Development of nano-composite materials for low-temperature solid oxide fuel cells (LT-SOFCs)

Solid oxide fuel cells (SOFCs) are efficient electrochemical devices, converting chemicalenergy into electricity. However, the main drawback for the wide commercial use of SOFCis its high operational temperature (around 750 ℃). Therefore, this research project mostlyfocuses on developing new nanostructured electrode composites and low-temperaturefabrication techniques to further improve the performance of SOFCs at lower operatingtemperatures. The first approach to reach lower operating temperatures for SOFCs was todevelop a novel, low-cost, efficient and environmentally friendly synthesis method toimprove the microstructural properties of both the electrolyte and anode materials. In thisregard, gadolinium doped ceria (GDC) nanocrystalline powders were synthesized througha modified coprecipitation method using, for the first time, ammonium tartrate as anenvironmentally friendly, inexpensive, and novel precursor. The developed synthesismethod was successfully applied for the synthesis of a range of anode composites,including Ni-/GDC, Co/GDC, Co-Zn/GDC, Co/Cu-GDC, and Fe-Cu/GDC. A synergeticeffect was found among different constituents of the anode composites, where the stronginteraction between the well dispersed metal oxide nanocrystalline particles and the GDCcrystallite phase showed to shift the reduction temperature of the anode composites to lowertemperatures than those of bare anode constituents. Considering targeted objectives ofdeveloping low temperature SOFCs (LT-SOCs), having a broad choice of material andusing metallic parts, avoiding high temperature fabrication processes was of greatimportance in this project. With regards to the fabrication of anode supported SOFCs, allsynthesised anode and electrolyte powders illustrated a high sinteractivity, promoting thedensification of the GDC electrolyte film during the co-sintering process at considerablylow sintering temperatures (1100 ℃). The fabricated cells were evaluated using differentadvanced electrochemical techniques, such as electrochemical impedance spectroscopy(EIS), to evaluate mechanisms during different operating modes. Finally, theelectrochemical performance of the fabricated cells was studied under fuel cell operatingconditions

Catalytic Aspects of Fuel Cells: Overview and Insights

Heterogeneous catalysis plays a central role in the global energy paradigm, with practically all energy-related process relying on a catalyst at a certain point. The application of heterogeneous catalysts will be of paramount importance to achieve the transition towards low carbon and sustainable societies. This book provides an overview of the design, limitations and challenges of heterogeneous catalysts for energy applications. In an attempt to cover a broad spectrum of scenarios, the book considers traditional processes linked to fossil fuels such as reforming and hydrocracking, as well as catalysis for sustainable energy applications such as hydrogen production, photocatalysis, biomass upgrading and conversion of CO2 to clean fuels. Novel approaches in catalysts design are covered, including microchannel reactors and structured catalysts, catalytic membranes and ionic liquids. With contributions from leaders in the field, Heterogeneous Catalysis for Energy Applications will be an essential toolkit for chemists, physicists, chemical engineers and industrials working on energy

Synthesis and characterisation of nanocrystalline CuO–Fe2O3/GDC anode powders for solid oxide fuel cells

This paper deals with the development and potential application of a novel mixed ionic-electronic conductive anode composite comprised of copper and iron oxide based on gadolinium-doped ceria (CuO–Fe2O3/GDC) for solid-oxide fuel cell (SOFC). Synthesis of the nanocrystalline CuO–Fe2O3/GDC powders was carried out using a novel co-precipitation method based on ammonium tartrate as the precipitant in a mixed-cationic solution composed of Cu2+, Fe3+, Gd3+, and Ce3+. Thermal decomposition of the resultant precipitate after drying (at 55 °C) was investigated in a wide range of temperature (25–900 °C) using simultaneous DSC/TGA technique in air. The DSC/TGA results suggested the optimal calcination temperature of 500 °C for obtaining the nanocrystalline anode composite from the resultant precipitate. The synthesised CuO–Fe2O3/GDC samples were further characterised using XRD, dilatometry, FESEM, and EDX. Several single cells of SOFCs were fabricated in the anode-supported geometry using the synthesised CuO–Fe2O3/GDC composite as the anode, GDC/CuO composite as the electrolyte, and LSCF/GDC composite as the cathode layer. The fabricated cells were analysed using FESEM imaging and EIS analysis, where an equivalent circuit containing five R-CPE terms was used to interpret the EIS data. The module fitted well the impedance data and allowed for a detailed deconvolution of the total impedance spectra. The catalytic activity and uniformity of the synthesised nanocomposites was further evaluated using TPR analysis, demonstrating excellent activity at temperatures as low as 200 °C

