http://en.wikipedia.org/wiki/Electrode_potential
http://en.wikipedia.org/wiki/Standard_electrode_potential
http://www.chemguide.co.uk/physical/redoxeqia/introduction.html
http://tannerm.com/electrodePotential.html
http://hyperphysics.phy-astr.gsu.edu/HBASE/CHEMICAL/electrode.html
http://www.cliffsnotes.com/study_guide/Electrode-Potential.topicArticleId-21729,articleId-21713.html