Enabling Solar Water Oxidation by BiVO₄ in Strongly Acidic Solutions

Area of Science:

• Electrochemistry
• Materials Science
• Photocatalysis

Background:

• The oxygen evolution reaction (OER) is crucial for fuel and chemical production.
• Acidic conditions enhance reaction rates but pose stability challenges for materials like BiVO4.
• Developing stable OER in acidic media is essential for efficient electrochemical and photoelectrochemical processes.

Purpose of the Study:

• To achieve stable photoelectrochemical OER (POER) using a BiVO4 photoanode in strongly acidic solution (0.1 M HNO3, pH 1).
• To investigate the protective role of a Nb2O5 layer against BiVO4 dissolution.
• To explore the use of homogeneous Co2+ ions as an OER catalyst in conjunction with the protected photoanode.

Main Methods:

• Fabrication of a BiVO4 photoanode.
• Coating the BiVO4 with a Nb2O5 protection layer.
• Performing POER in 0.1 M HNO3 with and without the Nb2O5 layer.
• Introducing Co2+ ions into the electrolyte as a homogeneous catalyst.

Main Results:

• The Nb2O5 layer effectively suppressed the chemical and photoelectrochemical dissolution of BiVO4 in acidic media.
• Co2+ ions acted as an effective homogeneous OER catalyst, enhancing POER without forming a solid CoOx layer on Nb2O5.
• Unprotected BiVO4 showed enhanced but unsustainable POER due to dissolution, with subsequent Co3+ deposition.
• Stable POER was achieved with the Nb2O5/BiVO4 photoanode and homogeneous Co2+ catalyst.

Conclusions:

• Nb2O5 is an effective protective layer for BiVO4 in acidic photoelectrochemical applications.
• Homogeneous Co2+ ions can serve as efficient and stable OER catalysts in acidic solutions when used with a protected photoanode.
• This approach enables stable and efficient acidic POER, opening possibilities for sustainable energy and chemical production.