Conventional electrolysis uses electrical current to split water into hydrogen at the cathode (+) and oxygen at the anode (-). Steam electrolysis uses heat to provide some of the energy needed to split water.

The basic approach of the proposed system is as follows:

• Decompose water electrochemically into H₂ and O₂ on the cathode side of a high-temperature electrolyzer.

• Oxygen ions will migrate through an oxygen-ion-conductive solid oxide electrolyte.

• Gas mixtures on the cathode side (H₂+ H₂O) and on the anode side (CO + CO₂) will be reliably separated by the solid electrolyte.

• Depolarization of the anodic process will decrease the electrolysis voltage 5-10 times, and thus the electricity required for H₂ generation and the cost of produced H₂.

The SRI team expects energy efficiencies of 60%–70% with respect to primary energy consumption and 75%–90% with respect to total energy into the electrolyzer. Total expected energy consumption for the high-temperature steam electrolyzer is around 6–8 kWh/kg H₂.

SRI’s modular system design will allow scaling up and customization to meet a variety of site-specific needs. Deploying the system at locations where waste heat is available would reduce the electricity required for heating the system, and thus make it even more attractive.

The SRI project was one of eight Electrolysis posters delivered at the DOE 2005 Annual Merit Review held in May.

Resources:

• SRI Modular System for Hydrogen Generation & Oxygen Recovery

• DOE Hydrogen Production and Delivery: 2005 Annual Merit Review Proceedings