Correlating the Bandgaps of Earth-Abundant Metal Oxides to Photocurrent Generation for Water Splitting Applications

Overview

Objectives/Goals Solar-driven water splitting with earth-abundant, efficient and robust photoelectrode and catalyst materials can meet the challenges of providing sustainable energy globally. In my experiment, I sought to determine the correlation between the bandgaps of mixed metal oxide photoanodes for a photoelectrochemical cell and their photocurrent generation under visible light illumination. Methods/Materials Chemicals used were iron (iii) nitrate, zinc nitrate, sodium molybdate, copper (ii) nitrate, cerium nitrate, bismuth (iii) nitrate, vanadyl acetylacetonate, 2,4-pentanedione, sodium tetraborate decahydrate, and boric acid. Materials used to prepare metal oxide electrodes were FTO (fluorine-doped tin oxide) conductive glass plates, black spray paint, silver paint, glass tubing, wire, epoxy, and a kiln. Equipment used for photocurrent generation included an Ag/AgCl reference electrode, a Ni mesh, a potentiostat, and a light bulb. A UV-visible spectrophotometer equipped with an integrating sphere was used for bandgap measurements. Six earth-abundant mixed-metal oxide materials were prepared on FTO glass plates and made into electrodes. The materials# bandgaps were obtained from Tauc analysis of diffuse reflectance spectra that were measured in a spectrophotometer with integrating sphere. Photoelectrochemical performance was experimentally determined using cyclic voltammetry in aqueous electrolyte and under simulated sunlight illumination. Generated photocurrents were correlated with the materials# bandgaps and compared to a prediction of how efficiency depends on bandgap. Results Bismuth-containing metal oxides followed the predicted trend that materials with mid-range bandgaps (in this case, a bandgap of around 1.95 eV) produced the highest photocurrents, while materials with larger and smaller bandgaps produced smaller photocurrents. The iron-containing metal oxides all produced small photocurrents that did not follow the predicted trend, which could be due to other limiting factors such as carrier lifetime. Conclusions/Discussion Experimental data indicated that photoanode materials not based on iron oxide, such as doped bismuth vanadates, followed the theoretically predicted photocurrent densities that peak at an optimal bandgap of ~2.0 eV. Materials with bandgaps both larger and smaller than this value showed, as expected, lower maximum solar photocurrent densities.

Awards (1)

• Second Place

Competition history

• CSEF 2015 Chemistry · Entry S0613

Resources

• CSEF project summary ↗

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