Open Circuit Potential Measurements Research Articles

Part I: Non-faradaic electrochemical impedance-based DNA biosensor for detecting phytopathogen – Ralstonia solanacearum

Herein, we report for the first time the development of a label-free, non-faradaic, and highly sensitive DNA-based impedimetric sensor using micro-sized gold interdigitated electrodes (IDE) to detect a soil-borne agricultural pathogen Ralstonia solanacearum. A universal 30 oligomer single-stranded DNA (ssDNA) probe lpxC4 having specificity towards R. solanacearum is successfully immobilized on the surface of IDE along with mercaptohexanol. The electrochemical stability of the developed sensor surface is determined using open circuit potential measurements. The DNA probe immobilization protocol is validated using the changes configured on the surface of IDE by contact angle and ATR-FTIR analysis. The DNA target hybridization is detected using non-faradaic electrochemical impedance spectroscopy measurement with an ultra-low sample volume of 10 µL. The non-faradaic approach is verified by studying redox behavior using cyclic voltammetry. We investigate the hybridization of the surface-immobilized label-free probe with the complementary DNA targets obtained from infected eggplant saplings and cross-reactive studies with mismatched DNA strands. Our impedimetric sensor can detect target concentrations as low as 0.1 ng/µL. This standardization and detection of DNA hybridization serves as part I of the work and paves the way for further study in the detection of pathogenic field samples.

Electrocatalytic hydrogen evolution by a dinuclear copper complex and mechanistic elucidation through DFT studies.

A novel dinuclear copper complex, [CuII2(L1)2] (L1 = 2-{[2-(8-hydroxyquinolin-2-yl)-1H-benzimidazol-1-yl]methyl}quinolin-8-ol) was synthesised and characterised through various spectroscopic techniques. This dinuclear complex (as an electrocatalyst) was employed to examine the catalytic ability towards an electrochemical hydrogen evolution reaction (HER). Redox studies in 95/5 (v/v) DMF/H2O with the addition of 30-equivalent AcOH (acid source) led to higher catalytic activities for the HER. The evolved H2, as the resultant product, was detected and confirmed from gas chromatography to afford a faradaic efficiency of 93% at an applied potential of -1.9 V vs. SCE. Based upon measurements of open-circuit potential and electrocatalytic responses, the mechanistic route for the reduction process using [CuII2(L1)2] was elucidated. Density functional theory studies reveal that through a concerted proton-coupled electron transfer (PCET) path, the HER proceeded via the formation of a Cu-H bond with a low activation energy for the dehydrogenation reaction.

Recycled Aluminium Alloys and their Models: Role and Behaviour of Alloying Elements during Alkaline Etching

Alkaline etching is a common pretreatment for aluminum surfaces. Etching behavior was compared between an alloy based on post-consumer scrap (PCS) and several model alloys of rolled AA3005 and extruded AA6060 with systematically varied amounts of Mn, Cu and Ni. Analysis of concentrations of alloy elements in the etching solution by inductively coupled plasma mass spectrometry (ICP-MS) shows that significant fractions of the investigated elements Cu, Fe, Mg, Mn, Ni, and Zn dissolve. Surface analysis of samples in different stages of the etching process show (i) an increase in oxide layer thickness with etching time, (ii) an enrichment of important alloy elements and impurities (Cr, Cu, Fe, Mg, Mn, Si) near the metal/oxide interface, and (iii) the deposition of Mg, Fe, Si-containing aluminum hydroxide on the surface. A comparison with open circuit potential measurements and time-resolved electrochemical polarization resistance measurements enables a detailed analysis of the etching mechanism. The aluminum dissolution rate during etching is limited by the transport of species through the oxide precursor layer, thus is potential-independent. Differences in etching rates between different alloy classes, evidenced by mass loss measurements, are related to differences in the cathodic or anodic reaction mechanisms (hydrogen evolution or metal dissolution) during etching.

