CO₂ Reduction on Metal- and Nitrogen-Codoped Graphene: Balancing Activity and Selectivity via Coordination Engineering

Understanding the competition between the activity and selectivity allows us to rationally design catalysts for CO2 reduction to lower CO2 emission and mitigate the energy crisis. Herein, via the first-principles calculations, we enable to access the activity and selectivity of CO2 reduction on metal- and nitrogen-codoped graphene. It is found that the adsorption strength of the reaction intermediates is governed by the coordination environments of the doped metal atoms, causing a significant activity difference between different metal dopants. The adsorption free energy of CO was identified as a practical descriptor of the activity of both CO2 reduction and hydrogen evolution reaction (HER) according to the constructed linear relationship, which provides guidance for achieving the high CO2 reduction activity and the selectivity to CO simultaneously. Our finding is insightful for developing highly effective reduction catalysts based on the codoped carbon materials

Physisorbed, Chemisorbed, and Oxidized CO on Highly Active Cu−CeO₂(111)

With the use of the DFT+U method, the properties of Cu adsorbed on the stoichiometric CeO2(111) surface, Cu-doped CeO2(111) (denoted as Cu0.08Ce0.92O2) surface, and CO oxidation on the stoichiometric Cu0.08Ce0.92O2 surface are studied systematically. It is found that (i) Cu is stable both as an adsorbed atom on the surface and as dopant in the surface region. Cu adsorbed at the surface is Cu(+I) while Cu as a dopant atom is Cu(+II). (ii) The Cu dopant facilitates O-vacancy formation considerably, while Cu adsorption on the stoichiometric CeO2(111) surface may suppress oxygen vacancy formation. (iii) Physisorbed CO, physisorbed CO2, as well as chemisorbed CO (carbonate) species are observed on the Cu-doped CeO2(111) surface, in contrast, on the clean ceria(111) surface, only physisorbed CO was previously observed. C−O distances, adsorption energies, and surface-induced C−O vibrational frequency shifts were used to characterize these species

Density Functional Theory Study of Sn Adsorption on the CeO₂ Surface

The adsorption behaviors and electronic properties of Sn on the CeO2(111) surface were systematically investigated using the density functional theory (DFT) method. Our results suggested that Sn on the hollow site is more stable than that on the top oxygen site at the coverage of 0.25 ML, while Sn on the top oxygen site is the most stable configuration when the coverage of Sn is equal to or higher than 0.5 ML. Charge density difference (CDD) analysis indicates that electrons transfer from the Sn adatom to the substrate, leading to the reduction of Ce4+ to Ce3+ ion, which is in agreement with the experimental spectroscopy. The reduction degree of the substrate increases with the Sn coverage, which is well supported by the CDD and spin-resolved density of states (DOS) of the most stable xSn/CeO2(111) configurations. The adsorption of Sn can partially activate the surface oxygen of ceria. The tentative study of a probe molecule CO adsorption on the Sn/CeO2(111) surface indicates that CO adsorption is enhanced due to the strong tin–ceria interactions

Tuning d Orbital of Ni Single Atom by Encapsulating Ni Nanoparticle in Carbon Nanotube for Efficient Oxygen Evolution Reaction

Single atom catalysts (SACs) have received considerable attention due to their high-atomic-utilization efficiency and tunable activity and selectivity. Here, in combination of experiments and calculations, we demonstrated that the electronic structures and the oxygen evolution reaction (OER) activity of the confined Ni SAC in a nitrogen-doped carbon nanotube are modulated by the encapsulated Ni nanoparticle (Ni@NiNCNT). The synergistic interaction between Ni SAC and Ni nanoparticle endows the Ni@NiNCNT with a satisfactory OER performance of 358 mV to achieve 10 mA cm–2 current density and a Tafel slope of 89 mV dec–1, superior to the control samples and commercial RuO2. In addition, when employed as an air-cathode catalyst for rechargeable zinc–air batteries (ZABs), a Ni@NiNCNT modified battery outperformed a Pt/C+RuO2 modified battery, with a higher power density and superior constant current charge–discharge cycle stability for 40 h. Theoretical simulations further revealed that the Ni nanoparticle can remarkably optimize the adsorption strength of oxygen atom on Ni SAC, leading to a small overpotential of 0.22 V for the rate-limiting step of *O formation. Furthermore, the charge transfer from Ni nanoparticle to Ni SAC, which handles Ni-d orbital characters of Ni SAC and accordingly the adsorption strength toward oxygenates, is responsible for the origin of the OER activity. Our results provide a new way to tune electronic structures of the SAC and thus to tune its catalytic activity and should be insightful for designing new type electrocatalysts based on SAC

