(Invited) Microreactors for Characterization and Benchmarking of Photocatalysts

Abstract

In the field of photocatalysis the batch-nature of the typical benchmarking experiment makes it very laborious to obtain good kinetic data as a function of parameters such as illumination wavelength, irradiance, catalyst temperature, reactant composition, etc. Microreactors with on-line mass spectrometry, on the other hand, allow fast and automated acquisition of quantitative kinetic data. [1,2] As an example, we show how microreactor experiments on water splitting using Pt- or Rh-loaded GaN:ZnO photocatalysts quickly rank different catalysts according to their activity for gas-phase water splitting - but also how the activity scales with relative humidity and the crucial role of CrOx "capping" of the Pt- or Rh-co catalyst in order to prevent the loss of H2/O2 product via backward reaction on the precious metal. [3,4] The data suggests that protons transfer via the catalyst surface between the oxygen-evolving sites and the hydrogen evolving co-catalyst sites. Recently, the microreactor experimental platform is being developed to support in-situ UV-VIS-IR spectroscopy [5] and even the introduction of liquid aqueous electrolyte and electrodes - all while retaining high sensitivity time resolved mass spectrometric product detection. [6] [1] Vesborg et al. Chemical Engineering Journal, 160, p. 738-741 (2010) [2] Vesborg et al. J. Phys. Chem. C, 114, p. 11162-11168 (2010) [3] Dionigi et al. Energy & Env. Sci., 4, p. 2937-2942 (2011) [4] Dionigi et al. J. Catal., 292, p. 26-31 (2012) [5] Dionigi et al. Rev. Sci. Instr., 84, p. 103910 (2013) [6] Bøndergaard et al. "Fast and sensitive method for detecting volatile species in liquids", submitted