Promoting the conversion of CO2 to CH4via synergistic dual active sites

Mechanism of surface oxygen-containing species promoted electrocatalytic CO2 reduction

Oxygen-containing species have been demonstrated to play a key role in facilitating electrocatalytic CO2 reduction (CO2RR), particularly in enhancing the selectivity towards multi-carbon (C2+) products. However, the underlying promotion mechanism is still under debate, which greatly limits the rational optimization of the catalytic performance of CO2RR. Herein, taking CO2 and O2 co-electrolysis over Cu as the prototype, we successfully clarified how O2 boosts CO2RR from a new perspective by employing comprehensive theoretical simulations. Our results demonstrated that O2 in feed gas can be rapidly reduced into *OH, leading to the partial oxidation of Cu surface under reduction conditions. Surface *OH accelerates the formation of quasi-specifically adsorbed K+ due to the electrostatic interaction between *OH and K+ ions, which significantly increases the concentration of K+ near the Cu surface. These quasi-specifically adsorbed K+ ions can not only lower the C-C coupling barriers but also promote the hydrogenation of CO2 to improve the CO yield rate, which are responsible for the remarkably enhanced efficiency of C2+ products. During the whole process, O2 co-electrolysis plays an indispensable role in stabilizing surface *OH. This mechanism can be also adopted to understand the effect of high pH of electrolyte and residual O in oxide-derived Cu (OD-Cu) on the catalytic efficiency towards C2+ products. Therefore, our work provides new insights into strategies for improving C2+ products on the Cu-based catalysts, i.e., maintaining partial oxidation of surface under reduction conditions.

Research progress of dual-atom site catalysts for photocatalysis

Dual-atom site catalysts (DASCs) have sparked considerable interest in heterogeneous photocatalysis as they possess the advantages of excellent photoelectronic activity, photostability, and high carrier separation efficiency and mobility. The DASCs involved in these important photocatalytic processes, especially in the photocatalytic hydrogen evolution reaction (HER), CO2 reduction reaction (CO2RR), N2/nitrate reduction, etc., have been extensively investigated in the past few years. In this review, we highlight the recent progress in DASCs that provides fundamental insights into the photocatalytic conversion of small molecules. The controllable preparation and characterization methods of various DASCs are discussed. Subsequently, the reaction mechanisms of the formation of several important molecules (hydrogen, hydrocarbons and ammonia) on DASCs are introduced in detail, in order to probe the relationship between DASCs's structure and photocatalytic activity. Finally, some challenges and outlooks of DASCs in the photocatalytic conversion of small molecules are summarized and prospected. We hope that this review can provide guidance for in-depth understanding and aid in the design of efficient DASCs for photocatalysis.

N,S coordination in Ni single-atom catalyst promoting CO2RR towards HCOOH

Carbon-based single atom catalysts (SACs) are attracting extensive attention in the CO2 reduction reaction (CO2RR) due to their maximal atomic utilization, easily regulated active center and high catalytic activity, in which the coordination environment plays a crucial role in the intrinsic catalytic activity. Taking NiN4 as an example, this study reveals that the introduction of different numbers of S atoms into N coordination (Ni-NxS4-x (x = 1-4)) results in outstanding structural stability and catalytic activity. Owing to the additional orbitals around -1.60 eV and abundant Ni dxz, dyz, dx2, and dz2 orbital occupation after S substitution, N,S coordination can effectively facilitate the protonation of adsorbed intermediates and thus accelerate the overall CO2RR. The CO2RR mechanisms for CO and HCOOH generation via two-electron pathways are systematically elucidated on NiN4, NiN3S1 and NiN2S2. NiN2S2 yields HCOOH as the most favorable product with a limiting potential of -0.24 V, surpassing NiN4 (-1.14 V) and NiN3S1 (-0.50 V), which indicates that the different S-atom substitution of NiN4 has considerable influence on the CO2RR performance. This work highlights NiN2S2 as a high-performance CO2RR catalyst to produce HCOOH, and demonstrates that N,S coordination is an effective strategy to regulate the performance of atomically dispersed electrocatalysts.

