The document discusses proton exchange membrane (PEM) fuel cells and the advantages of operating them at high temperatures. PEM fuel cells use a polymer membrane as an electrolyte and operate at around 80°C. Operating at higher temperatures, such as over 100°C, provides benefits like improved cathode kinetics, higher tolerance to contaminants, and simplified water management due to the absence of liquid water. However, it also presents challenges like membrane dehydration reducing proton conductivity and degradation of fuel cell materials at elevated temperatures. Water management is also more difficult at higher temperatures due to the gradient of water content across the membrane.

1. INDIAN INSTITUTE OF TECHNOLOGY (BHU),
VARANASI
STUDY OF HIGH TEMPERATURE PEM BASED FUEL CELL
BY:-
JAFFER ALAM
ROLL NO. 18042015

2. Proton Exchange Membrane fuel Cell
o Proton exchange membrane fuel cells, also known as polymer electrolyte membrane (PEM)
fuel cells (PEMFC).
o In PEMFC the electrolyte used is a thin polymer membrane(such as a perfluorosulfonic
acid).
o Hydrogen flows into the fuel cell onto the anode and split into hydrogen ion and electrons.
o Hydrogen ions permeate across the electrolyte to the cathode.
o Electron flow through on external circuit and provide power.
o Oxygen is supplied to the cathode and this combine with electrons and hydrogen ions to
produce water.
o PEMFC operate at temperature of around 80 °C.
o Electrolyte is sandwich between two field flow plates to create a fuel cell.
o Each cell produce around 0.7 volts about enough power to run a light bulb.
o Its called four electron transfer process.

3. Advantages of high temperature operation
o Improved cathode kinetics
 Since Hydrogen Oxidation Reaction at the Pt nanoparticle/PEM interface is reversible, the
over potential for Hydrogen Oxidation Reaction is negligibly small compared with that of
Oxygen Reduction reaction when the anode is adequately hydrated.
o Effect of temperature on Erev and OCV
(
𝜕𝐸 𝑟𝑒𝑣
𝜕𝑇
) =
Erev –E0
rev
𝑇−298
( at constant pressure)
 It is observed that increasing the fuel cell temperature from 60 to 120 ◦C, while maintaining
a constant relative humidity (RH), caused the theoretical OCV to decrease from 1.22 to 1.14V
due to the increase in water partial pressure.

4. o Effect of temperature on the Tafel slope
 Experimentally, the Tafel slope corresponding to the Oxygen Reduction Reaction was found
to increase with temperature in the low current density region, while it was independent of
temperature in the high current density region.
o Improved tolerance of the catalyst to contaminants
 It is reported that at 80 ◦C, CO concentrations as low as10–20 ppm causes a
significant loss in cell performance. As a consequence, purification of the reformate
gas is necessary in order to reduce CO concentrations to <10 ppm.
 Operation at higher temperatures increases the ability of the fuel cell anode to
perform in the presence of small amounts of CO by decreasing the coverage of CO
on the catalyst surface.

5. o Vapor water versus liquid water for O2 mass transport improvement
 High temperature operation facilitates oxygen transport through the gas diffusion layers and
the cathode catalyst layers and should lead to an increase in fuel cell performance in the mass
transport controlled regime.
o Simpler flow field design without the presence of two phase flow in
the channel
 In high temperature fuel cell there is proportionally little or no liquid water present in the fuel
cell above 100 ◦C liquid water management will be simplified, and flow fields may be
designed without having to consider two-phase flow.
o Other benefits of high temperature operation
 At higher temperature waste heat can also be recovered as steam, which in turn can be used
either for direct heating, steam reforming, or pressurized operation.
 the overall system efficiency is significantly increased.
 High temperature fuel cells are expected to contain minimal liquid water.

6.  Under higher temperature operating conditions, the overall system efficiency is significantly
increased.
 The absence of liquid water in the membranes, catalyst layers, and flow fields of high
temperature fuel cells circumvents the need to undertake complex shutdown procedures.
 The absence of frozen water may also speed up cold start-up of a fuel cell stack.

7. Water Management
 Cell operating below 100 ◦C, a lack of water in the membranes and gas diffusion electrodes
decreases their proton conductivity and significantly increases the cell resistance.
 Excessive water in the cathode causes “flooding”, which restricts oxygen transport through
the porous gas diffusion electrode.
 Operating a cell above at 100 ◦C may mitigate potential problems associate with flooding
but they exacerbate issues associated with dehydration.
 The production of water at the cathode results in a gradient of water content across the
membrane that may result in back diffusion of water from cathode to anode.
 The issue of water transport from cathode to anode is expected to be greatly exacerbated
for high temperature membranes operating above 100 ◦C where liquid water is absent.

8. Challenges of operating PEMFCs at high temperature
 At higher operating temperature, membrane dehydration and the subsequent decrease in
proton conductivity is a significant issue.
 Various components of PEMFCs experience structural and chemical degradation at elevated
temperatures.
 Excessive cell temperature cause membrane and electrode dehydration, shrinkage and
cracking.
 While being heated between 35 and 280 ◦C in an inert atmosphere, Nafion® loses ∼5
wt.%, producing water and small amounts of sulfur dioxide and carbon dioxide.
 Degradation of engineering materials and mechanical failure of fuel cell material such as
seals, gaskets, and bipolar plates.

9. References
o Jianlu Zhang a, Zhong Xie a, Jiujun Zhang a,∗, Yanghua Tang a, Chaojie Songa,Titichai
Navessin a, Zhiqing Shi a, Datong Songa, Haijiang Wang a, David P. Wilkinson a,b, Zhong-
Sheng Liu a, Steven Holdcroft - High temperature PEM fuel cells.
o Sara Barati a, Mahdi Abdollahi b,*, Behnam Khoshandam a, Mohsen Mehdipourghazi -
Highly proton conductive porous membranes based on polybenzimidazole/ lignin blends
for high temperatures proton exchange membranes: Preparation, characterization
andmorphology- proton conductivity relationship.