IB Metals Research Articles

The Performance of Ethylene Partial Oxidation on Group IB Metal Stepped Surfaces

Group IB metal catalysts, particularly Ag, Au, and Cu, exhibit particular selectivity for ethylene oxide (EO) formation, while Ag demonstrating the highest performance so far. Previous studies have explored the EO formation mechanism on (100) and (111) surfaces of group IB metals, but the reaction mechanism on the (211) facet (analogous to the edge sites of a catalyst particle) remains poorly understood. Herein, we fill in the knowledge gap by analyzing ethylene partial oxidation to EO on the (211) surfaces of Ag, Au, and Cu through density functional theory (DFT) calculations, scaling relationship analysis, and microkinetic modeling. Our study demonstrates that the (211) surface decreases the energy barrier for the dissociation of oxygen molecules into oxygen atoms, while unfavorable for the production of EO. Therefore, we should preserve an appropriate concentration of (211) surface on the nanoparticles when designing catalysts for the ethylene epoxidation reaction.

Conversion mechanism of the atomically precise group IB metal nanoclusters by theoretical calculations

The controllable synthesis and design of group IB metal (i.e., Au/Ag/Cu) and their alloy nanoclusters (IB-NCs) rely on an elucidation of the conversion mechanism, bonding preference, and structure–property relationships. In the past decades, the development of cluster-to-cluster transformation and spectroscopic tracking strategy have provided important mechanistic insights that greatly help researchers improve synthetic skills and explore the application of IB-NCs. Specifically, with the aid of DFT calculations, the structural information of cluster-to-cluster conversion, including the intermediates and active sites, can be deduced from the atomic level. In this review, the conversion mechanisms of IB-NCs in the past three years have been reviewed to summarize the key factors influencing structural transformation and reactivity. The three types of cluster-to-cluster conversion (i.e., foreign metal source, foreign ligand, and other reagents/condition-induced conversion) were highlighted for further synthesis and design of functional nanoclusters.

Rotating Disk Electrode Studies of Benzaldehyde Oxidation on Group Ib Metals

Water electrolysis is a green means of producing hydrogen gas to be used as a fuel or reactant in key industrial processes such as ammonia production. The conventional system of oxygen evolution (OER) and hydrogen evolution (HER) suffers from slow kinetics at the anode and a high cell voltage limited by thermodynamics. One solution is to replace OER with another reaction such as an organic oxidation reaction that has a lower equilibrium potential and produces a valuable organic byproduct at the anode. Recent work has demonstrated that biomass-derived aldehydes such as furfural and 5-hydroxymethylfurfural can be selectively oxidized to their corresponding carboxylates and H2 on Cu-based anodes at low potentials (~0.1 VRHE) in alkaline media. In alkaline media, a hydroxide ion adds to the carbonyl carbon of an aldehyde molecule forming a gem diolate in solution phase. It is argued that dehydrogenation becomes more facile due to the weaker C-H bond of the gem diolate compared to the aldehyde form of the molecule. This may enable oxidation without the need for coadsorbed-OH. Additionally, aldehyde oxidation is only active on Au, Ag, and Cu electrodes at higher pHs.The aim of this work is to identify the conditions under which low potential oxidation of aldehydes and high anodic Faradaic efficiency to H2 occurs, namely, electrode material and applied potential. To avoid polymerization side reactions of furans in alkaline media, we studied benzaldehyde as a model compound which has also been shown to exhibit low potential oxidation and anodic H2. The activity (rate of aldehyde consumption) and selectivity (to anodic H2 versus H2O) were compared for the group Ib metals (Au, Ag, Cu), each of which demonstrates a relatively early onset potential (<0.4 VRHE) and generates anodic H2 at certain potentials. Rotating disk electrode studies with Koutecky-Levich analysis were conducted to separate mass transfer effects from kinetic current to compare the intrinsic activity of each electrode. Additionally, the average number electrons transferred per aldehyde molecule consumed was estimated from Koutecky-Levich analysis; the one-electron pathway combines the aldehyde hydrogens to H2 while the two-electron pathway requires an additional electron per aldehyde molecule to oxidize the hydrogen from the surface to form H2O. Rotating ring disk electrode studies were used to further validate the anodic H2 generation as a Pt ring was still able to oxidize H2 despite the presence of benzaldehyde. This was used as an additional means of estimating the selectivity to H2 as a function of potential.CVs for benzaldehyde oxidation on each metal are shown in Figure a. Peak current followed the order of Au > Ag >> Cu. Au reached a mass transfer limiting current, and Ag also showed an RPM dependence but did not reach full mass transfer limitations. Cu was the least active and did not show any mass transfer dependence. On the other hand, Cu has the earliest onset potential followed by Ag then Au. The average number of electrons transferred per aldehyde molecule according to RRDE measurements is shown in Figure b, where one electron represents H2 and two electrons represents H-oxidation to H2O. Cu had 100% selectivity to H2 over its entire potential window of activity (up to 0.45 VRHE). Au and Ag have high selectivity to H2 at low potentials but decreases to near zero H2 production in the range of 0.6-0.8 VRHE; the decrease in selectivity to H2 on Ag occurs slightly earlier than Au (~0.1 V). H2 selectivity is related to the inability of each metal to oxidize H to H2O at low potentials. Figure 1

