Hydrogen production from water on carbon-reduced indium oxide

Decomposition of water by a reduction-oxidation cycle using In₂O₃ has been carried out using active carbon as a reductant for the oxide. Reduction of In₂O₃ by the active carbon powder became noticeable at > 823 K. The CO gas evolved from the active carbon was responsible for the reduction at < 873 K. However, at > 873 K, the reduction proceeded by the direct action of carbon. The optimum temperature for the decomposition of water by the reduced indium oxide lies in the range of 573–673 K. At the higher temperatures, the hydrogen formed was consumed through its reaction with active carbon. The return of reduced indium oxide to its original In₂O₃ form and the accompanying decomposition of water were not complete. This was probably the result of an escape of the reduced species from the reactor because of their vapor transport during reduction. The quantity of hydrogen produced decreased sharply with repetition of the reduction-oxidation cycle. This is explained mainly by a decreasing number of contact points between the carbon and oxide powders.