Theoretical Insights into the Mechanism of Selective Nitrate‐to‐Ammonia Electroreduction on Single‐Atom Catalysts

Great enthusiasm in single-atom catalysts (SACs) for the nitrogen reduction reaction (NRR) has been aroused by the discovery of metal-Nx as a promising catalytic center. However, the poor activity and low selectivity of available SACs are far away from the industrial requirement. Through the first-principles high-throughput screening, we find that Fe-Fe distributed on graphite carbon nitride (Fe2/g-CN) can manipulate the binding strength of the target reaction species (compromises the ability to adsorb N2H and NH2), therefore achieving the best NRR performance among 23 transition metal (TM) centers. Our results show that Fe2/g-CN achieves a high theoretical Faradaic efficiency of 100% and, impressively, the lowest limiting potential of -0.13 V. Particularly, multiple-level descriptors shed light on the origin of NRR activity, achieving a fast prescreening among various candidates. Our predictions not only accelerate discovery of catalysts for ammonia synthesis but also contribute to further elucidate the structure-performance correlations.

High-Throughput Screening of Synergistic Transition Metal Dual-Atom Catalysts for Efficient Nitrogen Fixation.

Two-dimensional crystals have emerged as a class of materials that may impact future electronic technologies. Experimentally identifying and characterizing new functional two-dimensional materials is challenging, but also potentially rewarding. Here, we fabricate field-effect transistors based on few-layer black phosphorus crystals with thickness down to a few nanometres. Reliable transistor performance is achieved at room temperature in samples thinner than 7.5 nm, with drain current modulation on the order of 10(5) and well-developed current saturation in the I-V characteristics. The charge-carrier mobility is found to be thickness-dependent, with the highest values up to ∼ 1,000 cm(2) V(-1) s(-1) obtained for a thickness of ∼ 10 nm. Our results demonstrate the potential of black phosphorus thin crystals as a new two-dimensional material for applications in nanoelectronic devices.

http://absimage.aps.org/image/MAR14/MWS_MAR14-2013-005031.pdf

Black Phosphorus Field-effect Transistors

It remains a great challenge to design efficient electrocatalysts for nitrogen reduction reaction (NRR) with high activity and high selectivity. Herein, density functional theory calculations were ...

Computational Screening Single-Atom Catalysts Supported on g-CN for N2 Reduction: High Activity and Selectivity

Tuning the electronic structure of a single-atom catalyst (SAC) by controlling its coordination has been recently shown to be a rather promising strategy for further improving its catalytic performance in some electrochemical reactions. Herein, by means of density functional theory (DFT) computations, the impacts of the coordination structure of an Fe–N–C catalyst on its catalytic activity toward the nitrogen reduction reaction (NRR) were explored. Our results revealed that the NRR activity on the central Fe atom can be greatly improved by its coordination with a boron (B) dopant. In particular, the computed limiting potential of the NRR on Fe–B2N2 is −0.65 V, which is the lowest among all B doped Fe–N–C catalysts, suggesting its high NRR catalytic activity. Interestingly, the introduction of B coordination can effectively modulate the interaction of the single Fe atom with the N2H* species, thus improving its NRR catalytic performance. In addition, Fe–B2N2 exhibits high NRR selectivity by effectively suppressing the competing hydrogen evolution reaction (HER) both thermodynamically and kinetically. Therefore, the single Fe catalyst with N and B dual coordination can be utilized as a promising NRR electrocatalyst, which not only highlights the significant effect of local coordination on catalytic activity and selectivity for the NRR, but also provides a new opportunity to further develop more advanced single-atom catalysts for ammonia synthesis.

Coordination tunes the activity and selectivity of the nitrogen reduction reaction on single-atom iron catalysts: a computational study

Herein, the potential of single transition metal atoms (TM, from Ti to Au) supported on g-C3N4 (TM/g-C3N4) for the oxygen reduction reaction (ORR) was investigated by first-principles calculations. It was demonstrated that the TM atoms can remain stable in the cavity of g-C3N4 and interact with the substrate via charge transfer from the TM atoms to g-C3N4. Among all the TM/g-C3N4 samples, Pd/g-C3N4 stands out with a low overpotential of 0.46 V, showing good performance for ORR; thus, it has great potential to replace the noble Pt catalyst. The ORR activity of TM/g-C3N4 is a function of ΔE*OH (an energy descriptor). Furthermore, the d-band center and ICOHP (electronic structure descriptors) can quantitatively describe the variation trend of ΔE*OH in addition to Bader charge analysis (a charge transfer descriptor). Considering the number of d orbital electrons and the electronegativity of TM, φ (an intrinsic descriptor) can be applied to predict and reveal the origin of the ORR activity. A bridge from intrinsic characteristics to electronic structures, to charge transfer, to electronic structures and then to adsorption energy has been established, which is conducive to better reveal the ORR activity origin and provide guidance for designing effective ORR electrocatalysts.

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Revealing the oxygen reduction reaction activity origin of single atoms supported on g-C3N4 monolayers: a first-principles study

Efficient water electrolyzers are constrained by the lack of low-cost and earth-abundant hydrogen evolution reaction (HER) catalysts that can operate at industry-level conditions and be prepared with a facile process. Here we report a self-standing MoC–Mo2C catalytic electrode prepared via a one-step electro-carbiding approach using CO2 as the feedstock. The outstanding HER performances of the MoC–Mo2C electrode with low overpotentials at 500 mA cm−2 in both acidic (256 mV) and alkaline electrolytes (292 mV), long-lasting lifetime of over 2400 h (100 d), and high-temperature performance (70 oC) are due to the self-standing hydrophilic porous surface, intrinsic mechanical strength and self-grown MoC (001)–Mo2C (101) heterojunctions that have a ΔGH* value of −0.13 eV in acidic condition, and the energy barrier of 1.15 eV for water dissociation in alkaline solution. The preparation of a large electrode (3 cm × 11.5 cm) demonstrates the possibility of scaling up this process to prepare various carbide electrodes with rationally designed structures, tunable compositions, and favorable properties. Scalable fabrication of Low-cost hydrogen evolution reaction (HER) catalysts that can operate at industry-relevant conditions is highly needed for efficient water electrolyzers. Here the authors show a scalable synthesis of a MoC-Mo2C heterojunction electrode with efficient HER activity and high stability at industrial conditions.

A durable and pH-universal self-standing MoC-Mo2C heterojunction electrode for efficient hydrogen evolution reaction.

It is highly desirable to design bifunctional electrocatalysts to realize highly efficient oxygen evolution/reduction reaction (OER/ORR). Herein, density functional theory (DFT) calculations were c...

Xiting Wang

Papers

Theoretical Insights into the Mechanism of Selective Nitrate‐to‐Ammonia Electroreduction on Single‐Atom Catalysts

Computational Screening Single-Atom Catalysts Supported on g-CN for N2 Reduction: High Activity and Selectivity

Revealing the oxygen reduction reaction activity origin of single atoms supported on g-C3N4 monolayers: a first-principles study

A durable and pH-universal self-standing MoC-Mo2C heterojunction electrode for efficient hydrogen evolution reaction.

Single-Atom Rhodium on Defective g-C3N4: A Promising Bifunctional Oxygen Electrocatalyst