Solar-to-Pharmaceutical Raw Material Production: Photoelectrochemical Naphthoquinone Formation Using Stabilized BiVO4 Photoanodes in Acid Media

Tomohiko Nakajima; Hiroyuki Tateno; Yugo Miseki; Tetsuo Tsuchiya; Kazuhiro Sayama

doi:10.1021/acsami.1c16777

Solar-to-Pharmaceutical Raw Material Production: Photoelectrochemical Naphthoquinone Formation Using Stabilized BiVO₄ Photoanodes in Acid Media

ACS Appl Mater Interfaces. 2021 Dec 8;13(48):57132-57141. doi: 10.1021/acsami.1c16777. Epub 2021 Nov 25.

Authors

Tomohiko Nakajima¹, Hiroyuki Tateno², Yugo Miseki³, Tetsuo Tsuchiya¹, Kazuhiro Sayama³

Affiliations

¹ Advanced Manufacturing Research Institute, National Institute of Advanced Industrial Science and Technology, Tsukuba Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan.
² Energy Process Research Institute, National Institute of Advanced Industrial Science and Technology, Tsukuba West 5, 16-1 Onogawa, Tsukuba, Ibaraki 305-8569, Japan.
³ Global Zero Emission Research Center, National Institute of Advanced Industrial Science and Technology, Tsukuba West, 16-1 Onogawa, Tsukuba, Ibaraki 305-8569, Japan.

PMID: 34823359
DOI: 10.1021/acsami.1c16777

Abstract

In the quest for efficient use of solar energy to produce high-value-added chemicals, we first achieved the photoelectrochemical (PEC) diketonization of naphthalene, using a BiVO₄/WO₃ photoanode, to obtain naphthoquinone, an important pharmaceutical raw material with excellent efficiency by solar energy conversion. In the electrochemical (EC) reaction using F-doped SnO₂ (FTO) substrates and a 0.5 M H₂SO₄ H₂O-acetone (60 vol %) mixed solution containing 5 mM naphthalene, we produced a small amount of naphthoquinone evolution in the dark. However, naphthoquinone (η_NQ)'s Faradic efficiency and its evolution rate at 1.7 V_Ag/AgCl were only 28.5% and 0.48 μmol·cm^-2·h^-1, respectively. The PEC reaction using a WO₃ photoanode had very low efficiency for naphthalene diketonization, with low η_NQ and evolution rate values at 1.1 V_Ag/AgCl of 0.3% and 0.039 μmol·cm^-2·h^-1, respectively. In contrast, the BiVO₄/WO₃ photoanode strongly enhanced the PEC reaction, and the η_NQ and evolution rates at 1.1 V_Ag/AgCl were boosted up to 37.5% and 4.7 μmol·cm^-2·h^-1, respectively. The evolution rate of the PEC reaction in the BiVO₄/WO₃ photoanode was 10 times higher than that of the EC reaction with the FTO substrate regardless of the very low bias voltage. This result suggests that the BiVO₄-based photoanode was very efficient for the selective oxidation of naphthalene even in acid media because of the acetone-mixed electrolyte's anti-photocorrosion effect and the multilayering of WO₃ and BiVO₄. At a naphthalene concentration of 20 mM, the naphthoquinone evolution rate reached its maximum value of 7.1 μmol·cm^-2·h^-1. Although η_NQ tended to decrease with the increase in the electric charge, it reached 100% at a low bias voltage of 0.7 V_Ag/AgCl. An intensity-modulated photocurrent spectroscopy analysis indicated the rate constant of charge transfer at the photoanode surface to the naphthalene molecules was strongly enhanced at a low bias voltage of 0.7-1.1 V_Ag/AgCl, resulting in the high η_NQ value. The acid-resistant BiVO₄/WO₃ photoanode functioned in acetone-mixed electrolytes enabled the realization of a new PEC oxidation reaction driven by solar energy to produce high-value-added pharmaceutical raw materials.

Keywords: BiVO4; acid resistance; anti-photocorrosion; diketonization of naphthalene; naphthoquinone; photoelectrodes; solar energy conversion.