Oxygen Molecule Activation on Single-Atom Catalysts with Cu, Ag, and Au: A Cluster Model Study

(M = Au, Ag, Cu;n= 1, 2, 3) clusters were used as a cluster model to study the activation of oxygen molecules on single-atom catalysts. Structures of clusters were studied by density functional calculations with global optimization. For each n, the most stable structures are quite similar for different metal types, and the oxygen molecule prefers to be adsorbed onto M atoms. It is found that the activation degree of oxygen is higher on clusters with non-noble metal Cu than that of Ag or Au containing clusters, by comparing the changes of O-O bond length and vibrational frequency, natural charge population analysis, Fuzzy bond order analysis, and energy barriers of O2 dissociation. CO oxidation was used as a probe reaction to study the reactivity of Cu-containing clusters, and it is found that the reactivity decreases with the increase of the size of silicon-oxygen clusters. Our results give a new aspect to understand the reaction mechanism of non-precious metal single-atom catalyst for oxygen activation with high efficiency.

Geometric structures,electronic characteristics,stabilities,catalytic activities,and descriptors of graphene-based single-atom catalysts

Single-atom catalysts(SACs)have been a research hotspot due to their high catalytic activity,selectivity,and atomic utilization rates.However,the theoretical research of SACs is relatively fragmented,which restricts further understanding of SAC stability and activity.To address this issue,we report our analysis of the geometric structures,electronic characteristics,stabilities,catalytic activities,and descriptors of 132 graphene-based singleatom catalysts(M/GS)obtained from density functional theory calculations.Based on the calculated formation and binding energies,a stability map of M/GS was established to guide catalyst synthesis.The effects of metal atoms and support on the charge of metal atoms are discussed.The catalytic activities of M/GS in both nitrogen and oxygen reduction reactions are predicted based on the calculated magnetic moment and the adsorption energy.Combined with the electronegativity and d-band center,a two-dimensional descriptor is proposed to predict the O adsorption energy on M/GS.More importantly,this theoretical study provides predictive guidance for the preparation and rational design of highly stable and active single-atom catalysts using nitrogen doping on graphene.

Nanostructured AlFeO_(3) thin films as a novel photoanode for photoelectrochemical water splitting

The earth-abundant and robust aluminum ferrite,AlFeO_(3)(AFO),is mainly studied in the context of ferroelectrics.Herein,we demonstrate that AFO can be used as a stable solar absorber in photoelectrochemical cells for solar water splitting,exhibiting attractive performance.This is the first report on the photoelectrochemical activity of AFO.AFO thin-film photoelectrodes prepared by solution-processing methods are composed of vertically oriented thin nanosheets,featuring the rhombohedral symmetry(R3c)and n-type conductivity.The as-prepared AFO photoanodes generate a photocurrent density of+0.78 mA·cm^(-2) at 1.23 V vs.reversible hydrogen electrode(RHE)with the photocurrent _(onset) potential(U_(onset))close to the flat band potential of 0.5 V vs.RHE in the presence of hole scavengers.Remarkably,the U_(onset) of AFO for solar water splitting coincides with the flat band potential as well,which is rare in n-type inorganic absorbers.We also report other properties of AFO associated with photoelectrochemical performance.AFO films exhibit a band gap energy of 2.31 eV and positive band edges with low dispersion.Moreover,the carrier lifetimes in AFO films are up to millisecond timescales under the mediation of defect traps.Based on the photoelectrochemical behavior and optoelectronic properties,we believe that AFO has great potential for application in photoelectrochemical cells.

The cycloaddition reaction of ethylene and methane mediated by Ir^(+) to generate a half-sandwich structure Ir HCp^(+)

The cycloaddition reactions of methane and ethylene mediated by Ir^(+) have been designed and studied by the techniques of mass spectrometry in conjunction with theoretical calculations.Studies have shown that Ir^(+) can mediate the cycloaddition reaction of CH4and two C_(2)H_(4) to generate a half-sandwich structure IrHCp^(+)(Cp=η^(5)-C_(5)H_(5))including pentamethylcyclopentadienyl ligand by continuous dehydrogenation reaction with the forming of three C-C bonds and seven C-H bonds.The orbital analysis indicates the mechanism of the cyclization reaction to generation of pentamethylcyclopentadienyl ligand with odd number carbon atom depends on the overlap ofπorbitals in-C_(2)H_(2) and carbene,which is more difficult than the forming of cyclobutadiene ligand and benzene.This study may help to understand the reaction mechanism in the cycloaddition reactions of organic compounds,which will be useful to guide the rational design of new catalysts with tailored selectivity and increased efficiency.