Electrocatalyst decorated hematite nanowire arrays for photoelectrochemical water splitting.

Abstract

Solar power is a leading option for renewable energy. However, storing solar energy is one of the leading pitfalls in this field, and one viable option is to store solar energy in chemical bonds, for example in H2 via water splitting. Hematite, α-Fe2O3, is one of the possible semiconductors that has been researched to drive photoelectrolysis of water. Hematite alone is not a decent material for photoelectrolysis because of the large activation energy required to begin the reaction. To make hematite more useful for photoelectrolysis an electrocatalyst, such as nickel oxide, is needed. In this experiment, nickel (II) nitrate was dissolved into distilled water; then, the solution was applied to hematite nanowires and exposed to atmospheric oxygen plasma. This left a coating of nickel oxide particles on the surface of the nanowires. The hematite with a nickel oxide catalyst can be used in this form to drive the water splitting reaction. After plasma deposition, it can also be placed in an oven at 550 ºC for an hour to anneal the sample, which creates a biphasic surface layer of nickel oxide and iron oxide. After annealing, the nickel oxide/hematite samples can be used to catalyze water splitting. The use of the electrocatalyst on the substrate improved the electrolysis of water by decreasing the overpotential by approximately 300mV. Annealing the nickel oxide and hematite decreases the overpotential by the same amount as the unannealed nickel oxide layer covering the Fe2O3. Both unannealed and annealed samples show photoactivity, but annealing increases the photovoltage. The physical properties are tested using transmission electron microscopy (TEM), and energy dispersive x-ray spectroscopy (EDX), which shows catalyst particles were created on the surface of the hematite nanowire array.3