Chemisorption

About: Chemisorption is a research topic. Over the lifetime, 16298 publications have been published within this topic receiving 554989 citations.

Modulating Single-Atom Palladium Sites with Copper for Enhanced Ambient Ammonia Electrosynthesis

Abstract: The electrochemical reduction of N2 to NH3 is emerging as a promising alternative for sustainable and distributed production of NH3 . However, the development has been impeded by difficulties in N2 adsorption, protonation of *NN, and inhibition of competing hydrogen evolution. To address the issues, we design a catalyst with diatomic Pd-Cu sites on N-doped carbon by modulation of single-atom Pd sites with Cu. The introduction of Cu not only shifts the partial density of states of Pd toward the Fermi level but also promotes the d-2π* coupling between Pd and adsorbed N2 , leading to enhanced chemisorption and activated protonation of N2 , and suppressed hydrogen evolution. As a result, the catalyst achieves a high Faradaic efficiency of 24.8±0.8 % and a desirable NH3 yield rate of 69.2±2.5 μg h-1 mgcat. -1 , far outperforming the individual single-atom Pd catalyst. This work paves a pathway of engineering single-atom-based electrocatalysts for enhanced ammonia electrosynthesis.

Molybdenum Carbide-Oxide Heterostructures: In Situ Surface Reconfiguration toward Efficient Electrocatalytic Hydrogen Evolution.

Abstract: Heterostructured Mo2 C-MoOx on carbon cloth (Mo2 C-MoOx /CC), as a model of easily oxidized electrocatalysts under ambient conditions, is investigated to uncover surface reconfiguration during the hydrogen evolution reaction (HER). Raman spectroscopy combined with electrochemical tests demonstrates that the MoVI oxides on the surface are in situ reduced to MoIV , accomplishing promoted HER in acidic condition. As indicated by density functional theoretical calculations, the in situ reduced surface with terminal Mo=O moieties can effectively bring the negative ΔGH* on bare Mo2 C close to a thermodynamic neutral value, addressing difficult H* desorption toward fast HER kinetics. The optimized Mo2 C-MoOx /CC only requires a low overpotential (η10 ) of 60 mV at -10 mA cm-2 in 1.0 m HClO4 , outperforming Mo2 C/CC and most non-precious electrocatalysts. In situ surface reconfiguration are shown on W2 C-WOx , highlighting the significance to boost various metal-carbides and to identify active sites.

Coadsorption of ethylene and potassium on platinum (111). 1. Formation of a .pi.-bonded state of ethylene

Abstract: High resolution electron energy spectroscopy (HREELS), temperature-programmed desorption (TPD), and ultraviolet photoelectron spectroscopy (UPS) have been combined to study the effect of preadsorbed potassium on the adsorption of ethylene on the platinum(111) single-crystal surface. Addition of potassium increases the relative amount of reversible ethylene adsorption at 100 K/. Upon coadsorption with potassium, the authors also observe a new low-temperature ethylene desorption state at 150 K, with E/sub d/ = 5-9 kcal mol/sup -1/, which is about one-half the binding energy of ethylene adsorbed on clean Pt(111). The origin of this new desorption state is the formation of a weakly interacting ethylene species, which is only slightly distorted from the gas-phase hybridization, as determined primarily by vibrational spectroscopy. An explanation is given for these effects in which the increased charge density at the platinum surface due to coadsorbed potassium inhibits the strong sigma-donation of adsorbed ethylene to platinum and greatly reduces the chemisorption bond strength.