(600ck) Kinetic Studies of Composite Plasmonic-Metal/Semiconductor Photocatalysts for Water Splitting

Photocatalytic water splitting offers a carbon-neutral option for producing hydrogen fuel by using sunlight as the energy source and water as the hydrogen source.  While there has been much progress made in recent years, current catalysts for water splitting still perform well below their maximum theoretical efficiencies. The kinetically limiting step in water splitting is the oxygen evolution half reaction, which requires four holes, and is typically carried out on semiconductor catalysts.  These semiconductors, predominantly titania, have issues including poor light absorbance, slow kinetics, and high rates of electron hole recombination. Adding metal nanoparticles to the semiconductors has led to some success in increasing light absorbance, improving kinetics, and lengthening the lifetime of the electron hole pairs.  We studied the kinetics of a composite plasmonic-metal/semiconductor photocatalyst under different light regimes— using wavelengths shorter than the semiconductor band gap where electron hole pairs can be excited on the semiconductor, and using wavelengths longer than the semiconductor band gap where electron hole pairs are generated on the metal.  The response of the metal depends on whether it is excited through interband transitions, which produces non-localized electron hole pairs, or through surface plasmon resonance (SPR), which produces highly localized electron hole pairs.  The information gained from these experiments provides a better understanding of the processes occurring during photocatalytic reactions on composite plasmonic-metal/semiconductor materials.