Modifying the cathodes of intermediate-temperature solid oxide fuel cells with a Ce0.8Sm0.2O2 sol–gel coating

To increase the performance of solid oxide fuel cells operated at intermediate temperatures (<700 °C), we used the electronic conductor La_0.8Sr_0.2MnO₃ (LSM) and the mixed conductor La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF) to modify the cathode in the electrode microstructure. For both cathode materials, we employed a Sm_0.2Ce_0.8O₂ (SDC) buffer layer as a diffusion barrier on the yttria-stabilized zirconia (YSZ) electrolyte to prevent the interlayer formation of SrZrO₃ and La₂Zr₂O₇, which have a poor ionic conductivity. These interfacial reaction products were formed only minimally at the electrolyte–cathode interlayer after sintering the SDC layer at high temperature; in addition, the degree of cathode polarization also decreased. Moreover to extend the triple phase boundary and improve cell performance at intermediate temperatures, we used sol–gel methods to coat an SDC layer on the cathode pore walls. The cathode resistance of the LSCF cathode cell featuring SDC modification reached as low as 0.11 Ω cm² in air when measured at 700 °C. The maximum power densities of the cells featuring the modified LSCF and LSM cathodes were 369 and 271 mW/cm², respectively, when using O₂ as the oxidant and H₂ as the fuel.     

Leveraging in-situ formation of Ni–Fe nanoparticles to promote the catalytic performance of Ruddlesden-Popper based electrode for symmetrical solid oxide fuel cells

Ruddlesden?Popper layered oxide, La_0.25Sr_2.75FeNiO_7-δ (LSFN) is evaluated as a potential electrode material for symmetrical solid oxide fuel cells. The in-situ formation of Ni–Fe alloy nanoparticles on the LSFN surface in reducing atmosphere can be believed to enhance the activity towards hydrogen oxidation reaction. LSFN exhibit maximum conductivity of 221.2 S/cm and 0.206 S/cm in air and hydrogen environment. Furthermore, LSFN is mixed with GDC powder to form a composite electrode for symmetric solid oxide fuel cells (SSOFC). Results show that with the combination of GDC, the maximum power density of YSZ-based SSOFC enlarges from 232.3 mW cm^?2 to 348.5 mW cm^?2, and related polarization resistance reduces from 0.359 Ω cm² to 0.108 Ω cm². The improved performance is attributed to the enlarged triple-phase boundary with the mixing of GDC. In addition, YSZ-based SSOFC with the LSFN-GDC composite electrode shows a stable performance in intermediate-temperature SSOFCs within 200 h, which indicates that LSFN-GDC composite material is a prospective symmetrical electrode for SSOFC.     

A novel approach to analyse incomplete design of experiments – Application to the study of the influence of operational parameters on the performance of a solid oxide fuel cell based micro-combined heat and power system

A SOFC based commercial μ-CHP system is characterized by Electrochemical Impedance Spectroscopy, using a 2⁴ full factorial test plan. The studied factors are: natural gas input power, ratio between oxygen and natural gas flow rates at the reformer inlet, stack average temperature and average operating cell voltage. Six replicates are performed in the domain centre. We performed equivalent circuit analysis and extracted three responses from each spectrum: ohmic resistance together with the two parameters of the CPE used in the model.However, one of our experiment is an outlier. To circumvent this problem, two methods described in the literature were applied: recalculation of missing response and introduction of a dynamic variable. Due their unsatisfactory results, we developed an innovative approach combining an iterative fitting of the multilinear model underlying any factorial design and an N-way ANOVA. Our method is successfully validated on the different 2⁴⁻¹ fractional designs deriving from the full factorial one.The only impacted response is the ohmic resistance. It increases as temperature decreases or as applied voltage increases. It is impacted by a strong synergistic effect of pressure and temperature and a compensating effect of pressure and applied voltage. No significant quadratic effect is observed.     

Investigation of the Fe doping effect on the B-site of the layered perovskite PrBa0.8Ca0.2Co2O5+δ for a promising cathode material of the intermediate-temperature solid oxide fuel cells

