Electricity storage and hydrogen generation system using the electrochemical reaction of lithium and water

An electricity storage and hydrogen generation system using the electrochemical reaction between lithium and water is proposed. Lithium has high energy density and can generate hydrogen and electricity without external energy input. The fundamental system structure is considered, and its generation performances are evaluated. At low currents, the reaction with water does not occur and no hydrogen is generated. This occurs because the oxygen is normally dissolved in water and is more reactive than water. When the current is increased, the oxygen concentration overpotential causes a cathode potential drop. When the cathode potential falls below -1.2 V (vs. Ag/AgCl), the reaction with water occurs, and hydrogen is generated. The reaction with water shows a smaller concentration overpotential than that with oxygen, indicating that the increased losses can be minimized even during high current operation. At a current density of 1.27 mA/cm2, hydrogen gas production efficiency reached 85%. Consideration of the proposed system from the perspective of using both the hydrogen and the electrical power shows that energy stored as lithium can be converted efficiently.