½O2 + 2e- + 2H+ → H2O
E0 = 1.23 V vs NHE
The simplest fuel cell: H2/O2
Work (energy)
O2 H2
fuel cell heat
H2O
What is a fuel cell?
A Fuel Cell is an electrochemical device converting chemical energy to electricity “chemical combustion”.
Grove's drawing of one of his experimental "gas batteries" from an 1843 letter (NOTE: 4 or 5 cells needed to electrolyse water in 1 cell!)
The Gas and O2 are reacting to produce electricity rather than heat: Overall cell reaction: H2 + ½O2 → H2O E0 = 1.23 V
Anode
H2 → 2H+ + 2e- E0 = 0 V vs NHE Cathode
A Leclanche battery
The history of fuel cells (1)
The world speed record in 1899, of 104 km h-1, was held by an electric vehicle, the “Jamais Contente”. In 1900 in the USA, there were 1681 steam-driven vehicles, 1575 electric vehicles and only 936 driven by petrol engines. All electric vehicles were powered by lead-acid batteries. A fuel tank is lighter than a lead-acid battery and can be „recharged‟ more rapidly. A tank of fuel gives a much longer range than a fully charged battery- current target of 300 km still remains elusive (battery should not exceed ca. 1/3 of total weight of vehicle)- Nissan Leaf range ca. 160 km. The advent of the self-starter (powered by a lead-acid battery!) finally clinched the relegation of electric vehicles to milk floats and fork-lift trucks.
Fuel cells
Professor Paul Christensen
School of Chemical Engineering and Advanced Materials
Paul.christensen@ Tel. 5472, room 1.03 Bedson Building
The history of fuel cells (2)
In the late 19th and early 20th centuries, coal was king But all attempts to make coal fuel cells failed, and fuel cells fell out of favour until the 1960‟s, when they underwent a revival due to interest from an out of this world source!
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A brief history of fuel cells
Electrolysis
Cathode: 2 H+(aq) + 2e− → H2(g)
Anode: 2 H2O(l) → O2(g) + 4 H+(aq) + 4e−
Overall reaction: 2 H2O(l) → 2 H2(g) + O2(g); E0 = 1.23 V
Francis Thomas Bacon (1904-1992) started his FC research in Newcastle whilst working for Parsons Engineering (1925 – 1940). After the war he moved to Cambridge. First viable power unit in 1950‟s: a 5 kW fuel cell utilising pure hydrogen and oxygen. The electrolyte was circulating 30 wt% aqueous potassium hydroxide, operated at 200°C & 5 MPa to prevent boiling of the electrolyte.
The history of fuel cells (3)
Monday 13 April 1970, 9.07 pm 200,000 miles out in space O2 cryotank 2 explodes on Apollo 13
The history of fuel cells (4)
The history of fuel cells (6)
1960‟s: On the basis of the Bacon Fuel Cell System, AllisChalmers built the first large vehicle equipped with a fuel. It was a farm tractor powered by a 15 kW stack consisting of over 1000 cells. With this 15 kW of power, the tractor generated enough power to pull a weight of about 1.5 tons.
The Apollo fuel cell power plant.
31 cells, 100 mA cm-2, in total 1.12kW at 28V.
110 kg
The history of fuel cells (5)
Bought by NASA for the Gemini space programme
Sir William Grove (2)
e-
Grove realized that if electrolysis, using electricity, could split water into hydrogen and oxygen then the opposite would also be true. Combining hydrogen and oxygen, with the correct method, would produce electricity.
1. 2. 3. 4. 5. 6. 7. 8. 9. A brief history of fuel cells The principles of fuel cells: thermodynamics and kinetics The fuel and oxidant The effect of temperature and pressure Connecting fuel cells together: the bipolar plate The 3-phase region The polarisation curve The efficiency of fuel cells Low temperature fuel cells 9.1. The alkaline fuel cell (AFC) 9.2. The proton exchange membrane fuel cell (PEMFC) Medium temperature fuel cells 10.1. The phosphoric acid fuel cell (PAFC) 10.2. The molten carbonate fuel cell (MCFC) High temperature fuel cells: the solid oxide fuel cell (SOFC) The Direct Methanol Fuel Cell (DMFC)
7 slots Assessment: assignment 5% Exam: one long + one short question Blackboard
Not on Recap
Recommended reading “Fuel cell systems explained”, J. Larminie, Wiley 2003. “Handbook of fuel cells : fundamentals, technology and applications”, W. Vielstich; H. A. Gasteiger; A. Lamm, Wiley. Essential reading: Introductory documents posted on BB: Thermodynamics, Kinetics and Electrochemistry. Do the „self-tests‟.