A simple descriptor for the nitrogen reduction reaction over single atom catalysts

The performance of supported catalysts is largely decided by metal-support interactions, which is of great significance for the rational design of catalysts. However, how to quantify the structure-activity relationship of supported catalysts remains a great challenge. In this work, taking MoS₂ and WS₂ supported single atom catalysts (SACs) as prototypes, a simple descriptor, namely, effective d electron number (labeled as Φ), is constructed to quantitatively describe the effect of metal-support interaction on the nitrogen reduction reaction (NRR) activity. This descriptor merely consists of intrinsic properties of the catalyst (including the number of d electrons, electronegativity of the metal atoms and generalized electronegativity of the substrate atoms) and can accurately predict the limiting potential (U_L) for the NRR, with no need for any density functional theory calculations. Moreover, this descriptor possesses superb expansibility that can be applied to other materials, including other metal dichalcogenide (MoSe₂, MoTe₂, WSe₂, WTe₂ and NbS₂) and even MXene (V₂CO₂, Ti₂CO₂ and Nb₂CO₂)-supported SACs. On this basis, a fast screening of excellent NRR catalysts among these systems is performed and three promising NRR catalysts (i.e. Mo@WTe₂, Mo@V₂CO₂ and Re@NbS₂) are successfully selected with U_L as low as -0.32, -0.24 and -0.31 V, respectively. This work offers new opportunities for advancing the rapid discovery of high-efficiency NRR catalysts, and the design principle is expected to be widely applicable to other catalytic systems and beyond.

Emerging materials for electrochemical CO2 reduction: progress and optimization strategies of carbon-based single-atom catalysts

The electrochemical CO₂ reduction reaction can effectively convert CO₂ into promising fuels and chemicals, which is helpful in establishing a low-carbon emission economy. Compared with other types of electrocatalysts, single-atom catalysts (SACs) immobilized on carbon substrates are considered to be promising candidate catalysts. Atomically dispersed SACs exhibit excellent catalytic performance in CO₂RR due to their maximum atomic utilization, unique electronic structure, and coordination environment. In this paper, we first briefly introduce the synthetic strategies and characterization techniques of SACs. Then, we focus on the optimization strategies of the atomic structure of carbon-based SACs, including adjusting the coordination atoms and coordination numbers, constructing the axial chemical environment, and regulating the carbon substrate, focusing on exploring the structure-performance relationship of SACs in the CO₂RR process. In addition, this paper also briefly introduces the diatomic catalysts (DACs) as an extension of SACs. At the end of the paper, we summarize the article with an exciting outlook discussing the current challenges and prospects for research on the application of SACs in CO₂RR.

First-principles study of CO2 hydrogenation to formic acid on single-atom catalysts supported on SiO2

The hydrogenation of CO₂ into valuable chemical fuels reduces the atmospheric CO₂ content and also has broad economic prospects. Support is essential for catalysts, but many of the reported support materials cannot meet the requirements of accessibility and durability. Herein, we theoretically designed a series of single-atom noble metals anchored on a SiO₂ surface for CO₂ hydrogenation using density functional theory (DFT) calculations. Through theoretical evaluation of the formation energy, hydrogen dissociation capacity, and activity of CO₂ hydrogenation, we found that Ru@SiO₂ is a promising candidate for CO₂ hydrogenation to formic acid. The energy barrier of the rate-determining step of the entire conversion process is 23.9 kcal mol^-1; thus, the reaction can occur under mild conditions. In addition, active and stable origins were revealed through electronic structure analysis. The charge of the metal atom is a good descriptor of the catalytic activity. The Pearson correlation coefficient (PCC) between metal charge and its CO₂ hydrogenation barrier is 0.99. Two solvent models were also used to investigate hydrogen spillover processes and the reaction path was searched by the climbing image nudged-elastic-band (CI-NEB) method. The results indicated that the explicit solvent model could not be simplified into a few solvent molecules, leading to a large difference in the reaction paths. This work will serve as a reference for the future design of more efficient catalysts for CO₂ hydrogenation.

Tuning Nitrate Electroreduction Activity via an Equilibrium Adsorption Strategy: A Computational Study

Converting nitrates into industrial-value chemicals is of great significance for environmental sustainability. Herein, the electrochemical nitrate reduction reaction (NO₃RR) performances of transition metal (TM) anchored g-C₃N₄ (TM/g-C₃N₄) were systematically evaluated using density functional theory and ab initio molecular dynamics. A novel equilibrium adsorption model was constructed to screen the excellent catalysts, accelerating high-throughput calculations. As found, Hf/g-C₃N₄ exhibits remarkable activity with a limiting potential of 0.11 V. Besides, the superior electrode selectivity overwhelmingly depresses the formation of byproducts and greatly speeds up the NO₃RR. The electronic structure analysis discloses the origin of the electrocatalytic activity for TM/g-C₃N₄ and indicates why the IVB group elements have an outstanding role. Finally, the formation energy of the clusters and ab initio molecular dynamics simulations prove their structure has fine stability. This work not only offers high-performance electrode candidates for the NO₃RR but also opens up a precedent of electrocatalysis in the field of wastewater treatment of explosives.