Designing highly efficient electrocatalyst for ORR and OER of transition metals doped g-C9N7: A density functional theory study

The application of fuel cells and metal-air batteries is limited by the rate of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Thus, the aim of this study is to find an efficient electrocatalyst to accelerate the reaction rate by DFT method. The structures of VIIB, VIII, IB, and IIB groups transition metals doped g-C9N7 as superb bifunctional electrocatalysts for ORR and OER are probed. The results show that Fe-, Pd-, and Au–C9N7 possess the superb ORR performance with the ORR overpotentials values of 0.35, 0.40, and 0.39 V, which gives them better performance than Pt(111). Moreover, Rh-, Pd-, and Pt–C9N7 have better OER performance with the OER overpotentials values of 0.30, 0.57, and 0.43 V, which makes them comparable to RuO2(110) and IrO2(110). Finally, the calculated bifunctional index (BI) results show that Pd–C9N7 can be used as an excellent bifunctional electrocatalyst because it has a minimum BI value of 0.97 V. This research has the potential to provide valuable theoretical direction into the use of M − C9N7 as electrocatalysts for both the ORR and OER.

High-performance screening of carbon-nitride single-atom catalysts for oxygen electrode reaction in rechargeable metal–air batteries

The sluggish kinetics of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), which are the oxygen electrode reactions, impede further advancements in metal–air batteries technology. The main objective is to investigate the bifunctional catalytic activity of the VIIB, VIII, IB, and IIB groups transition metals doped carbon-nitride material (C9N4, C10N9, C13N3, C14N12, and C19N3) as bifunctional electrocatalysts for oxygen electrode reaction in metal–air batteries by density functional theory methods in this paper. C9N4, C13N3, and C19N3 are better doping substrates than C10N9 and C14N12 for all transition metals. For ORR, Co-C9N4, Cu-C13N3, Rh-C13N3, Co-C19N3, Ni-C19N3, and Cu-C19N3 exhibit the overpotential values of 0.36, 0.37, 0.40, 0.47, 0.48, and 0.48 V, respectively. These values are comparable to or even better those of Pt(111), indicating their exceptional ORR catalytic activity. For OER, Rh-C9N4, Pt-C9N4, Co-C13N3, Rh-C13N3, and Ni-C19N3 possess the overpotential values of 0.42, 0.40, 0.40, 0.33, and 0.41 V, respectively, showcasing a remarkable similarity to that of RuO2(110). Rh-C13N3 exhibits superior bifunctional catalytic activity (Bifunctional Index = 0.73 V). This study offers essential theoretical guidance for the utilization of carbon-nitride single-atom catalysts as bifunctional electrocatalysts in the oxygen electrode reaction of rechargeable metal-air batteries.

