Berlin 2018 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 56: Materials for Energy Storage II (joint session KFM/CPP)

CPP 56.6: Vortrag

Mittwoch, 14. März 2018, 17:10–17:30, EMH 025

The impact of different Si surface terminations in the (001) n-Si/NiOx heterojunction on the oxygen evolution reaction (OER) by XPS and electrochemical methods — •Sven Tengeler, Mathias Fingerle, Wolfram Calvet, Céline Steinert, Bernhard Kaiser, Thomas Mayer, and Wolfram Jaegermann — Technische Universität Darmstadt

The interaction between (001) n-Si and NiOx was investigated with regard to the oxygen evolution reaction (OER), applicable either for water splitting or CO2 reduction. Thin layers of NiOx were deposited step by step by reactive sputter deposition and analyzed in-situ after each step using X-ray photoelectron spectroscopy (XPS) for Si with different surface preparations: H-termination, thermally grown oxide (2 Å) and native oxide (4 Å). Upon contact formation the initial flat band like situation in the Si substrates changed to a 0.35-0.4 eV upward band bending for all three heterojunctions, hole extraction barriers are low.

The observed similarities in the heterojunctions should result in the same similarities for the OER performance. However, cyclic voltammetry measurements reveal a shift of more than 0,2 V in dependence of the surface treatment. Using chopped light measurements, this underperformance could be attributed to a higher density of defect states at the Si surface. Apparently a 4 Å SiO2 layer is sufficient protection to prevent the formation of defect states during NiOx deposition, thinner protective layers or none at all result in increased defect states, while thicker layers perform poorly due to their high ohmic resistance.