Catalysis of core-shell nanoparticle M@Pt (M Co and Ni) for oxygen reduction reaction and its electronic structure in comparison to Pt nanoparticle

Potential of V-Si72, V-C72, and V-Al36N36 as catalysts for oxygen reduction reaction

CONTEXT

The capacities of V-Si72, V-C72, and V-Al36N36 nanocages to catalyze the ORR processes have been investigated. The acceptable pathways of ORR processes on V-Si72, V-C72, and V-Al36N36 nanocages have been examined by DSD-PBEPBE-D3/aug-cc-pVDZ, PW91PW91/aug-cc-pVDZ, and COSMO model in the gas phase and water. The ΔGreaction values of reaction steps of ORR pathways on V-Si72, V-C72, and V-Al36N36 nanocages are calculated. The Eadoption and Eformation of V-Si72, V-C72, and V-Al36N36 nanocages are negative values and these nanostructures are stable materials. The H2O has the lowest Eadsorption on V-Si72, V-C72, and V-Al36N36 nanocages. The *OH formation, creation of *OH-OH*, and formation of O* are rate-determining steps of ORR mechanisms. The overpotential values of ORR processes on V-Si72, V-C72, and V-Al36N36 nanocages are 0.41, 0.37, and 0.30 V, respectively. The V-Al36N36 nanocage have lower overpotential for ORR processes than V-Si72 and V-C72 nanocages by DSD-PBEPBE-D3/aug-cc-pVDZ, PW91PW91/aug-cc-pVDZ, and COSMO model in the gas phase and water. The V-Al36N36 nanocage have more negative ∆Greaction for reaction steps of ORR than V-Si72 and V-C72 nanocages. The V-Al36N36 nanocage with lower overpotential is proposed as an effective catalyst for ORR processes via studied pathways.

METHODS

The DSD-PBEPBE-D3/aug-cc-pVDZ method has been used to optimize and calculate the frequencies of V-Si72, V-C72, and V-Al36N36 nanocages in GAMESS software. The complexes of O, OH, OOH, and H2O with V-Si72, V-C72, and V-Al36N36 nanocages are optimized and frequencies are determined by the DSD-PBEPBE-D3/aug-cc-pVDZ method. The Gactivation and ∆Greaction of ORR pathways on V-Si72, V-C72, and V-Al36N36 nanocages are calculated by DSD-PBEPBE-D3/aug-cc-pVDZ, PW91PW91/aug-cc-pVDZ, and COSMO model in the gas phase and water.

Computational Design of Ni6@Pt1M31 Clusters for Multifunctional Electrocatalysts

High-efficiency and low-cost multifunctional electrocatalysts for hydrogen evolution reaction (HERs), oxygen evolution reaction (OERs) and oxygen reduction reaction (ORRs) are important for the practical applications of regenerative fuel cells. The activity trends of core-shell Ni6@M32 and Ni6@Pt1M31 (M = Pt, Pd, Cu, Ag, Au) were investigated using the density functional theory (DFT). Rate constant calculations indicated that Ni6@Pt1Ag31 was an efficient HER catalyst. The Volmer-Tafel process was the kinetically favorable reaction pathway for Ni6@Pt1M31. The Volmer-Heyrovsky reaction mechanism was preferred for Ni6@M32. The Pt active site reduced the energy barrier and changed the reaction mechanism. The ORR and OER overpotentials of Ni6@Pt1Ag31 were calculated to be 0.12 and 0.33 V, indicating that Ni6@Pt1Ag31 could be a promising multifunctional electrocatalyst. Ni6@Pt1M31 core-shell clusters present abundant active sites with a moderate adsorption strength for *H, *O, *OH and *OOH. The present study shows that embedding a single Pt atom onto a Ni@M core-shell cluster is a rational strategy for designing an effective multifunctional electrocatalyst.

Single atom alloys vs. phase separated alloys in Cu, Ag, and Au atoms with Ni(111) and Ni, Pd, and Pt atoms with Cu(111): a theoretical exploration

A single-atom alloy (SAA) consisting of an abundant metal host and a precious metal guest is a promising catalyst to reduce the cost without a loss of activity. DFT calculations of Ni- and Cu-based alloys nX/M(111) (X = Cu, Ag, or Au for M = Ni; X = Ni, Pd, or Pt for M = Cu; n = 1-4) reveal that a phase-separated alloy (PSA) is produced by Cu atoms with Ni(111) but an SAA is produced by Au atoms with Ni(111) and Pd and Pt atoms with Cu(111). In the Ni(111)-based Ag alloy and Cu(111)-based Ni alloy, the relative stabilities of the SAA and PSA depend on coverages of Ag on Ni(111) and Ni on Cu(111). The interaction energy (E_int) between the X_n cluster and M(111) host is larger than that between one X atom and the M(111) host, because the X_n cluster forms more bonding interactions with the M(111) host than does one X atom. When going from one X atom to the X₄ cluster, the E_int values of Au and Pt clusters respectively with Ni(111) and Cu(111) increase to a lesser extent than those of Cu and Ni clusters respectively with Ni(111) and Cu(111). Consequently, Au and Pt atoms tend to form SAAs respectively with Ni(111) and Cu(111) hosts compared to Cu and Ni atoms. This trend in the E_int value is determined by the valence orbital energies of the X atom and the X_n cluster. Cu atoms in nCu/Ni(111) have a slightly positive charge but Ag atoms in nAg/Ni(111), Au atoms in nAu/Ni(111), and Ni, Pd, and Pt atoms in nX/Cu(111) (X = Ni, Pd, or Pt) have a negative charge. The negative charge increases in the order Ag < Au in nX/Ni(111) and Ni < Pd < Pt in nX/Cu(111). The Fermi level decreases in energy in the order nCu/Ni(111) ≥ Ni(111) > nAg/Ni(111) > nAu/Ni(111) and Cu(111) ≥ nNi/Cu(111) > nPd/Cu(111) > nPt/Cu(111). The d valence band center decreases in energy in almost the same order. The CO adsorption energy decreases in the order Ni(111) ∼ nCu/Ni(111) > nAg/Ni(111) ∼ nAu/Ni(111) and Cu(111) > nNi/Cu(111) > nPd/Cu(111) > nPt/Cu(111). These properties are explained based on the electronic structures.

Sublayer Stable Fe Dopant in Porous Pd Metallene Boosts Oxygen Reduction Reaction

Engineering the morphology and electronic properties simultaneously of emerging metallene materials is an effective strategy for enhancing their performance as oxygen reduction reaction (ORR) electrocatalysts. Herein, a highly efficient and stable ORR electrocatalyst, Fe-doped ultrathin porous Pd metallene (Fe-Pd UPM) composed of a few layers of 2D atomic metallene layers, was synthesized using a simple one pot wet-chemical method and characterized. Fe-Pd UPM was measured to have enhanced ORR activity compared to undoped Pd metallene. Fe-Pd UPM exhibits a mass activity of 0.736 A mg_Pd^-1 with a loss of mass activity of only 5.1% after 10 000 cycles at 0.9 V versus the reversible hydrogen electrode (vs RHE) in 0.1 M KOH solution. Density functional theory (DFT) calculations reveal that the stable Fe dopant in the inner atomic layers of Fe-Pd UPM delivers a much smaller overpotential during O* hydrogenation into OH*. The morphology, porous structure, and Fe doping were verified to have enhanced ORR activity. We believe that the rational design of metallene materials with porous structures and interlayer doping is promising for the development of efficient and stable electrocatalysts.