Tin (Sn) is known to be a good catalyst for electrochemical reduction of CO to formate in 0.5 M KHCO. But when a thin layer of SnO is coated over Cu nanoparticles, the reduction becomes Sn-thickness dependent: the thicker (1.8 nm) shell shows Sn-like activity to generate formate whereas the thinner (0.8 nm) shell is selective to the formation of CO with the conversion Faradaic efficiency (FE) reaching 93% at -0.7 V (vs reversible hydrogen electrode (RHE)). Theoretical calculations suggest that the 0.8 nm SnO shell likely alloys with trace of Cu, causing the SnO lattice to be uniaxially compressed and favors the production of CO over formate. The report demonstrates a new strategy to tune NP catalyst selectivity for the electrochemical reduction of CO via the tunable core/shell structure.

We report a general approach to NiAu alloy nanoparticles (NPs) by co-reduction of Ni(acac)2 (acac = acetylacetonate) and HAuCl4·3H2O at 220 °C in the presence of oleylamine and oleic acid. Subject to potential cycling between 0.6 and 1.0 V (vs reversible hydrogen electrode) in 0.5 M H2SO4, the NiAu NPs are transformed into core/shell NiAu/Au NPs that show much enhanced catalysis for hydrogen evolution reaction (HER) with Pt-like activity and much robust durability. The first-principles calculations suggest that the high activity arises from the formation of Au sites with low coordination numbers around the shell. Our synthesis is not limited to NiAu but can be extended to FeAu and CoAu as well, providing a general approach to MAu/Au NPs as a class of new catalyst superior to Pt for water splitting and hydrogen generation.

Synthesis of anisotropic nanostructures from materials with isotropic crystal structures often requires the use of seeds containing twin planes to break the crystalline symmetry and promote the preferential anisotropic growth. Controlling twinning in seeds is therefore critically important for high-yield synthesis of many anisotropic nanostructures. Here, we demonstrate a unique strategy to induce twinning in metal nanostructures for anisotropic growth by taking advantage of the large lattice mismatch between two metals. By using Au-Cu as an example, we show, both theoretically and experimentally, that deposition of Cu to the surface of single-crystalline Au seeds can build up strain energy, which effectively induces the formation of twin planes. Subsequent seeded growth allows the production of Cu nanorods with high shape anisotropy that is unachievable without the use of Au seeds. This work provides an effective strategy for the preparation of anisotropic metal nanostructures.

Surface engineering has proved effective in enhancing activities of CO 2 reduction reaction (CO 2 RR) on Cu. However, predictive guidance is necessary for the surface engineering to reach its full potential. We propose that the generalized coordination number (GCN) can be used as a descriptor to characterize CO 2 RR on Cu surfaces. A set of linear scaling relations between the binding energy of CO 2 RR intermediates and GCN are established to construct a volcano-type coordination−activity plot and from which we can derive the theoretical overpotential limit on Cu surfaces. We predict that the dimerized (111) surface yields the lowest possible overpotential on Cu for CO 2 RR to methane, and surface engineering by creating adatoms could lower CO 2 RR overpotentials and simultaneously suppress the competing hydrogen evolution reaction.

Penta-twinned Cu nanowires have a strain-tunable low overpotential for CO2 electroreduction.