Impedance Measurements on Illuminated p‐Indiumphosphide During Hydrogen Evolution

Abstract
Impedance measurements are presented on single crystalline, illuminated p‐type indiumphosphide photoelectrodes. The experiments show a shift of the flatband potentials towards more negative values during photoevolution of hydrogen. This shift amounts, both in acid and alkaline solution, to about −0.7 V at AM1, if no catalyst is deposited on the electrode surface. After platinum deposition, differences in the flatband potential are reduced to less than 100 mV, accompanied by a positive shift of the photocurrent onset for hydrogen evolution. – The results are interpreted in terms of electron trapping at the semiconductor‐electrolyte interface. The rate of charge transfer to the electrolyte (hydrogen evolution) is increased by platinum deposition, resulting in a decrease of the steady state concentration of trapped minority carriers. The model is linking the measured flatband potential shift under illumination to the kinetic overvoltage of multielectron transfer reactions at the semiconductor surface.

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