Effects of Group IB Metals of Au/Ag/Cu on Boosting Oxygen Evolution Reaction of Cobalt Hydroxide

AbstractDeveloping high‐activity, good‐stability oxygen evolution reaction (OER) catalysts is the key to solving the problem of hydrogen production from electrolytic water. Cobalt hydroxide (Co(OH)2) is a hopeful OER catalyst, but its poor conductivity and low inherent activity limit its OER performance. Herein, we used group IB metals of Au, Ag, and Cu to increase the OER performance of Co(OH)2via the electrodeposition method. All three metals can increase the carrier concentration and proportion of high‐valence cobalt ions. The analysis results disclose that the construction of Ag−Co(OH)2heterostructure can optimize the electronic structure through interfacial interactions, produce a moderate proportion of high‐valence cobalt centers, enhance the charge transport capacity and the adsorption of hydroxyl species, thus accelerating the OER kinetics and effectively improving the inherent catalytic activity. This work not only develops effective and steady catalysts but also provides a facile method to enhance the OER performance through interface engineering.

M supported on Al-defective Al2-δO3 (M = Fe, Co, Ni, Cu, Ag, Au) as catalysts for acetylene semi-hydrogenation: a theoretical perspective.

Semi-hydrogenation of acetylene is of great importance for both industry and academia. High prices and limited supplements of noble metals leave room for developing base metal catalysts. Experiments revealed the atomically dispersed Cu supported by Al2O3 with excellent long-term stability and high ethylene selectivity, but the physical nature has rarely been investigated theoretically. DFT calculations and microkinetic modeling revealed that the surface OH species could stabilize Cu1/Al2-δO3 and enhance its catalytic performance. The selectivity of ethylene formation decreases with increasing copper clusters (e.g., Cu1/Al2-δO3> Cu4/Al2-δO3> Cu8/Al2-δO3), meaning that the atomically dispersed copper may be a potential candidate for acetylene semi-hydrogenation. The structures of a series of single site catalysts M1/Al2-δO3 (M = Fe, Co, Ni, Ag, Au) are similar to that of Cu1/Al2-δO3, but their performances in catalyzing acetylene semi-hydrogenation are different. M1/Al2-δO3 (M = Ag, Au) shows higher selectivity than Cu1/Al2-δO3, while M1/Al2-δO3 (M = Fe, Co, Ni) demonstrates a higher turnover frequency (TOF) of ethylene than Cu1/Al2-δO3. Moreover, our results indicate that the Ni1-Cu1/Al2-δO3 alloy shows both high activity and ethylene selectivity. The present results show a compensation between the reactivity and the selectivity, suggesting that alloys of VIIIB metals with IB metals like Ni1-Cu1/Al2-δO3 may be efficient candidate catalysts in acetylene selective hydrogenation.

Recent Advances in Aerobic Photo-Oxidation over Small-Sized IB Metal Nanoparticles

Aerobic photo-oxidation is a kind of green catalytic process that give valuable chemicals because of its mild reaction conditions and high product selectivity. Recently, small-sized IB metal nanoparticles (NPs; e.g., Cu, Ag, and Au, sized 1–3 nm) upon the surface of titanium oxide show excellent photocatalytic performance. The introduction of IB metal NPs can enhance the separation of photo-generated holes/electrons during photo-oxidations. In this account, we summarize the recent progress of small-sized IB metal NPs catalyzed by aerobic photo-oxidations, including the conversion of methanol, ethanol, sulfide, and benzylamine. More importantly, the structure–property correlations at the atomic level are detailed and discussed, e.g., the insights into the activation of oxygen and the identification of catalytic active sites. Future investigations are needed to carry out and reveal the catalytic mechanisms and conversion pathways.

