Pore -tailored hollow mesoporous carbon spheres confined with Pd/PdO nanoparticles enable the coupling of efficient CO2 reduction and propylene oxidation

Abstract

Electrochemical CO₂ reduction reaction (CO₂RR) coupled with anodic propylene oxidation reaction (POR) represents an energy-efficient strategy for co-producing value-added chemicals; however, the precise control over bifunctional catalyst nanostructures remains challenging. Here, we engineer pore-tuned hollow mesoporous carbon spheres (HMCs-x, x = 5–20 nm) to confine size-optimized Pd/PdO nanoparticles (NPs), resolving activity-stability trade-offs in Pd-based electrocatalysts. Noticeably, pore dimensions dictate the spatial distribution of nanoparticles: HMCs-10 achieves uniform sub-5 nm Pd NPs confined in pores with good dispersion, while undersized (HMCs-5) or oversized (HMCs-20) pores induce external agglomeration or intrapore coalescence. This nanoconfinement enables exceptional bifunctionality. For the CO₂RR, Pd/HMCs-10 delivers a high CO faradaic efficiency of 85.5% at −0.6 V vs. RHE and partial current density of 12 mA cm⁻², outperforming its counterparts by more than 35% in CO faradaic efficiency. Operando FTIR and CO₂-TPD reveal enhanced *COOH intermediate stabilization and optimal CO₂ adsorption strength, while ultraviolet photoelectron spectroscopy (UPS) results confirm that the electron transfer is facilitated by the minimized work function. Additionally, PdO/HMCs-10 achieves a high propylene oxide faradaic efficiency of 47.11% at 1.6 V vs. Ag/AgCl, with a yield of 315 mmol g⁻¹ h⁻¹, attributed to accelerated charge transfer kinetics, as validated by in situ electrochemical impedance spectroscopy (in situ EIS). Integrating these catalysts in a CO₂RR∥POR electrolyzer co-produces CO and propylene oxide with a reduced cell voltage and increased energy savings. This work establishes a pore-confinement paradigm synchronizing metal-size optimization with hierarchical porosity, providing a blueprint for multifunctional electrocatalysts in sustainable electrosynthesis.