Publications by authors named "Bruno G Pollet"

31 Publications

Ultrasonically Surface-Activated Nickel Foam as a Highly Efficient Monolith Electrode for the Catalytic Oxidation of Methanol to Formate.

ACS Appl Mater Interfaces 2021 Jul 25;13(26):30603-30613. Epub 2021 Jun 25.

Hydrogen Energy and Sonochemistry Research group, Department of Energy and Process Engineering, Norwegian University of Science and Technology (NTNU), NO-7491 Trondheim, Norway.

Most of the current electrocatalysts for the methanol oxidation reaction are precious group metals such as Pt, Pd, and Ru. However, their use is limited due to their high cost, scarcity, and issues with carbon monoxide poisoning. We developed a simple method to prepare a nickel foam (NF)-based monolith electrode with a NiO nanosheet array structure as an efficient electrocatalyst toward the oxidation of methanol to produce formate. By a simple ultrasonic acid treatment and air oxidation at room temperature, an inert NF was converted to NiO/NF as a catalytically active electrode due to the uniform NiO nanosheet array that was rapidly formed on the surface of NiO/NF. In alkaline electrolytes containing methanol, the as-prepared NiO/NF catalysts exhibited a lower methanol oxidation reaction (MOR) potential of +1.53 V RHE at 100 mA cm compared to that of inert NF samples. The difference in potentials between the and the at that current density was found to be 280 mV, indicating that methanol oxidation occurred at lower potentials as compared to the oxygen evolution reaction (OER). We also observed that the NiO/NF could also efficiently catalyze the oxidation of CO without being poisoned by it. NiO/NF retained close to 100% of its initial activity after 20,000 s of methanol oxidation tests at high current densities above 200 mA cm. Because of the simple synthesis method and the enhanced catalytic performance and stability of NiO/NF, this allows methanol to be used as an OER masking agent for the energy-efficient generation of value-added products such as formic acid and hydrogen.
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http://dx.doi.org/10.1021/acsami.1c06258DOI Listing
July 2021

Does power ultrasound affect hydrocarbon Ionomers?

Ultrason Sonochem 2021 Jul 7;75:105588. Epub 2021 May 7.

Holdcroft Research Group, Department of Chemistry, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada. Electronic address:

The effect of low-frequency high-power ultrasound on hydrocarbon-based ionomers, cation exchange sulfonated phenylated polyphenylene (sPPB-H) and anion exchange hexamethyl-p-terphenyl poly(benzimidazolium) (HMT-PMBI), was studied. Ionomer solutions were subjected to ultrasonication at fixed ultrasonic frequencies (f = 26 and 42 kHz) and acoustic power (P = 2.1 - 10.6 W) in a laboratory-grade ultrasonication bath, and a probe ultrasonicator; both commonly employed in catalyst ink preparation in research laboratory scale. Power ultrasound reduced the polymer solution viscosity of both hydrocarbon-based ionomers. The molecular weight of sPPB-H decreased with irradiation time. Changes in viscosity and molecular weight were exacerbated when ultrasonicated in an ice bath; but reduced when the solutions contained carbon black, as typically used in Pt/C-based catalyst inks. Spectroscopic analyses revealed no measurable changes in polymer structure upon ultrasonication, except for very high doses, where evidence for free-radical induced degradation was observed. Ionomers subjected to ultrasound were used to prepare catalyst layers and membrane electrode assemblies (MEA)s. Despite the changes in the ionomer described above, no significant differences in electrochemical performance were found between MEAs prepared with ionomers pre-subjected to ultrasound and those that were not, suggesting that fuel cell performance is tolerant to ionomers subjected to ultrasound.
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http://dx.doi.org/10.1016/j.ultsonch.2021.105588DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8141775PMC
July 2021

Sonochemical conversion of CO into hydrocarbons: The Sabatier reaction at ambient conditions.

Ultrason Sonochem 2021 May 2;73:105474. Epub 2021 Feb 2.

Hydrogen Energy and Sonochemistry Research Group, Department of Energy and Process Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, Norway.

In this study, we investigated an alternative method for the chemical CO reduction reaction in which power ultrasound (488 kHz ultrasonic plate transducer) was applied to CO-saturated (up to 3%) pure water, NaCl and synthetic seawater solutions. Under ultrasonic conditions, the converted CO products were found to be mainly CH, CH and CH including large amount of CO which was subsequently converted into CH. We have found that introducing molecular H plays a crucial role in the CO conversion process and that increasing hydrogen concentration increased the yields of hydrocarbons. However, it was observed that at higher hydrogen concentrations, the overall conversion decreased since hydrogen, a diatomic gas, is known to decrease cavitational activity in liquids. It was also found that 1.0 M NaCl solutions saturated with 2% CO + 98% H led to maximum hydrocarbon yields (close to 5%) and increasing the salt concentrations further decreased the yield of hydrocarbons due to the combined physical and chemical effects of ultrasound. It was shown that CO present in a synthetic industrial flue gas (86.74% N, 13% CO, 0.2% O and 600 ppm of CO) could be converted into hydrocarbons through this method by diluting the flue gas with hydrogen. Moreover, it was observed that in addition to pure water, synthetic seawater can also be used as an ultrasonicating media for the sonochemical process where the presence of NaCl improves the yields of hydrocarbons by ca. 40%. We have also shown that by using low frequency high-power ultrasound in the absence of catalysts, it is possible to carry out the conversion process at ambient conditions i.e., at room temperature and pressure. We are postulating that each cavitation bubble formed during ultrasonication act as a "micro-reactor" where the so-called Sabatier reaction -CO+4H→UltrasonicationCH+2HO - takes place upon collapse of the bubble. We are naming this novel approach as the "Islam-Pollet-Hihn process".
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http://dx.doi.org/10.1016/j.ultsonch.2021.105474DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7875828PMC
May 2021

How do dissolved gases affect the sonochemical process of hydrogen production? An overview of thermodynamic and mechanistic effects - On the "hot spot theory".

