaction.

Hydrogen Evolution Activity of Platinum Nanoparticles Decorated on Silver Nanowire Networks and Graphite Electrodes

The catalytic activity of graphite (C) and conductive silver nanowire (AgNW) networks coated on glass and graphite substrates with low platinum content towards hydrogen evolution reaction (HER) is reported. The results exhibit that the chronoamperometric electrodeposition of platinum on AgNW substrates results in the formation of spherically shaped nanoparticle agglomerates aligned on the nanowires. Also, platinum doped graphite electrodes with a rough surface showed an efficient distribution of platinum nanoparticles (PtNPs). Studies of the electrocatalytic HER activity as a function of platinum loading indicate that the optimum loading is in the range of 60 µg/cm2 and further loading results only in a minor reduction of the overpotential. At low Pt content, a synergistic effect of the AgNW network in terms of enhancement of the HER performance was observed. Tafel analysis showed that in the low overpotential region, the Volmer reaction was the rate determining step for the graphite based electrodes. The graphite substrate in conductive connection with the nanowires was shown to significantly boost the hydrogen formation rate.

Evaluation of hydrogen evolution activity by bubbles growth rates as descriptor

Evaluation of the electrocatalytic behavior in the high current density region is critical toward the applications in the industrial water electrolysis system. Here, we utilized the bubble growth rate as descriptor for evaluation of hydrogen evolution reaction. Ag electrode was selected as a model electrode. Pressure-controlled cell was used for the evaluation of the bubble behavior under the wider range in the overpotential. Hydrogen bubble evolution behavior was evaluated by video observation under electrochemical potential control. Even in the presence of the complex processes such as nucleation, growth and detachment of the bubbles, the hydrogen evolution behavior is evaluated with respect to the classical Tafel analyses even in high overpotential region. These analyses provide the methods for the rapid screening toward the material discovery of the green hydrogen production in high current density region.

Gleditsia sinensic extract as green corrosion inhibitor for N80 steel in 1 M HCl

The inhibition efficiency of gleditsia sinensic extract (GSE) as green corrosion inhibitor for N80 steel has been evaluated by weightlessness test, electrochemical impedance spectroscopy (EIS) study, Potentiodynamic polarization (PDP) measurement and Density Functional Theory (DFT) calculations in 1M HCl solution. Consequently, the inhibition efficiency of GSE is increased with the concentrations, immersion time and corrosion temperature (except 60 °C). After 144 h of immersion at 30 °C, the inhibition efficiency of GSE at a concentration of 500 mg/L was as high as 92.34 %. The adsorption process was spontaneous exothermic and conformed to Langmuir's law of adsorption, while Tafel's analysis showed that GSE is a mixed type of inhibitor. In addition, the corrosion products have been examined by scanning electron microscopy (SEM) analysis, X-Ray Diffractomer (XRD) testing, Fourier transform infrared spectroscopy (FTIR-ATR), UV-Vis spectroscopy and contact angle (CA) measurements. Furthermore, the corrosion inhibition mechanism has also been investigated.

Ce-doped cobalt-based hydroxide assisted with low-temperature molten salt for industrial oxygen evolution reaction

Developing low cost and high-performance oxygen evolution electrocatalysts is significant to improve the efficiency of water electrolysis for large-scale hydrogen production. Cobalt hydroxide is a promising electrocatalyst for oxygen evolution reaction (OER), but its poor conductivity and activity seriously restrict the practical application. A simple one-step low temperature molten salt method was applied to successfully synthesize the Ce-doped cobalt hydroxide nitrate (Ce-CoNH/CF), which exhibits outstanding OER performance with a low overpotential of 448 mV at the current density of 1000 mA/cm2 in 1 mol/L KOH. The remarkable performance of Ce-CoNH/CF electrode in OER may be the comprehensive result of fast reaction kinetics, large electrochemical active specific surface area (ECSA) and small charge transfer resistance (Rct) as revealed by the Tafel, cyclic voltammetry (CV) and electrochemical impedance spectra (EIS) analysis. Under the simulated industrial test conditions (6 mol/L KOH, 70 °C), the Ce-CoNH/CF electrode still displays excellent OER performance.

