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.

Click here to access the full article published in Journal of The Electrochemical Society.

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:

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.

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].

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.  

[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:
[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:
[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:

Friday, December 17, 2010

Different types of fuel cells: which one will dominate the future?

Fuel cells are classified based on the electrolyte material they use – i) alkaline fuel cell (AFC), ii) phosphoric acid fuel cell (PAFC), iii) polymer electrolyte fuel cell (PEFC), iv) molten carbonate fuel cell (MCFC), and v) solid oxide fuel cell (SOFC). Besides, there are a couple of fuel cells which take their names from the fuel used, e.g. direct alcohol/methanol fuel cell (DAFC/DMFC) and direct carbon fuel cell (DCFC). In fact, DAFCs/DMFCs represent a special subcategory of PEFCs whereas DCFCs refer to the conceptual fuel cells (usually MCFCs or SOFCs) which make use of solid carbon fuel such as coal and biomass directly without an intermediate gasification step.

Here is an overview of the different types of fuel cells:

Alkaline fuel cell (AFC)

Electrolyte: Potassium hydroxide (KOH) solution retained in an asbestos matrix
Electrodes: Transition metals loaded with platinum or other electro-catalysts
Fuel: Hydrogen
Operating temperature: 65-220 deg. C
Electrical efficiency: ~60%
Applications: Military, space

- Superior cathode reaction kinetics
- Quick start-up due to low temperature operation
- Low weight and volume

- Extremely intolerant to carbon dioxide (as a result pure oxygen or the air free of carbon dioxide should be used as the oxidant)
- Electrolyte handling problems
- Relatively short lifetime

AFCs are widely known for space applications since their first use in NASA’s Apollo program in 1965. However, terrestrial applications of AFCs seem too costly due to the strict requirement of CO2-free fuel and oxidant. As a result, R&D work on AFCs has gone down in recent years.

Phosphoric acid fuel cell (PAFC)

Electrolyte: Liquid phosphoric acid soaked in a silicon carbide (SiC) matrix
Electrodes: Carbon loaded with platinum
Fuel: Hydrogen
Operating temperature: 150-220 deg. C
Electrical efficiency: ~40%
Applications: Distributed power generation

- Less sensitive to CO poisoning than PEFC and AFC
- Waste heat can be utilized in combined heat and power (CHP) applications/bottoming Rankine (steam turbine) cycle

- Corrosive nature of electrolyte which necessitates the use of expensive materials in the stack
- Poor operating reliability in the long term

PAFC represents the first fuel cell technology that was developed commercially and is still the only commercially available one. Over 250 units of PC-25, a 200 kW PAFC system developed by UTC Fuel Cells, are reported to have been sold and installed in different countries around the world since the early 1990s. Despite the success PAFCs achieved, interest in them started declining in the late 1990s mainly owing to their high cost coupled with insufficient operating reliability in the long-term.

Polymer electrolyte fuel cell (PEFC)
(Also known as proton exchange membrane/polymer electrolyte membrane (PEM) fuel cell (PEMFC))

Electrolyte: Fluorinated sulfonic acid polymer (commonly Nafion)
Electrodes: Carbon loaded with platinum
Fuel: Pure hydrogen
Operating temperature: 40-80 deg. C
Electrical efficiency: 40-60%
Applications: Automotive systems, portable applications, small scale distributed power

- No corrosion and electrolyte management problems
- Quick start-up due to low temperature operation
- High power density (over 2 kW/l and 2 W/cm2)

- Highly sensitive to impurities of hydrogen (does not tolerate >50 ppm of CO and has a low tolerance to sulfur particles and ammonia)
- Difficulty in water management ensuring sufficient hydration of the electrolyte membrane against flooding

With the availability of more stable proton exchange membranes such as Nafion (1960s) and the development of modern membrane electrode assembly (MEA) with reduced catalyst loadings (mid-1980s), PEFC technology has become potentially attractive especially for automotive applications. However, further reduction in system cost (such as the development of non-platinum catalysts and cheaper membranes) as well as improvement in long-term performance (mainly CO tolerance) is imperative in order to penetrate the markets.

