Cu-Pd Dual Single Atoms Promoting Selective CO₂ Photoreduction to C₂ Products in Seawater

The solar-powered CO₂ conversion via the photocatalysis route offers a sustainable pathway toward carbon neutrality while mitigating energy/environmental pressure. Nevertheless, the selective and efficient conversion of CO₂ via photoreduction to C₂ products remains a formidable challenge. Here, we engineered a dual-single-atom photocatalyst by controllably embedding Pd and Cu single atoms into a TiO₂ matrix. The optimized catalyst (Cu_0.5Pd_0.5/TiO₂) exhibits the outstanding yield (119.2 µmol/g_cat) and selectivity (84.8%) for acetic acid production from CO₂ photoreduction, performed in seawater and in a photothermal-aided reactor. Various in situ/ex situ characterizations were employed to investigate atomic-level structure-performance correlation and reaction mechanism in practical condition. In situ x-ray photoelectron spectroscopy, in situ atomic force microscopy-Kelvin probe force microscopy, transient-state surface photovoltage, and in situ electron paramagnetic resonance (EPR) collectively indicate that loading Pd and Cu single atoms onto TiO₂ apparently accelerates charge kinetics. This modification results in increased photogenerated electrons for CO₂ reduction, facilitating C─C coupling and hydrogenation reactions. Additionally, in situ infrared (IR) spectroscopy and theoretical computations affirm the pivotal function of Pd single atoms for lowering the energy barrier to form the ^*OCCO intermediate, apparently improving selectivity for acetic acid production. Overall, our work presents an innovative approach to tackle kinetic and thermodynamic challenges for light-induced CO₂-to-C₂ conversion.