纳米铁颗粒及其复合材料的界面设计及环境修复应用

近年来, 纳米铁颗粒(纳米零价铁)因其优异的催化/还原性能, 并且价廉、环境友好, 已成为主要的环境修复材料之一。目前, 纳米铁颗粒主要用于水体修复, 如: 重金属离子去除、有机物污染物降解和无机阴离子催化还原等。纳米铁颗粒易团聚和结构单一等问题会导致其活性低、稳定性差和去除种类单一。为了克服上述问题, 迫切需要研究纳米铁颗粒的界面设计。本文重点阐述纳米铁颗粒及其复合材料的可控制备、界面设计、在重金属去除和硝酸根去除转化中的应用以及在环境修复中的未来发展方向。     

Ultrathin PtNiM (M = Rh,Os, and Ir) Nanowires as Efficient Fuel Oxidation Electrocatalytic Materials

The development of new electrocatalysts with high activity and durability for alcohol oxidation is an emerging need of direct alcohol fuel cells. However, the commonly used Pt‐based catalysts still exhibit drawbacks including limited catalytic activity, high overpotential, and severe CO poisoning. Here a general approach is reported for preparing ultrathin PtNiM (M = Rh, Os, and Ir) nanowires (NWs) with excellent anti‐CO‐poisoning ability and high activity. Owing to their superior nanostructure and optimal electronic interaction, the ultrathin PtNiM NWs show enhanced electrocatalytic performance for both methanol oxidation reaction (MOR) and ethanol oxidation reaction (EOR). The optimal PtNiRh NWs show mass activity of 1.72 A mg^?1 and specific activity of 2.49 mA cm^?2 for MOR, which are 3.17 and 2.79 times higher than those of Pt/C. In particular, the onset potentials of PtNiRh NWs for MOR and EOR shift down by about 65 and 85 mV compared with those of Pt/C. Density functional theory calculations further verify their high antipoison properties for MOR and EOR from both an electronic and energetic perspective. Facilitated by the introduction of Rh and Ni, the stable pinning of the Pt 5d band associated with electron‐rich and depletion centers solves the dilemma between reactivity and anti‐CO poisoning.     

Carbon‐Based Metal‐Free Catalysts for Electrocatalytic Reduction of Nitrogen for Synthesis of Ammonia at Ambient Conditions

The electrocatalytic nitrogen reduction reaction (NRR) is a promising catalytic system for N₂ fixation in ambient conditions. Currently, metal‐based catalysts are the most widely studied catalysts for electrocatalytic NRR. Unfortunately, the low selectivity and poor resistance to acids and bases, and the low Faradaic efficiency, production rate, and stability of metal‐based catalysts for NRR make them uncompetitive for the synthesis of ammonia in comparison to the industrial Haber–Bosch process. Inspired by applications of carbon‐based metal‐free catalysts (CMFCs) for the oxygen reduction reaction (ORR) and CO₂ reduction reaction (CO₂RR), the studies of these CMFCs in electrocatalytic NRR have attracted great attention in the past year. However, due to the differences in electrocatalytic NRR, there are several critical issues that need to be addressed in order to achieve rational design of advanced carbon‐based metal‐free electrocatalysts to improve activity, selectivity, and stability for NRR. Herein, the recent developments in the field of carbon‐based metal‐free NRR catalysts are presented, along with critical issues, challenges, and perspectives concerning metal‐free catalysts for electrocatalytic reduction of nitrogen for synthesis of ammonia at ambient conditions.     

Insights into the Electrochemical Behavior of Manganese Oxides as Catalysts for the Oxygen Reduction and Evolution Reactions: Monometallic Core-Shell Mn/Mn3O4

