Graphene-based iron single-atom catalysts for electrocatalytic nitric oxide reduction: a first-principles study.

The electrocatalytic NO reduction reaction (NORR) emerges as an intriguing strategy to convert harmful NO into valuable NH3. Due to their unique intrinsic properties, graphene-based Fe single-atom catalysts (SACs) have gained considerable attention in electrocatalysis, while their potential for NORR and the underlying mechanism remain to be explored. Herein, using constant-potential density functional theory calculations, we systematically investigated the electrocatalytic NORR on the graphene-based Fe SACs. By changing the local coordination environment of Fe single atoms, 26 systems were constructed. Theoretical results show that, among these systems, the Fe SAC coordinated with four pyrrole N atoms and that co-coordinated with three pyridine N atoms and one O atom exhibit excellent NORR activity with low limiting potentials of -0.26 and -0.33 V, respectively, as well as have high selectivity toward NH3 by inhibiting the formation of byproducts, especially under applied potential. Furthermore, electronic structure analyses indicate that NO molecules can be effectively adsorbed and activated via the electron "donation-backdonation" mechanism. In particular, the d-band center of the Fe SACs was identified as an efficient catalytic activity descriptor for NORR. Our work could stimulate and guide the experimental exploration of graphene-based Fe SACs for efficient NORR toward NH3 under ambient conditions.

Similar electronic state effect enables excellent activity for nitrate-to-ammonia electroreduction on both high- and low-density double-atom catalysts.

Double-atom catalysts (DACs) for harmful nitrate (NO3-) electroreduction to valuable ammonia (eNO3RR) is attractive for both environmental remediation and energy transformation. However, the limited metal loading in most DACs largely hinders their applications in practical catalytic applications. Therefore, exploring ultrahigh-density (UHD) DACs with abundant active metal centers and excellent eNO3RR activity is highly desired under the site-distance effect. Herein, starting from the experimental M2N6 motif deposited on graphene, we firstly screened the low-density (LD) Mn2N6 and Fe2N6 DACs with high eNO3RR activity and then established an appropriate activity descriptor for the LD-DAC system. By utilizing this descriptor, the corresponding Mn2N6 and Fe2N6 UHD-DACs with dynamic, thermal, thermodynamic, and electrochemical stabilities, are identified to locate at the peak of activity volcano, exhibiting rather-low limiting potentials of -0.25 and -0.38 V, respectively. Further analysis in term of spin state and orbital interaction, confirms that the electronic state effect similar to that of LD-DACs enable the excellent eNO3RR activity to be maintained in the UHD-DACs. These findings highlight the promising application of Mn2N6 and Fe2N6 UHD-DACs in nitrate electroreduction for NH3 production and provide impetus for further experimental exploration of ultrahigh-density DACs based on their intrinsic electronic states.

Multifunctional nano MOF drug delivery platform in combination therapy.

Recent preclinical and clinical studies have demonstrated that for cancer treatment, combination therapies are more effective than monotherapies in reducing drug-related toxicity, decreasing drug resistance, and improving therapeutic efficacy. With the rapid development of nanotechnology, the combination of metal-organic frameworks (MOFs) and multi-mode therapy offers a realistic possibility to further improve the shortcomings of cancer treatment. This article focuses on the latest developments, achievements, and treatment strategies of representative multifunctional MOF combination therapies for cancer treatment in recent years, which include not only bimodal combination therapies, but also multi-modal synergistic therapies, further demonstrating the effectiveness and superiority of the MOF drug delivery systems in cancer treatment.

Tailoring the coordination environment of double-atom catalysts to boost electrocatalytic nitrogen reduction: a first-principles study.

