To prevent undesirable reactions between the cathode and electrolyte materials in cathode-supported solid oxide fuel cells (SOFCs), the co-sintering temperature of these two layers must be lowered. In the present work, we employed different strategies to lower the co-sintering temperature of cathode–electrolyte bilayers for micro-tubular SOFCs by increasing the cathode sintering shrinkage and adding sintering aids to the electrolyte. Strontium-doped lanthanum manganite (LSM) and yttria-stabilized zirconia (YSZ) were used as the cathode and electrolyte materials, respectively. To facilitate densification of the electrolyte layer by controlling the shrinkage of the cathode support, the particle size of the LSM powder was reduced by high-energy ball milling and different amounts of micro-crystalline cellulose pore former were used. Sintering aids, namely NiO and Fe2O3, were also added to the YSZ electrolyte to further improve its low-temperature sintering. Our results indicate that with the improvement in the cathode support shrinkage and use of the small amounts of sintering aids, the cathode–electrolyte co-sintering temperature can be reduced to 1250–1300 °C. It was also observed that the presence of the sintering aids helps to reduce the reactivity between the LSM cathode and YSZ electrolyte.
Click here to access the full article published in Ceramics International.
Wednesday, May 24, 2017
Thursday, August 25, 2016
Direct methane operation of a micro-tubular solid oxide fuel cell with a porous zirconia support
A novel
micro-tubular solid oxide fuel cell (SOFC) design with an inert support was
proposed for operation on direct hydrocarbon fuels with an improved stability.
In this design, the inert support also serves as a diffusion barrier between
the fuel stream and Ni cermet anode. The barrier effect leads to higher local
steam to carbon ratios in the anode, thus inhibiting carbon deposition. To
demonstrate this concept, we fabricated micro-tubular SOFCs with a porous
yttria-stabilized zirconia (YSZ) support. Ni, Ni-scandia-stabilized zirconia
(ScSZ), ScSZ, strontium-doped lanthanum manganite (LSM)–ScSZ, and LSM were used
as the anode current collector, anode, electrolyte, cathode, and cathode
current collector, respectively. Good electrochemical performance was achieved
with hydrogen and methane fuels in a temperature range 600–750 °C. Continuous
cell operation on direct methane fuel for >40 h at 750 °C under moderate
current densities delivered stable voltage without any evident performance
degradation due to carbon deposition. The absence of carbon deposition on the
anode and anode current collector layers was also confirmed by scanning
electron microscope images and energy-dispersive X-ray spectra. We further
discuss oxidation mechanism of the direct methane fuel and removal of the
carbon possibly formed in the anodic layers during stability testing.
Click here to access the full article published in Journal of Solid State Electrochemistry.
Friday, November 6, 2015
Fabrication and Evaluation of a Micro-Tubular Solid Oxide Fuel Cell with an Inert Support Using Scandia-Stabilized Zirconia Electrolyte
We have proposed a
novel micro-tubular solid oxide fuel cell (SOFC) design with an inert support
and an integrated current collector for the inner electrode to improve current
collection efficiency as well as reduction–oxidation stability of the cell. In
this work, a micro-tubular SOFC based on the proposed design was fabricated
using scandia-stabilized zirconia (ScSZ) as electrolyte owing to its high ionic
conductivity over a wide range of temperatures. Yttria-stabilized zirconia
(YSZ), Ni, Ni-ScSZ, strontium-doped lanthanum manganite (LSM)–ScSZ, and LSM
were used as the inert support, anode current collector, anode, cathode, and
cathode current collector, respectively. The electrochemical performance of the
fabricated cell was evaluated at temperatures between 600 and 850°C. Because of
the lower ohmic resistance across its components, the cell exhibited good power
generation performance at high and intermediate temperatures. Additionally, we
confirmed stable operation of the micro-tubular SOFC for over 60 h at 750°C.