Ultrason Sonochem 2021 Apr 24;72:105422. Epub 2020 Dec 24.

Hydrogen Energy and Sonochemistry Research Group, Department of Energy and Process Engineering, Faculty of Engineering, Norwegian University of Science and Technology (NTNU), NO-7491 Trondheim, Norway.

Although most of researchers agree on the elementary reactions behind the sonolytic formation of molecular hydrogen (H) from water, namely the radical attack of HO and HO and the free radicals recombination, several recent papers ignore the intervention of the dissolved gas molecules in the kinetic pathways of free radicals, and hence may wrongly assess the effect of dissolved gases on the sonochemical production of hydrogen. One may fairly ask to which extent is it acceptable to ignore the role of the dissolved gas and its eventual decomposition inside the acoustic cavitation bubble? The present opinion paper discusses numerically the ways in which the nature of dissolved gas, i.e., N, O, Ar and air, may influence the kinetics of sonochemical hydrogen formation. The model evaluates the extent of direct physical effects, i.e., dynamics of bubble oscillation and collapse events if any, against indirect chemical effects, i.e., the chemical reactions of free radicals formation and consequently hydrogen emergence, it demonstrates the improvement in the sonochemical hydrogen production under argon and sheds light on several misinterpretations reported in earlier works, due to wrong assumptions mainly related to initial conditions. The paper also highlights the role of dissolved gases in the nature of created cavitation and hence the eventual bubble population phenomena that may prevent the achievement of the sonochemical activity. This is particularly demonstrated experimentally using a 20 kHz Sinaptec transducer and a Photron SA 5 high speed camera, in the case of CO-saturated water where degassing bubbles are formed instead of transient cavitation.
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http://dx.doi.org/10.1016/j.ultsonch.2020.105422DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7803813PMC
April 2021

The effects of power ultrasound (24 kHz) on the electrochemical reduction of CO on polycrystalline copper electrodes.

Ultrason Sonochem 2021 Apr 3;72:105401. Epub 2020 Dec 3.

Hydrogen Energy and Sonochemistry Research Group, Department of Energy and Process Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, Norway.

The electrochemical CO reduction reaction (CO2RR) on polycrystalline copper (Cu) electrode was performed in a CO-saturated 0.10 M NaCO aqueous solution at 278 K in the absence and presence of low-frequency high-power ultrasound (f = 24 kHz, P ~ 1.23 kW/dm) in a specially and well-characterized sonoelectrochemical reactor. It was found that in the presence of ultrasound, the cathodic current (I) for CO reduction increased significantly when compared to that in the absence of ultrasound (silent conditions). It was observed that ultrasound increased the faradaic efficiency of carbon monoxide (CO), methane (CH) and ethylene (CH) formation and decreased the faradaic efficiency of molecular hydrogen (H). Under ultrasonication, a ca. 40% increase in faradaic efficiency was obtained for methane formation through the CO2RR. In addition, and interestingly, water-soluble CO reduction products such as formic acid and ethanol were found under ultrasonic conditions whereas under silent conditions, these expected electrochemical CO2RR products were absent. It was also found that power ultrasound increases the formation of smaller hydrocarbons through the CO2RR and may initiate new chemical reaction pathways through the sonolytic di-hydrogen splitting yielding other products, and simultaneously reducing the overall molecular hydrogen gas formation.
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http://dx.doi.org/10.1016/j.ultsonch.2020.105401DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7803681PMC
April 2021

Sonochemical dosimetry: A comparative study of Weissler, Fricke and terephthalic acid methods.

Ultrason Sonochem 2021 Apr 6;72:105413. Epub 2020 Dec 6.

School of Chemistry, University of Melbourne, VIC 3010, Australia. Electronic address:

Acoustic cavitation and sonochemical reactions play a significant role in various applications of ultrasound. A number of dosimetry methods are in practice to quantify the amount of radicals generated by acoustic cavitation. In this study, hydroxyl radical (OH) yields measured by Weissler, Fricke and terephthalic acid dosimetry methods have been compared to evaluate the validities of these methods using a 490 kHz high frequency sonochemical reactor. The OH yields obtained after 5 min sonication at 490 kHz from Weissler and Fricke dosimetries were 200 µM and 289 µM, respectively. Whereas, the OH yield was found to be very low (8 µM) when terephthalic acid dosimetry was used under similar experimental conditions. While the results agree with those reported by Iida et al. (Microchem. J., 80 (2005) 159), further mechanistic details and interfering reactions have been discussed in this study. For example, the amount of OH determined by the Weissler and Fricke methods may have some uncertainty due to the formation of HO in the presence of oxygen. In order to account for the major discrepancy observed with the terephthalic acid dosimetry method, high performance liquid chromatography (HPLC) analysis was performed, where two additional products other than 2-hydroxy terephthalic acid were observed. Electrospray ionization mass spectrometry (ESI-MS) analysis showed the formation of 2,5-dihydroxyterephthalic acid as one of the by-products along with other unidentified by-products. Despite the formation of additional products consuming OH, the reason for a very low OH yield obtained by this dosimetry could not be justified, questioning the applicability of this method, which has been used to quantify OH yields generated not only by acoustic cavitation, but also by other processes such as γ-radiolysis. The authors are hoping that this Opinion Paper may initiate further discussion among researchers working in sonochemistry area that could help resolve the uncertainties around using these dosimetry methods.
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http://dx.doi.org/10.1016/j.ultsonch.2020.105413DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7803795PMC
April 2021

Self-standing heterostructured NiC -NiFe-NC/biochar as a highly efficient cathode for lithium-oxygen batteries.

Beilstein J Nanotechnol 2020 2;11:1809-1821. Epub 2020 Dec 2.