Tailoring the coordination environment is an effective strategy to modulate the electronic structure and catalytic activity of atomically dispersed transition-metal (TM) catalysts, which has been widely investigated for single-atom catalysts but received less attention for emerging double-atom catalysts (DACs). Herein, based on first-principles calculations, taking the commonly studied N-coordinated graphene-based DACs as references, we explored the effect of coordination engineering on the catalytic behaviors of DACs towards the electrocatalytic nitrogen reduction reaction (NRR), which is realized through replacing one N atom by the B or O atom to form B, N or O, N co-coordinated DACs. We found that B, N or O, N co-coordination could significantly strengthen N2 adsorption and alter the N2 adsorption pattern of the TM dimer active center, which greatly facilitates N2 activation. Moreover, on the studied DACs, the linear scaling relationship between the binding strengths of key intermediates can be attenuated. Consequently, the O, N co-coordinated Mn2 DACs, exhibiting an ultralow limiting potential of -0.27 V, climb to the peak of the activity volcano. In addition, the experimental feasibility of this DAC system was also identified. Overall, benefiting from the coordination engineering effect, the chemical activity and catalytic performance of the DACs for NRR can be significantly boosted. This phenomena can be understood from the adjusted electronic structure of the TM dimer active center due to the changes of its coordination microenvironment, which significantly affects the binding strength (pattern) of key intermediates and changes the reaction pathways, leading to enhanced NRR activity and selectivity. This work highlights the importance of coordination engineering in developing DACs for the electrocatalytic NRR and other important reactions.

Palladium metallene for nitric oxide electroreduction to ammonia.

We demonstrate Pd metallene as an efficient catalyst for electrocatalytic NO reduction to NH3 (NORR), showing the maximum NO-to-NH3 faradaic efficiency of 89.6% with a corresponding NH3 yield rate of 112.5 µmol h-1 cm-2 at -0.3 V in neutral media. Theoretical calculations unveil that NO can be effectively activated and hydrogenated on the hcp site of Pd through a mixed pathway with a low energy barrier.

Tandem Electrocatalytic Nitrate Reduction to Ammonia on MBenes.

We demonstrate the great feasibility of MBenes as a new class of tandem catalysts for electrocatalytic nitrate reduction to ammonia (NO3 RR). As a proof of concept, FeB2 is first employed as a model MBene catalyst for the NO3 RR, showing a maximum NH3 -Faradaic efficiency of 96.8 % with a corresponding NH3 yield of 25.5 mg h-1 cm-2 at -0.6 V vs. RHE. Mechanistic studies reveal that the exceptional NO3 RR activity of FeB2 arises from the tandem catalysis mechanism, that is, B sites activate NO3 - to form intermediates, while Fe sites dissociate H2 O and increase *H supply on B sites to promote the intermediate hydrogenation and enhance the NO3 - -to-NH3 conversion.

Oxygen Vacancy Diffusion in Rutile TiO2: Insight from Deep Neural Network Potential Simulations.

Defects play a crucial role in the surface reactivity and electronic engineering of titanium dioxide (TiO2). In this work, we have used an active learning method to train deep neural network potentials from the ab initio data of a defective TiO2 surface. Validations show a good consistency between the deep potentials (DPs) and density functional theory (DFT) results. Therefore, the DPs were further applied on the extended surface and executed for nanoseconds. The results show that the oxygen vacancy at various sites are very stable under 330 K. However, some unstable defect sites will convert to the most favorable ones after tens or hundreds of picoseconds, while the temperature was elevated to 500 K. The DP predicated barriers of oxygen vacancy diffusion were similar to those of DFT. These results show that machine-learning trained DPs could accelerate the molecular dynamics with a DFT-level accuracy and promote people's understanding of the microscopic mechanism of fundamental reactions.

Self-Tandem Electrocatalytic NO Reduction to NH3 on a W Single-Atom Catalyst.

We design single-atom W confined in MoO3-x amorphous nanosheets (W1/MoO3-x) comprising W1-O5 motifs as a highly active and durable NORR catalyst. Theoretical and operando spectroscopic investigations reveal the dual functions of W1-O5 motifs to (1) facilitate the activation and protonation of NO molecules and (2) promote H2O dissociation while suppressing *H dimerization to increase the proton supply, eventually resulting in a self-tandem NORR mechanism of W1/MoO3-x to greatly accelerate the protonation energetics of the NO-to-NH3 pathway. As a result, W1/MoO3-x exhibits the highest NH3-Faradaic efficiency of 91.2% and NH3 yield rate of 308.6 µmol h-1 cm-2, surpassing that of most previously reported NORR catalysts.

Electrocatalytic NO Reduction to NH3 on Mo2C Nanosheets.