Overcoming the sluggish electrode kinetics of both oxygen reduction and evolution reactions (ORR/OER) with non-precious metal electrocatalysts will accelerate the development of rechargeable metal-air batteries and regenerative fuel cells. The authors investigated the electrochemical behavior and ORR/OER catalytic activity of core-porous shell Mn/Mn₃O₄ nanoparticles in comparison with other manganese dioxides (β- and γ-MnO₂), and benchmarked against Pt/C and Pt/C-IrO₂. Under reversible operation in O₂-saturated 5 M KOH at 22 °C, the early stage activity of core-shell Mn/Mn₃O₄ shows two times higher ORR and OER current density compared to the other MnO₂ structures at 0.32 and 1.62 V versus RHE, respectively. It is revealed that Mn(III) oxidation to Mn(IV) is the primary cause of Mn/Mn₃O₄ activity loss during ORR/OER potential cycling. To address it, an electrochemical activation method using Co(II) is proposed. By incorporating Co(II) into MnO_x, new active sites are introduced and the content of Mn(II) is increased, which can stabilize the Mn(III) sites through comproportionation with Mn(IV). The Co-incorporated Mn/Mn₃O₄ has superior activity and durability. Furthermore, it also surpassed the activity of Pt/C-IrO₂ with similar durability. This study demonstrates that cost-effective ORR/OER catalysis is possible.     

Ni Single Atoms on MoS2 Nanosheets Enabling Enhanced Kinetics of Li-S Batteries

The practical application of Li-S batteries is seriously hindered due to its shuttle effect and sluggish redox reaction, which requires a better functional separator to solve the problems. Herein, polypropylene separators modified by MoS₂ nanosheets with atomically dispersed nickel (Ni-MoS₂) are prepared to prevent the shuttle effect and facilitate the redox kinetics for Li-S batteries. Compared with pristine MoS₂ nanosheets, Ni-MoS₂ nanosheets exhibit both excellent adsorption and catalysis performance for overcoming the shuttle effect. Assembled with this novel separator, the Li-S batteries exhibit an admirable cycling stability at 2 C over 400 cycles with 0.01% per cycle decaying. In addition, even with a high sulfur loading of 7.5 mg cm⁻², the battery still provides an initial capacity of 6.9 mAh cm⁻² and remains 5.9 mAh cm⁻² after 50 cycles because of the fast convention of polysulfides catalyzed by Ni-MoS₂ nanosheets, which is further confirmed by the density functional theory (DFT) calculations. Therefore, the proposed strategy is expected to offer a new thought for single atom catalyst applying in Li-S batteries.     

Significantly Stabilizing Hydrogen Evolution Reaction Induced by Nb-Doping Pt/Co(OH)2 Nanosheets

High stability and efficiency of electrocatalysts are crucial for hydrogen evolution reaction (HER) toward water splitting in an alkaline media. Herein, a novel nano-Pt/Nb-doped Co(OH)₂ (Pt/Nb Co(OH)₂) nanosheet is designed and synthesized using water-bath treatment and solvothermal reduction approaches. With nano-Pt uniformly anchored onto Nb Co(OH)₂ nanosheet, the synthesized Pt/Nb Co(OH)₂ shows outstanding electrocatalytic performances for alkaline HER, achieving a high stability for at least 33 h, a high mass activity of 0.65 mA µg⁻¹ Pt, and a good catalytic activity with a low overpotential of 112 mV at 10 mA cm⁻². Both experimental and theoretical results prove that Nb-doping significantly optimizes the hydrogen adsorption free energy to accelerate the Heyrovsky step for HER, and boosts the adsorption of H₂O, which further enhances the water activation. This study provides a new design methodology for the Nb-doped electrocatalysts in an alkaline HER field by facile and green way.     

Leveraging Ligand and Composition Effects: Morphology-Tailorable Pt–Bi Bimetallic Aerogels for Enhanced (Photo-)Electrocatalysis

Metal aerogels (MAs) are emerging porous materials displaying unprecedented potential in catalysis, sensing, plasmonic technologies, etc. However, the lack of efficient regulation of their nano-building blocks (NBBs) remains a big hurdle that hampers the in-depth investigation and performance enhancement. Here, by harmonizing composition and ligand effects, Pt- and Bi-based single- and bimetallic aerogels bearing NBBs of controlled dimensions and shapes are obtained by facilely tuning the metal precursors and the applied ligands. Particularly, by further modulating the electronic and optic properties of the aerogels via adjusting the content of the catalytically active Pt component and the semiconducting Bi component, both the electrocatalytic and photoelectrocatalytic performance of the Pt–Bi aerogels can be manipulated. In this light, an impressive catalytic performance for electro-oxidation of methanol is acquired, marking a mass activity of 6.4-fold higher under UV irradiation than that for commercial Pt/C. This study not only sheds light on in situ manipulating NBBs of MAs, but also puts forward guidelines for crafting high-performance MAs-based electrocatalysts and photoelectrocatalysts toward energy-related electrochemical processes.     

