Evaluation of hydrogen production by molecular fragmentation of water and ammonia using theαFe2-xMxO3(M = Co, Ni, Cu, or Zn) as photoanodes

Hydrogen production from water splitting is a widely used technique and hematite is one of the most used semiconductors in these processes due to its favorable characteristics such as: adequate band gap, visible light absorption, high chemical stability, abundance in nature, among others. Research on hydrogen fuel production from ammonia instead of water is still very limited. Ammonia is a contaminant normally found in wastewater and annualy tons of ammonia or effluents containing this contaminant are thrown into the environment, making it an ideal reagent to produce hydrogen in a clean environmental process. Based on this knowledge, this work proposes the comparison of the photoelectrochemical performance of hematite doped with structural cations (zinc, copper, cobalt, and nickel) in the molecular fragmentation of water and ammonia to produce hydrogen. A structural characterization of the materials used and tests for PEC activity were performed. Pure hematite doped with ammonia as a substrate presented higher electrical current and it was not activated by visible light. When under visible light hematite-Co presented a discrete increase in the electrical current and, consequently, a small increase in the hydrogen production from water, whereas in the tests with ammonia, the copper-doped hematite was responsible for a slight increase in the electrical current.