Electrocatalytic Nitrate Reduction on Metallic CoNi-Terminated Catalyst with Industrial-Level Current Density in Neutral Medium.

Green ammonia synthesis through electrocatalytic nitrate reduction reaction (eNO3RR) can serve as an effective alternative to the traditional energy-intensive Haber-Bosch process. However, achieving high Faradaic efficiency (FE) at industrially relevant current density in neutral medium poses significant challenges in eNO3RR. Herein, with the guidance of theoretical calculation, a metallic CoNi-terminated catalyst is successfully designed and constructed on copper foam, which achieves an ammonia FE of up to 100% under industrial-level current density and very low overpotential (-0.15 V versus reversible hydrogen electrode) in a neutral medium. Multiple characterization results have confirmed that the maintained metal atom-terminated surface through interaction with copper atoms plays a crucial role in reducing overpotential and achieving high current density. By constructing a homemade gas stripping and absorption device, the complete conversion process for high-purity ammonium nitrate products is demonstrated, displaying the potential for practical application. This work suggests a sustainable and promising process toward directly converting nitrate-containing pollutant solutions into practical nitrogen fertilizers.

Synergistic Engineering of CoO/MnO Heterostructures Integrated with Nitrogen-Doped Carbon Nanofibers for Lithium-Ion Batteries.

The integration of heterostructures within electrode materials is pivotal for enhancing electron and Li-ion diffusion kinetics. In this study, we synthesized CoO/MnO heterostructures to enhance the electrochemical performance of MnO using a straightforward electrostatic spinning technique followed by a meticulously controlled carbonization process, which results in embedding heterostructured CoO/MnO nanoparticles within porous nitrogen-doped carbon nanofibers (CoO/MnO/NC). As confirmed by density functional theory calculations and experimental results, CoO/MnO heterostructures play a significant role in promoting Li+ ion and charge transfer, improving electronic conductivity, and reducing the adsorption energy. The accelerated electron and Li-ion diffusion kinetics, coupled with the porous nitrogen-doped carbon nanofiber structure, contribute to the exceptional electrochemical performance of the CoO/MnO/NC electrode. Specifically, the as-prepared CoO/MnO/NC exhibits a high reversible specific capacity of 936 mA h g-1 at 0.1 A g-1 after 200 cycles and an excellent high-rate capacity of 560 mA h g-1 at 5 A g-1, positioning it as a competitive anode material for lithium-ion batteries. This study underscores the critical role of electronic and Li-ion regulation facilitated by heterostructures, offering a promising pathway for designing transition metal oxide-based anode materials with high performances for lithium-ion batteries.

Spin-mediated promotion of Co catalysts for ammonia synthesis.

Over the past two decades, there has been growing interest in developing catalysts to enable Haber-Bosch ammonia synthesis under milder conditions than currently pertain. Rational catalyst design requires theoretical guidance and clear mechanistic understanding. Recently, a spin-mediated promotion mechanism was proposed to activate traditionally unreactive magnetic materials such as cobalt (Co) for ammonia synthesis by introducing hetero metal atoms bound to the active site of the catalyst surface. We combined theory and experiment to validate this promotion mechanism on a lanthanum (La)/Co system. By conducting model catalyst studies on Co single crystals and mass-selected Co nanoparticles at ambient pressure, we identified the active site for ammonia synthesis as the B5 site of Co steps with La adsorption. The turnover frequency of 0.47 ± 0.03 per second achieved on the La/Co system at 350°C and 1 bar surpasses those of other model catalysts tested under identical conditions.

Solvation of furfural at metal-water interfaces: Implications for aqueous phase hydrogenation reactions.

Metal-water interfaces are central to understanding aqueous-phase heterogeneous catalytic processes. However, the explicit modeling of the interface is still challenging as it necessitates extensive sampling of the interfaces' degrees of freedom. Herein, we use ab initio molecular dynamics (AIMD) simulations to study the adsorption of furfural, a platform biomass chemical on several catalytically relevant metal-water interfaces (Pt, Rh, Pd, Cu, and Au) at low coverages. We find that furfural adsorption is destabilized on all the metal-water interfaces compared to the metal-gas interfaces considered in this work. This destabilization is a result of the energetic penalty associated with the displacement of water molecules near the surface upon adsorption of furfural, further evidenced by a linear correlation between solvation energy and the change in surface water coverage. To predict solvation energies without the need for computationally expensive AIMD simulations, we demonstrate OH binding energy as a good descriptor to estimate the solvation energies of furfural. Using microkinetic modeling, we further explain the origin of the activity for furfural hydrogenation on intrinsically strong-binding metals under aqueous conditions, i.e., the endothermic solvation energies for furfural adsorption prevent surface poisoning. Our work sheds light on the development of active aqueous-phase catalytic systems via rationally tuning the solvation energies of reaction intermediates.

