(428b) Impact of Oxygen on Photocatalytic Nitrogen Fixation

Photocatalytic nitrogen fixation is an approach that may enable the synthesis of ammonia (NH3) from abundant feedstock (air and water) using only renewable energy (sun). Despite the potential sustainability of this approach, few photocatalyst exhibits desirable nitrogen fixation activity in an atmosphere made up of pure nitrogen let alone in air that contain oxygen and other impurities. Separation and purification of nitrogen from air is an energy intensive and expensive process. Therefore, truly sustainable approaches toward achieving photocatalytic nitrogen fixation should catalyze nitrogen reduction in air. The chief challenge with using air is the potential for oxygen reduction (ORR) to compete with nitrogen reduction reaction (NRR). Prior attempts to photocatalyze nitrogen fixation in air on titania, showed that ammonia production rates decreased by approximately 60% when compared with pure nitrogen gas^[1]. However, another electrochemical analysis reported that Fe2O3/TiO2 showed negligible change in ammonia production rate in nitrogen and in air[2]. This motivates the need to determine which co-catalyst can be employed to mitigate oxygen reduction reaction activity, to enable photocatalytic nitrogen fixation with air. Here we aim to screen rational metal co-catalyst for activity for nitrogen and oxygen reduction reaction using a rotating ring disk. We then demonstrate the photocatalytic activity through a series of photocatalytic experiments.

[1] Hirakawa, Hiroaki, et al. "Photocatalytic conversion of nitrogen to ammonia with water on surface oxygen vacancies of titanium dioxide." Journal of the American Chemical Society 139.31 (2017): 10929-10936.

[2] Manjunatha, Revanasiddappa, et al. "Electrochemical ammonia generation directly from nitrogen and air using an iron-oxide/titania-based catalyst at ambient conditions." ACS applied materials & interfaces 11.8 (2019): 7981-7989.