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[Display omitted] • Diameter can improve the catalytic performance of SACs for ORR/OER. • Local strain and curvature effects causes abnormal d -band center model of OH on SACs. • Co@N 4 CNTs diameter adjusts Co d -orbitals, enhancing catalyst activity. • Co@N 4 CNTs have good selectivity for ORR rather than HER. The advancement of metal-air batteries relies significantly on the development of highly efficient bifunctional catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Herein, we investigate the potential application of Co@N 4 -doped carbon nanotubes (Co@N 4 CNTs) as bifunctional catalysts using density functional theory calculations. We explore the stability and electronic properties of Co@N 4 CNTs by analyzing energies, bond lengths, conducting ab initio molecular dynamics simulations, and examining the density of states. Notably, the diameter of the nanotubes has a notable impact on the catalytic performance of Co@N 4 CNTs. A remarkable 54% improvement in catalytic activity when transitioning from (4, 4) to (24, 4) Co@N 4 CNTs, with η Bi from changing from 1.40 to 0.64 V. We have several exceptional catalysts with low overpotentials, including (18, 4), (22, 4), and (24, 4) Co@N 4 CNTs, which exhibit η Bi values of 0.68, 0.67, and 0.64 V, respectively. Moreover, we link the increased activity of Co@N 4 CNTs to the change of Co atom's partial d orbital energy, facilitated by adjustments in the diameter of Co@N 4 CNTs. This revelation offers valuable insights into the underlying factors driving the enhancement of catalytic activity through alterations in orbital energy levels. Our research uncovers several excellent catalysts and provides valuable insights for the design and development of efficient catalysts for metal-air batteries. [ABSTRACT FROM AUTHOR]

The active origins of heteroatom coordinated Fe-X m Y n SACs (X, Y = B, C, N, O, m+n = 4) toward NRR as a model reaction are elucidated at orbital level by thoroughly analyzing structural, energetic, and electronic parameters. [Display omitted] • Active origins of heteroatom coordinated Fe-X m Y n SACs (X, Y = B, C, N, O, m + n = 4) are analyzed comprehensively through structural, energetic, and electronic parameters. • Number and arrangement of heteroatoms play a key role in regulating the degree of d -orbital splitting (d SE) and magnetic moment of Fe center. • Both s - and d -orbitals of Fe contribute to Fe–N bonding. • Competition between Pauli repulsion and orbital interaction modulates adsorption behavior. Heteroatom-coordinated single-atom catalysts (SACs) supported by porous graphene exhibit high activity in electrochemical reduction reactions. However, the underlying active origins are complex and puzzling, hindering the development of efficient catalysts. Herein, we investigate the active origins of heteroatom-coordinated Fe-X m Y n SACs (X, Y = B, C, N, O, m + n = 4) toward nitrogen reduction reaction (NRR) as a model reaction, through comprehensive analysis of structural, energetic, and electronic parameters. Specifically, the number and arrangement of heteroatoms are found to significantly affect the degree of d -orbital splitting and magnetic moment of the Fe center. Moreover, d -orbital splitting energy (d SE), rather than the conventional d -band theory, explains the adsorption behavior of intermediates in multi-step electron–proton coupling (EPC) reactions. In addition, both s - and d -orbitals of Fe are found to be important for Fe–N bonding, which promotes charge transfer (CT) and N 2 activation. Importantly, CT is thought to influence the Pauli repulsion and orbital interaction. Correspondingly, relationships are unveiled between limiting potential (U limit) and adsorption energy Δ E (*NNH), d SE , CT, Fe–N bond. In all, this work provides orbital-level insights into the active origins of Fe-X m Y n SACs, contributing to the understanding of intrinsic mechanism and the design of electrocatalysts for multi-step EPC reactions. [ABSTRACT FROM AUTHOR]