Electrocatalytic reduction of NO to NH3 (NORR) emerges as a promising route for achieving harmful NO treatment and sustainable NH3 generation. In this work, we first report that Mo2C is an active and selective NORR catalyst. The developed Mo2C nanosheets deliver a high NH3 yield rate of 122.7 µmol h-1 cm-2 with an NH3 Faradaic efficiency of 86.3% at -0.4 V. Theoretical computations unveil that the surface-terminated Mo atoms on Mo2C can effectively activate NO, promote protonation energetics, and suppress proton adsorption, resulting in high NORR activity and selectivity of Mo2C.

Sub-nm RuOx Clusters on Pd Metallene for Synergistically Enhanced Nitrate Electroreduction to Ammonia.

The electrochemical nitrate reduction to ammonia reaction (NO3RR) has emerged as an appealing route for achieving both wastewater treatment and ammonia production. Herein, sub-nm RuOx clusters anchored on a Pd metallene (RuOx/Pd) are reported as a highly effective NO3RR catalyst, delivering a maximum NH3-Faradaic efficiency of 98.6% with a corresponding NH3 yield rate of 23.5 mg h-1 cm-2 and partial a current density of 296.3 mA cm-2 at -0.5 V vs RHE. Operando spectroscopic characterizations combined with theoretical computations unveil the synergy of RuOx and Pd to enhance the NO3RR energetics through a mechanism of hydrogen spillover and hydrogen-bond interactions. In detail, RuOx activates NO3- to form intermediates, while Pd dissociates H2O to generate *H, which spontaneously migrates to the RuOx/Pd interface via a hydrogen spillover process. Further hydrogen-bond interactions between spillovered *H and intermediates makes spillovered *H desorb from the RuOx/Pd interface and participate in the intermediate hydrogenation, contributing to the enhanced activity of RuOx/Pd for NO3--to-NH3 conversion.

Selenium-vacancy-rich WSe2 for nitrate electroreduction to ammonia.

Electrocatalytic nitrate reduction to ammonia (NO3RR) is an attractive route for renewable NH3 electrosynthesis. Herein, we demonstrated Se-vacancy-rich WSe2 (WSe2-x) nanoplatelets as a highly efficient NO3RR catalyst, exhibiting a NH3-Faradaic efficiency of 92.7 % with the corresponding NH3 yield of 2.42 mg h-1 cm-2 at -0.8 V, substantially surpassing Se-vacancy-free WSe2 nanoplatelets. Theoretical computations by density function theory calculations and molecular dynamics simulations revealed that the introduced Se-vacancy enabled the creation of unsaturated W sites as active centers to strongly activate the NO3- and reduce the reaction barriers to boost the NO3RR process.

Mo2C for electrocatalytic nitrate reduction to ammonia.

Electrocatalytic nitrate reduction to ammonia (NRA) shows great potential to simultaneously realize sustainable NH3 production and NO3- pollutant elimination. Herein, Mo2C, a typical transition metal carbide, is first demonstrated to be an efficient and durable NRA catalyst. The developed Mo2C nanoparticles anchored on reduced graphene oxide (Mo2C/RGO) show a maximum NH3-faradaic efficiency of 85.2% with a corresponding NH3 yield of 4.8 mg h-1 cm-2. Theoretical computations reveal that surface-terminated Mo sites of Mo2C can selectively absorb NO3- and effectively boost the NRA process through a NOH hydrogenation pathway.

Tunable Photocatalytic Water Splitting Performance of Armchair MoSSe Nanotubes Realized by Polarization Engineering.

The photocatalytic properties of Janus transition metal dichalcogenide (TMD) nanotubes are closely correlated with the electrostatic potential difference between their inner and outer surfaces (ΔΦ). However, due to some distraction from the tubular structures, it remains a great challenge to calculate their ΔΦ directly. Here, we creatively work out the ΔΦ of Janus MoSSe armchair single-walled nanotubes (A-SWNTs) with their corresponding building block models by first-principles calculations. The ΔΦ increases as the diameter reduces. After considering ΔΦ, we find that all of these MoSSe A-SWNTs possess suitable band-edge positions required for water redox reactions and high solar-to-hydrogen (STH) conversion efficiencies. The built-in field induced by the ΔΦ promotes the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) to proceed separately on the inner and outer surfaces. Especially, the photoexcited carriers exhibit adequate driving forces for OER and HER. Besides, constructing a double-walled nanotube can dramatically increase ΔΦ, which also further improves the separation and redox capacity of photoexcited carriers as well as the STH conversion efficiency. Moreover, all of these MoSSe armchair nanotubes have outstanding optical absorption in the visible light range. Our studies provide an effective strategy to improve the photocatalytic water-splitting performance of Janus TMD nanotubes.