P-Block Metal-Based Electrocatalysts for Nitrogen Reduction to Ammonia: A Minireview

Electrochemical nitrogen reduction reaction (NRR) to ammonia (NH₃) using renewable electricity provides a promising approach towards carbon neutral. What's more, it has been regarded as the most promising alternative to the traditional Haber-Bosch route in current context of developing sustainable technologies. The development of a class of highly efficient electrocatalysts with high selectivity and stability is the key to electrochemical NRR. Among them, P-block metal-based electrocatalysts have significant application potential in NRR for which possessing a strong interaction with the N 2p orbitals. Thus, it offers a good selectivity for NRR to NH₃. The density of state (DOS) near the Fermi level is concentrated for the P-block metal-based catalysts, indicating the ability of P-block metal as active sites for N₂ adsorption and activation by donating p electrons. In this work, we systematically review the recent progress of P-block metal-based electrocatalysts for electrochemical NRR. The effect of P-block metal-based electrocatalysts on the NRR activity, selectivity and stability are discussed. Specifically, the catalyst design, the nature of the active sites of electrocatalysts and some strategies for boosting NRR performance, the reaction mechanism, and the impact of operating conditions are unveiled. Finally, some challenges and outlooks using P-block metal-based electrocatalysts are proposed.     

Atomically Dispersed Fe/N4 and Ni/N4 Sites on Separate-Sides of Porous Carbon Nanosheets with Janus Structure for Selective Oxygen Electrocatalysis

Dual single atoms catalysts have promising application in bifunctional electrocatalysis due to their synergistic effect. However, how to balance the competition between rate-limiting steps (RDSs) of reversible oxygen reduction and oxygen evolution reaction (OER) and fully expose the active centers by reasonable structure design remain enormous challenges. Herein, Fe/N₄ and Ni/N₄ sites separated on different sides of the carbon nanosheets with Janus structure (FeNi_jns/NC) is synthesized by layer-by-layer assembly method. Experiments and calculations reveal that the side of Fe/N₄ is beneficial to oxygen reduction reaction (ORR) and the Ni/N₄ side is preferred to OER. Such Janus structure can take full advantage of two separate-sides of carbon nanosheets and balance the competition of RDSs during ORR and OER. FeNi_jns/NC possesses superior ORR and OER activity with ORR half-wave potential of 0.92 V and OER overpotential of 440 mV at J = 10 mA cm⁻². Benefiting from the excellent bifunctional activities, FeNi_jns/NC assembled aqueous Zn–air battery (ZAB) demonstrates better maximum power density, and long-term stability (140 h) than Pt/C+RuO₂ catalyst. It also reveals superior flexibility and stability in solid-state ZAB. This work brings a novel perspective for rational design and understanding of the catalytic mechanisms of dual single atom catalysts.     

Revealing component synergy of Ni‒Fe/black phosphorous composites synthesized by self-designed electrochemical method for enhancing photoelectrocatalytic oxygen evolution reaction

Developing high-activity and low-cost catalysts is the key to eliminate the limitation of sluggish anodic oxygen evolution reaction (OER) during electrocatalytic overall water splitting. Herein, Ni‒Fe/black phosphorous (BP) composites are synthesized using a simple three-electrode system, where exfoliation of bulky BP and synthesis of NiFe composites are simultaneously achieved. Under light illumination, the optimized Ni‒Fe/BP composite exhibits excellent photoelectrocatalytic OER performance (e.g., the overpotential is 58 mV lower than a commercial RuO₂ electrocatalyst at a current density of 10 mA·cm⁻²). The electron transfer on this composite is proved to follow a Ni‒BP‒Fe pathway. The electronic structure of this Ni‒Fe/BP composite is effectively regulated, leading to optimized adsorption strength of the intermediate OH* and improved intrinsic activity for the OER. Together with active sites on the support, this Ni‒Fe/BP composite possesses abundant electrochemical active sites and a bug surface area for the OER. The introduction of light further accelerates the electrocatalytic OER. This work provides a novel and facile method to synthesize high-performance metal/BP composites as well as the approaches to reveal their OER mechanisms.