Investigating the impact of various etching agents on Ti3C2Tx MXene synthesis for electrochemical energy conversion

MXenes represent a revolutionary class of two-dimensional (2D) materials that have garnered significant attention due to their unique properties, including excellent electrical conductivity, and remarkable mechanical strength. This study investigates the influence of different etching agents on the synthesis of MXenes for electrochemical energy conversion applications, particularly in methanol oxidation reactions (MOR). Morphological characterization, particle distribution and sizing, elemental analysis, and surface chemistry assessments were conducted using field emission scanning electron microscopy (FESEM), elemental mapping, transmission electron microscopy (TEM), x-ray diffraction (XRD), and x-ray photoelectron spectroscopy (XPS). Electrochemical techniques such as cyclic voltammetry (CV), electrochemical active surface area (ECSA), Tafel analysis, electrochemical impedance spectroscopy (EIS), and long-term stability assessment were employed. The study reveals that PtRu/MXene synthesized with the FeF3/HCl etching route exhibits the highest ECSA value and peak current density, being 12.3 times and 3.63 times higher than those achieved via the LiF/HCl etching route. The kinetic rate, tolerance to catalyst poisoning and long-term stability also show the better results for this etching route. These findings suggest promising potential for PtRu/MXene_FeF3/HCl as an effective anodic electrocatalyst in direct methanol fuel cell (DMFC) applications.

Size-controlled synthesis of cobalt phosphide (Co2P) nanoparticles and their application in non-enzymatic glucose sensors via a carbon fiber/Co2P composite

In this study, we synthesized Co2P nanoparticles using a solid-state phosphorization method and evaluated the electrocatalytic response to glucose oxidation reaction (GORs). The influence of synthesis conditions on the particle size, morphology of Co2P species and formation of byproducts is discussed. A lower molar ratio of the phosphorus precursor leads to a decrease in the generation of byproducts. In addition, the calcination temperature and time greatly influence the purity level of the Co2P species and its particle size. Thus, we obtained three pure Co2P nanoparticles with different sizes and morphologies. Significant differences in their electrocatalytic activity against the GOR are observed depending on the size of the particles, being the smaller ones the most efficient. Based on Tafel analysis, a higher catalytic activity was observed for the carbon fibre (CF)/Co2P composite compared to Co2P, which presented a greater onset potential and low response in current density. Tafel slopes close to 120 mV/dec were obtained for both materials, indicating that the mechanism is independent of the type of Co2P-based material used. Finally, the performance of the GCE/CF/Co2P sensor was demonstrated by amperometric measurements, with a sensitivity of 409 µAmM-1cm-2, a linear range between 39.4 µM and 150 µM, and a detection limit of 0.97 µM, analytical characteristics better than those obtained for other cobalt phosphide-based sensors reported in the literature. In addition, the GCE/CF/Co2P sensor shows excellent selectivity and demonstrated to be competitive compared to other Co-based non-enzymatic glucose sensors.

(Invited) Design of Reduced Shear Force Cu Cleaning Processes Via α-β-Unsaturated Chemistries for Enhanced BTA Residue Removal

As integrated circuit and logic devices continue to decrease, limiting induced defectivity during Chemical Mechanical Planarization (CMP) processes (polishing and substrate cleaning) is imperative. Defects resulting from the CMP process can be classified as mechanical (i.e., scratching), chemical (i.e., corrosion), or physiochemical (i.e., adsorbed contaminants) according to the mechanism of formation. Traditionally, a contact cleaning method implements a polyvinyl alcohol (PVA) brush to transfer cleaning chemistry to the substrate of interest and provides the necessary mechanical energy for defect removal. While this process effectively removes contaminants, its reliance on shear forces can induce secondary defect modes, such as scratching. One major challenge for the post-CMP cleaning of Cu substrates is the polymeric residue film comprised of BTA-Cu+ complexes that propagate during the CMP polishing process. The current and most effective mode to mitigate this “residue defect” is coupling brush-induced shear force with additives that promote interfacial redox reactions to remove residues through an undercutting mechanism. This work focuses on developing a “softer” and additive structure-based approach that drives less aggressive interfacial shear between the brush and wafer substrate. More specifically, α-β-unsaturated additives with diverse functionality (i.e., -unsaturated carboxylic acids, carboxylic acids, and unsaturated benzaldehydes) will be tested to evaluate their efficacy to “overcut” the organic residue via a proposed aza-Michael addition reaction pathway. This “overcutting” mechanism relies on additional modes of interaction (i.e., p-stacking, H-bonding, conformational relationships, etc.) with the BTA- Cu+ polymeric residue film. A suite of dynamic techniques (i.e., Tafel analysis, OCP vs. time, contact angle, additive diffusion analysis, and shear force) will attempt to correlate the additive structure and reaction mechanism to organic residue removal efficiency and measured interfacial shear forces. Initial results have shown that implementing an “overcutting” mechanism will decrease the overall shear force and significantly reduce the generation of secondary defects without sacrificing overall defect removal efficiency.