V (Nb) Single Atoms Anchored by the Edge of a Graphene Armchair Nanoribbon for Efficient Electrocatalytic Nitrogen Reduction: A Theoretical Study.

Efficient and low-cost electrocatalysts are urgently required for the electrocatalytic N2 reduction reaction (NRR) to produce valuable NH3. Single-atom catalysts (SACs) represent one class of promising candidates. Besides the defects on the basal plane, very recently, the one-dimensional edge universally existing in the finite graphene or carbon sheet has gained attention as the anchoring site for SACs, which may enable unique catalytic mechanism. Herein, using first-principles calculations, we systematically investigated the NRR over SACs of transition metals (Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Ru, Rh, Pd, Nb, Mo, and W) anchored by the N-modified edge of the graphene armchair nanoribbon (denoted as TM@GNR). Three criteria were employed to screen the best candidate from all the TM@GNR, including the high stability of TM@GNR, the preferable adsorption of N2 compared with H, and the lower applied potential for the first protonation of N2 compared with that of the active site. Accordingly, V(Nb)@GNR were theoretically demonstrated to be promising NRR electrocatalyst toward NH3 with low limiting potentials of -0.65 (-0.52) V, excellent selectivity of ∼100% (97%), and good stability. Particularly, NRR on the V@GNR and Nb@GNR precedes through a novel reaction mechanism with three spectator N2 molecules. Further analysis reveals that the strong capture and activation of N2 molecules by the edge-anchored V (Nb) atoms derives from their localized spin moment and atomic orbitals. Our studies emphasize the great potential of the edge of carbon materials to synthesize SACs for NRR and other reactions, and further reveal a novel NRR reaction mechanism on SACs.

Increasing electron density by surface plasmon resonance for enhanced photocatalytic CO2 reduction.

The photocatalytic CO2 reduction reaction is a multi-electron process, which is greatly affected by the surface electron density. In this work, we synthesize Ag clusters supported on In2O3 plasmonic photocatalysts. The Ag-In2O3 compounds show remarkedly enhanced photocatalytic activity for CO2 conversion to CO compared to pristine In2O3. In the absence of any co-catalyst or sacrificial agent, the CO evolution rate of optimal Ag-In2O3-10 is 1.56 µmol/g/h, achieving 5.38-folds higher than that of In2O3 (0.29 µmol/g/h). Experimental verification and DFT calculation demonstrate that electrons transfer from Ag clusters to In2O3 on Ag-In2O3 compounds. In Ag-In2O3 compounds, Ag clusters serving as electron donators owing to the SPR behaviour are not helpful to decline photo-induced charge recomnation rate, but can provide more electron for photocatalytic reaction. Overall, the Ag clusters promote visible-light absorption and accelerate photocatalytic reaction kinetic for In2O3, resulting in the photocatalytic activity enhancement of Ag-In2O3 compounds. This work puts insight into the function of plasmonic metal on enhancing photocatalysis performance, and provides a feasible strategy to design and fabricate efficient plasmonic photocatalysts.

Improving the Energetic Stability and Electrocatalytic Performance of Au/WSSe Single-Atom Catalyst with Tensile Strain.

In the areas of catalysis and renewable energy conversion, the development of active and stable electrocatalysts continues to be a highly desirable and crucial aim. Single-atom catalysts (SACs) provide isolated active sites, high selectivity, and ease of separation from reaction systems, becoming a rapidly evolving research field. Unfortunately, the real roles and key factors of the supports that govern the catalytic properties of SACs remain uncertain. Herein, by means of the density functional theory calculations, in the Au/WSSe SAC, built by filling the single Au atom at the S vacancy site in WSSe monolayer, we find that the powerful binding between the single Au atom and the support is induced by the Au d and W d orbital hybridization, which is caused by the electron transfer between them. The extra tensile strain could further stabilize the Au/WSSe by raising the transfer electron and enhancing the orbital hybridization. Moreover, by dint of regulating the antibonding strength between the single Au atom and H atom, the extra tensile strain is capable of changing the electric-catalytic hydrogen evolution reaction (HER) performance of Au/WSSe as well. Remarkably, under the 1% tensile strain, the reaction barrier (0.06 eV) is only one third of that of free state. This theoretical work not only reveals the bonding between atomic sites and supports, but also opens an avenue to improve the electric-catalytic performance of SACs by adjusting the bonding with outer factors.