A new insight into the CaO-induced inhibition pathways on PCDD/F formation: Metal passivation, dechlorination and hydroxide substitution.

Ca-based inhibitors (especially CaO) for PCDD/F (polychlorinated dibenzo-p-dioxin and dibenzofuran) formation are considered as economic inhibitors with low toxicity and strong adsorption of acidic gases (e.g., HCl, Cl2, and SOx), whereas the insight understanding of its inhibition mechanisms is scarcely explored. Herein, CaO was used to inhibit the de novo reaction for PCDD/F formation (250-450 °C). The evolution of key elements (C, Cl, Cu, and Ca) combined with theoretical calculations was systematically investigated. The concentrations and distribution of PCDD/Fs demonstrated the significant inhibition effect of CaO on I-TEQ (international toxic equivalency) concentrations of PCDD/Fs (inhibition efficiencies: > 90 %) and hepta~octa chlorinated congeners (inhibition efficiencies: 51.5-99.8 %). And the conditions (5-10 % CaO, 350 °C) were supposed to be the preferred conditions applied in real MSWIs (municipal solid waste incinerators). CaO significantly suppressed the chlorination of carbon matrix (superficial organic Cl (CCl) reduced from 16.5 % to 6.5-11.3 %) and the formation of unsaturated hydrocarbons or aromatic carbon (superficial CC decreased from 6.7 % to 1.3-2.1 %). Also, CaO promoted the dechlorination of Cu-based catalysts and Cl solidification (e.g., conversion of CuCl2 to CuO, and formation of CaCl2). The dechlorination phenomenon was validated by the dechlorination of highly chlorinated PCDD/F-congeners (via DD/DF chlorination pathways). Density functional theory calculations revealed that CaO facilitated the substitution of Cl by -OH on the benzene ring to inhibit the polycondensation of the chlorobenzene and chlorophenol (Gibbs free energy reduced from +74.83 to -36.62 and - 148.88 kJ/mol), which also indicates the dechlorination effect of CaO on de novo synthesis.

In Situ/Operando Methods for Understanding Electrocatalytic Nitrate Reduction Reaction.

With the development of industrial and agricultural, a large amount of nitrate is produced, which not only disrupts the natural nitrogen cycle, but also endangers public health. Among the commonly used nitrate treatment techniques, the electrochemical nitrate reduction reaction (eNRR) has attracted extensive attention due to its mild conditions, pollution-free nature, and other advantages. An in-depth understanding of the eNRR mechanism is the prerequisite for designing highly efficient electrocatalysts. However, some traditional characterization tools cannot comprehensively and deeply study the reaction process. It is necessary to develop in situ and operando techniques to reveal the reaction mechanism at the time-resolved and atomic level. This review discusses the eNRR mechanism and summarizes the possible in situ techniques used in eNRR. A detailed introduction of various in situ techniques and their help in understanding the reaction mechanism is provided. Finally, the current challenges and future opportunities in this research area are discussed and highlighted.

The surface states of transition metal X-ides under electrocatalytic conditions.

Due to conversion equilibrium between solvent and H- and O-containing adsorbates, the true surface state of a catalyst under a particular electrochemical condition is often overlooked in electrocatalysis research. Herein, by using surface Pourbaix analysis, we show that many electrocatalytically active transition metal X-ides (e.g., oxides, nitrides, carbides, and hydroxides) tend to possess the surface states different from their pristine stoichiometric forms under the pH and potential of interest due to water dissociation or generation. Summarizing the density functional theory calculated surface Pourbaix diagrams of 14 conditionally stable transition metal X-ide materials, we found that some of these surfaces tend to be covered by O-containing adsorbates at a moderate or high potential, while vacancies or H-covered surfaces may form at a low potential. These results suggest the possibility of poisoning or creation of surface sites beyond the pristine surface, implying that the surface state under reaction conditions (pH and potentials) needs to be considered before the identification and analysis of active sites of a transition metal X-ide catalyst. In addition, we provide an explanation of the observed theory and experiment discrepancy that some transition metal X-ides are "more stable in experiment than in theory." Based on our findings, we conclude that analyzing the surface state of transition metal X-ide electrocatalysts by theoretical calculations (e.g., surface Pourbaix diagram analysis), in situ/operando and post-reaction experiments are indispensable to accurately understand the underlying catalytic mechanisms.

Synergistic Structure and Iron-Vacancy Engineering Realizing High Initial Coulombic Efficiency and Kinetically Accelerated Lithium Storage in Lithium Iron Oxide.

