Perovskites for Photocatalysis: Determination of Band Structure

As our earth continue to be faced with the major issue that is global warming it is imperative to develop technology to reduce and reverse this trend. Although much research has been done into photocatalysts due to their potential for providing us with cheap, green, and sustainable energy through the photoreduction of carbon dioxide, the technology is still greatly plagued by inefficiencies. Many studies have focused on metal oxides, however their large band gaps (e.g TiO₂’s band gap of 3.2eV) and band edge positions cause them to be inefficient for this application. Perovskites, hybrids of two or more metal oxides, with the general formula ABO₃, could be the answer. The goal of this project is to determine the potential of perovskites to serve as an alternative to current metal oxide photocatalysts due to their adjustable band edges and band gaps, made possible by varying the metal composition.

In this study, LaCr_1-xFe_xO₃ (where x = {0, 0.25, 0.5, 0.75, 1}) perovskites were synthesized via the Pechini process. XRD (x-ray powder diffraction) was used to verify catalyst structure. Optical band gaps were determined through DRS (diffused reflectance spectroscopy) UV-vis spectroscopy. Band edges were obtained using an electrochemical cell, and Mott-Schottky analysis. Values were then compared to both the CO₂ reduction and H₂O splitting potentials to determine if these materials could be suitable as photocatalysts. It was found that through the replacement of Cr ions in LaCrO₃ with Fe ions that the band gap does not show a linear tread, but rather exhibits the smaller band gap of LaFeO₃. We find that both LaFe_0.25Cr_0.75O₃ and LaFe_0.75Cr_0.25O₃ show potential for CO₂ photoreduction and H₂O splitting in the visible light range with band gaps of ~ 2.0eV and appropriate band edges. It is demonstrated that the perovskite materials present a tunable band edge and adjustable band gap allowing for the potential for use as photocatalysts. Further research is needed to verify the effectiveness of these materials in the actual CO₂ photo-reduction.