Gadolinium-doped ceria nanopowders synthesized by urea-based homogeneous co-precipitation (UBHP)

Accardo, G.,Spiridigliozzi, L.,Cioffi, R.,Ferone, C.,Di Bartolomeo, E.,Yoon, Sung Pil,Dell’Agli, G. Elsevier 2017 Materials chemistry and physics Vol.187 No.-

<P><B>Abstract</B></P> <P>Gadolinium (10%)-doped ceria was successfully synthesized by using an urea-based co-precipitation method (UBHP). A single fluorite phase was obtained after a low temperature (400 °C) calcination treatment. The resulting powders showed grains of nanometric size with some agglomerations and an overall good sinterability. Pellets were sintered at 1300 and 1500 °C for 3 h. The ionic conductivity was measured by electrochemical impedance spectroscopy measurements and a correlation between electrical properties and microstructure was revealed. The promising conductivity values showed that the synthesized powders are suitable for intermediate temperature solid oxide fuel cells (IT-SOFCs) applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Urea-based homogeneous co-precipitation is applied to synthesize nanocrystalline GDC. </LI> <LI> Dense GDC samples at different sintering temperatures were characterized. </LI> <LI> SEM and TEM revealed a well define microstructure and controlled composition. </LI> <LI> Correlation between electrochemical properties by EIS and microstructure was discussed. </LI> <LI> UBHP method can be used to prepare high performance GDC electrolytes. </LI> </UL> </P>

Direct addition of lithium and cobalt precursors to Ce_0.8Gd_0.2O_1.95 electrolytes to improve microstructural and electrochemical properties in IT-SOFC at lower sintering temperature

Accardo, Grazia,Frattini, Domenico,Ham, Hyung Chul,Yoon, Sung Pil Elsevier 2019 CERAMICS INTERNATIONAL Vol.45 No.7

<P><B>Abstract</B></P> <P>To improve the microstructural and electrochemical properties of gadolinium-doped ceria (GDC) electrolytes, materials co-doped with 0.5–2 mol% of lithium and cobalt oxides were successfully prepared in a one-step sol gel combustion synthesis route. Vegard's slope theory was used to predict the dopant solubility and the sintering behaviour. The charge and size of the added dopant influence the atom flux near the grain boundary with a change in the lattice parameter. In fact, compared to traditional multi grinding steps, sol gel combustion facilitates molecular mixing of the precursors and substitution of the dopant cations into the fluorite structure, considerably reducing the sintering temperature. Adding precursors of lithium and cobalt, as dopant, increases the GDC densification and reduces its traditional sintering temperature down to 1000–1100 °C, with an improvement of electrochemical properties. Impedance analysis showed that the addition of 2 mol% of lithium or 0.5 mol% of cobalt enhances the conductivity with a consequent improvement of cell performances. High total conductivities of 1.26·10<SUP>−1</SUP> S cm<SUP>−1</SUP> and 8.72·10<SUP>−2</SUP> S cm<SUP>−1</SUP> at 800 °C were achieved after sintering at 1000 °C and 1100 °C for <SUP>2</SUP>LiGDC and <SUP>0.5</SUP>CoGDC, respectively.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Influence of nano zirconia on NiAl anodes for molten carbonate fuel cell: Characterization, cell tests and post-analysis

Accardo, Grazia,Frattini, Domenico,Moreno, Angelo,Yoon, Sung Pil,Han, Jong Hee,Nam, Suk Woo Elsevier Sequoia 2017 Journal of Power Sources Vol. No.

<P><B>Abstract</B></P> <P>Anode materials in Molten Carbonate Fuel Cells should have high creep resistance and good mechanical behavior to endure in high temperature-corrosive environments. In this work, zirconia nanoparticles (1–10% wt.) are added to NiAl anodes in order to investigate their effects on mechanical properties and single cell performances. Results show that nanoparticles strongly adhere to metal particles and bending strength increases from 6.08 to 11.33 kg<SUB>f</SUB> cm<SUP>−2</SUP> while creep strain is reduced from 7.55% to 3.25%. In the case of the anode with ZrO<SUB>2</SUB> 3% wt., the stable and high output voltage of 0.81 V at 150 mA cm<SUP>−2</SUP> is a promising result, compared to the literature. In addition, the solid contact angles between melted electrolyte and anode, for the NiAl reference sample and the ZrO<SUB>2</SUB> 3% wt. are 37.6° and 17°, respectively, showing the improved wettability of the modified anode. However, it seems to be a limit to the effective zirconia content as the contact angle of the anode with ZrO<SUB>2</SUB> 10% wt. is 58.1°, which indicates a low wetting ability. When zirconia content is too high, single cells have low performances due to high internal resistance and porosity reduction. The formation of a zirconate phase also occurs during operations.</P> <P><B>Highlights</B></P> <P> <UL> <LI> NiAl anodes with nano ZrO<SUB>2</SUB> are tested in MCFC single cell after characterization. </LI> <LI> Results show that nanoparticles improve mechanical and creep properties. </LI> <LI> The anode with ZrO<SUB>2</SUB> 3% wt. has the best performance over 1000 h operations. </LI> <LI> Post analysis shows zirconates formation at cathode for ZrO<SUB>2</SUB> contents over 5% wt. </LI> <LI> A high content of nanoparticles can diminish too much porosity and pore size. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Strengthening mechanism and electrochemical characterization of ZrO₂ nanoparticles in Nickel-Aluminum alloy for Molten Carbonate Fuel Cells

