Reversible Charge Transfer and Adjustable Potential Window in Semiconductor/Faradaic Layer/Liquid Junctions

Abstract

Semiconductor/Faradaic layer/liquid junctions have been widely used in solar energy conversion and storage devices. However, the charge transfer mechanism of these junctions is still unclear, which leads to inconsistent results and low performance of these devices in previous studies. Herein, by using Fe 2 O 3 and Ni(OH) 2 as models, we precisely control the interface structure between the semiconductor and the Faradaic layer and investigate the charge transfer mechanism in the semiconductor/ Faradaic layer/liquid junction. The results suggest that the short circuit severely restricts the performance of the junction for both solar water splitting cells and solar charging supercapacitors. More importantly, we also find that the charge-discharge potential window of a Faradaic material sensitively depends on the energy band positions of a semiconductor, which provides a new way to adjust the potential window of a Faradaic material. These new insights offer guidance to design high-performance devices for solar energy conversion and storage.

Mildly regulated intrinsic faradaic layer at the oxide/water interface for improved photoelectrochemical performance

“…10 Therefore, the intermediate layers can be considered as extrinsic faradaic layers. 11 The faradaic layers can accelerate both interface charge collection and oxygen evolution reaction (OER) kinetics and improve the performance of a photoelectrode. [12][13][14][15] Moreover, some recent studies have suggested that there is an intrinsic hydrated layer on the surface of metal oxide in ambient air or an electrolyte, 6,[16][17][18][19] which also has signicant effects on interface charge separation and transfer.…”

“… 10 Therefore, the intermediate layers can be considered as extrinsic faradaic layers. 11 The faradaic layers can accelerate both interface charge collection and oxygen evolution reaction (OER) kinetics and improve the performance of a photoelectrode. 12 – 15…”

A Capacitor‐type Faradaic Junction for Direct Solar Energy Conversion and Storage

“…The Si/WO 3 /H 2 SO 4(aq) /C exhibits an unbiased output power of 0.8 mW cm −2 in the dark. However, previously reported devices based on battery‐type chemical junctions [1, 13–20] cannot work under zero bias and indicate negligible output power during dark discharge (Supporting Information, Table S1). Therefore, this new capacitor‐type device achieves the highest dark output power among all of the reported two‐electrode solar rechargeable devices.…”

“…AF aradaic junction is composed of as emiconductor and aF arador,w hich is ac oupled electron-ion conductor and chemically changed during charge transfer across the interface. [1] Therefore,aFaradaic junction is ac hemical junction and indicates quite different features from some well-known physical junctions,s uch as Schottky junctions, [2][3][4][5] p-n junctions, [6][7][8] or direct Z-scheme junctions, [9][10][11] in which only electrons transfer at the interface (Supporting Information, Figure S1). Very importantly,aFarador in this chemical junction can be regenerated reversibly by controlling the interface charge transfer direction.…”

“…[1,12] Consequently,t he Faradaic junction can be regarded as apotential approach to realize recyclable solar energy conversion and storage.Inthis chemical junction, aF arador can also be replaced by redoxactive electrolyte to form as emiconductor/electrolyte junction due to its high capacitance. [12] In the past few decades,alot of effort has been taken to construct two-electrode solar rechargeable devices based on Faradaic junctions (Fe 2 O 3 /Ni(OH) 2 ,T iO 2 /Ni(OH) 2 ) [1,[13][14][15][16] or semiconductor/electrolyte junctions (CdSe/S 2À ,T iO 2 /Dye/ I À ). [17][18][19] However,u pt od ate,a ll of these devices can only be photo charged, but not dark discharged under zero bias.…”