Since electricity is typically more expensive than thermal energy, using SO 2 to decrease the required voltages for H 2 production from water has the potential to significantly decrease costs. In the overall cycle proposed here, it may be feasible to utilize the net positive entropy of the cycle (e.g. from gas generation during Step 1 or generation of steam in Sep 3) to pressurize the anolyte of the SO 2 -depolarized cell without the use of pumps to reduce the voltage needed. Further, the water and SO 2 distilled from the refluxing H 2 SO 4 in Step 3 can enter the anolyte at high temperature, eliminating the need to heat the solution to operating temperatures up to 140 °C. The use of electrolysis to produce the H 2 product can also ensure that the H 2 is highly pure and free from sulfur contaminants.