Transition metal oxides with high capacity still confront the challenges of low initial coulombic efficiency (ICE, generally <70%) and inferior cyclic stability for practical lithium-storage. Herein, a hollow slender carambola-like Li0.43 FeO1.51 with Fe vacancies is proposed by a facile reaction of Fe3+ -containing metal-organic frameworks with Li2 CO3 . Synthesis experiments combined with synchrotron-radiation X-ray measurements identify that the hollow structure is caused by Li2 CO3 erosion, while the formation of Fe vacancies is resulted from insufficient lithiation process with reduced Li2 CO3 dosage. The optimized lithium iron oxides exhibit remarkably improved ICE (from 68.24% to 86.78%), high-rate performance (357 mAh g-1 at 5 A g-1 ), and superior cycling stability (884 mAh g-1 after 500 cycles at 0.5 A g-1 ). Paring with LiFePO4 cathodes, the full-cells achieve extraordinary cyclic stability with 99.3% retention after 100 cycles. The improved electrochemical performances can be attributed to the synergy of structural characteristics and Fe vacancy engineering. The unique hollow structure alleviates the volume expansion of Li0.43 FeO1.51 , while the in situ generated Fe vacancies are powerful for modulating electronic structure with boosted Li+ transport rate and catalyze more Li2 O decomposition to react with Fe in the first charge process, hence enhancing the ICE of lithium iron oxide anode materials.

Ni activated Mo2C by regulating the interfacial electronic structure for highly efficient lithium-ion storage.

Regulating the electronic structure plays a positive role in improving the ion/electron kinetics of electrode materials for lithium ion batteries (LIBs). Herein, an effective approach is demonstrated to achieve Ni/Mo2C hybrid nanoparticles embedded in porous nitrogen-doped carbon nanofibers (Ni/Mo2C/NC). Density functional theory calculations indicate that Ni can activate the interface of Ni/Mo2C by regulating the electronic structure, and accordingly improve the electron/Li-ion diffusion kinetics. The charge at the interface transfers from Ni atoms to Mo atoms on the surface of Mo2C, illustrating the formation of an interfacial electric field in Ni/Mo2C. The formed interfacial electric field in Ni/Mo2C can improve the intrinsic electronic conductivity, and reduce the Li adsorption energy and the Li+ diffusion barrier. Thus, the obtained Ni/Mo2C/NC shows an excellent high-rate capability of 344.1 mA h g-1 at 10 A g-1, and also displays a superior cyclic performance (remaining at 412.7 mA h g-1 after 1800 cycles at 2 A g-1). This work demonstrates the important role of electronic structure regulation by assembling hybrid materials and provides new guidance for future work on designing novel electrode materials for LIBs.

Regulating the electronic structure of MoO2/Mo2C/C by heterostructure and oxygen vacancies for boosting lithium storage kinetics.

The electronic structure regulation of electrode materials can improve the ion/electron kinetics, which is beneficial to the cyclic performance and rate capability for lithium ion batteries (LIBs). Herein, we propose a facile strategy to achieve a MoO2/Mo2C/C heterostructure with abundant oxygen vacancies. Density functional theory calculations indicate that the heterostructure of MoO2/Mo2C/C can significantly promote the Li+/charge transfer and reduce the Li adsorption energy, and the abundant oxygen vacancies in MoO2/Mo2C/C can improve the intrinsic electronic conductivity and reduce the Li+ diffusion barrier. Benefiting from the multiscale coordinated regulation, the obtained MoO2/Mo2C/C film exhibits outstanding high rate capability (454.7 mA h g-1 at 5 A g-1) and remarkable cyclic performance (retaining 569 mA h g-1 over 1000 cycles at 2 A g-1). The insightful findings in this study can shed light on the behavior of the electron/ion structure regulation by the heterostructure and oxygen vacancies, which can guide future studies on designing other electrode materials with high-performance lithium-ion storage.

A spin promotion effect in catalytic ammonia synthesis.

The need for efficient ammonia synthesis is as urgent as ever. Over the past two decades, many attempts to find new catalysts for ammonia synthesis at mild conditions have been reported and, in particular, many new promoters of the catalytic rate have been introduced beyond the traditional K and Cs oxides. Herein, we provide an overview of recent experimental results for non-traditional promoters and develop a comprehensive model to explain how they work. The model has two components. First, we establish what is the most likely structure of the active sites in the presence of the different promoters. We then show that there are two effects dictating the catalytic activity. One is an electrostatic interaction between the adsorbed promoter and the N-N dissociation transition state. In addition, we identify a new promoter effect for magnetic catalysts giving rise to an anomalously large lowering of the activation energy opening the possibility of finding new ammonia synthesis catalysts.

