(126d) Electrochemical Generation of Hydrogen Via Thermochemical Cycles

Reforming carbon-based fuels (e.g., natural gas) to produced hydrogen results in impurities (e.g., CO), which can poison fuel-cell catalysts. Water electrolysis does produce highly pure hydrogen, but is consumes a substantial amount of electrical energy. Conversely, a variety of thermochemical cycles to produce pure hydrogen in an energy efficient manner. Two promising cycles are based on the internal recycle of either sulfuric acid or bromine. We present here an electrochemical process that produces pure hydrogen and recycles sulfuric acid and bromine via the electrochemical oxidation of SO2 and HBr, respectively. Both of these electrochemical reactions takes place in a proton exchange membrane (PEM) electrolyzer, similar in construction to a PEM fuel cell. The reactants, either SO2 or HBr, are fed to the anode and water is fed to cathode. Protons are formed at the anode, are transported across a Nafion membrane, and are reduced at the cathode to form hydrogen. We will show that the performance of the electrolytic reactor (i.e., current versus voltage) is a strong function of reactor design and operating conditions. This performance will dictates that size and energy consumption of a hydrogen production process.