Term
| name 4 main types of electrochemical energy conversion systems |
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Definition
fuel cell
electrolyzer
battery
flow cell |
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Term
| what was the first operating fuel cell called? |
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Definition
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Term
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Definition
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Term
| what are the 3 main components of a fuel cell? |
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Definition
electrolyte
electrodes
chemicals (fuel and oxidizer) |
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Term
| what is the function of the electrolyte? |
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Definition
| it conducts protons from anode to cathode |
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Term
| what are the 2 main functions of the electrodes? |
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Definition
they speed up the reactions and
reduce the charge transfer overpotentials |
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Term
| what are the 2 main functions of the gas diffusion layers? |
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Definition
they provide the desired mass transport of gases to the electrodes and
reduce the mass transport over potential |
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Term
| what does the AFC use as an electrolyte? |
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Definition
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Term
| what is the operating temp. range of the AFC? |
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Definition
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Term
| what does PEMFC stand for? |
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Definition
| proton exchange membrane fuel cell |
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Term
| what does the PEMFC use as an electrolyte? |
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Definition
| polymeric PEM (made of Nafion) |
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Term
| what is the operating temp. range of the PEMFC? |
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Definition
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Term
| what are the electrodes made of in the PEMFC? |
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Definition
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Term
| what does DMFC stand for? |
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Definition
| direct methanol fuel cell |
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Term
| what is the fuel for a DMFC? |
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Definition
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Term
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Definition
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Term
| what does the DMFC use as an electrolyte? |
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Definition
| polymeric PEM (made of Nafion) |
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Term
| what is the operating temp. range of the DMFC? |
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Definition
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Term
| what are the electrodes made of in the DMFC? |
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Definition
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Term
| the DMFC is __ efficient than the PEMFC. Why? |
|
Definition
less
the charge transfer overpotential is higher |
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Term
| what does SOFC stand for? |
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Definition
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Term
| what does the SOFC use as an electrolyte? |
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Definition
| ion-conducting ceramic (YSZ) |
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Term
| what is the operating temp. range of the SOFC? |
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Definition
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Term
| what are the electrodes made of in the SOFC? |
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Definition
anode: Nickel and YSZ
cathode: strontium-doped lanthanum-manganite |
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Term
| which fuel cell type is popular for stationary power generation systems? |
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Definition
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Term
| which fuel cells are not popular because of cost and durability problems? |
|
Definition
sulfuric acid fuel cell
molten carbonate fuel cell |
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Term
| what is the efficiency of a common fuel cell? |
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Definition
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Term
| polarization curves show __ vs __ |
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Definition
cell voltage
current density |
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Term
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Definition
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Term
| why is experimental OCP always below calculated OCP? |
|
Definition
1. there is a crossover of chemicals through the membrane
2. there is a small internal electron current |
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Term
| why are the PEMFC and SOFC polarization curves different at low current densities? |
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Definition
| there is a significant temperature dependence of the respective charge-transfer reactions at low current densities |
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Term
| which has a rapid initial drop in voltage at low current densities, PEMFC or SOFC? |
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Definition
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Term
| what are the no-loss voltage and OCP voltage of a PEMFC? |
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Definition
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Term
| what are the no-loss voltage and OCP voltage of a SOFC? |
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Definition
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Term
| in the middle part of the polarization curve, what is dominating? |
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Definition
| Ohmic resistivity of the cell |
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Term
| at high current density, the polarization curve of both PEMFC and SOFC __ |
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Definition
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Term
| max efficiency of a fuel cell is defined as __ |
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Definition
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Term
| efficiency of a FC under load is always __ than the max efficiency |
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Definition
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Term
| why is the efficiency of a FC under load always smaller than the max efficiency? |
|
Definition
because of increased overpotential and
resistance inside the cell |
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Term
| what is voltage efficiency? |
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Definition
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Term
| total efficiency is defined as __ |
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Definition
| ξtotal=ξthermal*ξvoltage*ξcurrent |
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Term
| what is current efficiency? |
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Definition
| ξcurrent=(calculated amt of chemical)/(measured amt of chemical) |
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Term
| what are typical values of current efficiency for a fuel cells and electrolytic cells? |
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Definition
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Term
| at equilibrium conditions (current is almost zero), how much of the energy in a PEMFC is lost as heat? |
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Definition
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Term
| when current is positive, how much of the energy of a PEMFC is lost as heat? |
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Definition
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Term
| in a PEMFC, how much of the heat comes from the entropy term and how much from the electrode overpotential and Joule heating? |
|
Definition
entropy term: 1/3
electrode overpotential and Joule heating: 2/3 |
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Term
| can the entropy of the fuel cell reaction ever be positive? |
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Definition
yes
for example C + (1/2)O2 -> CO and C + O2 -> CO2 cells |
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Term
| if the entropy of the fuel cell is positive, what does that mean for thermodynamic efficiency? |
|
Definition
it is over 100%
(because it is absorbing heat while operating) |
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Term
| is a heat removal mechanism necessary to keep a fuel cell from overheating? |
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Definition
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Term
| standard thermodynamic efficiency and thermodynamic efficiency at a given chemical composition are usually similar or dissimilar? |
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Definition
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Term
| is a heat removal mechanism necessary to keep an electrolytic cell from overheating? |
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Definition
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Term
| for the PEMFC, how many phases are present at the electrodes? |
|
Definition
3 phases at the anode
4 phases at the cathode |
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