(Invited) Investigating the Photoelectrocatalytic Activity of Titania for Nitrogen Fixation Using Rotating Ring-Disk Electrode Voltammetry

Abstract

Reports of photocatalytic nitrogen fixation on titania have surfaced for nearly eight decades [1]. Demonstrations have occurred in both the gas and aqueous phase, and with various environmental conditions (relative humidity, temperature, pressure). Nearly all experimental observations suggest that abiotic nitrogen photofixation may be possible at ambient temperature and pressure [2,3]. This is impactful as it promotes the possibility for nutrient based fertilizer production from environmentally abundant materials (minerals) using only the sun as a source of energy. However, the reaction pathway that results in ammonia production is not well understood. Furthermore, the wide band gap mineral coupled with the location of the band edges, suggest that nitrogen reduction not likely. Here, we aim to investigate photo-catalytic nitrogen fixation by titania in an aqueous environment through a series electrocatalytic rotating ring disk voltammetry experiments. We demonstrate that this experimental approach is effective at discerning the low-level ammonium concentration intrinsic to photocatalytic nitrogen fixation experiments through monitoring the ammonia oxidation peak at the ring electrode. Results show that that no ammonium is detected without illumination with both a rutile and mix-phased titania photocatalyst. With illumination ammonium was detected with the rutile phase titania, but not with the mixed phase photocatalyst. This suggest that mineral phase plays an important role in promoting nitrogen photofixation. Rotating ring disk electrode experiments may provide a new avenue to attain a higher degree of precision for detecting ammonia at low levels from both photo and electrocatalyst. [1]N. Dhar, E. Seshacharyulu and N. Biswas, Proc. Natl. Acad. Sci., India, 1941,7, 115–131 [2]A. J. Medford and M. C. Hatzell, ACS Catal., 2017, 2624–2643. [3]G. Schrauzer and T. Guth, J. Am. Chem. Soc. , 1977, 99, 7189–7193.