Dopant-rich surface alloying effects on photoexcited carrier pathways in Cu nanoclusters with adsorbed CH4 and CO2.

The photocatalytic conversion of methane (CH4) and carbon dioxide (CO2) into value-added chemicals offers a promising route for mitigating greenhouse-gas emissions and producing solar fuels. Here, we employ real-time time-dependent density functional theory (rt-TDDFT) to investigate collective electronic excitations, hot-carrier (HC) generation, and adsorbate-resolved carrier localization in Cu nanoclusters under a dopant-rich surface-alloy limit. Specifically, we compare Cu147 clusters whose surface Cu atoms are extensively substituted by Ag, Pd, or Pt, providing an idealized platform to isolate dopant-identity effects on light-matter interaction and carrier pathways. Our simulations reveal a clear dopant-dependent dichotomy. Ag-rich surface substitution enhances optical absorption and produces broader HC energy distributions, indicative of plasmon-modified collective electronic excitations that facilitate carrier transfer to both CH4 and CO2. In contrast, Pd- and Pt-rich surface substitution suppresses collective dipolar response but promotes stronger localization of photoexcited carriers near adsorbed CH4, consistent with enhanced chemo-selective electronic coupling. We emphasize that the present study reports excited-state electronic descriptors relevant to photocatalysis-such as HC energy distributions and adsorbate-projected carrier populations-rather than reaction pathways or catalytic rates. These results provide mechanistic insight into how surface alloy composition governs the balance between collective excitation and carrier localization in Cu-based nanoclusters, offering qualitative design principles for plasmon-assisted photocatalytic systems.