Effective Visible Light Exploitation by Copper Molybdo-tungstate Photoanodes.

Area of Science:

• Materials Science
• Photocatalysis
• Semiconductor Engineering

Background:

• Stable oxide semiconductors with narrow band gaps are crucial for efficient photoelectrocatalytic (PEC) applications, particularly for visible light utilization.
• Current materials often struggle to maximize the absorption of the visible light spectrum, limiting their effectiveness in solar energy conversion.
• Copper tungstate (CuWO$_4$) is a known semiconductor, but its band gap limits its performance under visible light.

Purpose of the Study:

• To investigate molybdenum-doped copper tungstate (CuW$_{1-x}$Mo$_x$O$_4$) as a photoactive material for photoanodes in PEC applications.
• To enhance the visible light photoactivity and spectral response of copper tungstate-based photoanodes.
• To understand the impact of molybdenum incorporation and electrode thickness on charge separation and injection efficiencies.

Main Methods:

• Synthesis of CuW$_{0.5}$Mo$_{0.5}$O$_4$ photoanodes with varying thicknesses (80-530 nm) using a solution-based multilayer film process.
• Characterization of optical band gap (E$_g$) and spectral response of the prepared electrodes.
• Photoelectrocatalytic (PEC) measurements using NaNO$_2$ as a hole scavenger to evaluate photocurrent generation and efficiency.

Main Results:

• CuW$_{0.5}$Mo$_{0.5}$O$_4$ exhibited a reduced optical band gap (2.0 eV) compared to CuWO$_4$ (2.3 eV), enabling photoactivity up to 650 nm.
• Thicker electrodes demonstrated improved exploitation of long-wavelength photons, enhancing overall photoactivity.
• Molybdenum incorporation improved charge separation and injection efficiencies, leading to enhanced photocurrent generation.

Conclusions:

• Molybdenum substitution in copper tungstate significantly enhances visible light photoactivity for PEC applications.
• The developed CuW$_{0.5}$Mo$_{0.5}$O$_4$ photoanodes offer improved solar spectrum utilization for chemical energy storage.
• Electrode thickness is a critical parameter for optimizing the performance of these novel photoanodes.