Pd–Bi Bimetallic Alloy on ZIF-8-Derived ZnO Semiconductor for Accelerated Photocatalytic CO ₂ to Methanol Production

We report a robust Pd–Bi nanoalloy integrated with distorted polyhedral ZnO derived from ZIF-8 for efficient photocatalytic reduction of CO 2 to methanol. The hybrid catalyst, denoted Pd x Bi 1– x /ZnO (PBZ), delivers a promising methanol yield of 1984 μmol g –1 with an AQY of 0.87% under 4 h of simulated solar irradiation using water as the electron donor, nearly twice that of pristine ZIF-8-derived ZnO. HR-TEM and HAADF-STEM confirm uniformly dispersed monoclinic Pd–Bi nanoalloys with controlled size evolution governed by the reduction potential disparity of the Pd and Bi precursors. PL and EPR analyses reveal that alloy incorporation suppresses electron–hole recombination and modulates ZnO surface defect states. XPS further validates strong interfacial electronic coupling among Pd, Bi, and Zn, leading to charge redistribution, low-valence Bi species, and metallic Pd. Transient photocurrent and EIS measurements of Pd 0.6 Bi 0.4 /ZnO show significantly enhanced charge separation and reduced interfacial resistance, consistent with prolonged charge carrier lifetimes from TCSPC. DFT calculations demonstrate that Pd 0.6 Bi 0.4 nanoalloys exhibit strong CO 2 adsorption and effectively stabilize oxygenated intermediates, enabling a thermodynamically favorable pathway toward methanol. The catalyst maintains excellent stability across multiple cycles. This work establishes an effective strategy for engineering defect-rich alloy oxide heterostructures for solar-driven conversion of CO 2 to fuel.