Iron Monomers or Trimers on Nitrogen-Doped Carbon: Which Is Better for the Electrocatalytic Nitrogen Reduction Reaction?

The electrocatalytic nitrogen reduction reaction (NRR) presents an alternative method for the Haber-Bosch process, and single-atom catalysts (SACs) to achieve efficient NRR have attracted considerable attention in the past decades. However, whether SACs are more suitable for NRR compared to atomic-cluster catalysts (ACCs) remains to be studied. Herein, we have successfully synthesized both the Fe monomers (Fe1) and trimers (Fe3) on nitrogen-doped carbon catalysts. Both the experiments and DFT calculations indicate that compared to the end-on adsorption of N2 on Fe1 catalysts, N2 activation is enhanced via the side-on adsorption on Fe3 catalysts, and the reaction follows the enzymatic pathway with a reduced free energy barrier for NRR. As a result, the Fe3 catalysts achieved better NRR performance (NH3 yield rate of 27.89 µg h-1 mg-1cat. and Faradaic efficiency of 45.13%) than Fe1 catalysts (10.98 µg h-1 mg-1cat. and 20.98%). Therefore, our research presents guidance to prepare more efficient NRR catalysts.

Breaking the Volcano-Shaped Relationship for Highly Efficient Electrocatalytic Nitrogen Reduction: A Computational Guideline.

The volcano-shaped relationship is very common in electrocatalytic nitrogen reduction reaction (e-NRR) and is usually caused by the competition between the first and last hydrogenation steps. How to break such a relationship to further improve the catalytic performance remains a great challenge. Herein, using first-principles calculations, we investigate a range of transition-metal (TM)-doped Cu-based single-atom alloys (TM1-Cu(111)) as catalysts for e-NRR. When the adsorption of N2 on the catalysts is strong enough, the inert N2 molecules can be effectively activated for the first hydrogenation step. Meanwhile, the last hydrogenation step is not affected by the scaling relationship and remains easy on all of the catalysts due to the unstable top-site adsorption of NH2, resulting in the break of the volcano-shaped relationship in e-NRR. Thus, only the first hydrogenation step is identified as the potential determining step. Four TM1-Cu(111) catalysts (TM = Re, W, Tc, and Mo) are selected as promising catalysts with limiting potential ranging from -0.38 to -0.56 V, showing outstanding e-NRR activity. Besides, the four catalysts also inhibit the competing hydrogen evolution reaction and long-term stability. Our work provides a guideline for breaking the volcano-shaped relationship in e-NRR and significant in the rational design of highly efficient electrocatalysts.

sp2/sp3 Hybridized Carbon as an Anode with Extra Li-Ion Storage Capacity: Construction and Origin.

Doping in carbon anodes can introduce active sites, usually leading to extra capacity in Li-ion batteries (LIBs), but the underlying reasons have not been uncovered deeply. Herein, the dodecahedral carbon framework (N-DF) with a low nitrogen content (3.06 wt %) is fabricated as the anode material for LIBs, which shows an extra value of 298 mA h g-1 during 250 cycles at 0.1 A g-1. Various characterizations and theoretical calculations demonstrate that the essence of the extra capacity mainly stems from non-coplanar sp2/sp3 hybridized orbital controlling non-Euclidean geometrical structure, which acts as new Li-ion active sites toward the excess Li+ adsorption. The electrochemical kinetics and in situ transmission electron microscope further reveal that the positive and negative curvature architectures not only provide supernumerary Li+ storage sites on the surface but also hold an enhanced (002) spacing for fast Li+ transport. The sp2/sp3 hybridized orbital design concept will help to develop advanced electrode materials.

Regulating Charge Transfer of Lattice Oxygen in Single-Atom-Doped Titania for Hydrogen Evolution.

Single-atom catalysts have attracted much attention. Reported herein is that regulating charge transfer of lattice oxygen atoms in serial single-atom-doped titania enables tunable hydrogen evolution reaction (HER) activity. First-principles calculations disclose that the activity of lattice oxygen for the HER can be regularly promoted by substituting its nearest metal atom, and doping-induced charge transfer plays an essential role. Besides, the realm of the charge transfer of the active site can be enlarged to the second nearest atom by creating oxygen vacancies, resulting in further optimization for the HER. Various single-atom-doped titania nanosheets were fabricated to validate the proposed model. Taking advantage of the localized charge transfer to the lattice atom is demonstrated to be feasible for realizing precise regulation of the electronic structures and thus catalytic activity of the nanosheets.

Spin transport properties of 1,4,5,8-naphthalenetetracarboxylic dianhydride based molecular devices.

