金属有机框架衍生多功能电催化材料的设计及性能研究

大规模储能技术需要多功能的能量转换与存储系统，包括金属-空气电池、金属-二氧化碳电池以及电解水系统。为了应对当前世界面临的能源危机，我们迫切需要开发多功能电催化剂。近年来，人们致力于为二氧化碳还原反应（CO2RR）、氧还原反应（ORR）、析氧反应（OER）和析氢反应（HER）设计高效且经济的电催化剂。但是，开发一种能够同时高效催化上述所有过程的单一催化剂仍然是一个巨大的挑战。本论文针地这一问题，开展了系统研究，以获得高催化活性的多功能电催化材料，具体研究成果如下： 首先设计、合成了高效的兼具ORR和OER双功能电催化剂。该催化剂是在惰性条件下热解经双氰胺改性的ZIF-67而获得。热解后，Co单原子均匀地分散在具有清晰形态、高孔隙率和独特结构的碳纳米管表面上。所得电催化剂对ORR和OER均表现出显著的催化性能，在碱性介质条件下的ORR过程中，催化剂的起始电位为0.99 V（相对于可逆氢电极RHE），比Pt/C的起始电位高。而且其半波电位为0.86 V（相对于RHE），还具有较小的塔菲尔斜率，呈现出较高的四电子还原选择性。此外，催化剂在OER过程中，当起始电位为1.53 V（相对于RHE）时，达到10mA/cm2时过电位为300 mV。 进一步，我们设计了一条高效多功能催化剂的简单合成策略，该催化剂能够在相应条件下催化上述所有过程，并且具有优异的活性和稳定性。该催化剂以N掺杂碳纳米管为基底，将双金属合金和单原子结合在一起。因此，该工作首次报道了具有多活性位点协同效应的四功能电催化剂在多种能量转换与存储系统中的应用。所得电催化剂对ORR、OER、HER和CO2RR均表现出优异的性能。在OER过程中，该催化剂的正起始电位（0.98 V）和半波电位（0.86 V）均高于Pt/C的。同时还具有250 mV的极低过电位（&eta;10），以及为0.62 V的ORR/OER电位差。在碱性介质中，该催化剂还表现出优异的HER性能（&eta;10 = 49 mV），并且在全水解过程中获得了目前为止较小的电池偏压（为1.57 V）。此外，在0.5 M的KHCO3介质中，该催化剂还获得了法拉第效率为99%的优异CO2RR性能。 进一步，合成了一种新型三功能Br掺杂和缺陷富集的多孔碳骨架（BrHT@CoNC），该复合结构对ORR、OER和HER均具有良好的电催化活性。通过热解由表面活性剂二甲基十八烷基溴化铵（DODAB）改性的ZIF-67，巧妙地将大量缺陷和Br掺杂结合到了多孔炭中。当BrHT@CoNC复合材料作为可充电锌-空电池和全水解的催化剂/电极时显示出巨大的潜力。新型电催化剂的研究结果将为研究此类材料以及设计更多优异的电催化剂开辟新的道路，这对未来的可再生能源技术具有革命性的意义。这些工作也为探索在一个独立电极上高效集成三个或多个功能的高性价比的电催化剂提供了方向。;Scalable energy storage technologies require multi-functional energy conversion and storage systems, including metal&ndash;air batteries, metal&ndash;CO2 batteries and water splitting. The development of multi-functional electrocatalysts is urgently needed to combat the current energy crisis faced by the world. Recently much effort has been devoted to design efficient and cost-effective electrocatalysts for CO2 reduction reaction (CO2RR), oxygen reduction reaction (ORR), oxygen evolution reactions (OER), and hydrogen evolution reactions (HER), but the development of single catalyst which can catalyze all the processes simultaneously and efficiently is still a great challenge and no reports are being published to the date. In the present work, report a simple strategy for designing highly efficient catalyst for both oxygen reduction (ORR) and oxygen evolution reactions (OER). The catalyst is derived from dicyandiamide modified ZIF-67 by subsequent pyrolysis under inert conditions. Co single atoms are well dispersed over the surface of entire carbon nanotubes network formed upon pyrolysis with well-defined morphology, high porosity and unique structural features. The prepared electrocatalyst has shown up remarkable performance for both ORR and OER. The bifunctional property of the material is best amongst the previously reported catalysts. The catalyst shows highly positive onset potential value of ~0.99 V vs. reversible hydrogen electrode (RHE) higher than that of Pt/C for ORR and half wave potential value of 0.86 V vs. RHE, also more positive than Pt/C in alkaline medium with small Tafel slope as well and high selectivity for four electron reduction process. A lower overpotential for OER