For many applications of well-defined gold nanoclusters, it's desirable to understand their structural evolution behavior under working conditions with molecular precision. Here we report the first systematic investigation on the size transformation product of Au22(SG)18 nanocluster under representative working conditions and highlight the surface effect on the transformation dynamics. Under thermal and aerobic conditions, the consecutive and pH dependent transformation from Au22 to both well-defined clusters and small Au(I)SR species were identified by the ESI-MS and UV-vis spectroscopy. By introducing perturbation on the Au22 surface, significant changes in the activation parameters were determined from the kinetic study of the Au22 transformation. This indicates the sensitivity of nanocluster transformation pathway the cluster surface. The systematic study on cluster transformation and sensitivity of cluster transformation to the surface revealed herein have significant implications for future attempts to design gold nanoparticles with adaptation to the working environment and the regeneration of active nanoparticles.

A series of nanocrystalline titanium (Ti) sub-oxides, including TiO, Ti2O3, Ti3O5, and Ti4O7, with high surface area and activity are successively synthesized using a facile synthesis method that combines the sol–gel and the energy-efficient vacuum-carbothermic (SG-VC) processes. The combination results in synergy in producing nanomaterials with high surface area (>100 m2 g–1), good conductivity, and rich intra-grain defect features, giving the oxides unique surface activities suitable for particular electrochemical applications. The phase compositions of the resulting powders are primarily determined by two process parameters, including the carbothermic carbon (C) content, expressed as the C-to-Ti molar ratio of the reactant powder, and the cooling protocol. Carbothermic C contents exceeding a threshold of C/Ti ∼ 3.7 exclusively produced non-Magnéli phase (MP) oxides including TiO and Ti2O3, while the MP oxides, Ti3O5 and Ti4O7, can be formed only with lower C contents combined with selected quenching protocols that kinetically limit oxygen replenishment during cooling. Examples of the resulting MP Ti4O7 powder exhibiting outstanding pseudocapacitive and oxygen evolution reaction catalytic behaviors are demonstrated.

Undercoordinated metal nanoclusters have shown great promise for various catalytic applications. However, their activity is often limited by the covalently bonded ligands, which could block the active surface sites. Here, we investigate the ligand removal process for Au25 nanoclusters using both thermal and electrochemical treatments, as well as its impact on the electroreduction of CO2 to CO. The Au25 nanoclusters are synthesized with 2-phenylethanethiol as the capping agent and anchored on sulfur-doped graphene. The thiolate ligands can be readily removed under either thermal annealing at ≥180 ○C or electrochemical biasing at ≤−0.5 V vs reversible hydrogen electrode, as evidenced by the Cu underpotential deposition surface area measurement, x-ray photoelectron spectroscopy, and extended x-ray absorption fine structure spectroscopy. However, these ligand-removing treatments also trigger the structural evolution of Au25 nanoclusters concomitantly. The thermally and electrochemically treated Au25 nanoclusters show enhanced activity and selectivity for the electrochemical CO2-to-CO conversion than their pristine counterpart, which is attributed to the exposure of undercoordinated Au sites on the surface after ligand removal. This work provides facile s