Molten carbonate fuel cell (MCFC)

Electrolyte: Mixture of molten carbonate salts (lithium carbonate + potassium carbonate/sodium carbonate) retained in a ceramic matrix (LiAlO2)
Electrodes: Nickel (anode) and nickel oxide (cathode)
Fuel: Hydrogen, CO, methane, etc
Operating temperature: 600-700 deg. C
Electrical efficiency: ~60%
Applications: Electric utility, large scale distributed power

- No need of expensive electro-catalysts
- Fuel flexibility (spontaneous internal reforming of hydrocarbon fuels)
- High grade waste heat (suitable for CHP applications/bottoming cycles)

- Very corrosive nature of the electrolyte
- Material problems due to high temperature operation
- High intolerance to sulfur (1.5 ppm max.)
- Slow start-up

MCFCs, one of the earliest fuel cells used in practical applications, are preferred for natural gas and coal-based power plants. However, poor long-term reliability has been the major hindrance to their commercialization, which is associated with the issues such as gradual dissolution of nickel oxide from the cathode, anode creep and corrosion of metal parts. Consequently, research and engineering work on MCFCs has gradually shrunk since the early 2000s and the interest of developers has shifted to another high temperature fuel cell, SOFC.

Solid oxide fuel cell (SOFC)

Electrolyte: Ceramics (mainly yttria stabilized zirconia (YSZ))
Electrodes: Composite of ceramics and metal (mainly Nickel-YSZ cermet) as anode and perovskite ceramics (mainly strontium doped lanthanum manganite (LSM)) as cathode
Fuel: Hydrogen, CO, methane, etc
Operating temperature: 600-1000 deg. C
Electrical efficiency: ~60%
Applications: Electric utility, large scale distributed power, auxiliary power units (APUs)


- No corrosion and electrolyte management problems
- No need of expensive electro-catalysts
- Fuel flexibility (spontaneous internal reforming of hydrocarbon fuels)
- High grade waste heat (suitable for CHP applications/bottoming cycles)

- Material problems due to high temperature operation
- Slow start-up

Elimination of electrolyte management problems, fuel flexibility and high electrical efficiencies have all made SOFC an attractive emerging technology for future power generation, especially in stationary applications. Though most of the benefits of SOFCs result from their high temperature operation, cost and durability issues associated with such high temperatures are yet to be solved. Therefore, current research on SOFCs in academia, industry and governmental laboratories is primarily focused on developing intermediate temperature SOFCs (IT-SOFCs) (operating at < 700 deg. C) which allow the use of low cost materials with improved durability and offer the same advantages as the conventional SOFCs do.

Direct methanol fuel cell (DMFC)

Electrolyte: Fluorinated sulfonic acid polymer
Electrodes: Carbon loaded with platinum
Fuel: Methanol
Operating temperature: 50-130 deg. C
Electrical efficiency: ~40%
Applications: consumer electronics (as a replacement of batteries)

- Direct use of liquid fuel (can be recharged like batteries by simply changing the cartridge of fuel)

- Lower efficiency due to methanol crossover problem
- Higher cost due to increased loading of noble metal at anode

Despite their low efficiency, DMFCs are expected to find their applications in consumer electronic products such as mobile phones, digital cameras and laptop computers in which energy density, compactness in design and convenience of refilling the fuel are of prime concern. To make DMFCs competitive with state-of-the-art lithium-ion batteries in consumer electronics, current research is focused on finding suitable electrolyte materials so as to minimize the fuel crossover problem and developing more active anode catalysts to enhance methanol oxidation.


Following bar graph shows the trend of research publications on various fuel cell technologies from 1970 until the current year based on the data obtained from Web of Science.

As there might be some alterations depending on the search keywords, it should be noted that for the above data, search keywords used are:

AFC – “Alkaline fuel cell”
PAFC – “Phosphoric acid fuel cell”
PEMFC – “PEM fuel cell”
MCFC – “Molten carbonate fuel cell”
SOFC – “Solid oxide fuel cell”
DMFC – “Direct methanol fuel cell”


Light duty vehicles

Following graph from Fuel Cell Today illustrates the annual growth of new units of fuel cell light duty vehicles from 1997 to 2007.

Large stationary power plants (> 10 kW)

Annual number of units and MW installed:

Annual technology mix, by percentage adopted:

Further surveys on fuel cell and hydrogen markets can be searched by topic here.

To sum up, there has been a considerable increase in the work on fuel cells over the past few decades indicating the inevitability of transition to fuel cells from the existing power generation technologies. During the course of technological development, some fuel cell technologies have gained more attention while others have lost their charm. Currently PEFCs and SOFCs seem to be the most promising candidates for mobile and stationary applications, respectively. Thus, it seems that these two fuel cell technologies are going to dominate not only the fuel cell industry but also the entire energy sector of the future. Nevertheless, other kinds of fuel cells such as AFCs may still be preferable for some niche applications.

Note: The first four illustrative figures are taken from FCTec.