Wednesday, August 5, 2015
Performance improvement and redox cycling of a micro-tubular solid oxide fuel cell with a porous zirconia support
The performance of a novel micro-tubular solid oxide fuel cell (SOFC) with an inert support and an integrated current collector for the inner electrode was improved by controlling its microstructural features. Multi-step dip coating and co-sintering methods were used to fabricate the cell containing porous yttria-stabilized zirconia (YSZ), Ni, Ni–YSZ, YSZ, strontium-doped lanthanum manganite (LSM)–YSZ, and LSM as the inert support, anode current collector, anode, electrolyte, cathode, and cathode current collector, respectively. To enhance gas diffusion through the YSZ support by properly tailoring its porosity, a combination of micro-crystalline cellulose and polymethyl methacrylate pore formers was used. Additionally, the porosity of the Ni current collector was improved and the LSM–YSZ cathode was sufficiently thick for high oxygen reduction activity. Owing to its optimized microstructure, the micro-tubular SOFC delivered excellent power output with maximum power densities of 710, 591, 445, and 316 mW cm−2 at 850, 800, 750, and 700 °C, respectively. The effect of redox cycling on cell performance was investigated by alternately exposing the anode to fuel and air atmospheres. The cell had good tolerance toward the redox phenomenon with no apparent degradation in its performance up to 10 redox cycles.
Click here to access the full article published in International Journal of Hydrogen Energy.
A previous work related to the above study has been published in Scientific Reports:
Click here to access the full article published in International Journal of Hydrogen Energy.
A previous work related to the above study has been published in Scientific Reports:
Saturday, March 8, 2014
A novel multistep dip-coating method for the fabrication of anode-supported microtubular solid oxide fuel cells
A novel multistep dip-coating method was developed and successfully applied to the fabrication of anode-supported microtubular solid oxide fuel cells (SOFCs) using carbon rods as combustible cores. The fabricated microtubular SOFCs consisted of Ni-yttria-stabilized zirconia (YSZ), YSZ, strontium-doped lanthanum manganite (LSM)-YSZ, and LSM as the anode, electrolyte, cathode, and cathode current collector materials, respectively. To investigate the role of anode porosity on cell performance, two types of anode supports were prepared: one without a pore former and the other with a 10 wt.% graphite pore former. The microstructural features of the microtubular SOFCs were examined using scanning electron microscope images whereas the electrochemical performance was characterized by electrochemical impedance spectroscopy measurements as well as I-V characteristic curves. The results showed that the method used is a simple and low-cost alternative to conventional methods for the fabrication of microtubular SOFCs. We found that the anode porosity played an important role in improving the overall performance of the microtubular SOFC by reducing the concentration polarization.
Click here to access the full article published in Journal of Solid State Electrochemistry.
Click here to access the full article published in Journal of Solid State Electrochemistry.
Monday, August 13, 2012
Performance enhancement of strontium-doped lanthanum manganite cathode by developing a highly porous microstructure
Abstract from the article published in Journal of Applied Electrochemistry
A simple and promising template method was applied for the development of a highly porous microstructure, referred to as a macroporous structure (having pore size >50 nm), for a solid oxide fuel cell strontium-doped lanthanum manganite (LSM) cathode. Using poly(methyl methacrylate) beads of 2.9 μm size as the pore-forming templates, a porosity value of ca. 63 % was achieved. The electrochemical performance of the developed macroporous cathode was evaluated by measuring electrochemical impedance spectra of the symmetrical cells as well as power density of the full cells. The results indicated that due to enhanced oxygen diffusion and reaction kinetics, the macroporous structure was effective in reducing the interfacial polarization resistance of the LSM cathode and hence attaining a higher cell performance.
The full article can be accessed from here. Happy reading! :)
Saturday, May 14, 2011
Fuel cells for future power generation: A Nepalese perspective
[Originally published in NEA-JC Newsletter (Year 4, Issue 2) (pp. 15-16)]
It has now become a well accepted scientific fact that human activities, particularly the burning of fossil fuels, are responsible for the greenhouse effect in the earth’s atmosphere resulting in global warming and climate change. Moreover, the reserve of fossil fuels itself is depleting continuously thereby making the issue of energy security more critical. Thus, there has been an urgent need to come up with the alternatives to the existing fossil-based energy systems. In order to address the environmental as well as energy security concerns, deployment of new energy conversion systems with higher efficiency and widespread exploitation of renewable energy resources seem indispensable. Fuel cell technology is expected to play a vital role in this regard.