Application of ginger and grapefruit essential oil extracts on the corrosion inhibition of mild steel in dilute 0.5 M H2SO4 electrolyte

Admixture of ginger and grapefruit essential oils (GPP) were studied for their corrosion inhibition properties on mild steel (MS) in 0.5 M H2SO4 solution by potentiodynamic polarization, open circuit potential measurement, electrochemical impedance spectroscopy, weight loss analysis and ATF-FTIR spectroscopy. Results from potentiodynamic polarization shows GPP significantly reduced the corrosion of MS from 8.430 mm/y at 0% GPP concentration to values between 1.979 mm/y and 0.565 mm/y. The corresponding inhibition efficiency values ranged from 76.52% to 93.5% and corrosion current density from 1.88 × 10−4 A/cm2 to 5.36 × 10−5 A/cm2. GPP displayed mixed-type inhibition at all GPP concentrations studied. The OCP plot at 0% GPP initiated at -0.495V compared to -0.443V and -0.451V at 1% and 3.5% GPP. At 9000s, the corresponding OCP values are -0.442V, -0.410V and -0.424V due to electropositive plot shift and passivation of MS surface at 1% and 3.5% GPP, though significant potential transients were present on the OCP plot at 1% GPP. The electrochemical impedance results indicate that the corrosion resistance of MS increased from 4.402 Ω cm2 to 99.318 Ω cm2 upon the addition of 3.5% GPP resulting in inhibition efficiency of 96%. Data from weight loss analysis shows decrease in corrosion rate from 184.48 mm/y to values between 8.94 mm/y and 6.25 mm/y. The corresponding inhibition efficiency values varies from 95.16% at 1% GPP to 96.61% at 3.5% GPP concentration. The ATF-FTIR results confirm the adsorption of GPP molecules on the surface of the carbon steel electrode.

Corrosion mechanism of Ti-6Al-4V morse taper dental implants connected to 316 L stainless steel prosthetic abutment

The aim of this work was to investigate the effect of galvanic coupling between stainless steel AISI 316 L abutment type Morse taper and implant made of ASTM F1108–14 Ti-6Al-4V alloy. The assembly of the two alloys was carried out using mechanical imbrication by means of successive strikes at 0.05 J force onto the abutment inserted in the implant along the centerline. Corrosion attack at the interface of the alloys was evaluated according to the number of strikes used for joining the parts. Corrosion resistance was evaluated for the samples by open circuit potential measurements as function of time and scanning vibrating electrode technique (SVET) and scanning ion selective electrode technique (SIET) in phosphate buffer solution with pH adjusted to 3.0, and into which hydrogen peroxide was added to simulate tissue inflammatory conditions. Samples were evaluated at the cross and longitudinal sections. Results indicated that the number of strikes used in assembling affected corrosion susceptibility. The lowest amount of corrosion products was associated to the highest number of strikes used. The corrosion resistance was related to the characteristics of the crevice between the implant and the abutment. • Galvanic corrosion between Ti grade V dental implants and AISI 316 L prosthetic abutment was investigated. • Localized attack susceptibility increased with the number of strikes to connect the Ti grade V dental implant and the AISI 316 L abutment. • Local electrochemical techniques were very useful in evaluating the corrosion of the coupled dental implant and prosthetic abutment.

Formation of protective surface films on carbon steel in mildly alkaline aqueous alkanolamine CO2 solutions

Electrochemical impedance spectroscopy (EIS) and open circuit potential (OCP) measurements, complemented by solution speciation predictions and ex situ surface analyses, were used to investigate film formation on carbon steel in CO2 saturated methyldiethanolamine(aq) solutions at 80 °C, pH 7.9–8.6. Pure FeCO3 films, evidenced by OCPs of ca. −0.5 to −0.4 V (SHE), were formed under anoxic conditions and provided corrosion protection to the underlying substrate, increasing charge transfer resistances tenfold. O2 ingress caused a positive OCP shift to ca. > +0.35 V (SHE), resulting in formation of traces of iron oxide at the interface, which was less protective.

Corrosion protection of stainless steel by a new and low‐cost organic coating obtained from cashew nutshell liquid

AbstractIn this work, the corrosion protection of 316L steel was promoted by an electro‐synthesized polymer obtained from the technical cashew nutshell liquid (t‐CNSL). Spectroscopic techniques confirmed the polymer formation. The polymer was dispersed in the ethyl acetate solvent and used to form coatings on 316L steel substrates. The coated samples were subjected to electrochemical tests in a saline environment. The coated electrode with poly(t‐CNSL) polymer was exposed to the corrosive medium for 24 days, and superior corrosion protection was observed compared with the uncoated sample. The open circuit potential measurements showed that the coated sample possessed a more positive corrosion potential when compared with the uncoated substrate. The electrochemical impedance spectroscopy results indicated that the coated electrode's polarization resistance (Rp) recorded ~1.0 MΩ cm2 after 24 days of exposure. A decrease in polarization resistance was observed with the exposure time due to the presence of micropores in the t‐CNSL coating. The polarization curves exhibited that the coated electrode with poly(t‐CNSL) has lower corrosion current density and less negative corrosion potential than the uncoated steel electrode. Therefore, t‐CNSL favors the manufacture of thin poly(t‐CNSL) coatings for corrosion protection purposes besides being a low‐cost material.

