Gapped and Rotated Grain Boundary Revealed in Ultra-Small Au Nanoparticles for Enhancing Electrochemical CO₂...

Although gapped grain boundaries have often been observed in bulk and nanosized materials, and their crucial roles in some physical and chemical processes have been confirmed, their acquisition at ultrasmall nanoscale presents a significant challenge. To date, they had not been reported in metal nanoparticles smaller than 2 nm owing to the difficulty in characterization and the high instability of grain boundary (GB) atoms. Herein, we have successfully developed a synthesis method for producing a novel chiral nanocluster Au₇₈(TBBT)₄₀ (TBBT=4-tert-butylphenylthiolate) with a 26-atom gapped and rotated GB. This nanocluster was precisely characterized using single-crystal X-ray crystallography and mass spectrometry. Additionally, an offset atomic defect linked to the peripheral Au(TBBT)₂ staple was found in the structure. Comparing it to similarly face-centered cubic-structured Au₃₆(TBBT)₂₄, Au₄₄(TBBT)₂₈, Au₅₂(TBBT)₃₂, Au₉₂(TBBT)₄₄, and ~5 nm nanocrystals, the bridging Au₇₈(TBBT)₄₀ nanocluster exhibited higher catalytic activity in the electroreduction of CO₂ to CO. This enhanced activity was explained through density functional theory calculations and X-ray photoelectron spectroscopy analysis, which highlight the impact of GBs and point defects on the surface properties of metal nanoclusters in balancing intermediate adsorption and product desorption.