Cocatalyst decoration has been recognized as an effective strategy in photocatalysis, yet the critical role of sing-atomic state on CO₂ photocatalytic reduction, distinguished from the oxide and elemental states, remains a mystery hitherto. Herein, single-atom Pd (Pd-SA), Pd oxides (PdO_x), and Pd nanoparticles (Pd-NP), were homogeneously anchored on g-C₃N₄ (CN) to investigate their CO₂ reduction behaviors under visible-light irradiation. Performance tests showed Pd species decoration improved the CH₄ production of CN, with Pd/CN-SA exhibiting the optimum yields (2.25 μmol g^–1), markedly higher than that of PdO_x/CN (1.08 μmol g^–1) and Pd/CN-NP (0.44 μmol g^–1). After comprehensive mechanism analysis with various characterization techniques, in-situ DRIFT spectra and DFT calculations, it was found that the conducive activation of CO₂, negative conduction band potentials, and excellent •H utilization efficiency, collaboratively contributed to the superior CH₄ production of Pd/CN-SA. Despite the larger electron density of Pd/CN-NP and PdO_x/CN, the moderate reduction ability of their photogenerated electrons restricted the further reduction of adsorbed CO₂ species and CO intermediate, limiting the enhancement of CO₂ reduction activity. Furthermore, the CH₄ evolutions of Pd/CN-NP and PdO_x/CN were also limited by the poor •H supply and inferior •H utilization efficiency, respectively. It is expected that the effect of chemical states, especially the critical role of single-atomic state, revealed in this work can inspire the rational design of more advanced photocatalysts for CO₂ reduction.

助催化剂修饰已被公认为光催化中的有效策略，但单原子态在CO ₂光催化还原中的关键作用，区别于氧化物和元素态，至今仍是一个谜。在此，将单原子 Pd (Pd-SA)、Pd 氧化物 (PdO _x ) 和 Pd 纳米粒子 (Pd-NP) 均匀锚定在 gC ₃ N ₄ (CN) 上，以研究它们在可见光下的CO ₂还原行为辐照。性能测试表明，Pd 物种修饰提高了 CN 的 CH ₄产量，Pd/CN-SA 表现出最佳产率 (2.25 μmol g ^–1 )，明显高于 PdO _x /CN (1.08 μmol g^–1 ) 和 Pd/CN-NP (0.44 μmol g ^–1 )。在使用各种表征技术、原位漂移光谱和 DFT 计算进行综合机理分析后，发现 CO ₂的有利于活化、负导带电位和出色的 •H 利用效率共同促成了优异的 CH ₄产量Pd/CN-SA。_{尽管Pd/CN-NP和PdO x} /CN具有较大的电子密度，但其光生电子的适度还原能力限制了吸附的CO ₂物种和CO中间体的进一步还原，限制了CO ₂还原活性的增强。此外，CH ₄Pd/CN-NP 和PdO _x /CN 的演化也分别受到•H 供应不足和•H 利用效率低下的限制。预计在这项工作中揭示的化学态的影响，尤其是单原子态的关键作用，可以激发对用于 CO 2 还原的更先进光催化剂的合理_设计。