Boron-Doped Diamond as a Quasi-Reference Electrode.

As a working electrode, boron-doped diamond (BDD) has been studied in detail in electrochemical processes because of its superior electrochemical properties. However, these characteristics have rarely been mentioned when BDD is used as a quasi-reference electrode (QRE). Herein, we conducted a systematic investigation on BDD electrodes, with different boron-doping levels (1 and 0.1%) and different surface terminations (hydrogen and oxygen) for their application as a QRE. A BDD electrode with 1% boron and a hydrogen-terminated surface achieved the best stability. Its open-circuit potential (OCP) exhibited less than 100 mV of potential drift over 6000 s and showed a minuscule half-wave potential difference (E1/2) of 0.0037 V in 0.1 mM K3[Fe(CN)6]/1 M KCl solution before and after the OCP measurement. Based on these observations, anions are found to contribute to the potential, which we preliminarily speculate as related to the capacitance caused by electrostatic adsorption on the positively charged hydrogen-terminated surface. The repeatability of measurement was verified through continuous cyclic voltammetry tests in 0.1 mM K3[Fe(CN)6]/1 M KCl, showing a maximum E1/2 difference of 0.042 V. The contribution of the redox couples was excluded, and the repeatability was considered to originate from its surface stability. Finally, a linear response of the optimized BDD as a QRE was validated (R2 > 0.99) by determination of free chlorine and dopamine concentrations, respectively. These results consolidate the existing fundamental research on BDD electrodes and promote the possibility of its application as a QRE in harsh environments or in vivo biological monitoring.

Pitting corrosion resistance of additive manufactured alloy 718 in alkaline brines at elevated temperatures

AbstractThe feasibility of additive manufacturing (AM) to produce industrial components, also for the oil and gas industry, has been demonstrated in the past. Therefore, current research efforts focus on demonstrating the reliability of AM materials subjected to demanding service conditions. In this regard, special attention has been paid to its corrosion resistance in harsh environments as one of the most critical properties in these applications. The beneficial combination of high strength, excellent thermal stability, and outstanding corrosion resistance makes alloy 718 (UNS N07718) the most used wrought and AM nickel alloy in the oil and gas industry. Wrought 718 has an extensive record of field performance in demanding oil and gas applications including directional drilling tools that undergo extreme mechanical loads in corrosive drilling fluids. On the other hand, limited data regarding the corrosion behavior of AM718 in typical drilling environments has been collected so far. In this research work, the pitting susceptibility of selective laser melted alloy 718 in simulated drilling environments has been studied. Open circuit potential measurements as well as cyclic potentiodynamic and potentiostatic polarization tests were used to characterize the pitting corrosion resistance of AM718 in alkaline brines at elevated temperatures. In addition, microstructural particularities in alloy 718 were investigated to explain the observed differences in the electrochemical behaviors.

Influence of natural seawater variables on the corrosion behaviour of aluminium-magnesium alloy

Corrosion is an important issue for alloys in natural seawater, where microorganisms can accelerate or mitigate corrosion. Al-Mg alloys are used for marine activities and various associated technologies. Here, the behaviour of AA5083 alloy was investigated in natural seawater with marine exposure lasting up to 50 days and detailing the first 8 days in two experimental series.Experimental work was carried out, including semi-field tests in natural seawater (biotic conditions) compared with abiotic conditions. The open circuit potential (OCP) measurements, during the immersion time, exhibited significantly different behaviours: an OCP downward displacement occurred under abiotic conditions, while, in biotic conditions OCP remained generally stable since the beginning of the immersion, revealing an inhibiting effect of the biological activity on the Al-Mg corrosion. This was accompanied by different surface modifications under biotic conditions: surface and cross-section characterization, performed by scanning electron microscopy with energy dispersive X-ray spectroscopy, showed less corrosion developed on the surface after 8-day immersion and formation of a protective layer during 50-day immersion.The present study shows that marine biological activity positively influences the Al alloy corrosion process, with surface modifications resulting in a protective effect counteracting the aggressiveness of chloride ions.

