Scientists from Palacký University Olomouc and VSB – Technical University of Ostrava in the Czech Republic jointly with their colleagues from Universidad CEU San Pablo in Madrid, Spain and Princess Nourah Bint Abdulrahman University in Saudi Arabia have created a photocatalyst that can simultaneously produce hydrogen from two different sources: water and an ammonia solution. This is the first universal material of this kind, as catalysts typically work with either water or ammonia. The new development makes the system more flexible: it can produce hydrogen from available feedstock or simultaneously purify ammonia wastewater, obtaining fuel from it.
The design of the new catalyst is quite simple. The scientists combined two materials: titanium dioxide and zinc indium sulfide. The former separates charges effectively, while the latter is better at absorbing visible light and extending the working range to the solar spectrum. Together, they form a so-called heterostructure in which charges are not lost, as they participate in the reaction in a targeted manner. Individual platinum atoms were added on top as a key element. This is important: platinum is used not as particles but literally atom by atom, resulting in minimal consumption of this expensive metal with increased efficiency.
When light falls on the material, charged particles are generated, such as electrons and positive charges. They trigger chemical reactions. The electrons gather on the platinum atoms, where hydrogen is formed. From this point on, the process depends on the environment. Water splits and releases hydrogen, whereas an ammonia solution decomposes into nitrogen and hydrogen. This way, the same material can simultaneously perform two different reactions.
Experiments have shown that the catalyst is highly efficient. Over 24 hours of continuous irradiation, hydrogen yield totaled some 108.76 millimoles per gram during water splitting and 12.44 millimoles per gram during ammonia decomposition. This is on par with the best-performing modern photocatalysts and significantly better than the starting materials individually. The system also remained stable for at least 72 hours of operation with virtually no loss of activity.
It should also be noted that ammonia does not require additional reagents, since it serves as a source of hydrogen. This makes the technology especially interesting from a practical viewpoint. Ammonia is a common wastewater pollutant that degrades water quality and disrupts ecosystem balance. The catalyst makes it possible to not just remove ammonia but convert it into a useful resource: pure hydrogen without carbon dioxide emissions.
The new material combines high efficiency with stability and has significant potential for solar hydrogen production. The next obvious step is to reduce its cost by cutting the platinum content or replacing it with more affordable materials.
