Two methods for increasing the exergy efficiency of thermochemical processes for the production of hydrogen from water and high temperature thermal energy are presented and compared. Increasing the exergy efficiency is equivalent to reducing the entropy production. Starting from a reference reactor for the decomposition of sulfuric acid, two new reactor designs are developed that both reduce the entropy production by 26%. The first design uses optimal control theory to obtain a more uniform distribution of the entropy production. As a result of this functional optimization we obtain optimal temperature profiles over the reactor length. This optimized design is found to perform the best, but it requires significant changes in the heating equipment ill order to approximately realize the optimal temperature profiles. A second design is obtained by increasing the reactor length. This leads to a higher pressure drop and requires additional compressor duty.