Fuel Cells as a Source of Energy Flashcards
State what fuel cells use to generate electricity
Chemical energy of hydrogen or other fuels to cleanly and efficiently generate electricity.
State whether or not a fuel cell is a type of galvanic cell
Yes.
State whether or not fuel cells run down or need recharging
No
Electricity is available for as long as fuel cells are supplied with…
Fuel
State what the major limitation of primary/secondary cells are
Cell must be discarded or recharged when the reaction reaches equillibrium
State an alternative term to describe primary and secondary cells
Galvanic cells
State the key difference between a fuel cell and a primary or secondary cell
Reactants do not have to be stored in the fuel cell, but must be continuously supplied from an external source.
State what fuel cells transform chemical energy into
Electrical energy
Compare and contrast the efficiency of fuel cells with thermal power stations
Fuel cells > Thermal Power Station Energy Efficiency because they directly convert chemical - electrical energy
State what a fuel cell employing hydrogen produces
Electricity, water, heat and very small amount of nitrogen dioxide and other emissions
State the 2 major parts of a fuel cell
- Hydrogen gas input
2. Oxygen gas input
State what the two gas compartments of a fuel cell are separated by
Two porous electrodes and an electrolyte solution
State what the electrode at the hydrogen compartment is termed
Anode
State what the electrode at the oxygen compartment is termed
Cathode
State what the electrodes within a fuel cell can be classified as
Porous
State whether the anode in a fuel cell is positively or negatively charged
Negatively
State whether the cathode in a fuel cell is positively or negatively charged
Positively
State what process occurs at the cathode of a fuel cell
Reduction
State what process occurs at the anode of a fuel cell
Oxidation
State how higher voltages can be obtained from fuel cells
Connecting a number of fuel cells in series to form a battery/fuel cell stack
State what the electrodes within a fuel cell must be
- porous
- conducting
State why electrodes within a fuel cell must be both porous and conducting
Allow the hydrogen and oxygen to come into contact with the ions in the electrolyte and to allow the redox half reactions to occur at their surface.
State what the size of the current that can be drawn from a fuel cell depends upon
The surface area of the electrodes
State why catalysts are employed within fuel cells
To increase the rate of reaction and the current that can be produced from a cell
Outline the purpose of porous electrodes
Allow reactants to diffuse through them to react with ions in the electrolyte
State what fuel most fuel cells are designed to use
Hydrogen
State what a fuel cell using hydrogen as a fuel source can be described as
A ‘zero-emission’ device
State whether the production of hydrogen can result in the production of significant levels of greenhouse gases/pollutants
Yes. Especially if produced via steam reforming (of natural gas, oil or coil)
State 2 practical methods of harvesting hydrogen gas sustainably
- Using electrical energy to convert water to hydrogen (electricity can be generated from renewable sources such as solar-power farms and wind farms)
- Collecting biogas from landfill sites and converting the methane to hydrogen via steam reforming
State what the widespread adoption of hydrogen as a primary fuel source would require
Massive expenditure on infrastructure
State the major reasons supporting challenges associated with hydrogen gas storage
Hydrogen is a gas at room temperature
State what temperature liquid hydrogen generally boils at
Extremely low temperatures
State whether a large or small quantity of energy is needed to liquify hydrogen
Large quantity
State what the requirements of a hydrogen gas tank are
Good insulation
State whether or not hydrogen gas must be stored in high pressure tanks
Yes. Hydrogen gas must be stored in high pressure tanks,
State why hydrogen gas pressure tanks must be so large to effectively replace a standard hydrocarbon fuel tank
High pressure hydrogen storage tanks need to be large to meet the energy availability within smaller hydrocarbon fuel tanks
Compare and contrast the energy availability of liquid hydrogen and a liquid hydrocarbon (e.g. petrol)
Petrol has a energy availability of four times greater
State what hydrogen can absorb to
The surface of materials such as metal hydrides, either as hydrogen molecules or as hydrogen atoms
State whether or not hydrogen can dissociate
Yes
State what hydrogen would dissociate and become absorbed into
Lattice structure of some solid materials
State whether or not hydrogen can react reversibly with a range of different chemicals
Yes.
Provide reasons supporting the levels of danger associated with hydrogen
Hydrogen burns more readily and a flame/spark will ignite almost any combination of hydrogen and air
State what the low density of hydrogen means for its levels of flammability
Low density means that hydrogen can rise rapidly and quickly disperse in ventilated areas - often without ignition
Compare and contrast danger associated with a fire in a petrol powered vehicle vs a hydrogen powered vehicle
Hydrogen-powered vehicle is less dangerous due to low density of hydrogen gas
Compare and contrast the fuel efficiency and emissions of fuel cells with internal combustion engines
Higher fuel efficiency and lower emissions overall from fuel cells
State what fuel cells convert chemical energy directly into
Electrical energy
State why the electrical energy conversion in fuel cells is more efficient than the series of energy conversions that take place in power stations
Fuel cells: chemical - electrical energy
Power stations: chemical - heat - mechanical - electrical energy
State what hydrogen fuel cells produce as by products
Water and heat
State whether any greenhouse gases are released from hydrogen fuel cells
No greenhouse gases are released
State for how long fuel cells will generate electricity
As long as the fuel is supplied
State whether or not fuel cells can use a variety of fuels
Yes
State whether or not fuel cells are expensive.
Yes. Still a developing technology.
State what alterations will be required for fuel cells to be used extensively for transport
Extensive network of hydrogen filling stations will need to be established
State a possible disadvantage of fuel cells generation of DC current
Many electrical appliances in the home require AC current and an inverter is thus required to change DC to AC at the appropriate voltage.
Identify a possible disadvantage associated with the sourcing of hydrogen for fuel cells
Mainly sourced from fossil fuels - which involves energy losses and generates greenhouse gases
State the major disadvantage of using hydrogen fuel in fuel cells
Safety associated with storage of fuel
Compare and contrast the function of primary/secondary cell with fuel cells
Primary/secondary cells - source of portable electrical energy
Fuel cells - continuous source of high electric current for portable/fixed applications
Compare and contrasts the life of the reactants within primary/secondary cells and fuel cells
Primary/secondary cells - reactants in primary & secondary cells are contained and can thus be depleted
Fuel cells - air/oxygen are supplied continuously
Compare and contrast the site of oxidation in primary/secondary cells and fuel cells
Primary/secondary cells - negatively charged anode
Fuel cells - negatively charged anode
Compare and contrast the site of reduction in primary/secondary cells and fuel cells
Primary/secondary cells - positively charged cathode
Fuel cells - positively charged cathode
Compare and contrast the porous region of primary/secondary cells and fuel cells
Primary/secondary cells - salt bridge
Fuel cells - porous electrodes
Compare and contrast the position of the electrolyte for primary/secondary cells and fuel cells
Primary/secondary cells - salt bridge (carries charge between electrodes)
Fuel cells - between two porous electrodes (carries charge between electrodes)
Compare and contrast the energy transformations of primary/secondary cells and fuel cells
Chemical - electrical energy
Compare and contrast the energy efficiency of primary/secondary cells and fuel cells
Primary/secondary cells - 60-90% efficient
Fuel cells - 40-60% efficient
