Plasmon-induced electron injection into the large negative potential conduction band of Ga2O3 for coupling with water oxidation

Abstract

In this study, an interfacial modification layer was applied to improve the plasmon-induced light energy conversion of a gallium(III) oxide (Ga₂O₃) photoelectrode, which possesses a much more negative conduction band potential compared with the reduction potential of photons to hydrogen. The plasmon-induced photocurrent generation under visible light irradiation was observed with Au nanoparticle-loaded Ga₂O₃ (Au-NPs/Ga₂O₃). An interfacial modification was carried out by depositing a titanium dioxide (TiO₂) thin-film layer on Au-NPs/Ga₂O₃via atomic layer deposition. Since the surface states of TiO₂ possess excellent hole-trapping ability, this interfacial modification remarkably improved the generation of plasmon-induced photocurrent in the visible region. The photoelectric conversion efficiency of interfacially modified Au-NPs/Ga₂O₃ showed a TiO₂ thin-film thickness dependence because the migration of hot carriers was suppressed with increasing TiO₂ thickness. The Au-NPs/Ga₂O₃ photoelectrode modified with 2 nm-thick TiO₂ showed the best photoelectric conversion performance, and the thermodynamic energy conversion efficiency under irradiation with 600 nm light was approximately two times larger than that of the Au-NPs/TiO₂-thin film due to the extremely negative onset potential of Au-NPs/Ga₂O₃ with TiO₂. Therefore, the plasmonic Ga₂O₃ photoanode with the interfacial TiO₂ modification could provide both a high reduction ability for H₂ evolution and an oxidation ability for water oxidation, because of the negative conduction band of Ga₂O₃ and the hole-trapping property from TiO₂, respectively.