In this study, an efficient catalytic system composed of deep eutectic solvents (DESs) was developed by adjusting the basicity of hydrogen bond donors (HBDs) to synthesize poly(isosorbide) carbonate (PIC) with high weight average molecular weight (Mw). It was demonstrated that the Mw of PIC prepared by using nearly neutral [EminOH]Cl–2EG was the highest. The results of the transesterification kinetics with different catalysts supported that the transesterification rate was significantly promoted as the basicity of DESs increased but their strong alkalinity inhibited the Mw of PIC. Therefore, the degradation of PIC was investigated to reveal the mechanism of the influence of basicity on the molecular weight of PIC. The strong alkalinity of DESs would cause the depolymerization of the macromolecular chains and ultimately limit the molecular weight of the product, proving the experimental fact that a near-neutral catalyst was more conducive to the Mw of PIC. Finally, a reasonable mechanism of synergistic catalysis was proposed based on 1H NMR spectroscopy, Fourier transform infrared spectroscopy (FT-IR) and experimental results. The metal-free, low-cost, high catalytic activity DES catalyst involved here is a practical candidate for advanced bio-based polycarbonate. [ABSTRACT FROM AUTHOR]

In this study, a series of high-activity imidazole-based dicationic ionic liquids (DILs) were designed and prepared as efficient catalysts for balancing the reactivity between the endo-hydroxyl group (endo-OH) and the exo-hydroxyl group (exo-OH) of isosorbide (ISO) to synthesize high molecular weight poly(isosorbide carbonate) (PIC). Meanwhile, the thermal performance of PIC was precisely optimized by regulating the chain configuration. The results showed that when the trace amounts (4.5 × 10−5 based on the ISO molar amount) of bis-(3-methyl-1-imidazole)-ethylene dibromide ([C2(Min)2][Br]2) were used, the weight average molecular weight (Mw) of PIC reached 98 700 g mol−1. It could be concluded from the results of the experiment and the stimulation that the high catalytic activity of DILs was attributed to the strong electrostatic interaction between the cation and the substrate and the effective balance of the reactivity of the endo-OH and the exo-OH. Furthermore, we found that the reduction of hydroxyl groups in the terminal groups and the increase of endo–endo (a1) structure in the repeating unit improved the thermal properties of PIC. Finally, 1H NMR, Fourier infrared spectroscopy, and density functional theory (DFT) calculations were used to verify the reaction process through anion and cation multi-site synergistic effect and a possible electrophilic–nucleophilic reaction mechanism was successfully obtained. [ABSTRACT FROM AUTHOR]

Synthesis of bioderived high-molecular-weight polycarbonates under metal-free condition is particularly challenging. Here, a green synthetic strategy of bio-based poly(isosorbide carbonate) (PIC) from renewable monomer isosorbide (ISB) and dimethyl carbonate (DMC) was developed by using organo-catalysts, which avoided the use of toxic and metal-containing chemicals. Due to high catalytic activity of the organo-catalysts, the reactivity of ISB and selectivity of carboxymethylated products were improved significantly, resulting in high-molecular-weight PIC. By using 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) as catalyst, an oligomer with [–OC(O)OCH3]/[–OH] ratio of 1.56 and PIC with weight-average molecular weight of 53 200 were obtained, which indicated that both ISB and DMC were effectively activated by TBD according to our proposed bifunctional activation mechanism. Furthermore, one-pot synthesis of copolymeric poly(diol-co-isosorbide carbonate)s from ISB, DMC and various diols was achieved, where the secondary hydroxyl group of ISB and the primary hydroxyl group of diols were dually activated by TBD, which has not been reported to the best of our knowledge. [ABSTRACT FROM AUTHOR]

[Display omitted] • NTiCO 2 , a Janus-type double-transition metal MXenes. • Pt-doped dual transition metal NTiCO 2 is stable. • Synergistic effect can improve the catalytic performance of SACs. • Two machine models, RFR and XGBR, are established. • The importance of features affecting catalytic activity is revealed. Oxygen reduction reaction and oxygen evolution reaction are pivotal in energy conversion. Herein, we systematically studied the catalytic performance of Pt-doped dual transition metal (DTM) Janus-MXenes as single-atom catalysts (SACs) using first-principles calculations and established machine learning (ML) models to explore the physical and chemical properties affecting the catalytic overpotential. Specifically, the stability of Janus-MXenes was first explored through cohesive energies, phonon dispersion and ab initio molecular dynamics simulations. The electronic properties of Pt-doped Janus-MXenes were investigated next. Some excellent catalysts, including Pt-V O -MnTiCO 2 (η ORR / O E R = 0.24/0.38 V) and Pt-V O -PdTiCO 2 (η ORR / O E R = 0.33/0.36 V), were found because of their ultralow overpotential. It's attributed to the tuning of the electronic properties of SACs by DTM. Importantly, ML models were used to reveal the importance of descriptors affecting overpotential, thereby uncovering the origin of the catalytic activity of SACs. Our work significantly reduces the research costs of SACs and serves as a guide for designing high-performance catalysts. [ABSTRACT FROM AUTHOR]