Low Carbon Energy Institute, China University of Mining and Technology, Xuzhou, Jiangsu 221008, China.

Lithium-oxygen batteries have attracted research attention due to their low cost and high theoretical capacity. Developing inexpensive and highly efficient cathode materials without using noble metal-based catalysts is highly desirable for practical applications in lithium-oxygen batteries. Herein, a heterostructure of NiFe and NiC inside of N-doped carbon (NiC -NiFe-NC) derived from bimetallic Prussian blue supported on biochar was developed as a novel self-standing cathode for lithium-oxygen batteries. The specific discharge capacity of the best sample was 27.14 mAh·cm at a stable discharge voltage of 2.75 V. The hybridization between the d-orbital of Ni and s and p-orbitals of carbon in NiC , formed at 900 °C, enhanced the electrocatalytic performance due to the synergistic effect between these components. The structure of NiC -NiFe-NC efficiently improved the electron and ion transfer between the cathode and the electrolyte during the electrochemical processes, resulting in superior electrocatalytic properties in lithium-oxygen batteries. This study indicates that nickel carbide supported on N-doped carbon is a promising cathode material for lithium-oxygen batteries.
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http://dx.doi.org/10.3762/bjnano.11.163DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7722627PMC
December 2020

Fractal-Like Flow-Fields with Minimum Entropy Production for Polymer Electrolyte Membrane Fuel Cells.

Entropy (Basel) 2020 Feb 4;22(2). Epub 2020 Feb 4.

Department of Energy and Process Engineering, Norwegian University of Science and Technology, 7491 Trondheim, Norway.

The fractal-type flow-fields for fuel cell (FC) applications are promising, due to their ability to deliver uniformly, with a Peclet number Pe~1, the reactant gases to the catalytic layer. We review fractal designs that have been developed and studied in experimental prototypes and with CFD computations on 1D and 3D flow models for planar, circular, cylindrical and conical FCs. It is shown, that the FC efficiency could be increased by design optimization of the fractal system. The total entropy production (TEP) due to viscous flow was the objective function, and a constant total volume (TV) of the channels was used as constraint in the design optimization. Analytical solutions were used for the TEP, for rectangular channels and a simplified 1D circular tube. Case studies were done varying the equivalent hydraulic diameter (D), cross-sectional area (D) and hydraulic resistance (D). The analytical expressions allowed us to obtain exact solutions to the optimization problem (TEP→min, TV=const). It was shown that the optimal design corresponds to a non-uniform width and length scaling of consecutive channels that classifies the flow field as a quasi-fractal. The depths of the channels were set equal for manufacturing reasons. Recursive formulae for optimal non-uniform width scaling were obtained for 1D circular D -, D -, and D -based tubes (Cases 1-3). Appropriate scaling of the fractal system providing uniform entropy production along all the channels have also been computed for D -, D -, and D -based 1D models (Cases 4-6). As a reference case, Murray's law was used for circular (Case 7) and rectangular (Case 8) channels. It was shown, that Dh-based models always resulted in smaller cross-sectional areas and, thus, overestimated the hydraulic resistance and TEP. The D -based models gave smaller resistances compared to the original rectangular channels and, therefore, underestimated the TEP. The D -based models fitted best to the 3D CFD data. All optimal geometries exhibited larger TEP, but smaller TV than those from Murray's scaling (reference Cases 7,8). Higher TV with Murray's scaling leads to lower contact area between the flow-field plate with other FC layers and, therefore, to larger electric resistivity or ohmic losses. We conclude that the most appropriate design can be found from multi-criteria optimization, resulting in a Pareto-frontier on the dependencies of TEP vs TV computed for all studied geometries. The proposed approach helps us to determine a restricted number of geometries for more detailed 3D computations and further experimental validations on prototypes.
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http://dx.doi.org/10.3390/e22020176DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7516599PMC
February 2020

Electroless Production of Fertilizer (Struvite) and Hydrogen from Synthetic Agricultural Wastewaters.

J Am Chem Soc 2020 11 21;142(44):18844-18858. Epub 2020 Oct 21.

Ralph E. Martin Department of Chemical Engineering, University of Arkansas, 3202 Bell Engineering Center, Fayetteville, Arkansas 72701, United States.

The drive toward sustainable phosphorus (P) recovery from agricultural and municipal wastewater streams has intensified. However, combining P recovery with energy conservation is perhaps one of the greatest challenges of this century. In this study, we report for the first time the simultaneous electroless production of struvite and dihydrogen from aqueous ammonium dihydrogen phosphate (NHHPO) solutions in contact with either a pure magnesium (Mg) or a Mg alloy as the anode and 316 stainless steel (SS) as the cathode placed in a bench-scale electrochemical reactor. During the electroless process (i.e., in the absence of external electrical power), the open circuit potential (OCP), the formation of struvite on the anode, and the generation of dihydrogen at the cathode were monitored. We found that struvite is formed, and that struvite crystal structure/morphology and precipitate film thickness are affected by the concentration of the HPO/NH in solution and the composition of the anode. The pure Mg anode produced a porous 0.6-4.1 μm thick film, while the AZ31 Mg alloy produced a more compact 1.7-9.9 μm thick struvite film. Kinetic analyses revealed that Mg dissolution to Mg followed mostly a zero-order kinetic rate law for both Mg anode materials, and the rate constants () depended upon the struvite layer morphology. Fourier-transform infrared spectrometry, X-ray diffraction, and scanning electron microscopy indicated that the synthesized struvite was of high quality. The dihydrogen and Mg in solution were detected by a gas chromatography-thermal conductivity detector and ion chromatography, respectively. Furthermore, we fully demonstrate that the reactor was able to remove ∼73% of the HPO present in a natural poultry wastewater as mainly struvite. This study highlights the feasibility of simultaneously producing struvite and dihydrogen from wastewater effluents with no energy input in a green and sustainable approach.
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http://dx.doi.org/10.1021/jacs.0c07916DOI Listing
November 2020

Editorial: Recent Development of Nanocatalysts for Hydrogen Production.