Uncovering strong π-metal interactions on Ag and Au nanosurfaces under ambient conditions via in-situ surface-enhanced Raman spectroscopy

Uncovering strong π-metal interactions on Ag and Au nanosurfaces under ambient conditions via in-situ surface-enhanced Raman spectroscopy

Ab-initio techniques, VASP and CASTEP, are used to investigate the electronic properties of B2 compounds formed between Ti and group VIII elements - a comparative study

Cesium-chloride (CsCl) based intermetallic alloys that are formed between Ti and Group VIIIB and IB metals (Fe, Ni, Ru, Rh, Pd, Os Ir, Pt and Au) are currently explored for various potential applications as hydrogen storage, shape memory and biomedical materials. These compounds display excellent structural properties such as high strength due to their stable B2 phase at elevated temperatures. However, when some are subjected to unfavourable conditions such as lower temperature they become unstable and undergo a phase transition to low symmetry phases. In this work, we conducted a detailed comparative study using both VASP and CASTEP codes to carry out the first-principles calculations. Phase stability and martensitic phase transition were evaluated from the enthalpies of formation, the density of states as well as the phonon dispersion curves. There was no frequency gap observed on phonons density of states (PHDOS) spectra of the investigated compounds containing noble transition metals due to higher d-orbital electron filling.

Understanding Trends in Ethylene Epoxidation on Group IB Metals

Understanding Trends in Ethylene Epoxidation on Group IB Metals

Impurity level properties in transition metal doped α-Ga2O3 for optoelectronic applications

Doping engineering is necessary in the preparation of high-performance devices based on ultra-wide bandgap semiconductors. However, we do not yet understand the impurity level properties and their effects on performance modulation of transition metal doped α-Ga2O3. Here, using first-principles calculations with a hybrid functional, we find that IB and IIB transition metal dopants exhibit relatively lower formation energies with a theoretically high hole concentration compared with Mg dopant. However, the induced acceptor levels are so deep that the impurity levels are transformed into AX centers. Although such AX centers hinder the formation of p-type conductivity, they can increase the optical absorption, ranging from deep ultraviolet to infrared regions. For electron-rich doped α-Ga2O3, the donor levels go from deep to shallow, then turn into deep levels again and finally to relatively shallow again as the transition metal dopant goes from group IIIB to VIIIB of the periodic table. Because ionic bonds are formed between O and a dopant (IVB to VB) with a raised d-orbital, covalent characteristics are observed for the O dopant (VIB to VIIIB) bonds with evident d-orbital splitting. These results add new insights into the impurity levels of α-Ga2O3, but also reveal potential applications of transition metal dopants in α-Ga2O3.

Recent Advances in Aerobic Photo‐Oxidation of Methanol to Valuable Chemicals

AbstractThe oxidation of photocatalytic methanol into valuable chemicals is of considerable importance to the growth of the chemical industry. TiO2 has been proven to be a catalyst for methanol photocatalytic oxidation to valued chemicals (e. g. methyl formate and dimethoxymethane) at room temperature with an inferior activity. Recently, it has become a hot research topic due to its low interaction temperature with fewer by‐products. Further, the introduction of IB metal particles (i. e. Cu, Ag, and Au) upon the surface of titania can drastically enhance the catalytic activity in the photo‐oxidation, which is mainly due to metal nanoparticles can optimally enhance the efficiency of the isolation of photo‐generated holes and electrons as well as dissociate oxygen molecules. Herein, we review recent progress of the photocatalysis of methanol toward the production of chemicals over different photocatalysts (e. g., TiO2P25, M NPs/TiO2, where M=CuO, Ag2O, Au, PtO, etc). Moreover, we also glean an understanding of the catalytic mechanism and conversion pathway at play, which is confirmed by STM, in‐situ ATR‐IR, DFT simulations, etc. The reaction pathway of photo‐oxidation is different from that in the thermal process. A pivotal intermediate is absorbed formaldehyde (HCHO*), which is formed via an oxidative dehydrogenation over the redox sites of catalysts. Then the generated HCHO* directly reacts with neighboring methanol to give methyl formate (on redox sites) and dimethoxymethane (on acidic sites through a scrambling movement).

