Facet-Dependent Co₃O₄ Nanocrystals for Efficient and Highly Selective Photothermal CO₂ Hydrogenation

Photothermal CO₂ hydrogenation with green H₂ for conversion into fuels or chemicals is a promising technology for efficient CO₂ conversion with low energy input. However, low catalytic activity and selectivity are one of the difficulties in photothermal catalysis, so it is crucial to develop photothermal catalysts with high catalytic activity. By employing crystalline surface engineering, specific highly active crystalline surfaces can be exposed, which have more active sites and can improve the photothermal performance of the catalysts to some extent. Based on this, two kinds of Co₃O₄ nanocrystals with exposed different facets are synthesized via the hydrothermal method, and the facet-dependent reactivity in photothermal CO₂ hydrogenation is explored. The results showed that the Co₃O₄ nanocubes with exposed (001) facets presented the CH₄ yield of 11.00 mmol h^-1 with 61.06% CO₂ conversion and 80% CH₄ selectivity, which is ≈39% higher than the yield of Co₃O₄ octahedrons enclosed by (111) facets. Co₃O₄ with exposing only (001) facets has a higher Co²⁺/Co⁰ ratio, thus resulting in better CO₂ adsorptions favoring the formic acid path to produce methane. This study provides a series of new facet-dependent photothermal catalyst designs and reveals for the first time the effect of thermal energy on catalyst conductivity.