Electrochemical detection and evaluation of the anomalous chloride extraction from water to 1,2-dichloroethane under the non-equilibrium conditions

Anomalous chloride extraction from water to 1,2-dichloroethane is detected by cyclic voltammetry and evaluated by the potential step amperometry of the background electrolyte combined with the open circuit potential measurements. The extraction process is affected by the composition of the organic phase. In the present study, the latter effect is elucidated and the mechanism of the solvent extraction of chloride is proposed. The mechanism couples the energetically unfavourable extraction of a hydrophobic salt (e.g., tetrapentylammonium tetraphenylborate, bis(triphenylphosphoranylidene) ammonium tetraphenylborate) from the organic to the aqueous phase with the favourable extraction of the chloride salt of the present hydrophobic cation in the opposite direction resulting in the chloride accumulation in the organic solvent phase. An evaluation and analysis of the ion flux suggests that the chloride anions are extracted to the organic phase in the form of the free anions and the anions bound to the ion-pairs, and for the most part as the hydrated salt clusters, the formation of which is likely to be the driving force of the extraction process. The transfer of the accumulated chloride anion back to the aqueous phase is responsible for the positive current shift of the cyclic voltammogram and the steady-state positive current recorded in the potential step amperometric measurements. First application of the novel potentiostatic assembly introducing the polarizable reference electrode for the organic solvent phase is demonstrated.

Analysis of the protection performance of admixed citronella and myrrh essential oil extracts on high carbon steel corrosion in CH3COOH and C6H8O7 solution

Protection performance of admixed citronella and myrrh essential oil extract (CNM) on the corrosion resistance of high carbon steel (HCS) in 3 M of CH3COOH and C6H8O7 solution was evaluated by potentiodynamic polarization, open circuit potential measurement, weight loss measurement, x-ray diffractometry and ATF-FTIR spectroscopy. Results showed CNM performed effectively in CH3COOH with optimal inhibition of 87.47% and 80.12% at 1.67% concentration from potentiodynamic polarization and weight loss. CNM performed poorly in C6H8O7 solution with highest value of 41.29% and 43.81% at 1.67% CNM concentration from both tests. In both acids inhibition efficiency increased with increase in CNM concentration coupled with the exhibition of mixed-type inhibition effect. Open circuit potential plots show CNM significantly reduces the activation barrier for HCS to corrode wherewith the plots in the presence of CNM extract where significantly electropositive compared to the plot from C6H8O7 solution without CNM. In CH3COOH, the action of protonated CNM molecules and CH3CO2− anions results in the formation of complexes that increases the reactivity of HCS surface and its thermodynamic tendency to corrode despite effective inhibition performance. X-ray diffractometry shows admixed extract caused significant decrease in intensity/counts for diffraction peaks of Fe2O3 and Fe3O4 compounds on the spectrum plots compared to the plots without the extracts. ATF-FTIR spectroscopy shows significant reduction in transmittance at specific range of wavenumbers occurred within CNM/CH3COOH solution after corrosion, and on HCS surface after corrosion in the presence of the extracts compared to CNM/CH3COOH before corrosion. This contrast the results obtained from CNM/C6H8O7 solution.

Corrosion behaviour of maize husk reinforced aluminium (1070) metal matrix composites in chloride-sulphate solution