What is a fuel cell?
A fuel cell is an electrochemical device that generates electricity directly from the chemical energy in fuels. The fuel generally used is hydrogen; however, depending upon the type of fuel cell, hydrocarbon fuels can also be used. When hydrogen is used as fuel, what happens inside a fuel cell is essentially the reverse process of electrolysis. In electrolysis, water molecules split into hydrogen and oxygen molecules by consuming electricity whereas in fuel cell reaction, hydrogen and oxygen molecules combine to produce water and electricity. In other words, fuel cells are batteries running on the continuous supply of fuel and oxidant (pure oxygen or air). Unlike conventional power generation systems, fuel cells do not involve intermediate conversion of chemical energy to thermal and mechanical energies. Consequently, of all the existing energy conversion systems, fuel cells offer the highest efficiency along with the lowest levels of pollutant emissions.
Nepal’s case
Being a developing country where majority of the population relies on subsistence farming in rural areas, per capita energy consumption of Nepal is one of the lowest in the world. According to the Economic Survey of the Ministry of Finance [1], total energy consumed in the fiscal year 2008/09 was reported to be 9,396 thousand Tons of Oil Equivalent (TOE) (where 1 TOE = 42 GJ), 87.1% of which was obtained from traditional sources comprising fuel wood, agricultural residues and livestock residues. Figure 1 summarizes the share of different energy sources used in Nepal in the fiscal year 2008/09 [1].
Although current energy supply is dominated by traditional sources, with the growing trend of urbanization and industrialization, commercial sources are becoming more important. In 1988, the share of commercial sources in total energy consumption was only 5.2% [2], which has been more than double by now. As Nepal does not have any commercially exploitable fossil fuel reserves, the only domestic source of commercial energy is the electricity generated from hydroelectric power plants. In fact, Nepal is known for its tremendous potential for hydroelectricity, thanks to more than 6,000 rivers flowing from the high mountains in north to the plain land in south. Total hydropower potential of Nepal is estimated to be 83,000 MW, of which 42,000 MW is considered technically and economically feasible [3]. Unfortunately a very small portion of the total potential (<1%) has been harnessed so far.
As of the fiscal year 2008/09 data, Nepal’s total installed capacity for electricity generation was 714 MW, of which 661 MW was shared by hydroelectricity [1]. This installed capacity, however, was not sufficient to meet the customer demand. Annual Report of the Nepal Electricity Authority [4] shows that the annual electricity demand for the fiscal year 2009/10 was recorded 4367.13 GWh whereas domestic generation could supply only 3076.69 GWh. This resulted in up to 12 hours of rolling blackouts a day in the country. While such mismatch in demand and supply is primarily due to lack of enough installed capacity, poor load factor of the installed plants is also equally responsible. Most of the hydroelectric plants in Nepal are based on run-of-the-river scheme giving rise to significant fluctuation in the actual electricity generation in wet and dry seasons. Moreover, there exist significant diurnal variations in the supply to demand ratio.
Considering the above scenario, Ale and Shrestha [5] proposed to utilize the surplus power from hydroelectric plants in wet season and off-peak hours to produce hydrogen by electrolysis which could be subsequently used to substitute the existing fossil fuels in transportation, cooking, etc and also to meet the peak demands by converting hydrogen back to electricity with the help of fuel cells. Their study showed that 27,000 tons to 140,000 tons of hydrogen could be produced annually by utilizing the surplus energy from hydropower at 20% and 100%, respectively by 2020. Moreover, it suggested that it is financially lucrative to invest on new hydropower plants for producing hydrogen in order for the complete replacement of petroleum products considering the revenue generated from Clean Development Mechanism (CDM), electricity sale and saving on fuel import. Ale and Shrestha [6] also looked into the possibility of using hydrogen produced from hydropower surplus to replace the fossil fuel based transportation system in Kathmandu valley and concluded that all the vehicles in the valley can be powered by hydrogen produced from only 50% of the surplus energy by 2020. Thus, hydropower is the one potential sector where Nepal can get benefitted by adopting hydrogen and fuel cell technologies.
