Synergistic Photoelectrochemical Synthesis of Formate from CO₂ on {121} Hierarchical Co₃O₄

To propel the thermodynamically unfavorable conversion of greenhouse CO 2 to renewable fuel with remarkable efficacy, we here proposed a visible-light-driven synergistic photoelectrochemical (PEC) synthesis of formate from CO 2 . Formate was the only C1 product photoelectrochemically generated on the fabricated hierarchical Co 3 O 4 electrode. Results showed that up to 384.8 ± 7.4 μmol of formate was produced within 8 h owing to the synergistic PEC reduction process. This enhanced production of formate, outnumbering most of the reported work, was further found to be indispensable of the superior photocatalytic and electrocatalytic reduction performance of the as-prepared electrode. Research further elucidated that the photocatalytic activity was intimately related with the hierarchical Co 3 O 4 microstructure, in which a single-crystalline microflower was interconnected by thin nanopetals on one-dimensional rhombus nanorod. Additionally, the construction of {121̅} facet allowed high Co 3+ exposure on Co 3 O 4 surface, remarkably enhancing the transient and steady state photoelectrochemical reductive response of CO 2 and HCO 3 – than other electrodes. It further revealed that the judicious merging of these superior photocatalytic and electrocatalytic performances as synergistic photoelectrochemical contributed to the considerably increasing utilization of surface reduction active sites for CO 2 and HCO 3 – .