Frattini, D.,Accardo, G.,Moreno, A.,Yoon, S.P.,Han, J.H.,Nam, S.W. Korean Society of Industrial and Engineering Chemi 2017 Journal of industrial and engineering chemistry Vol.56 No.-

<P>In this work the positive effect of zirconia nanoparticles in Nickel-Aluminum anodes is investigated: Results showed that, as the zirconia content increases, bending strength and creep resistance are improved. Mechanical strength increases from 5.94 to 11.38 kg(f) cm(-2) and creep is reduced up to 3.31%. Morphology and microstructural analysis revealed that nanoparticles adhere strongly on the surface of larger metal particles and microstructure is strengthened at grain level. The diffusion of Aluminum atoms into different vacancies reduces dislocations movement. A part these mechanisms, charge and mass transfer resistance are lower and the internal resistance after 500 h at 650 degrees C is 0.24 m Omega cm(2). (C) 2017 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.</P>

A novel Nickel-Aluminum alloy with Titanium for improved anode performance and properties in Molten Carbonate Fuel Cells

Frattini, Domenico,Accardo, Grazia,Moreno, Angelo,Yoon, Sung Pil,Han, Jong Hee,Nam, Suk Woo Elsevier Sequoia 2017 Journal of Power Sources Vol. No.

<P><B>Abstract</B></P> <P>The anode materials of MCFC require more investigations in order to boost performances at long term. In literature, many NiAl modified alloys have been proposed but not always enhanced cell performance and improved mechanical properties are achieved together. In this work, differently from previous literature, the use of Ti in a NiAl/Ti system is proposed as an effective strategy to enhance both mechanical and electrochemical properties. Results show that bending strength and stiffness increase whereas creep deformation under high pressure-temperature is lower, i.e. around 5–6%, compared to 7.5% of the standard benchmark. The preliminary cell tests carried out show also how the performance, in terms of current and voltage output, is better for anodes with Ti addition with a maximum power density of 165 mW cm<SUP>−2</SUP> at 300 mA cm<SUP>−2</SUP> for Ti 5% compared to 149 mW cm<SUP>−2</SUP> of Ni5Al at the same current density. Finally, the best electrochemical behavior is found for the Ti 5% sample as it achieved the lowest internal and charge transfer resistance at the end of tests. These results suggest that NiAl/Ti systems can be eligible anode materials and are worthy to be investigated more in order to attract a renewed interest for development of MCFCs.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Titanium is used for the first time as alloying metal in NiAl-based MCFCs anode. </LI> <LI> Physical and mechanical properties of ternary anodes are characterized. </LI> <LI> Results show that mechanical and creep properties are improved remarkably. </LI> <LI> The anode with Ti 5 % wt. has the best performance in single cell tests. </LI> </UL> </P>

Optimization of glucose concentration and glucose/yeast ratio in yeast microbial fuel cell using response surface methodology approach

Christwardana, Marcelinus,Frattini, Domenico,Accardo, Grazia,Yoon, Sung Pil,Kwon, Yongchai Elsevier 2018 Journal of Power Sources Vol.402 No.-