Front Chem 2020 9;8:576. Epub 2020 Jul 9.

School of Chemistry and Materials Engineering, Huizhou University, Huizhou, China.

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http://dx.doi.org/10.3389/fchem.2020.00576DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7363963PMC
July 2020

Does power ultrasound (26 kHz) affect the hydrogen evolution reaction (HER) on Pt polycrystalline electrode in a mild acidic electrolyte?

Ultrason Sonochem 2020 Dec 26;69:105238. Epub 2020 Jun 26.

Hydrogen Energy and Sonochemistry Research Group, Department of Energy and Process Engineering, Faculty of Engineering, Norwegian University of Science and Technology (NTNU), NO-7491 Trondheim, Norway.

In this study, we investigated the effects of power ultrasound (26 kHz, up to ∼75 W/cm, up to 100% acoustic amplitude, ultrasonic horn) on the hydrogen evolution reaction (HER) on a platinum (Pt) polycrystalline disc electrode in 0.5 M HSO by cyclic and linear sweep voltammetry at 298 K. We also studied the formation of molecular hydrogen (H) bubbles on a Pt wire in the absence and presence of power ultrasound using ultra-fast camera imaging. It was found that ultrasound significantly increases currents towards the HER i.e. a ∼250% increase in current density was achieved at maximum ultrasonic power. The potential at a current density of -10 mA/cm under silent conditions was found to be -46 mV and decreased to -27 mV at 100% acoustic amplitude i.e. a ΔE shift of ∼+20 mV, indicating the influence of ultrasound on improving the HER activity. A nearly 100% increase in the exchange current density (j) and a 30% decrease in the Tafel slope (b) at maximum ultrasonic power, was observed in the low overpotential region, although in the high overpotential region, the Tafel slopes (b) were not significantly affected when compared to silent conditions. In our conditions, ultrasound did not greatly affect the "real" surface area (A) and roughness factor (R) i.e. the microscopic surface area available for electron transfer. Overall, it was found that ultrasound did not dramatically change the mechanism of HER but instead, increased currents at the Pt surface area through effective hydrogen bubble removal.
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http://dx.doi.org/10.1016/j.ultsonch.2020.105238DOI Listing
December 2020

The use of non-cavitating coupling fluids for intensifying sonoelectrochemical processes.

Ultrason Sonochem 2020 Sep 23;66:105087. Epub 2020 Mar 23.

Hydrogen Energy and Sonochemistry Research Group, Department of Energy and Process Engineering, Norwegian University of Science and Technology (NTNU), NO-7491 Trondheim, Norway. Electronic address:

For the first time, we have investigated the beneficial effects of non-cavitating coupling fluids and their moderate overpressures in enhancing mass-transfer and acoustic energy transfer in a double cell micro-sonoreactor. Silicon and engine oils of different viscosities were used as non-cavitating coupling fluids. A formulated monoethylene glycol (FMG), which is a regular cooling fluid, was also used as reference. It was found that silicon oil yielded a maximum acoustic energy transfer (3.05 W/cm) from the double jacketed cell to the inner cell volume, at 1 bar of coupling fluid overpressure which was 2.5 times higher than the regular FMG cooling fluid. It was also found that the low viscosity engine oil had a higher acoustic energy value than that of the high viscosity engine oil. In addition, linear sweep voltammograms (LSV) were recorded for the quasi-reversible FeFe redox couple (equimolar, 5 × 10 M) on a Pt electrode in order to determine the mass-transport limited current density (j) and the dimensionless Sherwood number (Sh). From the LSV data, a statistical analysis was performed in order to determine the contribution of acoustic cavitation in the current density variation |Δj|. It was found that silicon oil at 1 bar exhibited a maximum current density variation, |Δj| of ~2 mA/cm whereas in the absence of overpressure, the high viscosity engine oil led to a maximum |Δj| which decreased gradually with increasing coupling fluid overpressure. High viscosity engine oil gave a maximum Sh number even without any overpressure which decreased gradually with increasing overpressure. The Sh number for silicon oil increased with increasing overpressure and reached a maximum at 1 bar of overpressure. For any sonoelectrochemical processes, if the aim is to achieve high mass-transfer and acoustic energy transfer, then silicon oil at 1 bar of overpressure is a suitable candidate to be used as a coupling fluid.
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http://dx.doi.org/10.1016/j.ultsonch.2020.105087DOI Listing
September 2020

Seeking minimum entropy production for a tree-like flow-field in a fuel cell.

Phys Chem Chem Phys 2020 Apr 19;22(13):6993-7003. Epub 2020 Mar 19.

PoreLab, Department of Chemistry, Norwegian University of Science and Technology, NTNU, Trondheim, Norway.

Common for tree-shaped, space-filling flow-field plates in polymer electrolyte fuel cells is their ability to distribute reactants uniformly across the membrane area, thereby avoiding excess concentration polarization or entropy production at the electrodes. Such a flow field, as predicted by Murray's law for circular tubes, was recently shown experimentally to give a better polarization curve than serpentine or parallel flow fields. In this theoretical work, we document that a tree-shaped flow-field, composed of rectangular channels with T-shaped junctions, has a smaller entropy production than the one based on Murray's law. The width w of the inlet channel and the width scaling parameter, a, of the tree-shaped flow-field channels were varied, and the resulting Peclet number at the channel outlets was computed. We show, using 3D hydrodynamic calculations as a reference, that pressure drops and channel flows can be accounted for within a few percents by a quasi-1D model, for most of the investigated geometries. Overall, the model gives lower energy dissipation than Murray's law. The results provide new tools and open up new possibilities for flow-field designs characterized by uniform fuel delivery in fuel cells and other catalytic systems.
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http://dx.doi.org/10.1039/c9cp05394hDOI Listing
April 2020

Sonoelectrochemistry for energy and environmental applications.

