How do redox reactions interconvert electrical energy and chemic energy?
I guess the answer is by transferring or supplying electrons externally.
If we just let reaction happens in a test tube, then electron transfer will happen in the solution. You cannot collect these electrons. But if you separate the reactants with products, by external wire, then to make the reaction happen, electrons will have to move along the wire, then we get electrical energy. That is for a galvanic cell.
For a voltaic cell, you supply electrical energy to change the energy of the electron. These electrons can then move from electrode across electrode-solution interface into solution, for a reduction reaction. Which means you consume electrical energy and form a new chemical substance, and you convert electrical energy to chemical energy.