Theoretical insights into the electroreduction of nitrate to ammonia on graphene-based single-atom catalysts.

Electrocatalytic reduction of harmful nitrate (NO3-) to valuable ammonia (eNO3RR) is critical and attractive for both environmental remediation and energy transformation. A single atom catalyst (SAC) based on graphene represents one of the most promising eNO3RR catalysts. However, the underlying catalytic mechanism and the intrinsic factors dictating the catalytic activity trend remain unclear. Herein, using first-principles calculations, eNO3RR on TMN3 and TMN4 (TM = Ti-Ni) doped graphene was thoroughly investigated. Our results reveal that FeN4 doped graphene exhibits excellent eNO3RR performance with a low limiting potential of -0.38 V, agreeing with the experimental finding, which can be ascribed to the effective adsorption and activation of NO3-via the charge "acceptance-donation" mechanism and its moderate binding due to the occupation of the d-p antibonding orbital. In particular, we found that eNO3RR activities are well correlated with the intrinsic properties of TM centers and their local environments. With the established activity descriptor, several other graphene-based SACs were efficiently screened out with excellent eNO3RR performance. Our studies could not only provide an atomic insight into the catalytic mechanism and activity origin of eNO3RR on graphene-based SACs, but also open an avenue for the rational design of SACs for eNO3RR towards ammonia by regulating the metal center and its local coordination environment.

Designing Multifunctional Donor-Acceptor-Type Molecules to Passivate Surface Defects Efficiently and Enhance Charge Transfer of CsPbI2Br Perovskite for High Power Conversion Efficiency.

High-density and multitype surface defects of CsPbI2Br perovskite induce charge recombination and accumulation, hindering its device efficiency and stability. However, the surface defect types of CsPbI2Br perovskite are still unclear, and conventional organic molecules only passivate one specific defect and cannot achieve good overall passivation. Here, density functional theory is used to explore surface defect types and properties of CsPbI2Br with calculating the defect formation energy and electronic structure. Results show that the dominant deep-level defects are cationic defects (PbBr) under Br-poor conditions and anionic defects (Ii and Bri) under moderate and Br-rich conditions, originating from Pb-Pb bonding and I-I bonding. Multifunctional organic molecules containing donor and acceptor groups are used to passivate both cationic and anionic defects simultaneously. It turns out that the deep-level defects are effectively decreased by forming strong interaction of N-Pb, O-Pb, and halide-Pb bonds. Moreover, the electron and hole transfers from perovskite to molecules increase dramatically to -9.06 × 1012 and 2.60 × 1012 e/cm2 and maybe improve the efficiency of power conversion. Our findings not only reveal the surface defect properties of CsPbI2Br, but also offer an approach for designing new multifunctional passivators for perovskite solar cells with high conversion efficiency.

Electrocatalytic two-electron oxygen reduction over nitrogen doped hollow carbon nanospheres.

The two-electron oxygen reduction reaction (2e- ORR) has become a hopeful alternative for production of hydrogen peroxide (H2O2), but its practical feasibility is hindered by the lack of efficient electrocatalysts to achieve high activity and selectivity. Herein, we successfully synthesized outstanding nitrogen doped hollow carbon nanospheres (NHCSs) for electrochemical production of H2O2. In 0.1 M KOH, NHCSs exhibit superior and sustained catalytic activity for the 2e- ORR with an unordinary selectivity of 96.6%. Impressively, such NHCSs manifest an ultrahigh H2O2 yield rate of 7.32 mol gcat.-1 h-1 and a high faradaic efficiency of 96.7% at 0.5 V in an H-cell system. Density functional theory calculations were performed to further reveal the catalytic mechanism involved.