Copper Tantalate by a Sodium‐Driven Flux‐Mediated Synthesis for Photoelectrochemical CO ₂ Reduction

Abstract Copper‐tantalate, Cu 2 Ta 4 O 11 (CTO), shows significant promise as an efficient photocathode for multi‐carbon compounds (C 2+ ) production through photoelectrochemical (PEC) CO 2 reduction, owing to its suitable energy bands and catalytic surface. However, synthesizing CTO poses a significant challenge due to its metastable nature and thermal instability. In this study, this challenge is addressed by employing a flux‐mediated synthesis technique using a sodium‐based flux to create sodium‐doped CTO (Na‐CTO) thin films, providing enhanced nucleation and stabilization for the CTO phase. To evaluate the PEC performance and catalytic properties of the films, copper(II) oxide (CuO) at the Na‐CTO surface is selectively etched. The etched Na‐CTO shows a lower dark current, with decreased contribution from photocorrosion, unlike the non‐etched Na‐CTO which has remaining CuO on the surface. Furthermore, Na‐CTO exhibits 7.3‐fold ethylene selectivity over hydrogen, thus highlighting its promising potential as a photocathode for C 2+ production through PEC CO 2 reduction.