실리콘 및 금속산화물 기반의 광전기화학적 물 분해 연구

Abstract

Photoelectrochemical (PEC) water-splitting cells, a promising way to convert solar energy into storable hydrogen fuel, typically consist of semiconductor photoelectrode and electrocatalyst. The semiconductorelectrocatalyst interface affects the PEC performance of the electrode but little has been known to date. We have found that a porous, electrolyte-permeable NiOx thin film revealed a superior water oxidation behavior onto a SiO2-grown n-Si photoanode, in comparison to a dense NiOx film. In a porous NiOx film, the built-in potentials and Fermi-levels of the NiOx/Si junction were varied in-situ with oxidation. As a result, a thermodynamic open-circuit potential (Voc), which is normally limited by the amount of photovoltage (Vph), is observed to decouple from the value of Vph. The Voc of 550 mV was finally achieved in porous NiOx/Si junctions presenting ~200 mV of Vph. The combination of two absorbers which have different band gap will increase the free energy available. The free energy must be greater than the energy needed for water splitting (1.23 eV) plus the overpotential losses for the water splitting reaction to occur. Here we explored TiO2 photoanode integratedwith highly doped, normal doped, and p+n homojunction Si photovoltaics. Further enhancement of the tandem structure was carried out by highly ordered nanopillar array of Si surface. The nanostructured TiO2/np+-Si effected unassisted water splitting with Voc of 1.56 V.