Furthermore, fuel cells can play a key role in the effective utilization of intermittent renewable energy sources such as solar and wind. Nepal’s total solar energy potential is estimated to be as high as 26.6 million MW [7] as there are about 300 sunny days a year with an average solar radiation of 3.6 –6.2 kWh/m2/day [8]. On the other hand, wind energy potential of Nepal is anticipated to be more than 3,000 MW [9]. However, both solar and wind energy systems need high capacity energy storage mediums to supply stable power. Therefore, production of hydrogen as an intermediate energy carrier and subsequent conversion of hydrogen to electricity is a possible approach for such renewable energy facilities in future.
Another renewable energy source, biomass also offers possibilities for the application of fuel cells. Though traditional biomass sources like firewood are infamous for their adverse impact on environment and human health, modern forms of biomass energy such as biogas, gasifier gas and biofuels are viewed as sustainable alternatives. The potential of biogas production in Nepal is estimated to be around 12,000 million m3 per year which is equivalent to 29 million GJ [10]. Gasifier gas which is obtained from the thermochemical conversion of solid biomass [11], and different kinds of liquid biofuels such as bioethanol [12] and Jatropha (Sajiwan) oil [13] also show good prospects in Nepal. As certain kinds of fuel cells such as the Solid Oxide Fuel Cell (SOFC) can run on direct hydrocarbon fuels, these biomass sources (with minimum processing) can be fed to fuel cells to generate electric power with high efficiency and minimum emissions.
To sum up, fuel cells can be expected to find their applications in several sectors in Nepal. Deployment of hydrogen and fuel cell technologies will help not only to produce clean and sustainable power but also to reduce country’s over-dependence on imported petroleum products.
References
[1] Economic Survey: Fiscal Year 2009/10, Ministry of Finance, Kathmandu, Jul. 2010.
[2] S. Pokharel, “An econometric analysis of energy consumption in Nepal,” Energ. Policy, vol. 35, pp. 350–361, 2007.
[3] H. M. Shrestha, “Cadastre of hydropower resources,” Ph.D. dissertation, Moscow Power Inst., Moscow, 1966.
[4] A Year in Review: Fiscal Year 2009/10, Nepal Electricity Authority, Kathmandu, 2010.
[5] B. B. Ale and S. O. Bade Shrestha, “Hydrogen energy potential of Nepal,” Int. J. Hydrogen Energ., vol. 33, pp. 4030–4039, 2008.
[6] B. B. Ale and S. O. Bade Shrestha, “Introduction of hydrogen vehicles in Kathmandu Valley: A clean and sustainable way of transportation,” Renew. Energ., vol. 34, pp. 1432–1437, 2009.
[7] Energy Sector Synopsis Report – 1992/93, Water and Energy Commission Secretariat, Kathmandu, 1994.
[8] Economic Survey: Fiscal Year 2001/2002, Ministry of Finance, Kathmandu, Jul. 2002.
[9] Achievements in Wind Energy (2011, Apr. 18). [Online]. Available: http://www.aepc.gov.np/index.php?option=com_content&view=article&id=167&Itemid=173
[10] Energy Synopsis Report – 1994/95, Water and Energy Commission Secretariat, Kathmandu, 1996.
[11] Biomass Gasification for Thermal Application and Electricity (2011, Apr. 18). [Online]. Available: http://www.redp.org.np/phase3/latestupdates/news.php?n=5
[12] D. Khatiwada and S. Silveira, “Net energy balance of molasses based ethanol: The case of Nepal,” Renew. Sustain. Energ. Rev., vol. 13, pp. 2515–2524, 2009.
[13] Biodiesel in Nepal (2011, Apr. 18). [Online]. Available: http://www.nepalitimes.com/issue/2006/09/08/Nation/12461
It has now become a well accepted scientific fact that human activities, particularly the burning of fossil fuels, are responsible for the greenhouse effect in the earth’s atmosphere resulting in global warming and climate change. Moreover, the reserve of fossil fuels itself is depleting continuously thereby making the issue of energy security more critical. Thus, there has been an urgent need to come up with the alternatives to the existing fossil-based energy systems. In order to address the environmental as well as energy security concerns, deployment of new energy conversion systems with higher efficiency and widespread exploitation of renewable energy resources seem indispensable. Fuel cell technology is expected to play a vital role in this regard.