Layered perovskites can be considered as promising cathode materials for intermediate-temperature solid oxide fuel cell because of their fast oxygen kinetics compared to simple perovskites. Among them, the cobalt-based layered perovskites are considered as very promising cathode materials due to its high conductivity and fast oxygen kinetics, but they are unstable under operating condition. Doping other transition metal such as Fe, Mn, Cu, and Ni can be considered to solve the instability of the cobalt-based layered perovskites.In this paper, we investigated Fe doped cobalt-based layered perovskite, PrBa_0.8Ca_0.2Co_2-xFe_xO_5+δ (x = 0, 0.5, and 1.0), as prospective cathode materials in terms of their crystal structures, thermal expansion behavior, electro- and electro-chemical properties. The PrBa_0.8Ca_0.2Co_1.5Fe_0.5O_5+δ shows improved maximum power density of 1.89 W cm⁻² and polarization resistance of 0.080 Ω cm² at 600 °C as compared with un-doped PrBa_0.8Ca_0.2Co₂O_5+δ while maintaining suppressed thermal expansion. Based on these results, PrBa_0.8Ca_0.2Co_1.5Fe_0.5O_5+δ can be considered as a promising cathode material for intermediate-temperature solid oxide fuel cell.     

Evaluation of the thermal and structural stability of planar anode-supported solid oxide fuel cells using a 10 × 10 cm2 single-cell test

The present work investigated the thermal and structural stability of planar anode-supported solid oxide fuel cells (SOFCs) using a 10 × 10 cm² single-cell test. First, the gasket study was performed in which the sealing efficiency and hydrodynamics were examined to obtain the control parameters for sealing design. Two types of high-temperature gaskets were evaluated for application in the SOFC test, both with sealing efficiencies over 99.99%; both of them did not ensure the gas tightness perfectly, and we selected the fuel cell material gasket due to a lower leak factor than the Magnex gasket at whole inlet flow rates. After this gasket sealing test, the thermal and structural stability of a planar anode-supported SOFC was evaluated by changing temperature repeatedly between room temperature and 850 °C. For the first high flow test, the open circuit voltage (OCV) agreed with the theoretical value, and the voltage decreased linearly as the current density increased. In addition, the measured temperature distribution had a similar trend compared with the previous numerical analysis during the first reduction condition. However, after lowering the temperature and raising it again, the OCV during the second low flow test decreased and fuel crossover loss occurred; additionally, the voltage decreased irregularly as the current density increased. After completing the tests and dissembling the single cell specimen, the cracked mark was placed in the center of the cell like the calculated and measured results. From the dispersed oxygen contents in the anode using scanning electron microscope (SEM) and energy dispersive X-ray (EDX) spectroscopy, we concluded that the crack was induced by the reduction and oxidation (RedOx) cycle instability from even a small leakage through the gasket. Finally, we found that the planar SOFC was vulnerable to the thermal RedOx cycle induced by non-perfect sealing, and it was confirmed that the requirement of the gas tightness should be fulfilled in order to obtain the longer life and the higher stability for the solid oxide fuel cell.     

Effects of PdO modification on the performance of La0.6Sr0.4Co0.2Fe0.8O3−δ cathodes for solid oxide fuel cells: A first principle study

Effects of palladium (Pd) impregnation on the performance of La_0.6Sr_0.4Co_0.2Fe_0.8O_3?δ (LSCF) cathodes are investigated with density functional theory plus U (DFT + U) and experimental methods. In-situ high temperature X-ray diffractometer results show that the impregnated Pd species exist at states of palladium oxide (PdO) at 700 °C. The measured electrochemical impedance spectroscopy at 700 °C indicates PdO modification promotes the catalytic activity of LSCF cathodes. The modification structure of PdO on LSCF surfaces and effects of PdO modification on the performance of LSCF cathodes are investigated with DFT + U methods. The results show that B-8 with PdO molecule modification by a parallel posture on LSCF surface is the most stable structure. O₂ prefers to be adsorbed on AO-terminated surfaces rather than that on BO₂-terminated ones. The oxygen surface adsorption activity of LSCF surface is improved by PdO modification. The calculated partial densities of states (PDOS) and Fermi level of O₂ adsorption on LSCF surfaces imply that the charge transfer is easier with PdO modification than that without PdO modification because PdO acts as a metal-like modification. The PdO modification on LSCF surface leads to a better oxygen surface adsorption activity of LSCF cathodes.     

Which is the preferable biogas utilisation technology for anaerobic digestion of agricultural crops in Ireland: Biogas to CHP or biomethane as a transport fuel?