Unraveling charge transfer pathways and mechanisms in CdS@CoWO4 Z-scheme heterojunction photocatalysts for high-efficiency environmental remediation

Recently, direct Z-scheme heterojunction catalysts have become an important hotspot in photocatalytic applications due to their much stronger redox capabilities. Novel direct Z-scheme CdS@CoWO4 spherical heterojunction photocatalysts were ingeniously designed and synthesized herein. The structural characterization and morphology analysis demonstrated that homogeneous heterojunctions between CdS and CoWO4 were indeed formed in the composite photocatalysts. Moreover, CdS@CoWO4 heterojunction photocatalysts exhibited excellent degradation capability towards refractory micropollutants (Pharmaceutical intermediates, dyes, and industrial additives, etc) in wastewater. Especially, the strongest photocatalytic activity reflected by the highest reaction kinetic parameter (k = 8.13 × 10−2 min−1) was observed in the CdS-2CoWO4 catalyst with the mass ratio of CdS:CoWO4 = 1:2, which is nearly 4 and 58 times as high as that of pure CdS (k = 2.21 × 10−2 min−1) and CoWO4 (k = 1.39 × 10−3 min−1), respectively. First-principles study combined with the radical species trapping experiments revealed that the charge transfer pathways and mechanisms in these heterojunctions favor the direct Z-scheme rather than the traditional Type-II mode. A key built-in electric field formed at the contact interfaces of CdS and CoWO4 drives the Z-scheme charge transfer mechanism, which strengthens the redox capacity of photogenerated carriers and ultimately greatly enhances the photocatalytic activity of the heterojunction catalysts. It is worth applauding that CdS and CoWO4 can form such Z-scheme heterostructures in a wide span of component ratios, which is of great benefit for their practical applications in environmental remediation

Highly Conductive Ultrafine N‑Doped Silicon Powders Prepared by High-Frequency Thermal Plasma and Their Application as Anodes for Lithium-Ion Batteries

Silicon materials are widely regarded as highly promising candidate anodes for the next generation of lithium-ion batteries. However, the violent volume expansion and low intrinsic conductivity hinder their practical application. In this study, ultrafine N-doped silicon powders (N-doped Si) were prepared by using high-frequency thermal plasma (HF-plasma) technology, in which nanocrystallization and N doping were conducted in a single step without the formation of the Si3N4 phase. Through characterization of X-ray photoelectron spectroscopy, X-ray diffraction, and Raman analysis, it is ascertained that N is doped in silicon after HF-plasma treatment. According to the UV–vis and conductivity tests, N-doped Si has a notably narrower bandgap and a higher conductivity than those of undoped Si. N-doped Si with a submicrosphere (N–Si-0.5) delivered a reversible capacity of 974.1 mA h g–1 at 0.2 A g–1 after 50 cycles and an initial Coulombic efficiency (ICE) of 88.72%. Even at 6 A g–1, N–Si-0.5 can still exhibit a high reversible capacity of 200.5 mA h g–1, while Si without doping (N–Si-0.0) only gives a reversible capacity of 526.8 mA h g–1 at 0.2 A g–1 after 50 cycles with an ICE of 85.81% and an unnoticeable capacity at 6 A g–1. It is clear that Si shows higher ICE, better cycle stability, and rate performance. For further enhancement of the electrochemical performances of N-doped Si, the Si nanowires (NW-Si) were prepared. Experimental results showed that the initial capacity, ICE, and rate performance all gradually improved as the N2 flow rate increased. NW-Si-1.0 has an initial capacity of 2725.7 mA h g–1 and an ICE of 80.18%. Even at 6 A g–1, it can provide a reversible capacity of 584.7 mA h g–1. The enhanced electrochemical performances of N-doped Si can be ascribed to the introduction of the N dopant and nanowire, which raised carrier concentration, accelerated electron transfer, and alleviated volume expansion