Fuel cells Flashcards
what is a fuel cell
a fuel cell is an electrochemical cell in which a fuel donates electrons at on electrode and oxygen gains electrons at the other electrode, a fuel is continuously pumped in an electricity is continuously generated
how are fuel cells more efficient and renewab;le then coal-fired power stations
fuel cells convert the chemical energy of reactants directly into electrical energy and any waste generated from fuel cells can also be used for further electricity production
what kind of reaction occurs in a fuel cell
exothermic
a hydrogen oxygen fuel cell consists of
a reaction chamber with seperate inlets for hydrogen and oxygen gas, an outlet for the products, an electrolyte of aqeous sodium hydroxide and a semi-permeable membrane that seperatyes thw hydrogen and oxygen gases
what occurs in a hydrogen-oxygen fuel cell
two redox reactions occur simultaneously, the electrons fromk the oxidation of hydrogen gas travel towards tha anode for the reduction of oxygen
when the electrolyte is acidic, what does this mean
that H+ ions are floating around and half equations need to be choosen that inslude H+ not OH
when the electrolyte is alkaline, what does thjis mean
that OH- ions are floating around and half equations need to be choosen that include OH not H+
overall equation for hydrogen-oxygen fuel cell
2H2 + O2 → 2H2O + electrical energy
purpose of the electrode in a fuel cell
provides a surface for the oxidation/reduction reaction to occur. may also contain a cataluyst to maximise the speed of reaction
what kind of electrode is used in fuel cells
a pourous one as this allows gases to access the electrolyte and the holes/pores allow a greater surface area for reactions to take place
electrolyte purpose in fuel cells
allows the movement of charged ions in order for a redox reaction to take p;ace (Oh or H)
advantages of hydrogen-oxygen fuel cells
water is the only product (environmental advantages), the reaction takes place at room temp without combustion, so all energy is converted into electrical energy (instead of heat/light) and there are no harmful oxides of nitrogen produced, which are usually formed in high temp combustion reactions where air is present
disadvantages of hydrogen-oxygen fuel cells
hydrogen is highly flammable, thick walled cylinders and pipes are needed to store hydrogen, the production of hydrogen is a by-product of crude oil (reliesw on non-renewable, finite resources, hydrogen has a low energy per volume
why does hydrogen have a low energy to volume ratio
whilst hydrogen has a high energy density, its a gas so its energy per unit volume is low
what kind of conditions does a methanol fuel cell occur in
acidic
what are the products of a methanol fuel cell
water, excess fuel and carbon dioxide
what is the half equation for the oxidation of methanol
CH3OH(aq) + H2O(l) = CO2 (g) + 6H+ (aq) + 6e- (not in electrochemical series)
what is the half equation for the reduction of of oxygen (methanol fuel cell)
O2(g) + 4H+ + 4e- = 2H2O(l)
overall reaction for methanol fuel cell
2CH3OH(aq) + 3O2(g), →, 2CO2(g) + 4H2O
comparison between fuel cells and galvanic cells - energy transformations and efficiencies
fuel cell - constantly converts chemical energy to electrical energy (continuous reactants) and high efficiencies. glavanic cell - stores chemical energy for conversion to electrical energy, high efficiencies
comparison between fuel cells and galvanic cells - applications
fuel cells - power stations, rockets and cars. galvanic cells - cars, phones and computers
what conditions does a methane cell occur in
alkaline
oxidation of methane half equation
CH4 (g) + 8OH- (aq) = CO2 (g) + 6H2O (l) + 8e- (not in electrochemical series)
reduction of oxygen half equation (methane fuel cell)
O2(g) + 2H2O(l) + 4e- = 4OH-(aq)
overall equation for methane fuel cell
CH 4 + 2 O 2 ⟶ 2 H 2 O + CO 2.
what are the products of a methane fuel cell
excess air, h2O and CO2
