Growth and Photoelectrochemical Characterization of Epitaxial ZnTe Photocathodes for Carbon Dioxide Reduction

We report on growth and photoelectrochemical (PEC) characterization of single crystal, epitaxial zinc telluride (ZnTe) thin film photocathodes, highlighting their potential as efficient materials for photoelectrochemical CO₂ reduction. We investigated the photoelectrochemical stability and catalytic selectivity of ZnTe photocathodes in a CO₂-saturated electrolyte (0.1 M KHCO₃) using a three-electrode compression cell. Utilizing degenerately doped (100) ZnTe, we have demonstrated high selectivity (60%) for CO₂ reduction to CO without cocatalysts.<br/><br/>To gain a deeper understanding of the fundamental charge transport and reactivity mechanisms of ZnTe, we utilized molecular beam epitaxy (MBE) to grow single crystalline, degenerately-doped ZnTe thin films on gallium arsenide (GaAs) substrate oriented along (100), (110), and (111)A. ZnTe thin films with thickness of 300 nm, grown in the temperature range of 340–360°C, were doped with nitrogen via <i>in situ</i> RF plasma nitrogen activation. Characterization techniques including RHEED, XRD, AFM, and Hall effect measurements confirmed their epitaxial nature and p-type conductivity with doping concentrations ranging from 10¹⁸ to 10²⁰ cm^-3. Notably, we have also observed a correlation between the CO₂R selectivity and the ZnTe film crystal orientation. This work can be leveraged to develop catalyst-free tandem ZnTe-based carbon dioxide reduction photocathodes.