In this study, we explore cocatalyst-free, single-crystalline, and epitaxial thin film zinc telluride (ZnTe) as a photocathode for CO2-to-CO conversion. The study systematically examines the impact of electronic properties and crystal orientation using nitrogen-doped, p-type ZnTe (ZnTe:N) photocathodes grown on GaAs substrates by molecular beam epitaxy (MBE). Heavily doped ZnTe:N (p ≅ 1020 cm–3) with a (100) orientation achieves a selective CO2-to-CO Faradaic efficiency of 62% over a 200-mV potential window (with current densities of ∼0.1 mA·cm–2) without additional surface modifications. ZnTe:N of (100), (110), and (111) crystal orientations demonstrate different photoactivity, with the (100) and (110) orientations exhibiting three times higher photocurrent density compared to the (111) orientation despite their similar electronic properties. Overall, this study provides a foundation for further development of ZnTe-based tandem devices for photoelectrochemical CO2 reduction.
Shiau et al. (Fri,) studied this question.