Photoelectrochemical Investigation of Solar Water Oxidation on Conditioned Ni(OH)2-coated &#945;-Fe2O3

Photoelectrochemical Investigation of Solar Water Oxidation on Conditioned Ni(OH)2-coated α-Fe2O3

Thomas Hamann^a, Kelley Young^a

^aMichigan State University, 411 Chemistry Building, Michigan State University, East Lansing, 4824, United States

Proceedings of International Conference on New Advances in Materials Research for Solar Fuels Production (SolarFuel14)

Montréal, Canada, 2014 June 25th - 26th

Organizer: Thomas Hamann

Poster, Kelley Young, 027
Publication date: 16th April 2014

Hematite (α-Fe₂O₃) is a promising photoanode material for solar water oxidation owing to its abundance, stability, substantial visible light absorption, and suitable energetics for H₂O oxidation. Efficient water oxidation with hematite, however, has been limited mainly due to a low minority carrier mobility, which results in the recombination of the photogenerated charge carries in the bulk and surface recombination of photogenerated holes with the conduction band electrons. It is well understood that surface recombination is results in the need for a large applied bias to facilitate water oxidation with α-Fe₂O₃ photoanodes. One strategy to mitigate the surface recombination is the addition of a surface coating such as a water oxidation catalyst in order to reduce recombination of photogenerated holes and improve water oxidation kinetics. Ni oxide based coatings including NiO, Ni(OH)₂, and NiOOH have been shown to reduce the onset of H₂O oxidation on the surface of hematite, though discrepancy exists as to the effect of the coatings on water oxidation with hematite. Herein atomic layer deposition (ALD) was employed to deposit Ni(OH)₂ onto thin-film α-Fe₂O₃, also prepared by ALD. The use of ALD allowed us to reducibly deposit conformal and uniform coatings of Ni(OH)₂ on hematite photoanodes with tunable thickness. It was found that 10nm of as-deposited Ni(OH)₂ is not a remarkable catalyst as compared to bare-Fe₂O₃. However, after photoelectrochemical conditioning, an approximate 300 mV cathodic shift was observed in the onset of water oxidation photocurrent compared to bare α-Fe₂O₃. The effect of Ni(OH)₂ was investigated through photoelectrochemical and electrochemical impedance spectroscopy measurements.

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