Efficient Photocatalytic CO₂ Reduction to C₂₊ Products with Pt_{1- x}Pd_xSn₄ Dirac Nodal Arc Semimetal

The photochemical CO₂ reduction reaction (CRR) represents a zero-carbon pathway for converting CO₂ into value-added chemicals, yet its industrial implementation has been constrained by low selectivity and product diversity. Dirac nodal arc semimetals characterized by ultrahigh carrier mobility (>25 000 cm²·V^-1·s^-1) offer a promising platform to search for efficient catalysts for CO₂ conversion. Herein, we demonstrate that strategic Pt incorporation into PdSn₄ optimizes the electronic structure and carrier dynamics of this Dirac semimetal. Experimental and theoretical analyses reveal that the resulting Pd─Sn─Pt local electronic structure redistributes charge density around Pd and Pt atoms, which facilitates C─C coupling via *OC─COH and *OC─CHOH intermediates and enhances carrier mobility by 40% versus the pristine PdSn₄ single crystal. The optimized Pd_0.4Pt_0.6Sn₄ single crystal achieves C₂H₄ i) formation rate of 328 µmol∙g^-1∙h^-1; ii) product selectivity of 73.1%; iii) electron-based selectivity of 89%. This work establishes electronic-structure-tunable Dirac semimetals as a new paradigm for multi-carbon photochemical CO₂ reduction, providing a design strategy for next-generation photocatalysts.