Elucidating Fundamental Structure-Function Relationships for Iridium Oxide Catalysts in PEM Water Electrolyzers

Proton exchange membrane water electrolysis (PEMWE) will contribute substantially towards decarbonization efforts and is expected to make up 40% of the green hydrogen market.1 A primary barrier for PEMWE scale-up is the detrimentally high usage of iridium for the oxygen evolution reaction catalyst. To achieve large-scale PEMWE deployment, loading reductions from 2-3 mgIr cm-2 to 0.10 mgIr cm-2 must occur.2 Such a feat can only be achieved through significant improvements in activity and durability. However, there exists a lack of fundamental understanding in how catalyst properties correlate to performance, thus hindering optimization efforts. The phenomena of catalyst activity/durability are frequently treated with purely empirical approaches, and thus the foundational knowledge needed for improved catalyst design—such as understanding how crystallinity and oxidation states impact performance in a membrane electrode assembly (MEA)—has not been well investigated.3 This work serves to bridge this gap in knowledge by correlating extensive structural characterization data with MEA activity and durability for six commercial IrOx catalysts. Properties such as oxidation states, chemical composition, local atomic/electronic configuration, crystallinity, surface area, and particle size distribution were elucidated for each catalyst in powder and/or MEA form. Following MEA conditioning, catalyst activity was benchmarked via polarization curves and Tafel analysis. Lastly, durability was evaluated by performing a 500h accelerated stress test (adapted from the H2New consortium), with electrochemical characterization conducted every 100h. The presence of amorphous character and the Ir3+ oxidation state was the best determinant of activity. Durability, on the other hand, was associated with greater crystalline character and more redox-stable cyclic voltammogram profiles. Correlations regarding chemical composition, local atomic/electronic configurations, particle size, and surface area will be discussed as well. Smolinka, T.; Wiebe, N.; Sterchele, P.; Palzer, A.; Lehner, F.; Jansen, M.; Kiemel, S.; Miehe, R.; Wahren, S.; Zimmermann, F. Studie IndWEDe: Industrialisierung Der Wasserelektrolyse in Deutschland: Chancen Und Herausforderungen Für Nachhaltigen Wasserstoff Für Verkehr, Strom Und Wärme.; 2018.Clapp, M.; Zalitis, C. M.; Ryan, M. Perspectives on Current and Future Iridium Demand and Iridium Oxide Catalysts for PEM Water Electrolysis. Catal Today 2023, 420 (March), 114140. https://doi.org/10.1016/j.cattod.2023.114140.Lazaridis, T.; Stühmeier, B. M.; Gasteiger, H. A.; El-Sayed, H. A. Capabilities and Limitations of Rotating Disk Electrodes versus Membrane Electrode Assemblies in the Investigation of Electrocatalysts. Nat Catal 2022, 5 (5), 363–373. https://doi.org/10.1038/s41929-022-00776-5.

Estimation of Onset Potential for Oxygen Evolution Reaction at Platinum Surface Via Discharge of the Adsorption Capacitance of Intermediate Species

Developments in onset potential estimation for oxygen evolution reaction seeks to overcome several disadvantages in existing methods. For example, in the current tangent intersection method from the Nonfaradaic to Faradaic region, the electrocatalyst with large pseudocapacitance shows a negative slope near the onset potential in the Nonfaradaic zone. In such systems, the intersection of tangents from the Nonfaradaic to Faradaic region fails to give the onset potential. Similarly, onset potential determination from the fixed current density (10 mA/cm2) can be inaccurate for electrocatalysts having a large pseudocapacitive current. In addition, the commonly utilized methods do not provide insight into the underlying physicochemical properties that modulate reactivity around the onset potential. We propose an approach based on reaction mechanism analysis integrated with electrochemical impedance to detect the onset potential via the capacitance variation generated from the intermediate species of OER. We demonstrate our proposed method via experiments on oxygen evolution reaction in the acidic medium on platinum as the model system. The impedance analysis of such a system from the Nonfaradaic to Faradaic region shows the capacitance generated from the intermediate species (S-OH) shows the maxima at the onset potential. Further, the Tafel analysis showed the S-OH step as the rate-determining step (RDS) in a low overpotential region. Additionally, the onset potential obtained from the tangent intersection from the Nonfaradaic to Faradaic region matches that obtained from the impedance analysis. We are in the process of extending the proposed approach to more complex systems with multiple product evolutions.

