Synergy between Palladium Single Atoms and Nanoparticles via Hydrogen Spillover for Enhancing CO₂ Photoreduction to CH₄.

Abstract

Selective photoreduction of carbon dioxide (CO₂ ) into carbon-neutral fuels such as methane (CH₄ ) is extremely desirable but remains a challenge since sluggish multiple proton-electron coupling transfer and various C₁ intermediates are involved. Herein, a synergistic function between single Pd atoms (Pd₁ ) and Pd nanoparticles (Pd_NPs ) on graphitic carbon nitride (C₃ N₄ ) for photocatalytic CO₂ methanation is presented. The catalyst achieves a high selectivity of 97.8% for CH₄ production with a yield of 20.3 µmol g_cat. ^-1 h^-1 in pure water. Mechanistic studies revealed that Pd₁ sites activated CO₂ , while Pd_NPs sites boosted water (H₂ O) dissociation for increased H* coverage. The H* produced by Pd_NPs migrate to the Pd₁ sites to promote multiple proton-electron coupling transfer via hydrogen spillover. Moreover, the adjacent Pd₁ and Pd_NPs effectively stabilized intermediates such as *CHO, thereby favoring the pathway for CH₄ production. This work provides a new perspective into the development of selective photocatalytic CO₂ conversion through the artful design of synergistic catalytic sites.