Page 190 - CW E-Magazine (26-9-2023)

Special Report

efficiency and power density, and good when methanol molecules diffuse fuels, including hydrogen, natural gas,
durability. They are able to efficiently through the electrolyte membrane and biogas. Its operating temperature
utilise a variety of fuels such as hydro- without being fully oxidised, reducing ranges from 600°C to 700°C. MCFCs
gen, natural gas, and methanol. How- overall efficiency and potentially caus- are particularly suitable for stationary
ever, PAFCs have a slower start-up time ing performance issues. Some fuel cells power generation applications.
due to their higher operating tempera- address these issues by reforming the
ture, and they may require a warm-up methanol before it reacts with the cata- However, the MCFC requires high
period to reach optimal performance. lyst, which imposes increased costs on operating temperatures, which can lead
They are also larger and heavier com- its implementation. to thermal stress and limited material
pared to some other fuel cell types, options. The molten carbonate electro-
which limits their use in certain applica- Solid acid fuel cells (SAFCs) lyte can corrode materials, necessitating
tions. Additionally, the phosphoric acid A solid acid is used as the electro- the use of corrosion-resistant materials
used as the electrolyte requires careful lyte in these fuel cells (caesium hydro- for the cell components. Additionally,
handling and containment measures. gen sulphate and caesium hydrogen the reliance on high-temperature opera-
phosphate). Molecular structures of the tion can contribute to slower start-up
Despite these challenges, PAFCs acid are ordered at low temperature; times and longer system warm-up periods,
have found applications in stationary at high temperature phase transition reducing their suitability for some
power generation, such as providing occurs increasing the conductivity. dynamic applications. Furthermore,
electricity for buildings. It is the the use of nickel-based catalysts in the
most developed and commercialised Alkaline fuel cells (AFCs) MCFC can lead to carbon deposition on
technology compared to the other fuel Aqueous alkaline solution is used the anode, affecting performance and
cells, with stationary installations of up to saturate a porous material, which is necessitating periodic cleaning. Cost
to 50-MW having been set up. Ongo- then used to separate the electrodes. is another consideration as the use of
ing research aims to further improve The cells are highly efficient and also nickel and other materials increases the
the performance, durability, and cost- produce heat and water, along with overall system cost.
effectiveness of PAFCs, making them electricity, and were used in the Apollo
a viable and efficient option for clean space programme. Microbial fuel cells (MFCs)
energy generation. MFCs use bioelectrochemical pro-
Solid oxide fuel cell (SOFCs) cesses to produce electricity. Instead of
Direct methanol fuel cells (DMFCs) These cells involve the use of a supplying hydrogen to the anode, sewage
DMFCs are similar to PEMFCs; solid oxide. They are highly efficient and water is used as a fuel. This is because
however, they use methanol as fuel, considerably low cost. Their efficiency in the anodic chamber, bacteria such as
instead of hydrogen. Similar to is approximately 85%. Their operating E-coli degrade organic waste into posi-
PEMFCs, the electrolyte used is a temperature is between 800°C and tive hydrogen ions, electrons and carbon
proton exchange membrane. 1000°C and they are limited to statio- dioxide. Hydrogen ions, or protons,
nary applications. migrate through the proton exchange
DMFCs offer advantages such as membrane to the cathode. The electron
high energy density, ease of fuel storage Molten carbonate fuel cells (MCFCs) travels through the conductive material
and transport, and potential for port- In a MCFC, the oxidation and re- from anode to cathode, generating elec-
able power applications. Methanol is a duction chambers are separated by a trical energy and oxidising oxygen and
liquid fuel, allowing for easier handling molten carbonate electrolyte, allowing the hydrogen ion, giving water.
and higher energy density compared to for the conduction of carbonate ions.
gaseous fuels like hydrogen. DMFCs It employs a porous ceramic matrix as This technology is still in the early
can be more compact and have fewer the electrolyte, which retains molten stages of development, having a low
components than some other fuel cell carbonate salts. The fuel and oxidant power density and producing carbon
types, making them suitable for port- are supplied to the electrodes through dioxide. However, they hold great poten-
able devices. a porous structure, and waste heat and tial for applications in wastewater treat-
unreacted gases are removed. ment and remote power generation.
However, DMFCs face challenges
related to methanol crossover and effi- The MCFC offers high efficiency Evaluation of different technologies
ciency. Methanol crossover occurs and the ability to utilise a variety of The fuel cell’s internal resistance is

190 Chemical Weekly September 26, 2023

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