Opportunities and Challenges in Electrolytic Propylene Epoxidation.

Propylene oxide (PO) is an important chemical. So far, its synthesis protocol relies on expensive oxidants. In contrast, direct epoxidation of propylene (DEP) using molecular oxygen is considered ideal for PO synthesis. Unfortunately, DEP has not met industrial demands due to the low propylene conversion and high side-product selectivity for known catalysts. Instead of a thermal process using molecular oxygen, electrolytic propylene oxidation can synthesize PO at room temperature, using the atomic oxygen generated from water-splitting. Herein, using density functional theory, surface Pourbaix analysis, scaling relation analysis, and microkinetic modeling, we show that (i) propylene epoxidation is facile on weak-binding catalysts if reactive atomic oxygen preexists; (ii) electrolytic epoxidation is facile to provide atomic oxygen for epoxidation, while hydroperoxyl formation does not overwhelm the epoxidation process at the potential of interest; (iii) propylene dehydrogenation is a competing step that forms side products. Finally, we discuss the opportunities and challenges of this green PO synthesis method.

Exploring the Health Narratives of Chinese Female Migrant Workers through Culture-Centered and Gender Perspectives.

Female migrant workers (FMWs) represent a marginalized group in China who not only face health disparities but also lack a voice in society. Drawing on the culture-centered approach (CCA) and gender perspective to co-construct health meanings with FMWs, this research aimed to answer the question of how FMWs narrate their health and to reveal the agency of the cultural members. The in-depth interview method was applied to record the health narratives of 30 participants from October 2016 to December 2016. The results showed that FMWs' understandings of health were beset by the cultural system of gender in poverty, exploited working conditions, and discrimination in the medical context. The participants identified minimum wage and medical insurance as the key structural obstacles to healthy lives in the city. Moreover, FMWs had the agency to exercise health practices that challenge the domination of biomedicine. With gender issue threaded throughout the contextualized health narratives, the role of the gender perspective could be viewed as a "contact zone" in CCA. FMWs' agency and its interactions with structures and culture indicate the significance of engaging the voices at the margins in health communication research and praxis.

Elucidation of the Synergistic Effect of Dopants and Vacancies on Promoted Selectivity for CO2 Electroreduction to Formate.

Sn-based materials are identified as promising catalysts for the CO2 electroreduction (CO2RR) to formate (HCOO- ). However, their insufficient selectivity and activity remain grand challenges. A new type of SnO2 nanosheet with simultaneous N dopants and oxygen vacancies (VO -rich N-SnO2 NS) for promoting CO2 conversion to HCOO- is reported. Due to the likely synergistic effect of N dopant and VO , the VO -rich N-SnO2 NS exhibits high catalytic selectivity featured by an HCOO- Faradaic efficiency (FE) of 83% at -0.9 V and an FE of > 90% for all C1 products (HCOO- and CO) at a wide potential range from -0.9 to -1.2 V. Low coordination Sn-N moieties are the active sites with optimal electronic and geometric structures regulated by VO and N dopants. Theoretical calculations elucidate that the reaction free energy of HCOO* protonation is decreased on the VO -rich N-SnO2 NS, thus enhancing HCOO- selectivity. The weakened H* adsorption energy also inhibits the hydrogen evolution reaction, a dominant side reaction during the CO2RR. Furthermore, using the catalyst as the cathode, a spontaneous Galvanic Zn-CO2 cell and a solar-powered electrolysis process successfully demonstrated the efficient HCOO- generation through CO2 conversion and storage.

Synergy effects on Sn-Cu alloy catalyst for efficient CO2 electroreduction to formate with high mass activity.

To acquire the synergy effects between Sn and Cu for the jointly high Faradaic efficiency and current density, we develop a novel strategy to design the Sn-Cu alloy catalyst via a decorated co-electrodeposition method for CO2 electroreduction to formate. The Sn-Cu alloy shows high formate Faradaic efficiency of 82.3% ± 2.1% and total C1 products Faradaic efficiency of 90.0% ± 2.7% at -1.14 V vs. reversible hydrogen electrode (RHE). The current density and mass activity of formate reach as high as (79.0 ± 0.4) mA cm-2 and (1490.6 ± 7.5) mA mg-1 at -1.14 V vs. RHE. Theoretical calculations suggest that Sn-Cu alloy can obtain high Faradaic efficiency for CO2 electroreduction by suppressing the competitive hydrogen evolution reaction and that the formate formation follows the path of CO2 â†’ HCOO* â†’ HCOOH. The stepped (2 1 1) surface of Sn-Cu alloy is beneficial towards selective formate production.