p-Block element-doped silicon nanowires for nitrogen reduction reaction: a DFT study

Theoretical prediction of emerging high-performance trifunctional ORR/OER/HER single-atom catalysts: transition metals anchored into π-π conjugated graphitic carbon nitride (g-C10N3)

The design of high-performance trifunctional oxygen reduction/oxygen evolution/hydrogen evolution reactions (ORR/OER/HER) electrocatalysts has become the current research focus. In this work, we report a series of single-atom catalysts formed by nine kinds of transition metal (Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, and Pt) anchored in g-C10N3 (namely TM@g-C10N3) as promising trifunctional electrocatalysts to replace precious metal catalysts by density functional theory methods. All TM@g-C10N3 have good thermodynamic and electrochemical stability. Especially, Rh@g-C10N3 and Ir@g-C10N3 exhibit extremely low ORR/OER overpotentials with the values of 0.26/0.28 V and 0.34/0.41 V, respectively. Besides, their hydrogen adsorption free energy values are close to Pt(111), with their values being 0.16 and -0.16 eV, respectively. The calculated results indicate that Rh@g-C10N3 and Ir@g-C10N3 can become trifunctional electrocatalysts with great probability. Through the analysis of the dynamic mechanism for Rh@g-C10N3, it can be concluded that the four-electron ORR pathway is more conducive to occurring on Rh@g-C10N3 because the energy barrier forming this pathway is lower. Besides, the step of *OH + H+ + e- → * + H2O has the highest energy barrier in dynamics, which is consistent with this step being a potential determining step in thermodynamics. Ultimately, the solvation effect considered has little effect on the catalytic performance of screened Rh@g-C10N3 and Ir@g-C10N3, and even at a high temperature of 500 K, the structures of these two catalysts have no significant distortion after 2 ps simulations. Our calculations will provide clear guidance for future experimental synthesis and design of such catalysts.

Tailoring Fe0 Nanoparticles via Lattice Engineering for Environmental Remediation

Lattice engineering of nanomaterials holds promise in simultaneously regulating their geometric and electronic effects to promote their performance. However, local microenvironment engineering of Fe0 nanoparticles (nFe0) for efficient and selective environmental remediation is still in its infancy and lacks deep understanding. Here, we present the design principles and characterization techniques of lattice-doped nFe0 from the point of view of microenvironment chemistry at both atomic and elemental levels, revealing their crystalline structure, electronic effects, and physicochemical properties. We summarize the current knowledge about the impacts of doping nonmetal p-block elements, transition-metal d-block elements, and hybrid elements into nFe0 crystals on their local coordination environment, which largely determines their structure-property-activity relationships. The materials' reactivity-selectivity trade-off can be altered via facile and feasible approaches, e.g., controlling doping elements' amounts, types, and speciation. We also discuss the remaining challenges and future outlooks of using lattice-doped nFe0 materials in real applications. This perspective provides an intuitive interpretation for the rational design of lattice-doped nFe0, which is conducive to real practice for efficient and selective environmental remediation.

Si3C Monolayer as an Efficient Metal-Free Catalyst for Nitrate Electrochemical Reduction: A Computational Study

Nitrate electroreduction reaction to ammonia (NO3ER) holds great promise for both nitrogen pollution removal and valuable ammonia synthesis, which are still dependent on transition-metal-based catalysts at present. However, metal-free catalysts with multiple advantages for such processes have been rarely reported. Herein, by means of density functional theory (DFT) computations, in which the Perdew-Burke-Ernzerhof (PBE) functional is obtained by considering the possible van der Waals (vdW) interaction using the DFT+D3 method, we explored the potential of several two-dimensional (2D) silicon carbide monolayers as metal-free NO3ER catalysts. Our results revealed that the excellent synergistic effect between the three Si active sites within the Si3C monolayer enables the sufficient activation of NO3- and promotes its further hydrogenation into NO2*, NO*, and NH3, making the Si3C monolayer exhibit high NO3ER activity with a low limiting potential of -0.43 V. In particular, such an electrochemical process is highly dependent on the pH value of the electrolytes, in which acidic conditions are more favorable for NO3ER. Moreover, ab initio molecular dynamics (AIMD) simulations demonstrated the high stability of the Si3C monolayer. In addition, the Si3C monolayer shows a low formation energy, excellent electronic properties, a superior suppression effect on competing reactions, and high stability, offering significant advantages for its experimental synthesis and practical applications in electrocatalysis. Thus, a Si3C monolayer can perform as a promising NO3ER catalyst, which would open a new avenue to further develop novel metal-free catalysts for NO3ER.

Nanostructured silicon photocatalysts for solar-driven fuel production

Solar-driven production of fuels such as hydrogen, hydrocarbons, and ammonia using semiconducting photocatalysts has the potential to be a sustainable alternative to current chemical processes. In recent years, silicon (Si) nanostructures have been recognized as a promising photocatalyst for hydrogen generation and organic oxidation reactions owing to its abundance, biocompatibility, and cost. While bulk Si has been studied extensively, on the nanoscale, plenty of opportunities exist to understand and engineer optimally performing Si photocatalysts. This perspective will highlight key results on the use of Si nanostructures for photocatalytic H₂ production, CO₂ reduction via light and heat-driven chemical looping, and current challenges in utilizing it for fuel-forming reactions. A brief guide on how these challenges can be addressed in the future and other unexplored questions that remain in the field are also discussed.

Defective 2D silicon phosphide monolayers for the nitrogen reduction reaction: a DFT study

Electroreduction of N₂ is a highly promising route for NH₃ production. The lack of efficient catalysts that can activate and then reduce N₂ into NH₃ limits this as a pragmatic application. In this work, a 2D layered group IV-V material, silicon phosphide (SiP), is evaluated as a suitable substrate for the electrochemical nitrogen reduction reaction (ENRR). To capture N₂, one phosphorus (P) defect was introduced on the plane of SiP. DFT calculations found that the defective SiP monolayer (D1-SiP, which is defined by the P-defect on SiP) exhibits enormous prospects towards the ENRR because of enhanced electron conductivity, good activation on N₂, lower limiting potential (U_L = -0.87 V) through the enzymatic pathway, smooth charge transfer between the catalyst and the reaction species, and robust thermal stability. Importantly, D1-SiP demonstrates the suppressed activities on producing of H₂ and N₂H₄ side-products. This research demonstrates the potential of 2D metal-free Si-based catalysts for nitrogen fixation and further enriches the study of group IV-V materials for the ENRR.

Insight into the Reactivity of Carbon Structures for Nitrogen Reduction Reaction

Graphene-based structures have been widely reported as promising metal-free catalysts for nitrogen reduction reaction. To explain the reactivity origin, various structures have been proposed and debated, including defects, functional groups, and doped heteroatoms. This computational work demonstrates that these structures may evolve from one to another under electrochemical conditions, generating weakly coordinated carbons, which have been identified as the active sites for N₂ adsorption and activation.