What is a fuel cell?
A fuel cell is an electrochemical device that generates electricity directly from the chemical energy in fuels. The fuel generally used is hydrogen; however, depending upon the type of fuel cell, hydrocarbon fuels can also be used. When hydrogen is used as fuel, what happens inside a fuel cell is essentially the reverse process of electrolysis. In electrolysis, water molecules split into hydrogen and oxygen molecules by consuming electricity whereas in fuel cell reaction, hydrogen and oxygen molecules combine to produce water and electricity. In other words, fuel cells are batteries running on the continuous supply of fuel and oxidant (pure oxygen or air). Unlike conventional power generation systems, fuel cells do not involve intermediate conversion of chemical energy to thermal and mechanical energies. Consequently, of all the existing energy conversion systems, fuel cells offer the highest efficiency along with the lowest levels of pollutant emissions.
Nepal’s case
Being a developing country where majority of the population relies on subsistence farming in rural areas, per capita energy consumption of Nepal is one of the lowest in the world. According to the Economic Survey of the Ministry of Finance [1], total energy consumed in the fiscal year 2008/09 was reported to be 9,396 thousand Tons of Oil Equivalent (TOE) (where 1 TOE = 42 GJ), 87.1% of which was obtained from traditional sources comprising fuel wood, agricultural residues and livestock residues. Figure 1 summarizes the share of different energy sources used in Nepal in the fiscal year 2008/09 [1].
 |
| Figure 1. Share of energy sources in Nepal: (a) contribution in total consumption; (b) breakdown of traditional sources; (c) breakdown of commercial sources. |
Although current energy supply is dominated by traditional sources, with the growing trend of urbanization and industrialization, commercial sources are becoming more important. In 1988, the share of commercial sources in total energy consumption was only 5.2% [2], which has been more than double by now. As Nepal does not have any commercially exploitable fossil fuel reserves, the only domestic source of commercial energy is the electricity generated from hydroelectric power plants. In fact, Nepal is known for its tremendous potential for hydroelectricity, thanks to more than 6,000 rivers flowing from the high mountains in north to the plain land in south. Total hydropower potential of Nepal is estimated to be 83,000 MW, of which 42,000 MW is considered technically and economically feasible [3]. Unfortunately a very small portion of the total potential (<1%) has been harnessed so far.
As of the fiscal year 2008/09 data, Nepal’s total installed capacity for electricity generation was 714 MW, of which 661 MW was shared by hydroelectricity [1]. This installed capacity, however, was not sufficient to meet the customer demand. Annual Report of the Nepal Electricity Authority [4] shows that the annual electricity demand for the fiscal year 2009/10 was recorded 4367.13 GWh whereas domestic generation could supply only 3076.69 GWh. This resulted in up to 12 hours of rolling blackouts a day in the country. While such mismatch in demand and supply is primarily due to lack of enough installed capacity, poor load factor of the installed plants is also equally responsible. Most of the hydroelectric plants in Nepal are based on run-of-the-river scheme giving rise to significant fluctuation in the actual electricity generation in wet and dry seasons. Moreover, there exist significant diurnal variations in the supply to demand ratio.
Considering the above scenario, Ale and Shrestha [5] proposed to utilize the surplus power from hydroelectric plants in wet season and off-peak hours to produce hydrogen by electrolysis which could be subsequently used to substitute the existing fossil fuels in transportation, cooking, etc and also to meet the peak demands by converting hydrogen back to electricity with the help of fuel cells. Their study showed that 27,000 tons to 140,000 tons of hydrogen could be produced annually by utilizing the surplus energy from hydropower at 20% and 100%, respectively by 2020. Moreover, it suggested that it is financially lucrative to invest on new hydropower plants for producing hydrogen in order for the complete replacement of petroleum products considering the revenue generated from Clean Development Mechanism (CDM), electricity sale and saving on fuel import. Ale and Shrestha [6] also looked into the possibility of using hydrogen produced from hydropower surplus to replace the fossil fuel based transportation system in Kathmandu valley and concluded that all the vehicles in the valley can be powered by hydrogen produced from only 50% of the surplus energy by 2020. Thus, hydropower is the one potential sector where Nepal can get benefitted by adopting hydrogen and fuel cell technologies.