The effect of maize husk (MH) particulates on the corrosion resistance of 1070 aluminium alloy (AA70) matrix at 5% and 15% wt. content, and 150 μm and 300 μm particle size (AA70/MH composites) was studied in 3.5% NaCl, 0.0125 M H2SO4 and 3.5% NaCl/0.0125 M H2SO4 solutions. Potentiodynamic polarization technique, open circuit potential measurement, weight loss analysis, optical microscopy characterization, x-ray fluorescence and x-ray diffractometry were used for the investigation. Results show increase in MH %wt. content and particle size decreases the corrosion rate of AA70/MH composite. Data from potentiodynamic polarization and weight loss analysis shows AA70/MH composite at 15% wt. content and 300 μm particle size exhibited the lowest corrosion values of 0.135 mm y−1, 0.156 mm y−1 and 1.445 mm y−1, and −0.00043 mm y−1, 0.001 04 mm y−1 and 0.00218 mm y−1 in 3.5% NaCl, 0.0125 M H2SO4 and 3.5% NaCl/0.0125 M H2SO4 solutions. Optical representative images of the composites showed the presence of micro-pits on samples from NaCl solution, macro-pits and extensive surface deterioration from H2SO4 solution, and combined localized and total surface deterioration from NaCl-H2SO4 solution. Weight loss plots showed oxide formation significantly influenced the corrosion behavior of the alloys with respect to time. Open circuit potential plots showed AA70/MH composite at 5% wt. content and 150 um particle size was the most electronegative with the highest thermodynamic tendency to corrosion. Significant X-ray diffraction peaks from AA70/MH composite at 15% wt. content and 300 μm particle size showed the presence of corrosion resistant phase compounds of Al2O3 and Al(ZnS2) before and after corrosion.

Effect of Precursors on the Electrochemical Properties of Mixed RuOx/MnOx Electrodes Prepared by Thermal Decomposition.

Growing thin layers of mixed-metal oxides on titanium supports allows for the preparation of versatile electrodes that can be used in many applications. In this work, electrodes coated with thin films of ruthenium (RuOx) and manganese oxide (MnOx) were fabricated via thermal decomposition of a precursor solution deposited on a titanium substrate by spin coating. In particular, we combined different Ru and Mn precursors, either organic or inorganic, and investigated their influence on the morphology and electrochemical properties of the materials. The tested salts were: Ruthenium(III) acetylacetonate (Ru(acac)3), Ruthenium(III) chloride (RuCl3·xH2O), Manganese(II) nitrate (Mn(NO3)2·4H2O), and Manganese(III) acetylacetonate (Mn(acac)3). After fabrication, the films were subjected to different characterization techniques, including scanning electron microscopy (SEM), polarization analysis, open-circuit potential (OCP) measurements, electrochemical impedance spectroscopy (EIS), linear sweep voltammetry (LSV), cyclic voltammetry (CV), and galvanostatic charge-discharge (GCD) experiments. The results indicate that compared to the others, the combination of RuCl3 and Mn(acac) produces fewer compact films, which are more susceptible to corrosion, but have outstanding capacitive properties. In particular, this sample exhibits a capacitance of 8.3 mF cm-2 and a coulombic efficiency of higher than 90% in the entire range of investigated current densities.

Determination of Individual Gibbs Energies of Ion and Electron Transfer in Electrochemical Insertion Processes

Based on three-phase electrode models, we study to access the Gibbs energy contributions for the transfer of ions and electrons in Prussian blue analogs since they have long life cycles and high energy efficiency. Ni[Fe(CN)6] (HCFNi) and Cu[Fe(CN)6] (HCFCu) were preliminarily synthesized by a hydrothermal process. The obtained HCFNi powders were supported on a paraffin-impregnated graphite electrode in contact with an organic electrolyte, producing solid-state oxidation-reduction electrochemical reactions, which have been monitored by cyclic voltammetry and open circuit potential measurements in the presence of potassium as intercalating ion. The results show a behavior according to the Nernst equation as the potassium ion concentration varies, with a slope of 61.2 mV/dec. These experiments make it possible to access Gibbs free energy values for both transfers separately and replicate them for different insertion ions, such as Na+ and Li+.Figure: (Left) Open circuit potential measurements; (center) mid-peak potential measurements; and (right) cyclic voltammetry for Ni[Fe(CN)6] in potassium media. Figure 1

(Digital Presentation) Surface Photovoltage Provides Quasi Fermi Level Splitting and Minority Carrier Electrochemical Potential of BiVO4 /Liquid Junctions Under Illumination