This work focuses on tuning the NRR activity by constructing SACs based on MXenes substrates and elucidating the intrinsic factors that regulate the "acceptance-donation" mechanism by first principles calculations. [Display omitted] • NRR performance can be tuned by constructing SACs based on defective Ti 2 CO 2 and Ti 2 NO 2 MXenes. • Number of unpaired electrons in d orbitals (N un-d) determines occupation of d orbitals, thus regulating the "acceptance-donation" mechanism. • Δ E (*NNH) and N iso-d can be considered as promising descriptors for screening and designing effective SACs. • Insightful guidance is provided for electrochemical reactions with high bond-order molecules and multi-electron steps, e.g., NRR, ORR and CO 2 RR. Single-atom catalysts (SACs) show great potential for driving electrochemical nitrogen reduction reaction (NRR). However, the lack of physico-chemical understanding of the ambiguous activation mechanism impedes the development of electrocatalysts. In this work, using first principles calculations, we tuned NRR activity and elucidated regulation mechanism of N 2 activation by constructing SACs based on defective Ti 2 CO 2 and Ti 2 NO 2 MXenes. Interestingly, Mo@Ti 2 CO 2 -v and W@Ti 2 CO 2 -v show excellent NRR activity and selectivity with low limiting potentials of –0.27 and –0.27 V at the first hydrogenation (*N 2 →*NNH) and the last hydrogenation (*NH 2 →*NH 3) steps via distal pathway, respectively. The intrinsic activity tendency can be related to adsorption energy of intermediate *NNH (Δ E (*NNH)). Furthermore, electronic structure analysis demonstrates that number of unpaired electrons in d orbitals (N un-d) determines occupation of d orbitals, thus regulating the "acceptance-donation" mechanism. Particularly, transition metals with N un-d of 5 and 4 show moderate "acceptance-donation" interaction, thus achieving encouraging NRR performance. Moreover, Δ E (*NNH) and N un-d can be considered as promising descriptors for screening and designing effective SACs. Finally, our investigation not only contributes to discovery of novel SACs toward NRR, but also provides insightful guidance for other electrochemical reactions with high bond-order molecules and multi-electron steps, such as ORR and CO 2 RR. [ABSTRACT FROM AUTHOR]

[Display omitted] • Pt doped Janus-MXenes is stable. • Janus-MXenes can improve the catalytic activity of catalysts for ORR/OER. • Pt doped MXenes SACs show higher selectivity for ORR. Developing high-activity and low-cost oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) bifunctional catalysts is strategic to metal-air batteries. Herein, based on the idea that functionalized atoms can adjust the electronic properties of MXenes-based catalysts, we have screened some catalysts with high catalytic activity for ORR/OER using first-principles calculations. Specifically, we firstly explored the stability of Pt doped Ti 2 CNL ((N = F, Cl, Br and I, L = O, S and Se)) and Ti 2 CN(L) 2 though calculating the vacancy formation energy and binding energy. Moreover, compared the overpotential of Pt doped Ti 2 CN(L) 2 and Ti 2 CNL for ORR and OER, the Janus-MXenes configurations can tune the d -band center, work-function, density of state (DOS) and charge distribution of the catalysts, and then improve the catalytic performance of catalysts. Pt-V S -Ti 2 CSBr, Pt-V I -Ti 2 COI and Pt-V S -Ti 2 CSBr as ORR, OER and ORR/OER bifunctional catalysts were revealed due to their ultra-low overpotential of 0.35, 0.34 and 0.79 V, respectively. Additionally, compared to H ions, the catalyst preferentially adsorbs O 2 , thus ensuring the ORR advantage to proceed rather than hydrogen evolution reaction (HER). Even so, Pt-VO-Ti 2 COI, Pt-VS-Ti 2 CSI and Pt-VSe-Ti 2 CSeI have high activity for HER. Our work not only screened out catalysts with encouraging catalytic performance but also guided the design of high-performance catalysts. [ABSTRACT FROM AUTHOR]