Theoretical investigation on the reaction mechanism of photocatalytic CO2 reduction over NaTaO3 modified with metal cocatalysts (Ru, Rh, and Ag)

Abstract

The photocatalytic conversion of CO₂ into value-added chemicals represents a sustainable pathway for solar energy storage and carbon emission mitigation. Understanding the atomic-level mechanisms is crucial for designing efficient photocatalysts. This work provides the first systematic comparison of how Ru, Rh and Ag cocatalysts differentially modulate the electronic structure of NaTaO₃ and dictate distinct CO₂ reduction reaction (CO₂RR) pathways, revealing metal-specific mechanistic fingerprints. All three systems (Ru@NaTaO₃, Rh@NaTaO₃ and Ag@NaTaO₃) exhibit negative formation energies, confirming their thermodynamic feasibility. Metal decoration significantly reduces the work function by 0.58–0.65 eV, facilitating interfacial charge transfer and the occurrence of the photocatalytic reduction reaction. The Ru and Rh cocatalysts demonstrate superior CO₂ adsorption and activation compared to Ag, primarily because the upshifted d-band center strengthens reactant binding. The analysis on density of states demonstrates that Ru and Rh deposition creates metallic states within the bandgap, while Ag preserves the semiconductor characteristics through valence band hybridization. Our mechanistic studies demonstrate that the product selectivity is cocatalyst-dependent. Ru- and Rh-modified NaTaO₃ promote deep reduction to CH₄ with limiting potentials of −0.75 eV and −0.51 eV, respectively. Meanwhile, Ag modification favors the 2e⁻ pathway to CO with a limiting potential of −0.43 eV. Distinct reaction pathways (CH₄ vs. CO production) can be correlated with metal-specific electronic properties. This work elucidates the structure–activity relationships of transition metal cocatalysts in the photocatalytic CO₂RR, establishing fundamental design principles for developing high-efficiency NaTaO₃-based photocatalysts.