The utilisation of anaerobic digestion to produce biogas as an energy source is a mature technology in many European countries but is yet to be developed in Ireland. In 2009, the EU issued the Renewable Energy Source Directive 2009/28/EC which requires a 20% share of renewable energy sources (heat and electricity) in final energy consumption for all member states, respectively, including a 10% share of biofuels in the transport sector by 2020. The introduction of biogas to produce power and electricity in the form of CHP technology and biomethane as a transport fuel can help Ireland achieve the mandatory targets set by the directive. The key focus of the paper is to determine the optimum small to medium scale biogas technology and the impact the introduction of that technology infrastructure will have on renewable energy targets for Ireland. In terms of feedstock, agricultural sources such as energy crops and slurry offer a sustainable input to the anaerobic digestion process. The crop rotations under consideration consist of different arrangements of grass silage, maize silage and barley. Grass silage is found to be the most suitable crop for biogas energy production while biogas upgrading to biomethane as a transport fuel has the optimum technology potential in Ireland. To fuel a car operating on biomethane, 0.22 ha of grass land is required annually. Full scale national development of 5% of the area under grass in Ireland will contribute 11.4% of renewable energy to the total final transport energy demand by 2020, surpassing the target set by the Renewable Energy Source Directive 2009/28/EC.     

Electricity production from lignocellulosic biomass by direct coupling of a gasifier and a Nickel/Yttria-stabilized Zirconia-based solid oxide fuel cell. Part 1: From gas production to direct electricity production

This work presents the direct coupling of a gasification pilot according to the patented concept by S3D Company and of a Ni-YSZ-based SOFC. The composition of gas issued from the gasifier is rather stable, with H₂ ≈ 15%, CO ≈ 15%, CH₄ ≈ 1%, CO₂ ≈ 20% and N₂ ≈ 49%. Before injecting directly the gas on the cell, a preliminary test of the home-made cell consisting of an industrial Fiaxell Nickel/Yttria-stabilized Zirconia-based anode-electrolyte assembly covered by praseodymium nickelate oxide was performed with H₂N₂ mixtures. The cell is tested at 750 °C and 850 °C, with a maximum power density of 1.4 W cm^?2 at 850 °C when fueled with a 76%–24% H₂Ar mixture. The effect of the dilution of the gas is also studied, and validates the use of a bag containing the gas issued from the gasifier. In these conditions, using exclusively the fuel issued from biomass, without any additional purification steps, maximum power densities of 340 mW cm^?2 and 113 mW cm^?2 can be obtained at 850 °C and 750 °C respectively.     

Evaluating the impact of the administrative procedure and the landscape policy on grid connected PV systems (GCPVS) on-floor in Spain in the period 2004–2008: To which extent a limiting factor?

The growth of the Spanish photovoltaic (PV) sector in the period 2004–2008 rendered Spain a prominent place among top worldwide countries. Yet, this growth was rather uneven across the different Spanish regions which raised the interest on the drivers ultimately effecting these disparities. Especially controversial were the arguments about the influence of the administrative procedure and the landscape policy on the development of GCPVS on-floor. This study therefore discloses both two elements and evaluates their impact in a group of PV prominent Spanish regions and Catalonia, the latter used as a benchmark because of its comprehensive and stringent regulation on landscape protection, which was accused by the PV industry of thwarting the development of the GCPVS on-floor. Both quantitative and qualitative analyses were carried out. In particular two indexes were elaborated to determine the consistency of the arguments pointing to the landscape protection policy as a decisive barrier to GCPVS growth. First, when the analysis is made in relative terms, the ranking of PV prominent regions changes and many of the differences vanish. Second, rather than the preeminence of a landscape protection policy what really matters for GCPVS on-floor growth is the administrative procedure and the processing enabling its implementation.     

Renewable energy strategies for rural Africa: is a PV-led renewable energy strategy the right approach for providing modern energy to the rural poor of sub-Saharan Africa?

Rural areas continue to be home to majority of the population in Africa. The importance of providing modern energy to rural areas cannot, therefore, be overemphasised. Despite numerous efforts by Governments and donors in the region to promote solar photovoltaics (PVs) for rural electrification (almost every country in the region has had a rural electrification PV project), access to modern energy in rural Africa continues to be woefully low. In addition to being unaffordable to the rural masses, solar PV has the limitation that it can only be used for lighting and powering low-voltage appliances. This article reviews emerging trends in the rural energy sector of sub-Saharan Africa, and discusses the limitations of over-reliance on solar PV. It suggests possible options that could have greater impact on rural clean energy development. For the majority of rural households in the region, biomass fuels will continue to be the dominant fuel of choice. Efficient technologies for the use of biomass would, therefore, ensure that scarce biomass resources are effectively utilised, and reduce the negative impacts of biomass use on women and children's health. Solar thermal, windpumps, micro-/pico-hydropower and cleaner fuels such as kerosene and LPG, have not received adequate attention from policy makers. These energy options could significantly improve the performance of rural small- and micro-enterprises. This article argues that rural energy policies that emphasise a broader range of renewables and target income-generating activities are likely to yield greater benefits to the rural poor than the current policies that rely on the solar PV option.