The solar energy conversion efficiency of semiconductor-liquid junctions is determined by their photovoltage and by their photocurrent under illumination. Photoelectrochemistry (PEC) gives information on the current, but not on the photovoltage or the quasi Fermi level splitting (qFLS), which for slow redox couples is obscured by kinetic overpotentials and surface states. Here we show that surface photovoltage spectroscopy (SPS) provides direct measurement of the qFLS potential in BiVO4-electrolyte contacts. Measurements were done with a vibrating Kelvin probe on FTO deposited BiVO4 films in contact with aqueous electrolytes containing triiodide/iodide, oxygen/ hydrogen peroxide, or sulfate/sulfite redox couples and for iron-oxyhydroxide modified BiVO4 films. The triiodide/iodide couple, for example, yields qFLS=0.78 V under 49 mW/cm-2 (400 nm LED) illumination, comparable to the photovoltage from PEC (0.79 V). Furthermore, the reversibility of the redox reactions determines the reversibility of the SPS transients. For example, the triiodide/iodide couple gives nearly complete SPS reversibility on the 20 sec timescale, while the sulfate/sulfite couple gives an irreversible photovoltage signal. Lastly, by combining the SPS data with the majority carrier potential from open circuit potential measurements, the minority carrier electrochemical potentials, Efp can be obtained for all systems. For instance, Efp = 1.0 V vs RHE for the BiVO4 - triiodide/iodide junction and Efp = 0.26 V vs RHE for the sulfate/sulfite junction. These shows that BiVO4 can photoelectrochemically oxidize both redox couples, without applied bias. These results shed new light on the photoelectrochemistry of BiVO4, an important photoanode material for solar hydrogen production from water. Figure 1

(Digital Presentation) Spark Plasma Sintering Fabrication of α/β Interface in Mg Alloys and Analysis of Corrosion Behavior

In Mg alloys, corrosion behavior is known to be related to the microstructure. For example, AZ91D alloy contains an α matrix phase (Mg solid solution), β phases (Mg17Al12) and lamellar α+β microstructures. During the real-time in situ observation of the corrosion process under galvanostatic polarization, filiform corrosion proceeded along the outside of the β-phase (in lamellar α + β microstructure and along the α-mother phase[1]. However, the detailed mechanism of the initiation and growth of filiform corrosion is still unknown. An electrode area contains simplified α + β structure is needed to clarify the corrosion mechanism of Mg alloys. The fabrication of such specimen could be actualized by Spark Plasma Sintering (SPS).The advantage of SPS is that it can produce specimens with high efficiency and few pores. The energy from the pulsed current, self-heating of the workpiece, and particle-to-particle discharge are the combined driving force for sintering. In recent years, many experiments have been reported on the fabrication and strength evaluation of pure Mg and Mg alloys. However, only a few studies have been conducted on the fabrication and corrosion resistance of different phases.In this study, we attempted to fabricate the interface of β and α phases by SPS using pure Al powder and pure Mg powder and other materials. The characterization of different phases was carried out by XRD, EPMA and TEM. The corrosion behavior of the sintered specimens was then observed using an in-situ observation system during open circuit potential measurements. After measurements, the specimen surface was assessed using OM, AES, and FE-SEM.When a 0.25 mm thick Mg sheet was surrounded by pure Al powder, the temperature was set at 420 °C and kept for 30 minutes, a uniform white microstructure was found to form around the Mg sheet. The thickness is about 50 µm. EDS maps and point analysis show that this phase consists a β-phase (Mg17Al12) on the Mg sheet side and Mg23Al30 on the Al powder side. The thickness of the β-phase did not change obviously when the sintering time was extended to 1 hour. Finally, a β phase with a thickness of about 100 μm could be fabricated by using a specimen assembly method of outer Al powder, intermediate layer Mg powder. Analysis of corrosion behavior was done with this specimen. Z. Shao, M. Nishimoto, I. Muto, and Y. Sugawara, Corrosion Science, 192, 109834 (2021).

In Situ Visualization of the Hydrogen Distribution in an Fe Sheet Under Corrosion Conditions Using Polyaniline