of 300 mV is observed for onset potential of 1.53 V vs. RHE. Smaller value of overvoltage (rE) 0.78 V pronounces the excellency of material for bifunctional catalysis. In second project, we report a simple strategy for designing highly efficient catalyst capable of catalyzing all these process with excellent activity and stability under technological conditions. The catalyst integrates bimetallic alloy and single atoms, with N-doped CNTs acting as substrate. As a result, the first ever tetra-functional electrocatalyst utilizing synergetic effect of multiple active sites is reported for utilization in multi-model energy conversion and storage system. The prepared electrocatalyst has shown up remarkable performance for ORR, OER, HER and CO2RR. The catalyst exhibits more positive onset (0.98 V) and half wave potential (0.86 V) than Pt/C for ORR, extremely low overpotential (&eta;10) of 250 mV for OER and thus the lowest ORR/OER potential gap of 0.62 V. In alkaline medium, the catalyst also shows excellent HER performance with &eta;10 of 49 mV, resulting in the smallest cell bias of 1.57 V for overall water splitting to date. An excellent CO2RR with FE of 99% is achieved in 0.5 M KHCO3 medium. In another work, a novel trifunctional Br doped and defect-enriched porous carbon framework (BrHT@CoNC) is designed, which shows excellent electrocatalytic activity for oxygen reduction reaction (ORR), oxygen evolution reaction (OER) as well as hydrogen evolution reaction (HER). Combination of extensive defects and Br-doping into porous carbon is simply achieved by pyrolysis of the surfactant, dimethyldioctadecylammonium bromide (DODAB) modified ZIF-67. The BrHT@CoNC composite shows great potential as an economical catalyst/electrode for both rechargeable Zn&ndash;air batteries and overall water splitting. The successful doping of Br atoms into the carbon framework introduces more defects and thus electronic redistributions, which lead to excellent activity for electrocatalytic oxygen reduction reaction (ORR), oxygen evolution reaction (OER) as well as hydrogen evolution reaction (HER). For ORR, the prepared catalyst exhibits more positive onset and half wave potential (by 40 mV and 80 mV respectively) than commercial Pt/C. Overpotential (h10) of only 254 mV and 77 mV is required for OER and HER respectively in alkaline medium. The rechargeable Zn-air battery was assembled by using the catalyst as air cathode, which showed an output power density of 165 mW cm-2.The promising results shown by novel electrocatalysts will open up new paves for the scientific community to explore and investigate such materials and design more stellar electrocatalyst which could be revolutionary for future renewable energy technology. This work also provides avenue toward the exploration of cost effective heteroatom doped catalysts for efficient integration of three or more functions in one freestanding electrode.&nbsp;</p