Color Tunable Self-Trapped Emissions from Lead-Free All Inorganic IA-IB Bimetallic Halides Cs-Ag-X (X = Cl, Br, I).

Multi-metallic halides of group IA and IB metals are emerged as a new class of color tunable emitters. While chalcogenides and perovskites are extensively studied, these families of materials are little explored. In comparison, herein, lead and cadmium free bimetallic Cs-Ag-X (X = Cl, Br, I) halides are reported where the larger ion Ag+ helped in incorporating all the halide ions which in turn tune their emission color in spanning from 397nm (violet) to 820nm (near infrared) as a function of their composition. The synthesis method adopted here is the solvent free ball milling of respective halides of Cs and Ag and took the record shortest time and in bulk scale. From decay lifetimes, emissions from these bimetallic halides are found as a result of fast recombination of self-trapped excitons, which exhibited not only reasonably high quantum yield in the range of 17-68% but also excellent stability to air and moisture under ambient conditions. These also show wide Stokes shift with relatively longer decay lifetimes ranging above the exciton and below the surface trap or dopant induced emissions of inorganic semiconductors, indicating a new class of materials having unique identity of their optical behaviors.

First-principles prediction of two-dimensional copper borides

Ordered borides of group IB and IIB metals (Cu, Ag, Au, Zn, Cd, Hg), as the well-known immiscible materials, are practically unknown due to the small electronegativity difference and large mismatch in their atomic sizes. Nevertheless, such rule may be broken under extreme conditions, i.e., high pressure or low dimensionality. Here two-dimensional (2D) copper borides were predicted from ab initio evolutionary searches, identifying that two structures are metallic whereas another one is strikingly a nodal line semimetal. These results challenge the long lasting puzzle in the immiscible systems and add new members to the 2D materials.

Effect of IB-metal on Ni/SiO2 catalyst for selective hydrogenation of acetylene

The IB metal (Au, Ag and Cu) alloyed Pd single atom catalysts had been proved to be efficient in promoting the selectivity for hydrogenation of acetylene to ethylene. As a base metal in the same group as Pd, the Ni-based catalysts are also active for hydrogenation reactions. Herein, the effects of the IB metals on the Ni/SiO2 catalyst for the selective hydrogenation of acetylene were systematically studied. Different from the Pd/SiO2 catalyst, the monometallic Ni/SiO2 catalyst is not active at low temperatures. The addition of the IB metals to the Ni/SiO2 catalysts can greatly enhance the activity. Besides, the catalytic activity of the AuNix/SiO2 and CuNix/SiO2 catalysts increase with the reduction temperature, while the AgNix/SiO2 catalysts are not sensitive to the pretreatment temperature. The origin of the effect of the different IB metals on the Ni-based catalysts for selective hydrogenation of acetylene is discussed based on the characterizations by XRD, TPR and microcalorimetric measurements.

Cooperative bonding interactions of various oxygen species on the IB group metal anions

Series of MOx− (M = Cu, Ag, and Au; x = 1–3) complexes and one solitary kind of AgO5− were generated using a magnetron sputter cluster source, and their reactions with additional O2 were studied by combining a low temperature flow reactor and a time-of-flight mass spectrometer. The structures and bonding characters of these complexes were explored according to the observed reaction channels and systematic DFT calculations, in which OAgO−, OAg(η1-O2)−, and (η1-O3)Ag (η1-O2)− were newly observed complexes. The structure (η1-O3)Ag (η1-O2)− was further confirmed using the molecule tagging infrared photodissociation spectroscopy. The theoretical binding energies of oxygen species in MOx− (M = Cu, Ag, and Au; x = 1–3, and 5) are consistent with the experimental observations, which clearly show a cooperative effect of bonding interactions of various oxygen species on the Cu, Ag and Au anions. The contributions of (n-1)d, ns, and np components of the IB metals to their bonding interactions were discussed, which account for the above cooperative effect as well as the much stronger Cu–O bonds than corresponding Ag–O and Au–O bonds in MOx−.

