Two-dimensional g-C3N4 nanosheets with few-layer thickness, ensuring equivalent charge migrations to various Pd facets, provide an ideal model system for reliably examining the facet selectivity of Pd co-catalysts. It reveals that reduction of CO2 can occur better on Pd{111} facets while H2O prefers to generate H2 on Pd{100}.

"Aggregation-caused quenching" (ACQ) and "aggregation-induced emission" (AIE) are two well-known mechanisms for polymer luminescence. Here we proposed an alternative mechanism termed "aggregation-induced intersystem crossing" (AI-ISC). By aggregating certain fluorescent dye molecules, one can improve the energy matches between excited singlet and triplet states so as to promote the intersystem crossing (ISC) rate, and consequently prolong the lifetime of excited electrons by steering them into triplet states. First-principles calculations suggested that the enhanced ISC rate could substantially promote molecular phosphorescence in aggregated systems of originally fluorescent dye molecules, as later validated by experimental measurement. Meanwhile, the emission spectra experience a red shift along with the aggregation, providing a convenient knob to tune the phosphorescence wavelength. The proposed AI-ISC mechanism may open up a new design approach for the emerging luminescent material applications.

The electrocatalytic activity of transition-metal-based compounds is strongly related to the spin states. However, the underlying relationship connecting spin to catalytic activity remains unclear. Herein, we carried out density functional theory calculations on oxygen reduction reaction (ORR) catalyzed by Fe single-atom supported on C2N (C2N–Fe) to shed light on this relationship. It is found that the change of electronic spin moments of Fe and O2 due to molecular-catalyst adsorption scales with the amount of electron transfer from Fe to O2, which promotes the catalytic activity of C2N–Fe for driving ORR. The nearly linear relationship between the catalytic activity and spin moment variation suggests electronic spin moment as a promising catalytic descriptor for Fe single-atom based catalysts. Following the revealed relationship, the ORR barrier on C2N–Fe was tuned to be as low as 0.10 eV through judicious manipulation of spin states. These findings thus provide important insights into the relationship between catalytic activity and spin, leading to new strategies for designing transition metal single-atom catalysts.

Developing efficient single-atom catalysts (SACs) for nitrogen fixation is of great importance while remaining a great challenge. The lack of an effective strategy to control the polarization electric field of SACs limits their activity and selectivity. Here, using first-principles calculations, we report that a single transition metal (TM) atom sandwiched between hexagonal boron nitride (h-BN) and graphene sheets (namely, BN/TM/G) acts as an efficient SAC for the electrochemical nitrogen reduction reaction (NRR). These sandwich structures realize stable and tunable interfacial polarization fields that enable the TM atom to donate electrons to a neighboring B atom as the active site. As a result, the partially occupied p z orbital of a B atom can form B-to-N π-back bonding with the antibonding state of N 2 , thus weakening the NN bond. The not-strong-not-weak electric field on the h-BN surface further promotes N 2 adsorption and activation. The NRR catalytic activity of the BN/TM/G system is highly correlated with the degree of positively polarized charges on the TM atom. In particular, BN/Ti/G and BN/V/G are identified as promising NRR catalysts with high stability, offering excellent energy efficiency and suppression of the competing hydrogen evolution reaction.

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Supporting Information and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.

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Acceptor-doped, redox-active perovskite oxides such as La0.8Sr0.2FeO3 (LSF) are active for ethane oxidation to COx but show poor selectivity to ethylene. This article reports molten Li2CO3 as an effective “promoter” to modify LSF for chemical looping–oxidative dehydrogenation (CL-ODH) of ethane. Under the working state, the redox catalyst is composed of a molten Li2CO3 layer covering the solid LSF substrate. The molten layer facilitates the transport of active peroxide (O22−) species formed on LSF while blocking the nonselective sites. Spectroscopy measurements and density functional theory calculations indicate that Fe4+→Fe3+ transition is responsible for the peroxide formation, which results in both exothermic ODH and air reoxidation steps. With >90% ethylene selectivity, up to 59% ethylene yield, and favorable heat of reactions, the core-shell redox catalyst has an excellent potential to be effective for intensified ethane conversion. The mechanistic findings also provide a generalized approach for designing CL-ODH redox catalysts.