Comprehensive experimental design of a photoelectrochemical water oxidation composite photoanode B: CoO_x/BiVO₄

Based on the ongoing global energy crisis and sustainable development goals, synthesizing highly efficient and stable composite photoanodes to achieve the efficient conversion of solar energy into green energy, such as H₂, is essential in the photoelectrochemical (PEC) field. In this study, we design a comprehensive experiment centered on a composite photoanode—B: CoO_x/BiVO₄—for PEC water oxidation, grounded on the concept of integrating science and education as well as cutting-edge research findings of faculty members. Implementing such an experiment for undergraduate students not only helps bridge the gap between textbook knowledge and the related frontier of scientific research but also demonstrates the practical necessity for fostering high-level, energetic students equipped with innovative and creative capabilities.

Electrochemical deposition and solution impregnation were employed to fabricate an oxygen vacancy-rich B: CoO_x/BiVO₄ composite photoanode on an FTO substrate. By leveraging a large-scale instrument and equipment sharing platform from the state key laboratory of organic–inorganic composites, including scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffractometry, and X-ray photoelectron spectroscopy, the morphology, crystal structure, elemental composition, and oxygen vacancy of B: CoO_x/BiVO₄ were characterized, and the corresponding images and data were analyzed in detail. Further, the water oxidation performance of B: CoO_x/BiVO₄, including photocurrent density, stability, solar energy conversion efficiency, and charge separation/transfer efficiencies, was thoroughly investigated using linear sweep voltammetry, current–time curves, Mott–Schottky plot, polarization and surface charge transfer curves, and electrochemical impedance spectroscopy. In addition, the mechanism by which the oxygen vacancy-rich B: CoO_x cocatalyst promotes the water oxidation performance of BiVO₄ was explored.

As revealed by the aforementioned characterizations, the oxygen vacancy-rich B: CoO_x cocatalyst was successfully grown on the BiVO₄ photoanode surface. Microscopic characterizations and electrochemical measurements manifest that the oxygen vacancy-rich B: CoO_x cocatalyst decoration promotes photo-induced charge separation, provides rich surface catalytically active sites, accelerates charge transfer, and reduces the energy barrier for the water oxidation reaction, thereby boosting BiVO₄’s PEC activity. The optimized B: CoO_x/BiVO₄ composite photoanode exhibited an excellent PEC water oxidation performance, yielding a high photocurrent density of 3.20 mA cm^-2 at 1.23 V_RHE, and excellent stability for 5 h. Upon intermittent illumination for 180 min, the accumulation contents of O₂ and H₂ over the B: CoO_x/BiVO₄ photoanode and Pt cathode reached 104.5 and 53.4 µmol cm^-2, respectively.

The comprehensive experiment conducted in this study is to develop a highly active oxygen vacancy-rich B: CoO_x/BiVO₄ composite photoanode via electrochemical deposition and solution impregnation. It was designed as a leading-edge scientific endeavor, integrating B: CoO_x/BiVO₄ synthesis, structural characterizations, electrochemical properties, PEC water oxidation assays, experimental data and result analysis, and possible reasons for the performance enhancement of the as-fabricated composite photoanode. This comprehensive experimental training helps students to understand the preparation and optimization of photoanodes and the PEC water oxidation theory, thereby cultivating comprehensive experimental skills, scientific exploration, and innovation consciousness.