While catalysis is highly dependent on the electronic structure of the catalyst, the understanding of catalytic performance affected by electron spin regulation remains challenging and rare. Herein, we have developed a facile strategy to the manipulation of the cobalt spin state over covalent organic frameworks (COFs), COF-367-Co, by simply changing the oxidation state of Co centered in the porphyrin. Density functional theory (DFT) calculations together with experimental results confirm that CoII and CoIII are embedded in COF-367 with S = 1/2 and 0 spin ground states, respectively. Remarkably, photocatalytic CO2 reduction results indicate that COF-367-CoIII exhibits favorable activity and significantly enhanced selectivity to HCOOH, accordingly much reduced activity and selectivity to CO and CH4, in sharp contrast to COF-367-CoII. The results highlight that the spin-state transition of cobalt greatly regulates photocatalytic performance. Theoretical calculations further disclose that the presence of CoIII in COF-367-Co is preferable to the formation of HCOOH but detrimental to its further conversion, which clearly accounts for its distinctly different photocatalysis over COF-367-CoII. To the best of our knowledge, this is the first report on regulating photocatalysis by spin state manipulation in COFs.

Heterogeneous catalysis often involves molecular adsorptions to charged catalyst site and reactions triggered by catalyst charges. Here we use first-principles simulations to design oxygen reduction reaction (ORR) catalyst based on double transition metal (TM) atoms stably supported by 2D crystal C2N. It not only holds characters of low cost and high durability but also effectively accumulates surface polarization charges on TMs and later deliveries to adsorbed O2 molecule. The Co-Co, Ni-Ni, and Cu-Cu catalysts exhibit high adsorption energies and extremely low dissociation barriers for O2, as compared with their single-atom counterparts. Co-Co on C2N presents less than half the value of the reaction barrier of bulk Pt catalysts in the ORR rate-determining steps. These catalytic improvements are well explained by the dependences of charge polarization on various systems, which opens up a new strategy for optimizing TM catalytic performance with the least metal atoms on porous low-dimensional materials.

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.

Based on DFT calculations, we propose a TM@CN hybrid structure, in which the single-atom transition metal (TM = Pt, Pd, Co, Ni, Cu) is supported by graphitic carbon nitride (g-CN), as a promising high-performance OER catalyst. Our work reveals the importance of local TM coordination in catalysts for the OER, which would lead to a new class of low-cost, durable and efficient OER catalysts.

By performing density functional theory calculations, we have studied the CO pathway and non-CO pathway of methanol oxidation on the PtAu(111) bimetallic surface. CO is shown to possess larger adsorption energy on the PtAu(111) surface than that on the pure Pt(111) surface, and the non-CO pathway on the bimetallic surface is found to be energetically more favorable than the CO pathway. These calculated results propose that the improved electrocatalytic activity of PtAu bimetallic catalysts for methanol oxidation should be attributed to the alternation in the major reaction pathway from the CO pathway on the pure Pt surface to the non-CO pathway on the PtAu bimetallic surface rather than the easier removal of CO on PtAu catalysts than on pure Pt catalysts.

Ca Cu 3 Ti 4 O 12 (CCTO) ceramics are prepared by the conventional solid-state reaction method under various sintering temperatures from 1000to1120°C at an interval of 10°C. Microstructures and crystalline structures are examined by scanning electronic microscopy and x-ray diffraction, respectively. Dielectric properties and complex impedances are investigated within the frequency range of 40Hz–110MHz over the temperature region from room temperature to 350°C. It has been disclosed that the microstructures can be categorized into three different types: type A (with the small but uniform grain sizes), type B (with the bimodal distribution of grain sizes) and type C (with the large and uniform grain sizes), respectively. The largeness of low-frequency dielectric permittivity at room temperature is closely related to the microstructure. Ceramics with different types of microstructures show the diverse temperature-dependent behaviors of electrical properties. However, the existence of some common characteristics is also found among them. For all of the ceramics, a Debye-type relaxation emerges in the frequency range of 100Hz–100kHz at high measuring temperatures, which has the larger dielectric dispersion strength than the one known in the frequency range above 100kHz. Thus, the high-temperature dielectric dispersion exhibits a large low-frequency response and two Debye-type relaxations. Furthermore, all of the ceramics show three semicircles in the complex impedance plane. These semicircles are considered to represent individually different electrical mechanisms, among which the one in the low-frequency range arises most probably from the contribution of the domain boundaries, and the other two are ascribed to the contributions of the domains and the grain boundaries, respectively.

The electrocatalytic activity of transition-metal (TM)-based catalysts is correlated with the spin states of metal atoms. However, developing a way to manipulate spin remains a great challenge. Using first-principles calculations, we first report the crucial role of the spin of exposed Mo atoms around an S-vacancy in the electrocatalytic dinitrogen reduction reaction on defective MoS 2 nanosheets and propose a novel strategy for regulating the electronic spin moments by tuning a single-atom promoter (SAP). Single TM atoms adsorbed on a defective MoS 2 basal plane serve as SAPs via a noncontact interaction with an exposed Mo active site, inducing a significant spin polarization that promotes N 2 adsorption and activation. Interestingly, by changing only the adsorption site of the TM atom, we are able to change the spin moments of the Mo atom, over a wide range of tunable values. The spin moments can be tuned to largely improve the catalytic activity of MoS 2 toward the reduction of N 2 to NH 3 .

Graphene- or graphene oxide (GO)-supported metallic nanoparticles and single metal atom as potentially effective catalysts for chemical reactions have recently received extensive research interests. However, metal utilization in nanoparticle catalysts is limited and metal atoms readily drift on the graphene surface and consequently form aggregated large particles, making practical applications limited. Here, we report metal ions directly immobilized on GO as a novel GO-supported single-ion catalyst for chemiluminecence (CL) reactions. It is found that GO-supported cobalt ions with good stability could catalyze strongly luminol-HO and lucigenin-HO CL reactions, accompanied by dramatically enhanced CL emission. Theoretical studies reveal that the coupling between Co and GO induces effective polarization charges, improving chemical activity of the reaction site, which promotes the generation of intermediate radicals and accelerates the CL reactions. This work may be generalized to other GO-supported metal ions as catalysts for a wide range of chemical reactions. The developed GO-supported cobalt single-ion nanocomposites as nanointerfaces may find future applications in CL bioassays.