Colloidal Synthesis of Cu-M-S (M = V, Cr, Mn) Nanocrystals by Tuning the Copper Precursor Reactivity

New ternary and higher order inorganic materials are needed for a large variety of applications, yet their synthesis still represents a chemistry challenge. Herein, we focus on the synthesis of Cu-M-S nanocrystals (where M = V, Cr, Mn) via a wet-chemistry route and investigate their formation mechanisms. We reveal that the interplay between the copper precursor and the thiophilicity of the transition metal M is the key for the synthesis of pure phase Cu-M-S nanocrystals under the same reaction conditions. In particular, we observe that the interdiffusion kinetics of the intermediate species is crucial, and the extent of nucleation of the ternary product can be controlled by the copper precursor reactivity. The insights provided by this work contribute to open up new avenues toward the design of improved synthesis strategies to multinary nanocrystalline compounds

Ligand-mediated formation of Cu/metal oxide hybrid nanocrystals with tunable number of interfaces

Combining domains of different chemical nature within the same hybrid material through the formation of heterojunctions provides the opportunity to exploit the properties of each individual component within the same nano-object; furthermore, new synergistic properties will often arise as a result of unique interface interactions. However, synthetic strategies enabling precise control over the final architecture of multicomponent objects still remain scarce for certain classes of materials. Herein, we report on the formation of Cu/MOx (M = Ce, Zn and Zr) hybrid nanocrystals with a tunable number of interfaces between the two domains. We demonstrate that the organic ligands employed during the synthesis play a key role in regulating the final configuration. Finally, we show that the synthesized nanocrystals serve as materials platforms to investigate the impact of the Cu/metal oxide interfaces in applications by focusing on the electrochemical CO2 reduction reaction as one representative example

Colloidal Nanocrystals as Electrocatalysts with Tunable Activity and Selectivity

Correlating the catalyst activity, selectivity, and stability with its structure and composition is of the utmost importance in advancing the knowledge of heterogeneous electrocatalytic processes for chemical energy conversion. Well-defined colloidal nanocrystals with tunable monodisperse size and uniform shapes are ideal platforms to investigate the effect of these parameters on the catalytic performance. In addition to translating the knowledge from single-crystal studies to more realistic conditions, the morphological and compositional complexity attainable by colloidal chemistry can provide access to active catalysts which cannot be produced by other synthetic approaches. The sample uniformity is also beneficial to investigate catalyst reconstruction processes via both ex situ and operando techniques. Finally, colloidal nanocrystals are obtained as inks, a feature which facilitates their integration on different substrates and cell configurations to study the impact of interactions at the mesoscale and the device-dependent reaction microenvironment on the catalytic outcome. In this Review, we discuss recent studies in selected electrochemical reactions and provide our outlook on future developments on the use of well-defined colloidal nanocrystals as an emerging class of electrocatalysts

Synthesis of Cu/CeO_2-x Nanocrystalline Heterodimers with Interfacial Active Sites To Promote CO₂ Electroreduction

Synergistic effects at metal/metal oxide interfaces often give rise to highly active and selective catalytic motifs. So far, such interactions have been rarely explored to enhance the selectivity in the electrochemical CO2 reduction reaction (CO2RR). Herein, Cu/CeO2‑x heterodimers (HDs) are synthesized and presented as one of the prime examples where such effects promote CO2RR. A colloidal seeded-growth synthesis is developed to connect the two highly mismatched domains (Cu and CeO2‑x) through an interface. The Cu/CeO2‑x HDs exhibit state-of-the-art selectivity toward CO2RR (up to ∼80%) against the competitive hydrogen evolution reaction (HER) and high faradaic efficiency for methane (up to ∼54%) at −1.2 VRHE, which is ∼5 times higher than that obtained when the Cu and CeO2‑x nanocrystals are physically mixed. Operando X-ray absorption spectroscopy along with other ex-situ spectroscopies evidences the partial reduction of Ce4+ to Ce3+ in the HDs during CO2RR. A Density Functional Theory (DFT) study of the active site motif in reducing condition reveals synergistic effects in the electronic structure at the interface. The proposed lowest free energy pathway utilizes an O-vacancy site with intermediates binding to both Cu and Ce atoms, a configuration which allows one to break the CHO*/CO* scaling relation. The suppression of HER is attributed to the spontaneous formation of CO* at this interfacial motif and subsequent blockage of the Cu-sites