Discovery and optimization of Zn0.3Cd0.7S-based photocatalysts by scanning electrochemical microscopy and characterization of potential photocatalysts

• The potential Zn0.3Cd0.7S-based photocatalysts were identified by SECM.
• Ag0.3-(Zn0.3Cd0.7S)0.7 showed the highest photocurrent. Ag0.3-(Zn0.3Cd0.7S)0.7 was comprised of Ag2S and Zn0.3Cd0.7S.
• The band gap and flat band potential of the Ag0.3-(Zn0.3Cd0.7S)0.7 estimated to be 2.3 eV and −0.7 V vs Ag/AgCl.
• The IPCE value of Ag0.3-(Zn0.3Cd0.7S)0.7 was higher than the Zn0.3Cd0.7S.

Scanning electrochemical microscopy (SECM) with a scanning optical fiber was applied to rapidly identify potential Zn0.3Cd0.7S-based photocatalysts for water oxidation. Among the photocatalysts studied, the spot with the precursor composition Ag0.3-(Zn0.3Cd0.7S)0.7 shows the highest photocurrent in 0.1 M Na2SO4/Na2SO3 solution under both UV-visible and visible light irradiation. The X-ray diffraction and X-ray photoelectron spectrometric analyses reveal that the Ag0.3-(Zn0.3Cd0.7S)0.7 photocatalyst is comprised of monoclinic Ag2S and solid solution Zn0.3Cd0.7S phases with average crystallite size in the range 18–28 nm. The addition of 30%Ag2S to Zn0.3Cd0.7S photocatalysts enhances light absorption in the visible region. The SECM screening results are also confirmed with bulk film studies. The Ag0.3-(Zn0.3Cd0.7S)0.7 electrode exhibits highly efficient visible-light photocatalytic activity with an IPCE value above 20% for a light wavelength of 500 nm.