High-temperature steam electrolysis makes hydrogen by splitting very hot steam across a ceramic electrolyte at 700°C to 1,000°C. Because heat does part of the work, it needs about a third less electricity than other electrolysers & uses no precious metals. It works best beside nuclear plants, ammonia factories & steel mills that supply waste heat. The ceramics are brittle, wear out under heat & dislike frequent start-ups, so costs remain high. Bloom Energy, Sunfire, Topsoe & Ceres Power lead development, alongside installed capacity still small but growing.