In Situ X-ray Absorption Fine Structure Spectroscopy Measurement of Suspended Cobalt Oxide Nanoparticle Water...

Area of Science:

• Catalysis
• Photochemistry
• Materials Science

Background:

• Artificial photosynthesis aims to mimic natural processes for sustainable energy production.
• Efficient water oxidation catalysts operating at near-neutral pH are crucial for artificial photosynthesis.
• Cobalt oxide (CoO_x) nanoparticles are promising heterogeneous catalysts for water oxidation.

Purpose of the Study:

• To investigate the effect of different buffer solutions (phosphate vs. borate) on the performance of a supported CoO_x nanoparticle catalyst for photochemical water oxidation.
• To elucidate the role of the buffer environment in stabilizing active catalytic species using in situ X-ray absorption fine structure spectroscopy (XAFS).

Main Methods:

• Photochemical water oxidation experiments using a Ru(II) trisdiimine photosensitizer and sodium persulfate electron acceptor.
• In situ Co-K edge X-ray absorption fine structure spectroscopy (XAFS) to probe the catalyst's local structure and oxidation state.
• Comparative study in phosphate and borate buffer solutions at pH 7.9.

Main Results:

• Catalytic activity of CoO_x was 3-4 times higher in phosphate buffer compared to borate buffer.
• In phosphate buffer, the catalyst maintained a stable, high-valence CoOOH-like structure during photoirradiation.
• In borate buffer, CoOOH-like species were transient, leading to a mixture of less active Co species.

Conclusions:

• Phosphate buffers promote the generation and long-term stabilization of active CoOOH species, enhancing water oxidation efficiency.
• Borate buffers fail to sustain the active catalytic species, resulting in lower and unstable activity.
• Buffer selection is critical for designing robust catalytic systems for efficient water oxidation in artificial photosynthesis.