Ultrason Sonochem 2020 May 20;63:104960. Epub 2020 Jan 20.

Hydrogen Energy and Sonochemistry Research Group, Department of Energy and Process Engineering, Norwegian University of Science and Technology (NTNU), NO-7491 Trondheim, Norway. Electronic address:

Sonoelectrochemistry is the study of the effects and applications of ultrasonic waves on electrochemical processes. The integration of ultrasound and electrochemistry offers many advantages: fast reaction rates, enhanced surface activation, and increased mass transport at an electrode. Significant progress has been made in advancing basic and applied aspects of sonoelectrochemical techniques, which are herein reviewed by addressing the development and applications of sonoelectrochemical processes in energy and environmental areas. This review examines the experimental procedures that are used in various sonoelectrochemical techniques generally used for the synthesis of energy related materials (e.g., fuel cell electrocatalysts and materials for hydrogen production) and for the degradation of various organic compounds/pollutants. The challenges that remain for the sonoelectrochemical production of energy materials, the degradation of organic pollutants, and their associated reaction pathway mechanism(s) are also discussed. This review also highlights the significant improvements made to date. The provided information in this review may be helpful to scientists working in the research areas of environmental remediation, energy exploitation and exploration, as well as synthetic process-oriented research.
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http://dx.doi.org/10.1016/j.ultsonch.2020.104960DOI Listing
May 2020

From Bad Electrochemical Practices to an Environmental and Waste Reducing Approach for the Generation of Active Hydrogen Evolving Electrodes.

Angew Chem Int Ed Engl 2019 Nov 15;58(48):17383-17392. Epub 2019 Oct 15.

Institute of Chemistry of New Materials, The Electrochemical Energy and Catalysis group, University of Osnabrück, Barbarastrasse 7, 49076, Osnabrück, Germany.

The electrodeposition of noble metals using corresponding dissolved metal salts represents an interesting process for the improvement of the electrocatalytic hydrogen evolution reaction (HER) properties of less active substrate materials. The fact that only a small fraction of the dissolved noble metals reaches the substrate represents a serious obstacle to this common procedure. We therefore chose a different path. It was found that the HER activity of Ni42 alloy drastically increased (η=140 mV at j=10 mA cm ; pH 1) when a platinum counter electrode was used during polarization experiments in acid. This improvement was caused by a platinum transfer from the platinum anode to the steel cathode, a process which occurred simultaneously to the hydrogen evolution. The negligible accumulation of Pt (26 μg) in the electrolyte turns this straight-forward transfer procedure into a highly cost-effective, environmentally friendly, and waste reducing approach for the generation of cheap, stable and effective HER electrodes.
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http://dx.doi.org/10.1002/anie.201908649DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7155044PMC
November 2019

Does power ultrasound affect Nafion® dispersions?

Ultrason Sonochem 2020 Jan 31;60:104758. Epub 2019 Aug 31.

Hydrogen Energy and Sonochemistry Research Group, Department of Energy and Process Engineering, Norwegian University of Science and Technology (NTNU), NO-7491 Trondheim, Norway. Electronic address:

The effect of low frequency power ultrasound on Nafion® ionomer used for fabricating proton exchange membrane fuel cell (PEMFC) and water electrolyzer (PEMWE) catalyst inks was investigated. In this study, a series of Nafion® dispersions having three concentrations (10, 5, and 2.5% w/v) were studied under various irradiation durations (t), at fixed ultrasonic frequency (f = 42 kHz) and ultrasonic power (P > 2 W), under either controlled or unregulated bulk solution temperature conditions using a laboratory ultrasonic cleaning bath. Viscosity (η), thermal degradation, and glass transition temperature (T) for all Nafion® dispersion samples was measured and compared to untreated Nafion® samples. In our conditions, it was found that power ultrasound lowered the viscosity of all tested Nafion® dispersion samples; whilst thermogravimetric and differential scanning calorimetry analyses showed that for all ultrasonically irradiated samples, a negligible overall polymer degradation and no obvious change in T was observed under controlled and unregulated bulk temperature conditions. It was found that it is possible that acoustic cavitation causes depolymerisation followed by a polymerisation initiation step during ultrasonication. By comparing the ultrasonically treated and high-shear mixed samples, it was also observed that acoustic and hydrodynamic cavitation played an important role in the reduction of dispersion viscosity.
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http://dx.doi.org/10.1016/j.ultsonch.2019.104758DOI Listing
January 2020

Effect of power ultrasound and Fenton reagents on the biomethane potential from steam-exploded birchwood.

Ultrason Sonochem 2019 Nov 5;58:104675. Epub 2019 Jul 5.

Department of Energy and Process Engineering & ENERSENSE, NTNU, Trondheim, Norway.

The global demand for non-fossil energy sources is increasing rapidly. As a result, biogas presents a suitable alternative; however, first generation biofuels (e.g., sugar cane) potentially impact food crops globally. Second generation biofuels based on lignocellulose-based biomass are being used more frequently as they do not impact food crops. Furthermore, in Northern Europe, there is a significant interest in utilizing birchwood and paper mill waste for biogas production due to its high availability. The utilization of birchwood for biogas has significantly improved in recent years with the improvement of required pretreatment processes. To date, the most effective and economically feasible pretreatment in an industrial context is the steam explosion of lignocellulose-based biomass. Despite this, there is potential for releasing more digestible components from this biomass by efficiently degrading the lignocellulose components. This research presents another pretreatment that can be applied to steam-exploded wood based on ultrasonication and Fenton reagents. It was observed that by treating the steam exploded birchwood with ultrasonication and mild concentrations of Fenton reagents, an increase in the rate of biogas production was achievable. This would allow the increase in biogas yield of a continuously feed industrial anaerobic digester without increasing the size of the reactor.
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http://dx.doi.org/10.1016/j.ultsonch.2019.104675DOI Listing
November 2019

Recent developments in the sonoelectrochemical synthesis of nanomaterials.

