Tuning surface strain is a powerful strategy for tailoring the reactivity of metal catalysts. Traditionally, surface strain is imposed by external stress from a heterogeneous substrate, but the effect is often obscured by interfacial reconstructions and nanocatalyst geometries. Here, we report on a strategy to resolve these problems by exploiting intrinsic surface stresses in two-dimensional transition metal nanosheets. Density functional theory calculations indicate that attractive interactions between surface atoms lead to tensile surface stresses that exert a pressure on the order of 105atmospheres on the surface atoms and impart up to 10% compressive strain, with the exact magnitude inversely proportional to the nanosheet thickness. Atomic-level control of thickness thus enables generation and fine-tuning of intrinsic strain to optimize catalytic reactivity, which was confirmed experimentally on Pd(110) nanosheets for the oxygen reduction and hydrogen evolution reactions, with activity enhancements that were more than an order of magnitude greater than those of their nanoparticle counterparts.

Electrochemical reduction of CO2, an artificial way of carbon recycling, represents one promising solution for energy and environmental sustainability. However, it is challenged by the lack of active and selective catalysts. Here, we report a two-step synthesis of highly dense Cu nanowires as advanced electrocatalysts for CO2 reduction. CuO nanowires were first grown by oxidation of Cu mesh in air and then reduced by either annealing in the presence of hydrogen or applying a cathodic electrochemical potential to produce Cu nanowires. The two reduction methods generated Cu nanowires with similar dimensions but distinct surface structures, which have provided an ideal platform for comparative studies of the effect of surface structure on the electrocatalytic properties. In particular, the Cu nanowires generated by electrochemical reduction were highly active and selective for CO2 reduction, requiring an overpotential of only 0.3 V to reach 1 mA/cm(2) electrode current density and achieving Faradaic efficiency toward CO as high as ∼60%. Our work has advanced the understanding of the structure-property relationship of Cu-based nanocatalysts, which could be valuable for the further development of advanced electrocatalytic materials for CO2 reduction.

Electroreduction of CO2 represents a promising approach toward artificial carbon recycling for addressing global challenges in energy and sustainability. The foreground of this approach is dependent on the development of efficient electrocatalysts capable of selectively reducing CO2 to valuable (oxygenated) hydrocarbon products at low overpotentials. Here, we present an overview of the recent developments of Cu electrocatalysts for CO2 reduction. Our focus is placed on elucidation of the structure–property relationships of monometallic Cu electrocatalysts, which is believed to be the foundation for understanding alloys and other more complex catalytic systems. Reported mechanisms are discussed in terms of grain boundaries, open facets, residual oxides, subsurface oxygen, local pH effect, etc. After this discussion, remaining questions are raised for further development of advanced electrocatalysts for energy and chemically efficient CO2 reduction.

We report on Cu nanowires as highly active and selective catalysts for electroreduction of CO at low overpotentials. The Cu nanowires were synthesized by reducing pregrown CuO nanowires, with the surface structures tailored by tuning the reduction conditions for improved catalytic performance. The optimized Cu nanowires achieved 65% faradaic efficiency (FE) for CO reduction and 50% FE toward production of ethanol at potentials more positive than −0.5 V (versus reversible hydrogen electrode, RHE). Structural analyses and computational simulations suggest that the CO reduction activity may be associated with the coordinately unsaturated (110) surface sites on the Cu nanowires.

Electroreduction of CO 2 represents a promising solution for addressing the global challenges in energy and sustainability. This reaction is highly sensitive to the surface structure of electrocatalysts and the local electrochemical environment. We have investigated the effect of Cu nanoparticle shape on the electrocatalysis of CO 2 reduction by using gasdiffusion electrodes (GDEs) and flowing alkaline catholytes. Cu nanocubes of ∼70 nm in edge length are synthesized with {100} facets preferentially exposed on the surface. They are demonstrated to possess substantially enhanced catalytic activity and selectivity for CO 2 reduction, compared to Cu nanospheres of similar particle sizes. The electrocatalytic performance was further found to be dependent on the concentration of electrolyte (KOH). The Cu nanocubes reach a Faradaic efficiency of 60% and a partial current density of 144 mA/cm 2 toward ethylene (C 2 H 4 ) production, with the catalytic enhancement being attributable to a combination of surface structure and electrolyte alkalinity effects.