Understanding the charge transfer dynamics of the Cu₂WS₄-CNT-FeOOH ternary composite for photo-electrochemical...

Ternary transition metal chalcogenide (Cu₂WS₄) is a semiconductor with a band gap of 2.1 eV and could be a promising candidate for photoelectrochemical water splitting and solar energy conversion applications. Despite numerous reports on ternary transition metal chalcogenides, this semiconductor's ultrafast charge transfer dynamics remain unknown. Here, we report on charge carrier dynamics in a pristine Cu₂WS₄ system with the aid of ultrafast transient (TA) pump-probe spectroscopy and a hot carrier transfer process from Cu₂WS₄ to multi-walled carbon nanotubes (CNTs) and FeOOH has been observed. Furthermore, we have explored Cu₂WS₄-FeOOH having a type-II composite for photo-electrochemical (PEC) water oxidation and modified this with the addition of multi-walled carbon nanotubes to expedite the charge-transfer processes and photo-anodic performance. The photo-electrochemical studies demonstrate that the Cu₂WS₄-CNT, Cu₂WS₄-FeOOH, and Cu₂WS₄-CNT-FeOOH provide nearly 3-, 8- and 12-fold enhancement in photocurrent density relative to the bare Cu₂WS₄ photo-anode at 1.23 V vs. RHE. These photo-electrochemical studies support the results obtained from the TA investigation and further prove the higher charge separation in the ternary composite system. These studies probe the excited states and provide evidence of longer charge separation in the binary and ternary composites, responsible for their remarkable photo-electrochemical performance.