(217h) On the Combustion Synthesis and Characterization of GaxZn1-XOyN1-Y for Water Splitting Applications

Utilization of solar energy is a necessary path forward to deal with the looming energy crisis and worldwide effects of fossil fuel usage. A key component of this utilization is how to store excess solar energy for use on demand. One such method is splitting water into hydrogen and oxygen, both of which can be stored and either burned as fuel or used as feedstock components in industrial processes to synthesize high-value materials. Metal oxynitrides have shown great potential as photocatalysts for overall water splitting applications. Incorporation of nitrogen into metal oxides narrows the band gap to enable absorption of light in the visible spectrum. The typical synthesis of a metal oxynitride, however, requires annealing temperatures at or above 900 ^oC and nitridation by flowing pure ammonia gas for anywhere from 1 to 110 hours. Such harsh synthesis conditions can limit the discovery of new candidate materials.

We have prepared an array of gallium zinc oxynitrides (Ga_xZn_1-xO_yN_1-y) as a model system using a combustion synthesis method. Gallium zinc oxynitrides can be synthesized in 30 minutes in an air atmosphere at temperatures ranging from 400-750 ^oC. XPS analysis reveals that nearly 50% nitrogen substitution in the metal oxide lattice can be achieved, dependent on the ratio of gallium and zinc nitrates used as precursors. UV-visible spectroscopy also demonstrates that the band gap of the Ga_xZn_1-xO_yN_1-y materials can be controlled simply by altering the precursor ratio.

The as-synthesized products are photoactive under both UV-Visible and visible-only irradiation with and without hole scavengers present and without any co-catalysts. More importantly, photocurrent is measured in a 2-electrode setup with only pure water present. This presentation will discuss the physical and photoelectrochemical characterization of these materials to confirm successful synthesis, the current issues we are facing, paths forward to address these issues, and the ultimate goal of a high-throughput synthetic methodology.