Furthermore, fuel cells can play a key role in the effective utilization of intermittent renewable energy sources such as solar and wind. Nepal’s total solar energy potential is estimated to be as high as 26.6 million MW [7] as there are about 300 sunny days a year with an average solar radiation of 3.6 –6.2 kWh/m2/day [8]. On the other hand, wind energy potential of Nepal is anticipated to be more than 3,000 MW [9]. However, both solar and wind energy systems need high capacity energy storage mediums to supply stable power. Therefore, production of hydrogen as an intermediate energy carrier and subsequent conversion of hydrogen to electricity is a possible approach for such renewable energy facilities in future.
Another renewable energy source, biomass also offers possibilities for the application of fuel cells. Though traditional biomass sources like firewood are infamous for their adverse impact on environment and human health, modern forms of biomass energy such as biogas, gasifier gas and biofuels are viewed as sustainable alternatives. The potential of biogas production in Nepal is estimated to be around 12,000 million m3 per year which is equivalent to 29 million GJ [10]. Gasifier gas which is obtained from the thermochemical conversion of solid biomass [11], and different kinds of liquid biofuels such as bioethanol [12] and Jatropha (Sajiwan) oil [13] also show good prospects in Nepal. As certain kinds of fuel cells such as the Solid Oxide Fuel Cell (SOFC) can run on direct hydrocarbon fuels, these biomass sources (with minimum processing) can be fed to fuel cells to generate electric power with high efficiency and minimum emissions.
To sum up, fuel cells can be expected to find their applications in several sectors in Nepal. Deployment of hydrogen and fuel cell technologies will help not only to produce clean and sustainable power but also to reduce country’s over-dependence on imported petroleum products.
References
[1] Economic Survey: Fiscal Year 2009/10, Ministry of Finance, Kathmandu, Jul. 2010.
[2] S. Pokharel, “An econometric analysis of energy consumption in Nepal,” Energ. Policy, vol. 35, pp. 350–361, 2007.
[3] H. M. Shrestha, “Cadastre of hydropower resources,” Ph.D. dissertation, Moscow Power Inst., Moscow, 1966.
[4] A Year in Review: Fiscal Year 2009/10, Nepal Electricity Authority, Kathmandu, 2010.
[5] B. B. Ale and S. O. Bade Shrestha, “Hydrogen energy potential of Nepal,” Int. J. Hydrogen Energ., vol. 33, pp. 4030–4039, 2008.
[6] B. B. Ale and S. O. Bade Shrestha, “Introduction of hydrogen vehicles in Kathmandu Valley: A clean and sustainable way of transportation,” Renew. Energ., vol. 34, pp. 1432–1437, 2009.
[7] Energy Sector Synopsis Report – 1992/93, Water and Energy Commission Secretariat, Kathmandu, 1994.
[8] Economic Survey: Fiscal Year 2001/2002, Ministry of Finance, Kathmandu, Jul. 2002.
[9] Achievements in Wind Energy (2011, Apr. 18). [Online]. Available: http://www.aepc.gov.np/index.php?option=com_content&view=article&id=167&Itemid=173
[10] Energy Synopsis Report – 1994/95, Water and Energy Commission Secretariat, Kathmandu, 1996.
[11] Biomass Gasification for Thermal Application and Electricity (2011, Apr. 18). [Online]. Available: http://www.redp.org.np/phase3/latestupdates/news.php?n=5
[12] D. Khatiwada and S. Silveira, “Net energy balance of molasses based ethanol: The case of Nepal,” Renew. Sustain. Energ. Rev., vol. 13, pp. 2515–2524, 2009.
[13] Biodiesel in Nepal (2011, Apr. 18). [Online]. Available: http://www.nepalitimes.com/issue/2006/09/08/Nation/12461
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