Ultrason Sonochem 2019 Dec 29;59:104711. Epub 2019 Jul 29.

Hydrogen Energy and Sonochemistry Research Group, Department of Energy and Process Engineering, Faculty of Engineering, Norwegian University of Science and Technology (NTNU), NO-7491 Trondheim, Norway.

In recent years, the synthesis and use of nanoparticles have been of special interest among the scientific communities due to their unique properties and applications in various advanced technologies. The production of these materials at industrial scale can be difficult to achieve due to high cost, intense labour and use of hazardous solvents that are often required by traditional chemical synthetic methods. Sonoelectrochemistry is a hybrid technique that combines ultrasound and electrochemistry in a specially designed electrochemical setup. This technique can be used to produce nanomaterials with controlled sizes and shapes. The production of nanoparticles by sonoelectrochemistry as a technique offers many advantages: (i) a great enhancement in mass transport near the electrode, thereby altering the rate, and sometimes the mechanism of the electrochemical reactions, (ii) a modification of surface morphology through cavitation jets at the electrode-electrolyte interface, usually causing an increase of the surface area and (iii) a thinning of the electrode diffusion layer thickness and therefore ion depletion. The scalability of sonoelectrochemistry for producing nanomaterials at industrial scale is also very plausible due to its "one-pot" synthetic approach. Recent advancements in sonoelectrochemistry for producing various types of nanomaterials are briefly reviewed in this article. It is with hope that the presentation of these studies therein can generate more interest in the field to "catalyze" future investigations in novel nanomaterial development and industrial scale-up studies.
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http://dx.doi.org/10.1016/j.ultsonch.2019.104711DOI Listing
December 2019

Highly Efficient and Stable Catalyst Based on Co(OH)@Ni Electroplated on Cu-Metallized Cotton Textile for Water Splitting.

ACS Appl Mater Interfaces 2019 Aug 7;11(33):29791-29798. Epub 2019 Aug 7.

State Key Laboratory Base for Eco-Chemical Engineering, College of Chemical Engineering , Qingdao University of Science and Technology , Qingdao 266042 , China.

The concept of using renewable energy to power water electrolyzers is seen as a favorable approach for the production of green and sustainable hydrogen. The electrochemical water splitting can be significantly and efficiently enhanced using bifunctional catalysts, which are active toward both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Herein, a stable and high-performance catalyst based on hybrid-metal/metal-hydroxide nanosheet arrays electroplated onto Cu-metallized cotton textile (Co(OH)@Ni) was designed and fabricated as a bifunctional electrocatalyst for complete water-splitting reactions. It was found that the interconnected α-Co(OH) nanosheets were evenly formed onto the metalized cotton textile, and the optimized Co(OH)@Ni sample exhibited an overpotential of +96 mV at 10 mA cm, with excellent stability toward HER. The as-prepared catalyst also showed superior electrochemical activity and durability toward OER, which was found to be comparable to those of conventional precious group metal-based catalysts. In addition, when Co(OH)@Ni were assembled as electrodes in a water electrolyzer (1 M KOH), a cell voltage of 1.640 V was achieved at a current density of 10 mA cm, enabling it to be a promising bifunctional catalyst for water electrolysis in real applications.
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http://dx.doi.org/10.1021/acsami.9b07371DOI Listing
August 2019

N-doped porous transition metal-based carbon nanosheet networks as a multifunctional electrocatalyst for rechargeable zinc-air batteries.

Chem Commun (Camb) 2019 Mar;55(20):2924-2927

State Key Laboratory Base for Eco-Chemical Engineering, College of Chemical Engineering, Qingdao University of Science and Technology, Qingdao, 266042, China.

The development of cost-effective and highly efficient multi-functional oxygen reduction reaction and oxygen evolution reaction catalysts has attracted much research attention due to their great potential applications in many advanced clean energy storage and conversion technologies. Herein, highly efficient N-doped three-dimensional porous Co-Co3O4/C nanosheet network materials have been developed as bifunctional electrocatalysts for rechargeable zinc-air batteries.
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http://dx.doi.org/10.1039/c9cc00391fDOI Listing
March 2019

Does power ultrasound affect heterogeneous electron transfer kinetics?

Authors:
Bruno G Pollet

Ultrason Sonochem 2019 Apr 31;52:6-12. Epub 2018 Dec 31.

Hydrogen Energy and Sonochemistry Research Group, Department of Energy and Process Engineering, Faculty of Engineering, Norwegian University of Science and Technology (NTNU), NO-7491 Trondheim, Norway. Electronic address: http://www.brunogpollet.com.

Most of the observations seen in the application of power ultrasound in electrochemistry or also known as sonoelectrochemistry are due to enhanced mass-transport of electroactive species from the bulk solution to the electrode surface caused by efficient stirring, acoustic streaming and cavitation. However, fundamental studies on the effect of ultrasound on electrode kinetics i.e. on the electron-transfer are scarce. The main question still remains to be answered: Does power ultrasound affect heterogeneous electron transfer kinetics? This opinion paper discusses the effect of ultrasonic frequency and intensity upon the electrode kinetic parameters such as the half-wave potential (E) and the apparent heterogeneous rate constant (k). A few sonoelectrochemical studies have highlighted changes in half-wave potential and in apparent heterogeneous rate constant for both quasi-reversible and irreversible systems when the data were compared to silent conditions. These observations are thought to be due to the contribution of mass-transport and macroscopic temperature effects, as well as the continuous cleaning of the electrode surface caused by the collapse of high-energy cavitation bubbles and the production of high velocity jets of liquid. However, there still remains mechanistic controversy in assigning whether these findings could also be due to localised temperature increases, the contribution of sonolysis products or solely due to enhanced mass-transport at the electrode surface. Thus, the effect of stirring, macroscopic temperature and sonication time upon these electrode kinetic parameters is also shown to be important factors in comparing the validity of any sonoelectrochemical effects.
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http://dx.doi.org/10.1016/j.ultsonch.2018.12.017DOI Listing
April 2019

Hollow core-shell structured [email protected] spheres as novel electrode for enzyme free glucose sensing.

