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

Abstract

The oxidative-coupling of 5-amino-1H-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 H2 simultaneously using solar energy with high efficiency.