Surface-Modified Ta3N5 Photoanodes for Sunlight-Driven Overall Water Splitting by Photoelectrochemical Cells

Tomohiro Higashi,Masao Katayama,Kazuhiro Takanabe,Yudai Kawase,Hiroshi Nishiyama,Kazunari Domen,Yutaka Sasaki

doi:10.3390/catal11050584

Tomohiro Higashi, Masao Katayama + Show 5 more

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https://doi.org/10.3390/catal11050584

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Abstract

The development of visible-light-responsive semiconductor-based photoelectrodes is a prerequisite for the construction of efficient photoelectrochemical (PEC) cells for solar water splitting. Surface modification with an electrocatalyst on the photoelectrode is effective for maximizing the water splitting efficiency of the PEC cell. Herein, we investigate the effects of surface modification of Ta3N5 photoanodes with electrocatalysts consisting of Ni, Fe, and Co oxides, and their mixture, on the PEC oxygen evolution reaction (OER) performance. Among the investigated samples, NiFeOx-modified Ta3N5 (NiFeOx/Ta3N5) photoanodes showed the lowest onset potential for OER. A PEC cell with a parallel configuration consisting of a NiFeOx/Ta3N5 photoanode and an Al-doped La5Ti2Cu0.9Ag0.1S5O7 (LTCA:Al) photocathode exhibited stoichiometric hydrogen and oxygen generation from water splitting, without any external bias voltage. The solar-to-hydrogen energy conversion efficiency (STH) of this cell for water splitting was found to be 0.2% at 1 min after the start of the reaction. In addition, water splitting by a PEC cell with a tandem configuration incorporating a NiFeOx/Ta3N5 transparent photoanode prepared on a quartz insulating substrate as a front-side electrode and a LTCA:Al photocathode as a back side electrode was demonstrated, and the STH was found to be 0.04% at the initial stage of the reaction.

Highlights

We focused on the surface modification of Ta3 N5 photoanodes as a means of enhancing the efficiency of overall water splitting in the PEC cell
The present study considers overall water splitting using a tandem PEC cell composed of a Ta3 N5 /SiO2 transparent photoanode as the front-side electrode and a LTCA:Al photocathode as the back-side electrode
The photocurrent generated by the NiFeCoOx /Ta3 N5 /Ta and NiFeOx /Ta3 N5 /Ta photoanodes increased with increasing electrode potential

Summary

Introduction

One approach to PEC water splitting involves the use of a PEC cell that combines a photocathode for the hydrogen evolution reaction (HER) and a photoanode for the oxygen evolution reaction (OER) [1,7,8,9] This PEC cell can relax the requirements for water splitting, such as the positions of the conduction band minimum and valence band maximum of the individual photoelectrodes [8,9], through a two-step light excitation process. This process makes it possible to drive a spontaneous overall water splitting reaction under simulated sunlight illumination without the application of an external bias voltage

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Conclusion