There are several processes being investigated for using the heat from the next generation nuclear reactors to produce hydrogen. The efficient separation of gases at high temperatures can improve the efficiency of at least two of the leading candidates, thermochemical water splitting and high temperature electrolysis. Through a series of reactions, the Sulfur-Iodine (SI) thermochemical process facilitates the splitting of water into hydrogen and oxygen. In the SI process all the chemicals are recycled except for water. The SI process is efficient, scalable to large sizes, and consumes no expensive chemical reagents; however, it has one major disadvantage. The thermal decomposition of sulfuric acid requires high temperatures (800 to 900 °C). However, there is a potential to lower the peak temperature by 200+ °C if the decomposition products of sulfuric acid, O2, H2O, and SO2, can be separated from SO3 using an inorganic membrane. First generation membranes have been fabricated and we will present preliminary separation data showing the potential to separate the product gases from SO3. We will also present results of the stability of these membranes under simulated operational conditions. High temperature electrolysis employs a solid oxide electrolyzer to split water into hydrogen and oxygen. As the oxygen is produced, it transports through the electrolyte layer of the electrolyzer leaving behind on the feed side a mixture of only the product hydrogen and the residual steam. The efficiency of this process can be improved by recovering the unreacted steam and feeding it back to the inlet to the electrolyzer without costly cooling and reheat steps. Inorganic membranes have the potential to separate the hydrogen from the steam at the operating temperature of 800°C. Preliminary data showing membrane separation performance and thermal stability will be presented.