High-strength steels are known to be susceptible to hydrogen embrittlement. Even small amounts of hydrogen which enter the high-strength steels under corrosion conditions could cause the hydrogen embrittlement. In order to elucidate the mechanism of hydrogen entry in corrosive environments, and to prevent the corrosion-induced hydrogen embrittlement, the simultaneous analysis of the corrosion behavior and the hydrogen entry is required. Some techniques, such as scanning Kelvin probe force microscope, have been reported for visualizing the hydrogen distribution in metals with a high spatial resolution. However, it is still challenging to visualize the hydrogen distribution of an observation area of several tens of millimeters with high spatial and temporal resolutions. In this study, we succeeded the visualization of the distribution of hydrogen entering a pure Fe sheet immersed in a NaCl aqueous solution using a conductive polymer.A pure Fe sheet (99.5 %) was used as a specimen. The Fe sheet was electrically polished in a mixed solution of perchloric acid and acetic acid. The thickness of the Fe sheet was 0.4 mm after the polishing. In order to visualize the hydrogen distribution in the Fe sheet, a polyaniline (PANI) layer was formed on one side of the Fe sheet. It was reported that the PANI layer changes its color owing to the reaction with atomic state hydrogen in Fe sheets.1 To enhance the sensitivity of the PANI layer to hydrogen, a Ni interfacial layer was formed between the PANI layer and the Fe sheet. The PANI layer was formed on the Ni interfacial layer through electrolytic polymerization at a constant voltage of 1 V in a 0.5 M H2SO4-0.5 M aniline aqueous solution. On the other side (bare Fe side) of the Fe sheet, an electrode area of 1 cm × 1 cm was prepared using a resin. Only the bare Fe side was immersed in a 0.1 M NaCl aqueous solution. In addition to the open-circuit potential measurements, the corrosion behavior was observed in situ using a digital camera during the corrosion test. The PANI layer was exposed to air without contacting the NaCl solution. During the corrosion test, the color of the PANI layer was observed in situ using another digital camera. It was confirmed that the small amount of hydrogen entering the Fe sheet due to corrosion can be visualized using the PANI layer. The distribution of hydrogen that entered the Fe sheet was analyzed based on the color distribution of the PANI layer. The in situ simultaneous observation of the corrosion behavior and the hydrogen entry revealed that the hydrogen entry was promoted on the dissolved area of the Fe sheet in the NaCl solution. Reference H. Kakinuma, S. Ajito, T. Hojo, M. Koyama, E. Akiyama, Adv. Mater. Interfaces, 2101984 (2022).

Non-Faradaic Electrochemical Energy Transduction Using Catalytic Motors

Mechanical energy generated by self-powered catalytic motors encourages researchers to explore whether their dynamics can be harnessed in developing inexpensive and efficient energy transduction and storage platforms. Herein, we present a non-Faradaic electrochemical energy transduction strategy using buoyancy-driven self-propelled catalytic motors within an electrochemical setup containing a fluorinated tin oxide working electrode and a sustained salt gradient. During propulsion, the motors facilitated advective transfer of ions from the bottom of the fuel solution to the electrode and subsequent formation of an electric double layer capacitor (EDLC) over it. The magnitude of EDLC charging was estimated using open circuit potential (OCP) measurements, which was found to increase with the number of motors in solution. We also observed instantaneous potential spikes over the OCP signal profile, when a motor struck the electrode surface, the frequency of which gets enhanced with the increase in motor speed through the solution. We quantify the OCP generated as a function of number of motors and composition of the fuel solution and also offer an explanation of the energy transduction mechanism in the system. It is expected that catalytic motor-assisted non-Faradaic energy generation will establish itself as an important energy harvesting pathway and when miniaturized, will open up avenues for fabricating autonomous power sources for smart sensors and other devices.

Mechanistic insight into photochemical and photoelectrochemical degradation of organic pollutants with the use of BiVO4 and BiVO4/Co-Pi

In this work we clarify the role of hydroxyl radicals (•OH), superoxide anion radicals (O2•−) and the holes in photocatalytic and photoelectrocatalytic degradation of organic pollutants on BiVO4, and critically discuss different mechanisms of the process reported in the literature. The generation of O2•−anion radicals was monitored by the reaction with Nitro Blue Tetrazolium chloride (NBT), while the formation of •OH was controlled by transformation of terephthalic acid into fluorescent 2-hydroxyterephtalic acid. The band diagram of BiVO4 was constructed on the base of the Efb determined from the measurements of open circuit potential (OCP) and photocurrent onset potential, and the mechanism of photodegradation of caffeine (CAF) on BiVO4 was proposed. It was shown that the photodegradation rate constant of CAF may be increased from 2.1·10−3 to 4.6 10−3 min−1 by modification of BiVO4 surface with cobalt phosphate (Co-Pi) co-catalyst. The presence of Co-Pi resulted in the increase of the electron life-time and suppression of the electron-hole recombination in BiVO4. The 26-fold increase of the degradation rate constant, to the value 5.5·10−2 min−1, was achieved by application of an external potential of 0.6 V vs Ag/AgCl to the BiVO4 electrode and the mechanism of photoelectrocatalytic process was proposed.