Using density functional theory combined with the nonequilibrium Green's function method, spin-dependent transport properties of molecular devices consisting of the 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTCDA) molecule anchored via C and O linkages to zigzag graphene nanoribbon (ZGNR) electrodes were systematically investigated. Calculation results showed that the two connection modes display a good spin transport performance in both parallel (P) and anti-parallel (AP) configurations. Particularly, oxygen connection significantly improves the spin filtration effect. These observations were validated by analyzing spin-resolved transmission spectra, band structures and spatial distribution of molecular orbitals within the bias window. Further comparison of the results of different models indicated that the linkage plays a crucial role in improving the spin transport properties for the proposed NTCDA-ZGNR system, giving them potential applications in high-performance multifunctional spintronic devices.

First-principles study on screening doped TiO2(B) as an anode material with high conductivity and low lithium transport resistance for lithium-ion batteries.

As a promising anode material, TiO2(B) has attracted much attention in recent years due to its high power and capacity performances. First-principles calculations are performed here to reveal the electronic properties and the transport of lithium (Li) in the bulk TiO2(B) with and without atomic doping. It is found that a 4-fold coordinated O atom has the lowest formation energy and the smallest bandgap and is the atom that most easily forms an O-vacancy (Ov). In this work, a series of p-type (N, P, As), n-type (F, Cl, Br), and isoelectronic (S, Se, Te) dopants in TiO2(B) are studied. For n-type dopants, the substitution of the F atom has no significant effect on the electronic structure, which results in the lowest formation energy. This result demonstrates that the F atom can provide high intrinsic stability. Analysis of the insertion process of Li in doped TiO2(B) shows that N-doping is the most competitive choice because it not only introduces a lower bandgap of TiO2(B) but it also has the highest binding energy with Li. The advantage of N-doping is derived from the self-compensation effect. Also, three possible transport paths of Li in TiO2(B) were studied via the CI-NEB method. The results show that the energy barrier of all diffusion paths of F doping is lower than that of pure TiO2(B), where path 2 along the b-axis channel has the lowest energy (0.32 eV). This study is expected to shed some light on the electronic structures of TiO2(B) and the transport properties of Li in it.

Facile synthesis of a bismuth nanostructure with enhanced selectivity for electrochemical conversion of CO2 to formate.

Electrochemically converting carbon dioxide (CO2) to formate offers a promising approach for energy conversion and storage. Bismuth is believed to be one of the promising candidates for CO2 electroreduction, but the poor selectivity and complexity of synthesis limit its real application on a large scale. In this work, a facile one-step-reduction method was developed to prepare a bismuth nanostructure in aqueous solution. Owing to its enhanced reactive sites and exposed crystal plane, the prepared Bi nanostructure exhibits excellent performance for CO2 electroreduction, which reaches the maximum faradaic efficiency for formate as high as 92% at a potential of -0.9 V versus a reversible hydrogen electrode. Additionally, the large current density and remarkable durability also reveal its high intrinsic CO2 electroreduction activity. The density functional theory calculation confirms that the formation of intermediate *OCHO that finally converts to formate is thermodynamically favorable on Bi high-index planes. We anticipate that such a facile synthesis strategy and excellent electrocatalytic performance of the Bi nanostructure will be easy to scale up, realizing its industrialization applications in CO2 electrochemical conversion.

Carbon Nitride Supramolecular Hybrid Material Enabled High-Efficiency Photocatalytic Water Treatments.

Surface defects in relation to surface compositions, morphology, and active sites play crucial roles in photocatalytic activity of graphitic carbon nitride (g-C3N4) material for highly reactive oxygen radicals production. Here, we report a high-efficiency carbon nitride supramolecular hybrid material prepared by patching the surface defects with inorganic clusters. Fe (III) {PO4[WO(O2)2]4} clusters have been noncovalently integrated on surface of g-C3N4, where the surface defects provide accommodation sites for these clusters and driving forces for self-assembly. During photocatalytic process, the activity of supramolecular hybrid is 1.53 times than pure g-C3N4 for the degradation of Rhodamine B (RhB) and 2.26 times for Methyl Orange (MO) under the simulated solar light. Under the mediation of H2O2 (50 mmol L-1), the activity increases to 6.52 times for RhB and 28.3 times for MO. The solid cluster active sites with high specific surface area (SSA) defect surface promoting the kinetics of hydroxide radicals production give rise to the extremely high photocatalytic activity. It exhibits recyclable capability and works in large-scale demonstration under the natural sunlight as well and interestingly the environmental temperature has little effects on the photocatalytic activity.