Mater Sci Eng C Mater Biol Appl 2019 Feb 25;95:174-182. Epub 2018 Oct 25.

College of Chemical Engineering, Qingdao University of Science and Technology, Qingdao 266042, China. Electronic address:

This study reports a novel hollow [email protected] material used as a catalyst for enzyme free glucose detection. [email protected] is successfully synthesized by a facile in-situ growth method. The obtained [email protected] exhibits a hollow structure with a CuS rich surface. Compared to CuO spheres, electrochemical results reveal that the [email protected] material exhibits a much higher catalytic activity toward glucose oxidation due to synergistic effect between CuO and CuS. The as-prepared [email protected] produces a high sensitivity, a fast sensing response, a wide linear range in concentrations of 1-1000 μM, and an excellent selectivity, thus prove to be a promising catalyst for enzyme free glucose detection.
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http://dx.doi.org/10.1016/j.msec.2018.10.082DOI Listing
February 2019

MnO/N-Doped Mesoporous Carbon as Advanced Oxygen Reduction Reaction Electrocatalyst for Zinc-Air Batteries.

Chemistry 2019 Feb 25;25(11):2868-2876. Epub 2019 Jan 25.

State Key Laboratory Base for Eco-Chemical Engineering, College of Chemical Engineering, Qingdao University of Science and Technology, Qingdao, 266042, P. R. China.

The development of alternative electrocatalysts exhibiting high activity in the oxygen reduction reaction (ORR) is vital for the deployment of large-scale clean energy devices, such as fuel cells and zinc-air batteries. N-doped carbon materials offer a promising platform for the design and synthesis of electrocatalysts due to their high ORR activity, high surface area, and tunable porosity. In this study, materials in which MnO nanoparticles are entrapped in N-doped mesoporous carbon (MnO/NC) were developed as electrocatalysts for the ORR, and their performances were evaluated in zinc-air batteries. The obtained carbon materials had large surface area and high electrocatalytic activity toward the ORR. The carbon compounds were fabricated by using NaCl as template in a one-pot process, which significantly simplifies the procedure for preparing mesoporous carbon materials and in turn reduces the total cost. A primary zinc-air battery based on this material exhibits an open-circuit voltage of 1.49 V, which is higher than that of conventional zinc-air batteries with Pt/C (Pt/C cell) as ORR catalyst (1.41 V). The assembled zinc-air battery delivered a peak power density of 168 mW cm at a current density of about 200 mA cm , which is higher than that of an equivalent Pt/C cell (151 mW cm at a current density of ca. 200 mA cm ). The electrocatalytic data revealed that MnO/NC is a promising nonprecious-metal ORR catalyst for practical applications in metal-air batteries.
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http://dx.doi.org/10.1002/chem.201806115DOI Listing
February 2019

Sonochemical and sonoelectrochemical production of hydrogen.

Ultrason Sonochem 2019 Mar 22;51:533-555. Epub 2018 Sep 22.

Department of Energy and Process Engineering, Faculty of Engineering, Norwegian University of Science and Technology (NTNU), NO-7491 Trondheim, Norway. Electronic address:

Reserves of fossil fuels such as coal, oil and natural gas on earth are finite. The continuous use and burning of these fossil fuel resources in the industrial, domestic and transport sectors has resulted in the extremely high emission of greenhouse gases, GHGs (e.g. CO) and solid particulates into the atmosphere. Therefore, it is necessary to explore pollution free and more efficient energy sources in order to replace depleting fossil fuels. The use of hydrogen (H) as an alternative fuel source is particularly attractive due to its very high specific energy compared to other conventional fuels and its zero GHG emission when used in a fuel cell. Hydrogen can be produced through various process technologies such as thermal, electrolytic, photolytic and biological processes. Thermal processes include gas reforming, renewable liquid and biooil processing, biomass and coal gasification; however, these processes release a huge amount of greenhouse gases. Production of electrolytic hydrogen from water is an attractive method to produce clean hydrogen. It could even be a more promising technology when combining water electrolysis with power ultrasound to produce hydrogen efficiently where sonication enhances the electrolytic process in several ways such as enhanced mass transfer, removal of hydrogen and oxygen (O) gas bubbles and activation of the electrode surface. In this review, production of hydrogen through sonochemical and sonoelectrochemical methods along with a brief description of current hydrogen production methods and power ultrasound are discussed.
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http://dx.doi.org/10.1016/j.ultsonch.2018.08.024DOI Listing
March 2019

Achieving highly practical capacitance of MnO by using chain-like CoB alloy as support.

Nanoscale 2018 Apr;10(16):7813-7820

Institute of Chemical Engineering, Qingdao University of Science and Technology, Qingdao, 266042, China.

