Magnetic field improved photoelectrochemical synthesis of 5,5′-azotetrazolate energetic salts and hydrogen in a hematite photoanode-based cell

The oxidative-coupling of 5-amino-IH-tetrazole (5AT) into 5,5'-azotetrazolate is the initial and critical step for the synthesis of 5,5'-azotetrazolate energetic salts. Unfortunately, there are several disadvantages of insufficient security and inconvenient purification in the conventional chemical-oxidation method of 5AT-coupling. Here, we report the solar simultaneous initiation of 5AT oxidative-coupling and hydrogen evolution in a photoelectrochemical (PEC) cell that consisted of a Ti doped Fe2O3 film (Ti-Fe2O3) photoanode and a Pt wire cathode. A stable Faradaic efficiency of 65% for the 5AT oxidative-coupling into 5,5'-azotetrazolate was achieved on the Ti-Fe2O3 film photoanode at room temperature. Simultaneously, hydrogen evolution was initiated on the Pt wire cathode by the photogenerated electrons of Ti-Fe2O3 film photoanode with about 99% Faradaic efficiency. Our investigations indictaed that the 5AT oxidative-coupling on the Ti-Fe2O3 photoanode is a holes-driven reaction which is kinetically favorable relative to water oxidation. Since the non-radiative recombination of electrons and holes on the Ti-Fe2O3 film photoanode could be reduced in the presence of a magnetic field, a higher synthesis efficiency of sodium 5,5'-azotetrazolate and hydrogen was achieved in the PEC cell under a magnetic field of 0.5 T. The present work provides a green approach to produce 5,5'-azotetrazolate salts and H-2 simultaneously using solar energy with high efficiency. (C) 2019 Elsevier Ltd. All rights reserved.