Theoretical insights into single-atom catalysts

Schematic diagram of theoretical models and applications of single atom catalysts. A review on the theoretical models, intrinsic properties, and the related application of SACs.

A di-boron pair doped MoS2 (B2@MoS2) single-layer shows superior catalytic performance for electrochemical nitrogen activation and reduction

Developing efficient electrocatalysts to convert nitrogen into ammonia represents a major chemistry challenge and is of great significance for sustaining life. A lot of recent studies have been focusing on the single-atom electrocatalysts for the N₂ reduction reaction (NRR), yet the double-atom or few-atom catalysts, based on the non-metal catalytic center, in particular, have been rarely investigated. Herein from DFT simulations, we report diatomic boron doped single-layer MoS₂, B2@MoS₂, as the potential electrocatalyst for the nitrogen reduction reaction, and compare it with single boron atom doped MoS₂, B@MoS₂, based on thermodynamics, selectivity, and kinetics analysis. The results reveal that this novel diatomic modified catalyst exhibits excellent structural and thermodynamic stability, and shows significant improvement in the conductivity of MoS₂ which is essential for the electrocatalytic NRR. Furthermore, the B2@MoS₂ catalyst can effectively activate the inert N₂ and promote N₂ reduction to NH₃via the enzymatic mechanism, and shows much better electrocatalytic activity than B@MoS₂, as reflected by the significantly reduced overpotential (0.02 V vs. 0.30 V) and the much lower activation barrier (1.24 eV vs. 2.84 eV). Particularly, the close-to-zero overpotential predicted for B2@MoS₂ is lower than those of most ever-reported single-atom electrocatalysts. The extraordinary activity of B2@MoS₂ is closely related to the efficient electron transport as well as the synergism effect of diatomic boron. Our predictions hence suggest B2@MoS₂ as a superior promising catalyst for efficient dinitrogen fixation and reduction.

WO3 nanosheets rich in oxygen vacancies for enhanced electrocatalytic N2 reduction to NH3

The Haber-Bosch process for industrial-scale NH3 production suffers from harsh conditions and serious CO2 release. Electrochemical N2 reduction is an alternative approach to synthesize NH3 under ambient conditions, but it requires highly-efficient electrocatalysts for the N2 reduction reaction (NRR). In this Communication, we demonstrate that WO3 nanosheets rich in oxygen vacancies (R-WO3 NSs) exhibit greatly enhanced NRR performances. In 0.1 M HCl, such R-WO3 NSs achieve a large NH3 yield of 17.28 μg h-1 mgcat.-1 and a high faradaic efficiency of 7.0% at -0.3 V vs. a reversible hydrogen electrode, much superior to the WO3 nanosheets deficient in oxygen vacancies (6.47 μg h-1 mgcat.-1 and 1.02%). Remarkably, R-WO3 NSs also show high electrochemical stability.

Using Pd-Doped γ-Graphyne to Detect Dissolved Gases in Transformer Oil: A Density Functional Theory Investigation

To realize a high response and high selectivity gas sensor for the detection dissolved gases in transformer oil, in this study, the adsorption of four kinds of gases (H₂, CO, C₂H₂, and CH₄) on Pd-graphyne was investigated, and the gas sensing properties were evaluated. The energetically-favorable structure of Pd-Doped γ-graphyne was first studied, including through a comparison of different adsorption sites and a discussion of the electronic properties. Then, the adsorption of these four molecules on Pd-graphyne was explored. The adsorption structure, adsorption energy, electron transfer, electron density distribution, band structure, and density of states were calculated and analyzed. The results show that Pd prefers to be adsorbed on the middle of three C≡C bonds, and that the band gap of γ-graphyne becomes smaller after adsorption. The CO adsorption exhibits the largest adsorption energy and electron transfer, and effects an obvious change to the structure and electronic properties to Pd-graphyne. Because of the conductance decrease after adsorption of CO and the acceptable recovery time at high temperatures, Pd-graphyne is a promising gas sensing material with which to detect CO with high selectivity. This work offers theoretical support for the design of a nanomaterial-based gas sensor using a novel structure for industrial applications.

Defective Graphene on the Transition-Metal Surface: Formation of Efficient Bifunctional Catalysts for Oxygen Evolution/Reduction Reactions in Alkaline Media

Supported single-atom catalysts (SACs) have attracted enormous attention because of their high selectivity, activity, and efficiency, compared to conventional nanoparticles and metal bulk catalysts. However, all of these unique merits rely on the stability of the SAC, as reported by many investigators. To avoid aggregation of single-metal atoms and maintain the high performance of the SAC, various substrates have been tried to support them, particularly on graphene nanosheets. A spontaneous interface phenomenon between graphene and the Co (and Ni) substrate discovered in this work is that the holes in the graphene layer can stimulate metal atoms to pop up from a metal substrate and fill the double vacancy in graphene (DV-G) and stabilize on the graphene surface. The unique structure of the lifted metal atom is expected to be useful for the bifunctional SAC for electrocatalytic oxygen evolution reactions (OERs) and oxygen reduction reactions (ORRs). Our first-principles calculations indicate that the DV-G on the Co(0001) surface can serve as an excellent bifunctional OER/ORR catalyst in alkaline media with extremely low overpotentials of 0.39 V for OER and only 0.36 V for ORR processes, which are even lower than those for previously reported bifunctional catalysts. We believe that the catalytic activity stems from the interface coupling effect between the DV-G and metal substrate, as well as the charge redistribution in the graphitic sheet.

Platinum single-atom catalysts: a comparative review towards effective characterization

This review summaries the characterization techniques for Pt single-atom catalysts and focuses on FT-EXAFS spectroscopy to study the coordination environment of Pt–M for atomically dispersed Pt catalysts on diverse supports.

Molecule-level graphdiyne coordinated transition metals as a new class of bifunctional electrocatalysts for oxygen reduction and oxygen evolution reactions

Graphdiyne (GDY) could provide a unique platform for synthesizing uniform single-atom catalysts (SACs) with high catalytic activity toward oxygen reduction (ORR) and oxygen evolution (OER) reactions.