Functionality and design of Co-MOFs: unique opportunities in electrocatalysts for oxygen reduction reaction

Zeolitic imidazolate framework (ZIF)-derived electrocatalysts have emerged as efficient, environmentally innocuous, low-cost, non-noble-metal alternatives to precious group metals for the oxygen reduction reaction (ORR) and utilization in clean and sustainable energy systems such as metal-air batteries and fuel cells. Recently, there has been tremendous interest in ZIF-based materials due to the large N content and M-N bonds in the parent ZIF backbone and derived nanostructures, which are responsible for their high ORR catalytic activity. This review summarizes the origin of the activity of ZIF-based materials and their recent progress and focuses specifically on advancements in ZIF-67-based materials for efficient ORR electrocatalysis. Furthermore, this review also outlines the recent strategies for designing more efficient catalysts based on ZIF-67, such as doping with heteroatoms, alloying with various metallic species, and compositing with carbonaceous nanostructures, and discusses their underlying mechanisms. Finally, insight into the remaining challenges and directions for future perspectives and research is provided

Br/Co/N Co-doped porous carbon frameworks with enriched defects for high-performance electrocatalysis

Defect engineering through heteroatom doping is one of the most important strategies towards the development of catalytic active materials for energy related applications. Herein, a novel trifunctional Br/Co/N Co-doped and defect-enriched porous carbon framework (BrHT@CoNC) is designed, which shows excellent electrocatalytic activity for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) as well as the hydrogen evolution reaction (HER). Introduction of extensive defects by heteroatom-doping is simply achieved by pyrolysis of the surfactant, dimethyldioctadecylammonium bromide (DODAB) modified ZIF-67. The BrHT@CoNC composite shows great potential as an economical catalyst/electrode for both rechargeable Zn-air batteries and overall water splitting devices. This work opens a new avenue toward the exploration of cost effective heteroatom doped catalysts for efficient integration of three or more functions into one freestanding electrode.</p

Solar‐Triggered Engineered 2D‐Materials for Environmental Remediation: Status and Future Insights

Abstract Modern‐day society requires advanced technologies based on renewable and sustainable energy resources to face the challenges regarding environmental remediation. Solar‐inspired photocatalytic applications for water purification, hydrogen and oxygen evolution, carbon dioxide reduction, nitrogen fixation, and removal of bacterial species seem to be unique solutions based on green and efficient technologies. Considering the unique electronic features and larger surface area, 2D photocatalysts have been broadly explored for the above‐mentioned applications in the past few years. However, their photocatalytic potential has not been optimized yet to the adequate level of practical and commercial applications. Among many strategies available, surface and interface engineering and the hybridization of different materials have revealed pronounced potential to boost the photocatalytic potential of 2D materials. This feature review recapitulates recent advancements in engineered materials that are 2D for various photocatalysis applications for environmental remediation. Various surface and interface engineering technologies are briefly discussed, like anion–cation vacancies, pits, distortions, associated vacancies, etc., along with rules and parameters. In addition, several hybridization approaches, like 0D/2D, 1D/2D, 2D/2D, and 3D/2D hybridization, etc., are also deeply investigated. Lastly, the application of these engineered 2D materials for various photocatalytic applications, challenges, and future perspectives is extensively explored

Efficient Tetra-Functional Electrocatalyst with Synergetic Effect of Different Active Sites for Multi-Model Energy Conversion and Storage

Energy crisis and global warming due to excessive CO2 emissions are the two major challenges of the world. Conversion of CO2 into useful fuels along with rechargeable metal air batteries and water splitting is one way to combat the energy crisis, which is bottlenecked due to the lack of multifunctional electrocatalyst. Herein simple but multifunctional electrocatalyst, which combined CoNi nanoalloy, N-doped carbon nanotubes, and single atomic Ni sites together is reported. The prepared electrocatalyst has shown remarkable performance for CO2RR, ORR, OER, and HER. The practical utilization of the catalyst is mansifested by a dual model metal CO2/air battery and water electrolyzer. An excellent CO2RR with FE of 99% is achieved in 0.5 M KHCO3 medium. The catalyst exhibits more positive onset (0.98 V) and half wave potential (0.86 V) than Pt/C for ORR, extremely low overpotential (eta(10)) of 250 mV for OER, and thus the lowest ORR/OER potential gap of 0.62 V. In alkaline medium, the catalyst also shows excellent HER performance with eta(10) of 49 mV, resulting in the smallest cell bias of 1.57 V for overall water splitting to date. This work provides a new pathway to design more stellar multifunctional electrocatalyst for sustainable and clean renewable energy technology

