Function and Electronic Structure of the SnO₂ Buffer Layer between the α-Fe₂O₃ Water Oxidation Photoelectrode and the Transparent Conducting Oxide Current Collector

Abstract

The tin oxide buffer layer between the transparent conducting oxide current collector and the hematite photoelectrode causes considerable water oxidation enhancement of that electrode. The water oxidation onset potential is lowered by 180 mV. The lifetime of photogenerated charge carriers is increased by a factor of 10. For the investigation of structure and function of the buffer layer, we designed a wedge-shaped multilayer film assembly. Oxygen 1s X-ray photoemission spectra suggest a decrease of oxygen vacancy concentration near the interface of α-Fe 2 O 3 and FTO−SnO 2 , when the SnO 2 buffer layer is introduced. This SnO 2 buffer layer increases the crystallinity of the hematite layer. The oxygen 1s near-edge X-ray absorption fine structure shows that the buffer layer increases the Fe 3d−O 2p hybridization and affects the quasi-Fermi level of electrons in α-Fe 2 O 3 . There is some indication that the α-Fe 2 O 3 layer contains an adverse hole state in the valence band which disappears when the α-Fe 2 O 3 layer is grown on the SnO 2 layer. This layer induces improved orbital overlap with subsequent improved charge transfer between the absorber α-Fe 2 O 3 and the current collector FTO. Our experiments indicate that performance enhancement by this buffer layer is of electronic structure origin.

Tuning the Electronic Structure of Cobalt Selenide on Copper Foam by Introducing a Ni Buffer Layer for Highly Efficient Electrochemical Water Splitting

“…They have shown that addition of copper is expected to boost the metallic character of the catalyst that allows for faster charge transfer . In recent years, a number of studies on the growth of thin buffer layers on different substrates have been performed and have led to the enhancement of water oxidation via the improvement of its properties. − Song et al have synthesized an electrocatalyst with Ni interfacing between Ni 3 N and nickel foam (Ni 3 N/Ni/NF) for the HER and hydrogen oxidation reaction (HOR) . The catalyst imparted close to zero onset potential in alkaline and neutral electrolytes, demanding an overpotential of only 12–19 mV to afford a current density of −10 mA cm –2 for HER.…”

Nanostructured α‐Fe2O3 Photoelectrodes with Transparent and Conducting Sb‐Doped SnO2 Films Deposited by Atomic Layer Deposition

“…[52][53][54][55][56][57][58][59][60][61][62] However, nanostructuring always entails elongation of the electron path to the current collector, which hinders efficient transport of electrons. Here, heterostructuring [63,64] with conductive but still transparent layers can be a direct solution. We adopted our ATO ALD process to form a conductive layer inside a nanotubular array of α-Fe 2 O 3 to see its efficacy for electron transport by comparing the PEC performance with that of the cell without an ATO layer, as schematically shown in Figure 6.…”

Advances in Engineered Metal Oxide Thin Films by Low-Cost, Solution-Based Techniques for Green Hydrogen Production

“…The porous nature of the films, beneficial for catalysis, can also bring some drawbacks that are associated with shunting recombination in the area where the substrate is in contact with the electrolyte. To avoid this problem, the addition of an isolating underlayer of a few nanometers-such as Ga 2 O 3 [157], TiO 2 [158], SnO 2 [159], or even the deposition of a top polymeric layer [61]-has been successfully explored. Our group's latest work incorporated the underlayer approach to the improved PP methodology [160].…”