The practical performance of MnO2 as a capacitor material is limited mainly by its poor electronic conductivity. Arranging MnO2 on the conductive backbone to form a unique hierarchical nanostructure is an efficient way to enhance its capacitor performance. Herein, a hierarchically core-shell structure, in which thin γ-MnO2 sheets are grown on amorphous CoB alloy nano-chains ([email protected]), is produced via a simple and scalable solution-phase procedure at room temperature. A specific capacitance of 612.0 F g-1 is obtained for the [email protected] capacitor electrode at a discharge current density of 0.5 A g-1, a value higher than those obtained for other conductive materials supported MnO2 electrodes reported in the literature. A rate retention value of 60.9% of its initial capacitance is obtained when the discharge current density increased by 12-fold. It is found that after 6000 charge-discharge cycles at 2 A g-1, the specific performance of [email protected] is 86.5%. The excellent capacitor performance of [email protected] is explained to be due to the hierarchical core-shell structure, in which the CoB alloy nano-chain backbone provides a transport pathway for the electron, and the porous MnO2 outer layers provide the channel for mass transfer, hence allowing further exposure to active sites. The combination of high capacitor performance and low-cost synthesis makes the core-shell [email protected] a promising cathode material for alkaline electrolyte supercapacitors.
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http://dx.doi.org/10.1039/c8nr01004hDOI Listing
April 2018

Enhanced Cycleability of Amorphous MnO₂ by Covering on α-MnO₂ Needles in an Electrochemical Capacitor.

Materials (Basel) 2017 Aug 24;10(9). Epub 2017 Aug 24.

Institute of Chemical Engineering, Qingdao University of Science and Technology, Qingdao 266042, China.

An allomorph MnO₂@MnO₂ core-shell nanostructure was developed via a two-step aqueous reaction method. The data analysis of Scanning Electron Microscopy, Transmission Electron Microscopy, X-Ray Diffraction and N₂ adsorption-desorption isotherms experiments indicated that this unique architecture consisted of a porous layer of amorphous-MnO₂ nano-sheets which were well grown onto the surface of α-MnO₂ nano-needles. Cyclic voltammetry experiments revealed that the double-layer charging and Faradaic -capacity of the MnO₂@MnO₂ capacitor electrode contributed to a specific capacitance of 150.3 F·g at a current density of 0.1 A·g. Long cycle life experiments on the as-prepared MnO₂@MnO₂ sample showed nearly a 99.3% retention after 5000 cycles at a current density of 2 A·g. This retention value was found to be significantly higher than those reported for amorphous MnO₂-based capacitor electrodes. It was also found that the remarkable cycleability of the MnO₂@MnO₂ was due to the supporting role of α-MnO₂ nano-needle core and the outer amorphous MnO₂ layer.
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http://dx.doi.org/10.3390/ma10090988DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5615643PMC
August 2017

Sonoelectrochemical one-pot synthesis of Pt - Carbon black nanocomposite PEMFC electrocatalyst.

Ultrason Sonochem 2017 Mar 13;35(Pt B):591-597. Epub 2016 May 13.

National Technical University of Athens, School of Chemical Engineering, Zografou Campus, 9 Heroon Polytechneiou St., 15773 Zografou-Athens, Greece; Institut für Energieforschung und Physikalische Technologien, Clausthal University of Technology, Leibnizstr. 4, 38678 Clausthal-Zell., Germany; Clausthaler Zentrum für Materialforschung (CZM), Agricola Str. 2, 38678 Clausthal-Zellerfeld, Germany. Electronic address:

Simultaneous electrocatalytic Pt-nanoparticle synthesis and decoration of Vulcan XC-72 carbon black substrate was achieved in a novel one-step-process, combining galvanostatic pulsed electrodeposition and pulsed ultrasonication with high power, low-frequency (20kHz) ultrasound. Aqueous chloroplatinic acid precursor baths, as well as carbon black suspensions in the former, were examined and decoration was proven by a combination of characterization methods, namely: dynamic light scattering, transmission electron microscopy, scanning electron microscopy with EDX-analysis and cyclic voltammetry. In particular, PVP was shown to have a beneficial stabilizing effect against free nanoparticle aggregation, ensuring narrow size distributions of the nanoparticles synthesized, but is also postulated to prevent the establishment of a strong metal-substrate interaction. Current pulse amplitude was identified as the most critical nanoparticle size-determining parameters, while only small size particles, under 10nm, appeared to be attached to carbon black.
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http://dx.doi.org/10.1016/j.ultsonch.2016.05.023DOI Listing
March 2017

Regrowth in ship's ballast water tanks: Think again!

Mar Pollut Bull 2016 Aug 13;109(1):46-48. Epub 2016 May 13.

Coldharbour Marine Ltd., R&D Centre, Baxter House, Robey Close, Linby, Nottinghamshire, NG15 8AA, England, United Kingdom.

With the imminent ratification of the International Maritime Organisation's Ballast Water Management Convention, ship owners and operators will have to choose among a myriad of different Ballast Water Treatment Systems (BWTS) and technologies to comply with established discharge standards. However, it has come to our attention that decision-makers seem to be unaware of the problem of regrowth occurring in ballast water tanks after treatment. Furthermore, the information available on the subject in the literature is surprisingly and unfortunately very limited. Herein we summarise previous research findings that suggest that regrowth of bacteria and phytoplankton could occur 18h to 7days and 4 to 20days after treatment, respectively. By highlighting the problem of regrowth, we would like to encourage scientists and engineers to further investigate this issue and to urge ship owners and ship operators to inform themselves on the risks of regrowth associated with the implementation of different BWTS.
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http://dx.doi.org/10.1016/j.marpolbul.2016.04.061DOI Listing
August 2016

A Co3W3C promoted Pd catalyst exhibiting competitive performance over Pt/C catalysts towards the oxygen reduction reaction.

Chem Commun (Camb) 2014 Jan 25;50(5):566-8. Epub 2013 Nov 25.

The State Key Laboratory of Optoelectronic Materials and Technologies, and Guangdong Province Key Laboratory of Low-carbon Chemistry & Energy Conservation, School of Physics and Engineering, Sun Yat-sen University, Guangzhou, 510275, PR China.

A novel Co3W3C promoted Pd electrocatalyst shows competitive performance over Pt/C towards the oxygen reduction reaction in acidic media.
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http://dx.doi.org/10.1039/c3cc48240eDOI Listing
January 2014
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