Nitrogen-rich core-shell structured particles consisting of carbonized zeolitic imidazolate frameworks and reduced graphene oxide for amperometric determination of hydrogen peroxide

Core-shell structured particles were prepared from carbonized zeolitic imidazolate frameworks (ZIFs) and reduced graphene oxide (rGO). The particles possess a nitrogen content of up to 10.6%. The loss of nitrogen from the ZIF is avoided by utilizing the reduction and agglomeration of graphene oxide with suitable size (&gt;2 mu m) during pyrolysis. The resulting carbonized ZIF@rGO particles were deposited on a glassy carbon electrode to give an amperometric sensor for H2O2, typically operated at a voltage of -0.4V (vs. Ag/AgCl). The sensor has a wide detection range (from 5 x 10(-6) to 2 x 10(-2) M), a 3.3 mu M (S/N = 3) detection limit and a 0.272 mu A.mu M(-1.)cm(-2) sensitivity, much higher than that of directly carbonized ZIFs. The sensor material was also deposited on a screen-printed electrode to explore the possibility of application.</p

Cobalt Single Atoms Immobilized N‑Doped Carbon Nanotubes for Enhanced Bifunctional Catalysis toward Oxygen Reduction and Oxygen Evolution Reactions

Novel Co atoms immobilized carbon nanotubes (CoSAs@CNTs) are synthesized by structural engineering of the zeolitic imidazolate framework (ZIF-67) upon treatment with dicyandiamide (DCD). A unique morphology and promising electrochemical performance are shown by the Co atoms immobilized CNTs. The electrocatalyst remarkably exhibits a highly positive onset potential of 0.99 V and half-wave potential of 0.86 V, both even more positive than the commercial Pt/C catalyst, and the current density is also greater than that of the Pt/C catalyst in alkaline media. A decent performance is observed in acidic media also. The electrocatalyst is extraordinarily stable to harsh environments. A promising performance for the oxygen evolution reaction (OER) is demonstrated by the electrocatalyst, while for bifunctional electrocatalysis a small overvoltage of 0.78 V is observed with onset potential at the lower overpotential of 300 mV announcing the advantage of its usage for practical energy conversion and storage systems. This novel study may provide a new road map for fuel cell technology

A review of photocatalytic characterization, and environmental cleaning, of metal oxide nanostructured materials

Industrial waste is the primary source of highly toxic organic pollutants and heavy metal contaminants. Treatment of such effluence is necessary to mitigate environmental pollution to provide a clean ecosystem for living species. Various approaches have been effectively utilized for the removal of industrial waste particularly, photocatalysis being an effective, economical, and time-efficient approach to remove toxic ions. Large organic molecules found in pesticides and dyes can be removed with relative ease using nano-photocatalysts with a wide energy band gap, which is one of its major merits. For this purpose, a combination of various metal oxides with relevant materials is generally employed to activate visible regions in photocatalysts. Moreover, modification in physical parameters such as surface area of the catalyst, crystallinity, particle size and morphology, band gap, and microstructure is undertaken, which serves to enhance the photocatalytic activity. Here, advanced techniques that are presently used to synthesize different types of photocatalysts and their potential use in the degradation of the organic dye have been described in detail. The focus of the current review is various metal oxide NPs such as ZnO, TiO2, WO3, SnO2, and CuO with potential applications in photocatalysis, their structural characteristics, classification, and their photocatalytic mechanism. The review covers the influence of dopants on morphological, electrical, optical, and photocatalytic activity of selected nanocomposite systems. Moreover, the current review grasps extensive literature on the role of metal oxides as a photocatalyst that will facilitate researchers by providing guidelines to design more suitable nano-photocatalytic systems