<P><B>Abstract</B></P> <P>In this work the influence of two practical parameters, i.e. glucose concentration and glucose/yeast ratio, on performance of yeast-based microbial fuel cells (yeast-MFC) is investigated. The novel carbon felt pretreated with polyethylenimine is adopted as anode in open-air single chamber yeast-MFCs. The combination of the two parameters is optimized using response surface methodology with statistical approach. The optional presence of methylene blue as mediator is also included for comparison. Experimental dataset is initially built as reference and 4 mathematical equations are derived to predict the response regarding open circuit voltage (OCV) and maximum power density (MPD). By varying glucose concentration and glucose/yeast ratio, computed response surfaces show different responses are obtained and an optimum point exists within the range investigated. Finally, the optimized combinations for yeast-MFCs with/without mediator are predicted and response is verified in real experiment. The model tends to slightly overestimate the response, but accuracy is within confident range for both OCV and MPD. In fact, MPD obtained for the optimized yeast-MFC without mediator is 340.9 mW m<SUP>−2</SUP>, 3.2% lower than model, while it is 374.4 mW m<SUP>−2</SUP>, 5% lower than model, for the case including mediator. The discrepancy of OCV prediction is below 3%, making the approach reliable.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Single chamber yeast microbial fuel cell with a novel anode is optimized. </LI> <LI> Response Surface Methodology was used to tune 2 operational parameters. </LI> <LI> Dataset of experimental response with or without methylene blue was created. </LI> <LI> The shape of response surface shows that a non-trivial optimum point exists. </LI> <LI> The optimal point was experimentally checked and error was only 3–5%. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Effects of methylene blue and methyl red mediators on performance of yeast based microbial fuel cells adopting polyethylenimine coated carbon felt as anode

Christwardana, Marcelinus,Frattini, Domenico,Accardo, Grazia,Yoon, Sung Pil,Kwon, Yongchai Elsevier 2018 Journal of Power Sources Vol.396 No.-

<P><B>Abstract</B></P> <P>The electron transfer mechanisms of yeast <I>Saccharomyces cerevisiae</I> employing two different mediators, methylene blue (MB) and methyl red (MR), are suggested. The effects of the mediators on Microbial fuel cells (MFCs) performances are investigated when yeast and glucose are the biocatalyst and the substrate, respectively. Yeast tends to stand as floating cell rather than attached to supporting electrode. Therefore, to combine direct and mediated electron transfer mechanisms of yeast, two mediators and carbon felt modified with polyethyleneimine (PEI) (CF-PEI) are adopted and their roles are evaluated. As a result, CF-PEI surface is functionalized with amino groups that can attract and entrap more yeast cells. The cyclic voltammetry (CV) curves representing the mechanisms demonstrate that electron transfer rate constant of MB (0.44 s<SUP>−1</SUP>) is higher than MR (0.37 s<SUP>−1</SUP>). In addition, the performances of the yeast-MFC adopting MB (429.29 ± 42.75 mW m<SUP>-2</SUP> at ∼1200 mA m<SUP>−2</SUP>) are better than those of the yeast-MFC adopting MR and the yeast-MFC without mediator. The reason is that MB is effectively adsorbed by yeast and collects more electrons than MR. These benefits of MB are reflected in a more efficient electron transfer chain and minimize the side reactions deactivating the catalyst.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Methylene blue and methyl red as mediators in yeast-MFC are investigated. </LI> <LI> Electron transfer by methylene blue is mostly promoted. </LI> <LI> MPD of yeast-MFC using methylene blue is 430 mW m<SUP>2</SUP>. </LI> <LI> Absorption of methylene blue inside yeast is optically inspected. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Early-stage performance evaluation of flowing microbial fuel cells using chemically treated carbon felt and yeast biocatalyst

Christwardana, Marcelinus,Frattini, Domenico,Accardo, Grazia,Yoon, Sung Pil,Kwon, Yongchai Elsevier 2018 APPLIED ENERGY Vol.222 No.-

<P><B>Abstract</B></P> <P>The performance of closed-loop flowing-type microbial fuel cells using differently pretreated carbon felts is measured. Yeast cultivated from <I>S. cerevisiae</I> is used as biocatalyst, while glucose is the substrate. For the pretreatment of felt, acetone, nitric acid, and polyethyleneimine are employed. First the optimal conditions for yeast cultivation are quantitatively determined. As a result, a high yeast growth rate (1.083 h<SUP>−1</SUP>) and the optimal yeast growing time (48 h) for cell tests are obtained. The differently pretreated felts are analyzed by X-ray photoelectron spectroscopy, electrochemical impedance spectroscopy and optical microscopy. Conductivity, charge transfer resistance, and CdbndO and CsbndN groups dangled on the felt are crucial parameters determining the performance of the microbial fuel cell. Particularly, the conjugation effects of pi-pi bonds and lone pairs facilitating the attachment of yeast to the CdbndO and CsbndN groups on the carbon felt promote (i) mutual adhesion between them and (ii) growth of yeast on CF-PEI. This correlation is confirmed by optical analysis of the felts after the cell tests. To evaluate the early-stage performance of the microbial fuel cells using the different felts, polarization curves are measured. In the measurements, the maximum power density of the cells depends on the superficial state of felts, while the performance of the cell using the PEI-treated felt is best, at 256.3 ± 11.5 mW·m<SUP>−2</SUP>. These data match other results attained by pretreatments.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Yeast and chemically treated CF effects on MFC performance are investigated. </LI> <LI> CdbndO/CsbndN dangled on CF-PEI are key bonds for performance enhancement. </LI> <LI> Pi-pi bond conjugation and lone electron pair induce performance enhancement. </LI> <LI> High yeast growth rate and optimal yeast growing time are determined. </LI> <LI> MPD of MFC using CF-PEI is 256.3 mW m<SUP>2</SUP>. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Electro-morphological, structural, thermal and ionic conduction properties of Gd/Pr co-doped ceria electrolytes exhibiting mixed Pr³⁺/Pr⁴⁺ cations

