Photoactivated Ion Transport: Role of Intrinsic Defects and Plasmonics for Efficient Ionic Power Harvesting

The process of photosynthesis in green plants and energy conversion in certain archaea are inseparable from photoregulated ion pumping. Two-dimensional (2D) nanofluidic membranes, emerging as competitive candidates for constructing ion pumps, present intriguing prospects for harvesting light energy. However, the inevitable presence of defects during the synthesis of 2D materials underscores the critical need to understand their impact on ion transport dynamics within nanofluidic systems. Here, we present a chemically engineered asymmetric nanofluidic membrane (ANM) by intercalating molybdenum trioxide (MoO₃) with controlled oxygen vacancies into graphene oxide laminates, systematically investigating the defect chemistry-governed photo-activated ion transport. Upon photoexcitation, MoO₃ nanosheets exhibit tunable surface plasmon resonance (SPR) through photochemical H⁺ intercalation, leading to an augmentation of oxygen vacancies and an elevated concentration of free electrons. These vacancies enrich MoO₃ with excess localized surface electrons, enabling tunable SPR that creates negative charge centers and significantly enhances space charge through defect-induced polarization. Density functional theory (DFT) calculations reveal the atomic-level mechanism of vacancy-enhanced cation transport, showing a notable 188% increase in the adsorption energy of K⁺ at MoO₃ surfaces with two vacancy sites compared to one vacancy (-13.66 vs -4.74 eV). Under asymmetric photo irradiation, the system achieves a peak power density of approximately 439.2 W/cm² in equilibrium ionic solutions, realizing a photonic-to-ionic energy conversion efficiency of 7.98 × 10^-4% via synergistic effects of defects and plasmonics. Our research pioneers the elucidation of the regulation and underlying mechanisms of intrinsic defects on active ion transport within nanofluidic membranes, while fostering a novel perspective on photon-electron-ion interplay within nanofluidic environments.