Electrochemical Evaluation of Penta‐Coordinated Fe Phthalocyanine During the Oxygen Reduction Reaction in Various Acidic Solutions

AbstractIron phthalocyanine (FePc) was penta‐coordinated with pyridine ligand (Py) grafted on carbon nanotube (CNT), to form (FePc‐Py‐CNT). The complex was studied as a catalyst for the oxygen reduction reaction ORR in seven different supporting electrolytes: OH− (0.1 M), OH− (1 M), NO3− (1 M), HSO4− (1 M), ClO4− (1 M), Br− (1 M), Cl− (1 M), to unveil anion‐poisoning effects and mechanism. Through cyclic voltammetry and polarization curves in N2 and O2 saturated atmospheres, thermodynamic and kinetic data were acquired. In acid media, the formal potential Fe(III)/(II) (E0’Fe(III)/(II)) of the complex is biased to more negative potentials by the anion presence. Similar effects were observed for the onset potential (Eonset) during polarization curves for the ORR. When the ORR was performed in the presence of either ClO4−, or HSO4−, anions, Tafel analysis showed different values depending if were derived from the low or from the high overpotential regions, revealing an inner‐sphere electron transfer mechanism (ISET). The Tafel values derived from measurements in the presence of Cl− and Br− anions do not change when extracted at low or at high overpotentials evidencing an outer‐sphere reaction mechanism (OSET). Gibbs free energies were derived from poisoning tests confirming the ISET and OSET mechanisms. The poisoning effect is responsible for the immediate loss of performance for these catalysts during the ORR in acidic media.

Discerning the role of a site cation in ACoO3 perovskites for boosting Co3+/Co2+ redox cycle for pollutant degradation: DFT calculation, mechanism and toxicity evolution

The degradation of persistent and refractory pollutants, particularly plastic and resins manufacturing wastewater, poses a significant challenge due to their high toxicity and high concentrations. This study developed a novel hybrid ACoO3 (A = La, Ce, Sr)/PMS perovskite system for the treatment of multicomponent (MCs; ACN, ACM and ACY) from synthetic resin manufacturing wastewater. Synthesized perovskites were characterized by various techniques i.e., BET, XRD, FESEM with EDAX, FTIR, TEM, XPS, EIS, and Tafel analysis. Perovskite LaCoO3 exhibited the highest degradation of MCs i.e., ACN (98.7%), ACM (86.3%), and ACY (56.4%), with consumption of PMS (95.2%) under the optimal operating conditions (LaCoO3 dose 0.8 g/L, PMS dose 2 g/L, pH 7.2 and reaction temperature 55 °C). The quantitative contribution (%) of reactive oxygen species (ROS) reveals that SO4•− are the dominating radical species, which contribute to ACN (58.3% for SO4•− radicals) and ACM degradation (46.4% for SO4•− radicals). The tafel plots and EIS spectra demonstrated that perovskites LaCoO3 have better charge transfer rates and more reactive sites that are favorable for PMS activation. Further, four major degradation pathways were proposed based on Fukui index calculations, as well as GC-MS characterization of intermediate byproducts. Based on a stability and reusability study, it was concluded that LaCoO3 perovskites are highly stable, and minimal cobalt leaching occurs (0.96 mg/L) after four cycles. The eco-toxicity assessment performed using QSAR model indicated that the byproducts of the LaCoO3/PMS system are non-toxic nature to common organism (i.e., fish, daphnids and green algae). In addition, the cost of the hybrid LaCoO3/PMS system in a single cycle was estimated to be $34.79 per cubic meter of resin wastewater.

Nonidealities in CO2 Electroreduction Mechanisms Revealed by Automation-Assisted Kinetic Analysis.

