(513fk) Unbalanced Charge on Nicop/TiO2 Sensitized System for Rapid H2 Generation from Hydrolysis of Ammonia Borane

Ammonia borane (NH₃BH₃) is a promising candidate for hydrogen storage and instantaneously producing pure hydrogen with moderate operation conditions for mobile and stationary applications due to the nontoxicity, stability, high solubility in water and the ability of releasing hydrogen through hydrolysis. The premise of catalyst for NH₃BH₃ hydrolysis is an unbalanced surface charge for simultaneous activation of B-H and O-H bonds.

Herein we want to introduce a sensitized system constructed by NiCoP/TiO₂ act as an extremely charge-unbalanced catalyst for rapid hydrogen evolution from NH₃BH₃ under visible light. In this system, the H₂ generation rate from hydrolysis of NH₃BH₃ is increased to 2.0 folds with Ea reduced to a half and the full visible light (420~800 nm) can be used to promote the reaction. These results can be attributed to NiCoP significantly enhancing the light absorption region and tuning the electronic structure of metal phosphide. The matched band structure enables photo-generated electrons migrating from NiCoP to TiO₂. Oppositely, when monometallic phosphides are combined with TiO₂, no obvious enhancement can be observed because charge transfer cannot happen between monometallic phosphides and TiO₂ due to the unmatched band structures. Thus the key to the concept is the photo-excitation of NiCoP and electron injecting into TiO₂. Experimental results also confirm that the reduction of protonic H by negatively charged sites is the key step to hydrolysis of NH₃BH₃. Above mentioned mechanism was interpreted by XPS, UV-vis, photoelectrochemical analysis, quenching experiments and other characterizations.

This work provides a new and highly efficient way for NH₃BH₃ hydrolytic generating hydrogen as a new kind of energy for on-board hydrogen storage-releasing system.