Synthesis and characterisation of nanocrystalline CuO–Fe2O3/GDC anode powders for solid oxide fuel cells

This paper deals with the development and potential application of a novel mixed ionic-electronic conductive anode composite comprised of copper and iron oxide based on gadolinium-doped ceria (CuO–Fe2O3/GDC) for solid-oxide fuel cell (SOFC). Synthesis of the nanocrystalline CuO–Fe2O3/GDC powders was carried out using a novel co-precipitation method based on ammonium tartrate as the precipitant in a mixed-cationic solution composed of Cu2+, Fe3+, Gd3+, and Ce3+. Thermal decomposition of the resultant precipitate after drying (at 55 °C) was investigated in a wide range of temperature (25–900 °C) using simultaneous DSC/TGA technique in air. The DSC/TGA results suggested the optimal calcination temperature of 500 °C for obtaining the nanocrystalline anode composite from the resultant precipitate. The synthesised CuO–Fe2O3/GDC samples were further characterised using XRD, dilatometry, FESEM, and EDX. Several single cells of SOFCs were fabricated in the anode-supported geometry using the synthesised CuO–Fe2O3/GDC composite as the anode, GDC/CuO composite as the electrolyte, and LSCF/GDC composite as the cathode layer. The fabricated cells were analysed using FESEM imaging and EIS analysis, where an equivalent circuit containing five R-CPE terms was used to interpret the EIS data. The module fitted well the impedance data and allowed for a detailed deconvolution of the total impedance spectra. The catalytic activity and uniformity of the synthesised nanocomposites was further evaluated using TPR analysis, demonstrating excellent activity at temperatures as low as 200 °C

A Highly Efficient Hydrogen Generation Electrolysis System using Alkaline Zinc Hydroxide Solution

Alkaline water electrolysis is a well-established conventional technique for hydrogen production. However, due to its relatively high energy consumption, the cost of hydrogen produced by this technique is still high. Here in this work, we report for the first time the application of alkaline zinc hydroxide solution (composed of sodium zincate and potassium zincate in NaOH and KOH solutions, respectively) as an efficient, simple and recursive electrolyte for producing clean hydrogen through a continuous dual-step electrolysis process. The ionic conductivity, electrodes current density, and hydrogen evolution rate were measured in a wide range of the electrolyte concentrations (0.1-0.59 M). Also, the cell efficiency was studied at different ranges of current density (0.09-0.25 A/cm2) and applied potential (1.8-2.2 V). Results indicated that the application of alkaline zinc hydroxide solution at the optimum electrolyte concentration can enhance the hydrogen evolution rate minimally by a factor of 2.74 (using sodium zincate) and 1.47 (using potassium zincate) compared to the conventional alkaline water electrolysers. The results of this study could be helpful to better understand the electrochemical behaviour of the alkaline water electrolysers when sodium zincate and potassium zincate are used as ionic activators for enhancing hydrogen evolution

Nanocrystalline gadolinium-doped ceria (GDC) for SOFCs by an environmentally-friendly single step method

Nanocrystalline gadolinium-doped ceria (GDC) was synthesized by a single step, low cost and environmentally friendly method using ammonium tartrate as an inexpensive, green and novel precipitant. The precipitate obtained during the process was calcined at 400 and 600 °C and the effect on the final microstructural properties of the powders of differing process variables were studied. The synthesized GDC samples were analysed using a range of different techniques, including XRD, TG/DSC, FESEM, STEM, and FT-IR and Raman spectroscopies. The thermal (TG/DSC), XRD and Raman spectroscopic analyses confirm the formation of a single crystalline phase with a cubic (fluorite) unit cell and formed at a low calcination temperature (400 °C). XRD profiles permitted estimation of crystallite sizes as < 20 nm, which was further confirmed by STEM and FESEM micrographs indicating the formation of quasi-spherical particles with uniform particle sizes in the range 10–30 nm. This study will aid understanding of effects of process variables on the properties of doped metal-oxide powders prepared using the carboxylate rout