In electrocatalysis, mechanistic analysis of reaction rate data often relies on the linearization of relatively simple rate equations; this is the basis for typical Tafel and reactant order dependence analyses. However, for more complex reaction phenomena, such as surface coverage effects or mixed control, these common linearization strategies will yield incomplete or uninterpretable results. Cohesive kinetic analysis, which is often used in thermocatalysis and involves quantitative model fitting for data collected over a wide range of reaction conditions, requires more data but also provides a more robust strategy for interrogating reaction mechanisms. In this work, we report a robotic system that improves the experimental workflow for collecting electrochemical rate data by automating sequential testing of up to 10 electrochemical cells, where each cell can have a different electrode, electrolyte, gas-phase reactant composition, and applied voltage. We used this system to investigate the mechanism of carbon dioxide electroreduction to carbon monoxide at several immobilized metal tetrapyrroles. Specifically, at cobalt phthalocyanine (CoPc), cobalt tetraphenylporphyrin (CoTPP), and iron phthalocyanine (FePc), we see signatures of complex reaction mechanisms, where observed bicarbonate and CO2 order dependences change with applied potential. We illustrate how phenomena such as electrolyte poisoning and potential-dependent degrees of rate control can explain the observed kinetic behaviors. Our mechanistic analysis suggests that CoPc and CoTPP share a similar reaction mechanism, akin to one previously proposed, whereas the mechanism for FePc likely involves a species later in the catalytic cycle as the most abundant reactive intermediate. Our study illustrates that complex reaction mechanisms that are not amenable to common Tafel and order dependence analyses may be quite prevalent across this class of immobilized metal tetrapyrrole electrocatalysts.

The Influence of Metal Impurities on NiOOH Electrocatalytic Activity in the Oxygen Evolution Reaction

AbstractThe energy transition and the implementation of new electrochemical technologies will result in an increased reliance on critical raw materials for electrodes. Their large‐scale application will ultimately mean working with lower grade materials. Here we study the influence of metal impurities on nickel foam electrocatalysts. We do this by electrodepositing known amounts of first‐row transition metals (Cu, Cr, Mn, Fe, Co and Ni) on nickel foam and studying their performance in the oxygen evolution reaction (OER) as a model reaction. The electrodes’ performance is studied using cyclic voltammetry (CV), linear sweep voltammetry (LSV), Tafel analysis, stepwise chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS). Combining these results with microscopy analysis, we show that even small amounts of transition‐metal impurities have profound effects on the catalytic performance of nickel electrodes. The changes affect the OER onset potential (the energy that the system requires to convert OH– to O2) and the Tafel slope of each electrode (the electrode's initial activity in the OER onset region). Our results highlight the implications of such impurities on electrode design and future large‐scale application.

Multi-walled carbon nanotubes modified corn straw biochar as high-performance anode in microbial fuel cells

In this study, the feasibility of multi-walled carbon nanotubes in modifying corn straw biochar electrode and the subsequent enhancement in electrical conductivity of the modified electrode and reactor performance were investigated in this study. The Layer-by-Layer self-assembly method was used as the modification method. The electrochemical activity, power output capacity and pollutant removal performance of the Microbial fuel cell with modified corn straw biochar anode. The characterization techniques included scanning electron microscope, electrochemical impedance spectroscopy, Tafel analysis and polarization curve. The successful adhesion of multi-walled carbon nanotubes onto the surface of corn straw biochar was revealed by scanning electron microscope analysis. The microbial fuel cell with multi-walled carbon nanotubes modified corn straw biochar anode achieved the lowest solution resistance of 9.86 Ω and charge transfer resistance of 3.56 Ω. Compared with the MFC with unmodified electrode, power density (2.68 W m−2) and coulombic efficiency (70.52 %) were demonstrated to increase by 58.6 % and 24.6 % in the MFC with modified electrode, respectively.

Fabrication of humidity monitoring sensor using porous silicon nitride structures for alkaline conditions

Porous silicon nitride structures were fabricated for a humidity sensor. The porous silicon structures were fabricated by the metal-assisted chemical etching process, and the conformal silicon nitride thin film was deposited by the atomic layer deposition process. The optimized porous sensor with the 10 nm-thick silicon nitride thin film had a hydrophilic surface and compared to other sensors, had an excellent humidity sensing response. Especially, it showed a superior humidity sensing response at 1 kHz with fast response and recovery times of 13.3 s and 12.4 s, respectively, were observed. Based on the electrochemical impedance spectroscopy results, the equivalent circuits and humidity sensing mechanism were discussed. The chemical stability of the silicon nitride was characterized using Tafel analysis in alkaline electrolytes. Additionally, the sensor's humidity sensing capabilities were tested under cement-embedded conditions.