Compare and Contrast the Types of Cells for the Hydrogen–Oxygen System

• 2 H2(g) + O2(g)  2 H2O(l)

(spontaneous—produces electrical current; occurs in a voltaic cell)

• 2 H2O(l)  2 H2(g) + O2(g)

(nonspontaneous—consumes electrical current; occurs in an electrolytic cell)