Synthesis and Characteristics of Nanocrystalline Ni1-xCoxO/GDC Powder as a Methane Reforming Catalyst for SOFCs

This paper has described the application of nickel-doped catalytic constituents based on gadolinium-doped ceria (GDC) for fabrication of the solid-oxide fuel cell (SOFC) anode layer integrated with an in-situ methane-reforming layer (MRL). Nanocrystalline powders of Ni1-xCo3xO1+3x/GDC and Ni1-xCuxO/GDC with various compositions (x = 0.3, 0.5, 0.7) were synthesised using an ultrasound-assisted method followed by a thermal treatment to be applied for fabrication of the integrated MRL and the SOFC anode layer, respectively. Thermogravimetric analysis showed that the synthesized powders should be optimally calcined at 700 °C to exhibit improved crystallinity and catalytic activity. The morphological analysis showed the formation of nanocrystalline powders with particle size ranging from 4-86 nm that was confirmed by the crystal size analysis using XRD results. The elemental analysis by EDX indicated a successful distribution of the constituent ceramic and bimetallic phases after the addition of a sonication stage. The results of FT-IR and Raman spectroscopy confirmed lack of solvents residual after calcination that was in agreement with residual moisture content values obtained from TGA data. The fabricated anode-MRL bilayers had an adequate porosity (36.7%) and shrinkage (33.5%) after adding carbon particles as a pore former (at a loading fraction of 5.9 wt.%). The catalytic performance measurements of the MRL showed a methane conversion of 13% at maximum activity with a weight hour space velocity (WHSV) of 60 L/gh that was mainly due to carbon deposition in the reaction condition

Characteristics and performance of urea modified Pt-MWCNTs for electro-oxidation of methanol

Multiwall carbon nanotubes are modified by urea (MWCNTs-U), as an amide group, through a simple amination method to be used as support for Pt nanoparticles in methanol electrooxidation reaction (MOR). The amination method involves a covalent grafting of urea molecules onto the surface of acid treated multiwall carbon nanotubes (MWCNTs-A) using O-(7-azabenzotriazol-1-yl)-N,N,N′,N′-tetramethyluronium hexafluorophosphate (HATU) as the coupling agent. Platinum nanoparticles are impregnated on the surface of MWCNTs-U using NaBH4. Pt/MWCNTs-U shows an enhanced electrocatalytic activity and durability with exposing larger accessible surface area and 27% higher active surface area compared to Pt/MWCNTs-A. In addition, urea incorporation can improve the electrocatalyst tolerance against CO-poisoning, due to the enhanced formation kinetics of the chemisorbed hydroxyl groups. The onset potential of COads oxidation indicates a decrease from 553 mV to 530 mV for Pt/MWCNTs-A and Pt/MWCNTs-U, respectively. It is observed that in the presence of amide group the forward peak current density and exchange current density, in CV and LSV experiments, respectively increase from 378 to 515 mA/mgPt and 1.59 × 10−8 A/cm2 to 2.12 × 10−8 A/cm2. These results are also in a good agreement with the theoretical activation energies obtained from Arrhenius plots, indicating a decrease from 41.7 to 38.8 kJ/mol methanol in the case of Pt/MWCNTs-A and Pt/MWCNTs-U, respectively

Synthesis and Electrochemical Properties of Bi2MoO6/Carbon Anode for Lithium-Ion Battery Application

High capacity electrode materials are the key for high energy density Li-ion batteries (LIB) to meet the requirement of the increased driving range of electric vehicles. Here we report the synthesis of a novel anode material, Bi2MoO6/palm-carbon composite, via a simple hydrothermal method. The composite shows higher reversible capacity and better cycling performance, compared to pure Bi2MoO6. In 0–3 V, a potential window of 100 mA/g current density, the LIB cells based on Bi2MoO6/palm-carbon composite show retention reversible capacity of 664 mAh·g−1 after 200 cycles. Electrochemical testing and ab initio density functional theory calculations are used to study the fundamental mechanism of Li ion incorporation into the materials. These studies confirm that Li ions incorporate into Bi2MoO6 via insertion to the interstitial sites in the MoO6-layer, and the presence of palm-carbon improves the electronic conductivity, and thus enhanced the performance of the composite materials