Electronic band structure of cuprous and silver halides: An all-electron GW study

Group IB metal halides (CuX and AgX, X=Cl, Br and I) are widely used in optoelectronic devices and photochemical catalysis due to their appropriate optical and electronic properties. First-principles calculations have confronted difficulties in accurately predicting their electronic band structures. Here we study CuX and AgX with many-body perturbation theory in the $GW$ approximation, implemented in the full-potential linearized augmented plane waves (FP-LAPW) framework. Comparing the quasi-particle band structures calculated with the default LAPW basis and the one extended by high-energy local orbitals (HLOs), denoted as LAPW+HLOs, we find that it is crucial to include HLOs to achieve sufficient numerical accuracy in $GW$ calculations of these materials. Using LAPW+HLOs in semi-local density functional approximation based $GW_0$ calculations leads to good agreement between theory and experiment for both band gaps and the splitting between metal (Cu or Ag) $d$ and X-$p$ states. It is indicated that quasi-particle band structures of CuX and AgX are crucially influenced by the numerical accuracy of $GW$ implementations, similar to what was found in ZnO [Jiang, H.; Blaha, P. Phys. Rev. B 2016, 93, 115203]. This work emphasizes the importance of numerical accuracy in the description of unoccupied states for quasi-particle band structure of materials with the $d^{10}$ electronic configuration.

Effects on the amorphous Ga2O3 film surfaces by sub-IB-metal-nano-layers

AbstractThis work reports by the first time a method to control the geometry of Ga2O3 films nanocrystallites at 350 °C. The formation of controlled shaped nano-crystallites of γ-Ga2O3 from amorphous Ga2O3 films grown by RF-Sputtering at room temperature driven by nano-layers of group IB metals (Cu, Ag or Au) is studied. The reported results can be explained by the role of subsurface metal nano-layers and the non-equilibrium nature of the sputtering processes. To study the effects on the surface structure and their optical properties arrays of amorphous-Ga2O3/IB-metal/amorphous-Ga2O3 were annealed in dry N2 atmosphere at 350 °C by 50, 100 and 150 min. The experimental results can be explained by the evolution of the amorphous character of the films amorphous films towards the nanocrystalline γ-Ga2O3 phase driven by the metal nano-layer seed nature. As the annealing time was increased the transition from amorphous-Ga2O3 to the nanocrystalline γ-Ga2O3 phase was detected by X-ray diffraction analysis. The transition to the nanocrystalline γ-Ga2O3 is demonstrated by the formation of octahedral, triangle and ball shape nanocrystallites with sizes of ∼5 to 50 nm according to FE-SEM analysis. The influence of the metal nano-layer is clearly seen by the shift of the plasmon frequency resonance produced by the Ga2O3/IB-metal/Ga2O3 arrays in the region from 400 to 600 nm caused by the modification of the interface Ga2O3/IB-metal produced by the applied annealing stages.

TDDFT Study of the Optical Spectra of Free and Supported Binary Coinage Metal Hexamers: Effect of Doping and Support

We present an extensive first-principles time-dependent density-functional theory study of the optical response of small (M/M′)6 and (M)3(M′)3 six-atom clusters (unary and equimolar binary hexamers of group IB metals: Cu, Ag, and Au), both in the gas-phase and supported on the MgO(100) surface, chosen as a model of a simple oxide substrate. UV–vis spectra are predicted and analyzed in detail in terms of ground- and excited-state wave functions and the involved Kohn–Sham orbitals, to rationalize origin and features of optical absorption in these systems. The interaction with the surface, in particular with the electric field generated by the charge-separated substrate, is found to induce a fragmentation and a shift toward lower energies of the absorption peaks, which is in tune with available experimental information and can be beneficial in terms of applications of these systems as photoenhancers or promoters. The orientation of the transition dipole moment with respect to the support (whether parallel or...