Spiridigliozzi, L.,Dell'Agli, G.,Accardo, G.,Yoon, S.P.,Frattini, D. Elsevier 2019 CERAMICS INTERNATIONAL Vol.45 No.4

<P><B>Abstract</B></P> <P>Gd<SUB>0.2-x</SUB>Pr<SUB>x</SUB>Ce<SUB>0.8</SUB>O<SUB>1.90</SUB>, (x = 0, 0.02, 0.04, 0.06, 0.08, 0.10) has been synthesized by means of a simple co-precipitation route based on ammonium carbonate as the precipitating agent. The as-synthesized precursors are cerium-gadolinium-praseodymium amorphous hydroxycarbonates, which are nanometric in size with highly homogeneous morphology, leading to reactive doped and co-doped nanocrystalline (≈13 nm) ceria after a mild thermal treatment (2 h at 600 °C). The obtained results highlight the very positive effect of Pr on the powders’ sintering behaviour, which favour a better densification of the final pellets, thus improving both their microstructure (with relative densities of 97–99% after sintering at 1250 °C for 3 h) and electrochemical properties (up to 1.25·10–1 S cm<SUP>−1</SUP> at 800 °C for sample 6Pr) compared to the state-of-art ceria-based electrolytes. Through a comprehensive characterization, a relation was formed between the Pr content and the microstructural features of the sintered pellets and their electrical behaviour. The amount of Pr doping was investigated over a wide range and 6 mol% has been established to be optimal (possessing the lowest electronic conductivity contribution). Definitely, these results indicate that Gd<SUB>0.2-x</SUB>Pr<SUB>x</SUB>Ce<SUB>0.8</SUB>O<SUB>1.90</SUB> has an excellent set of characteristics, both microstructural and electrical, and a convenient fabrication process, thus making it perfectly suitable for IT-SOFC practical applications.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Study on LiI and KI with low melting temperature for electrolyte replenishment in molten carbonate fuel cells

Bae, Jae Kwan,Kim, Hyun-Woo,Accardo, Grazia,Kim, Ghun Sik,Ham, Hyung Chul,Jang, Seong-Cheol,Cho, Yong Soo,Yoon, Sung Pil Elsevier 2019 International journal of hydrogen energy Vol.44 No.47

<P><B>Abstract</B></P> <P>Molten carbonate fuel cells (MCFCs) are regarded as the closest fuel cell to commercialization due to their high capacity and energy efficiency. However, they are operated at a high temperature (620 °C or higher), where liquid electrolyte loss occurs during operation; hence, their lifetime is limited. For the long-term operation of MCFCs, it is essential to develop a novel method to replenish the electrolyte during operation. However, it is very difficult to directly inject the electrolyte, (Li<SUB>0.62</SUB>K<SUB>0.38</SUB>)<SUB>2</SUB>CO<SUB>3</SUB>, into each unit cell of the stack unless it is supplemented through liquid or gas phase at low temperature. It was verified whether LiI and KI, which have low melting points and high vapor pressures, could replenish the lost electrolyte in MCFCs. In this study, the LiI and KI injected into the unit cell in liquid phase showed a similar tendency to the Li/K carbonate electrolyte. This is because LiI and KI react with the CO<SUB>2</SUB>/O<SUB>2</SUB> gases supplied to the cathode during MCFC operation to form Li/K carbonate electrolytes.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Electrolyte precursors (LiI and KI) were selected by thermodynamic calculation. </LI> <LI> LiI and KI with low melting temp. are suitable for electrolyte replenishment. </LI> <LI> LiI and KI supplements are effective in ensuring stable performance for MCFCs. </LI> </UL> </P>