Computational Discovery of Nickel-Based Catalysts for CO₂ Reduction to Formic Acid

Electrochemical reduction of CO₂ into chemical fuels is crucial to clean energy production and environment remediation. First-principles calculations are performed to elucidate reaction mechanism of CO₂ reduction to formic acid on Ni-based catalysts. The origin of CO poisoning is examined and a novel design strategy is proposed to eliminate CO poisoning. Three design criteria are derived based on which computational screening is performed to identify several Ni-based near-surface-alloys (NSAs) with both high selectivity and reactivity. The effect of elastic strain on CO₂ reduction is studied on these NSAs. We predict that Ni/Ti, Cu/Ni, and strained Cu/Ni NSAs could lead to highly selective and efficient production of formic acid

Multiscale Computational Design of Core/Shell Nanoparticles for Oxygen Reduction Reaction

We propose a multiscale computational framework to design core/shell nanoparticles (NPs) for oxygen reduction reaction (ORR). Essential to the framework are linear scaling relations between oxygen adsorption energy and surface strain, which can be determined for NP facets and edges from first-principles and multiscale QM/MM calculations, respectively. Based on the linear scaling relations and a microkinetic model, we can estimate ORR rates as a function of surface strain on core/shell NPs. Employing the multiscale framework, we have systematically examined the ORR activity on Pd-based core/shell NPs as a function of their shape, size, shell thickness, and alloy composition of the core. Three NP shapesicosahedron, octahedron, and truncated octahedronare explored, and the truncated octahedron is found to be the most active and the icosahedron is the least active. Ni_<i>x</i>Pd_1–<i>x</i>@Pd NPs with high Ni concentrations and thin shells could exhibit higher ORR rates than the pure Pt(111) surface and/or Pt NPs. Ag_<i>x</i>Pd_1–<i>x</i>@Pd in the truncated octahedron shape and high Ag concentrations are predicted to be even more active than Ni_<i>x</i>Pd_1–<i>x</i>@Pd NPs under the same conditions. The highly active Ag_<i>x</i>Pd_1–<i>x</i>@Pd and Ni_<i>x</i>Pd_1–<i>x</i>@Pd NPs are thermodynamically stable

Generalized Surface Coordination Number as an Activity Descriptor for CO₂ Reduction on Cu Surfaces

Surface engineering has proved effective in enhancing activities of CO₂ reduction reaction (CO₂RR) 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 CO₂RR on Cu surfaces. A set of linear scaling relations between the binding energy of CO₂RR 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 CO₂RR to methane, and surface engineering by creating adatoms could lower CO₂RR overpotentials and simultaneously suppress the competing hydrogen evolution reaction

First-Principles Prediction of Oxygen Reduction Activity on Pd–Cu–Si Metallic Glasses

We carry out first-principles simulations to assess the potential of Pd–Cu–Si metallic glasses as catalysts for oxygen reduction reaction (ORR) using oxygen adsorption energy (<i>E</i>_O) as a descriptor. We find that the substitution of Cu on crystalline Pd(111) surface improves the ORR activity while the substitution of Si on the surface is in general detrimental to the ORR activity. Compressive strains are found to weaken oxygen binding on the surface and thus enhance the ORR activity. On the basis of the analysis of <i>E</i>_O distribution on the Pd metallic glasses surfaces, we find that for Si-deficient adsorption sites, the local ORR activity could exceed that on pure Pd surface, while Si-rich sites exhibit a rather poor ORR activity. The Pd metallic glasses can sustain a much higher compression than the crystalline counterpart, thus their ORR activity can be improved substantially under a large compression. It is predicted that low-Si Pd metallic glasses could be excellent ORR catalysts under compression

Density Functional Theory Study of the Oxygen Chemistry and NO Oxidation Mechanism on Low-Index Surfaces of SmMn₂O₅ Mullite

SmMn₂O₅ mullite has recently been reported to be a promising alternative to traditional Pt-based catalysts for environmental and energy applications. By performing density functional theory calculations, we have systematically investigated lattice oxygen reactivity and oxygen adsorption/dissociation/migration behaviors on low-index surfaces of SmMn₂O₅ mullite with different terminations. On the basis of the oxygen chemistry and thermodynamic stability of different facets, we conclude that (100)³⁺, (010)⁴⁺, and (001)⁴⁺ are reactive toward NO oxidation via either the Mars van Krevelen (MvK) or Eley–Rideal (ER) mechanism. Concrete NO → NO₂ reaction paths on these candidate mechanisms have also been calculated. Both the (010)⁴⁺ and (001)⁴⁺ surfaces presented desirable activities. Bridge MnO sites on (010)⁴⁺ surface are identified to be the most active for NO oxidation through the ER mechanism with the lowest barrier of ∼0.38 eV. We have also identified that on all active sites considered in the current study, the rate-determining step in NO → NO₂ oxidation reaction is the NO₂ desorption. Our study gives an insight into the mechanisms of NO oxidation on SmMn₂O₅ mullite at the atomic level and can be used to guide further improvement of its catalytic performance

Lattice-Mismatch-Induced Twinning for Seeded Growth of Anisotropic Nanostructures

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

Tuning Sn-Catalysis for Electrochemical Reduction of CO₂ to CO via the Core/Shell Cu/SnO₂ Structure

Tin (Sn) is known to be a good catalyst for electrochemical reduction of CO₂ to formate in 0.5 M KHCO₃. But when a thin layer of SnO₂ 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 SnO₂ shell likely alloys with trace of Cu, causing the SnO₂ 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 CO₂ via the tunable core/shell structure

A New Core/Shell NiAu/Au Nanoparticle Catalyst with Pt-like Activity for Hydrogen Evolution Reaction

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