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1.
    
FeOxHy and Fe-containing Ni/Co oxyhydroxides are the most-active catalysts for the oxygen evolution reaction (OER) in alkaline media. However, the activity of Fe sites appears strongly dependent on the electrode-substrate material and/or the elemental composition of the matrix in which it is embedded. A fundamental understanding of these interactions that modulate the OER activity of FeOxHy is lacking. We report the use of cyclic voltammetry and chronopotentiometry to assess the substrate-dependent activity of FeOxHy on a number of commonly used electrode substrates, including Au, Pt, Pd, Cu, and C. We also evaluate the OER activity and Tafel behavior of these metallic substrates in 1 M KOH aqueous solution with Fe3+ and other electrolyte impurities. We find that the OER activity of FeOxHy varies by substrate in the order Au>Pd≈Pt≈Cu>C. The trend may be caused by differences in the adsorption strength of the Fe oxo ion on the substrate, where a stronger adhesion results in more adsorbed Fe at the interface during steady-state OER and possibly a decreased charge-transfer resistance at the FeOxHy-substrate interface. These results suggest that the local atomic and electronic structure of [FeO6] units play an important role in catalysis of the OER as the activity can be tuned substantially by substrate interactions.  相似文献   

2.
La0.3(Ba0.5Sr0.5)0.7Co0.8Fe0.2O3?δ is a promising bifunctional perovskite catalyst for the oxygen reduction reaction and the oxygen evolution reaction. This catalyst has circa 10 nm‐scale rhombohedral LaCoO3 cobaltite particles distributed on the surface. The dynamic microstructure phenomena are attributed to the charge imbalance from the replacement of A‐site cations with La3+ and local stress on Co‐site sub‐lattice with the cubic perovskite structure.  相似文献   

3.
    
An apparent increased interest has been recently devoted towards the previously untrodden path for anionic point defect engineering of electrocatalytic surfaces. The role of vacancy engineering in improving photo- and electrocatalytic activities of transition metal oxides (TMOs) has been widely reported. In particular, oxygen vacancy modulation on electrocatalysts of cobalt-based TMOs has seen a fresh spike of research work due to the substantial improvements they have shown towards oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Oxygen vacancy engineering is an effective scheme to quintessentially tune the electronic structure and charge transport, generate secondary active surface phases, and modify the surface adsorption/desorption behavior of reaction intermediates during water splitting. Based on contemporary efforts for inducing oxygen vacancies in a variety of cobalt oxide types, this work addresses facile and environmentally benign synthesis strategies, characterization techniques, and detailed insight into the intrinsic mechanistic modulation of electrocatalysts. It is our foresight that appropriate utilization of the principles discussed herein will aid researchers in rationally designing novel materials that can outperform noble metal-based electrocatalysts. Ultimately, future electrocatalysis implementation for selective seawater splitting is believed to depend on regulating the surface chemistry of active and stable TMOs.  相似文献   

4.
    
Highly efficient electrocatalysts play important roles in electrochemical water splitting for hydrogen production, including the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). Metal-organic frameworks (MOFs) are porous crystalline materials, exhibiting strong potential as precursors for obtaining outstanding electrocatalysts. MOF-based electrocatalysts, including MOFs and MOF-derived electrocatalysts, have become an increasingly important part of catalysts in the field of electrochemical water splitting, but their catalytic performance, especially their activity and stability, still have a lot of room for improvement. In this paper, the preparation strategy of MOF-based electrocatalysts and improvement methods of catalytic properties were reviewed, including morphology-controlled methods and composition-controlled methods. We also focused on the structure–property relationships, which determine the electrocatalytic activity for water splitting reactions. Finally, the challenges and development prospects were discussed for the MOF-based electrocatalysts, which might provide some insight for future applications in electrochemical water splitting.  相似文献   

5.
    
Heterogeneous single-site catalysts (SSCs), widely regarded as promising next-generation catalysts, blend the easy recovery of traditional heterogeneous catalysts with desired features of homogeneous catalysts: high fraction of active sites and uniform metal centers. We previously reported the synthesis of Pt-ligand SSCs through a novel metal-ligand self-assembly method on MgO, CeO2, and Al2O3 supports (J. Catal. 2018 , 365, 303–312). Here, we present their applications in the industrially-relevant alkene hydrosilylation reaction, with 95 % yield achieved under mild conditions. As expected, they exhibit better metal utilization efficiency than traditional heterogeneous Pt catalysts. The comparison with commercial catalysts (Karstedt and Speier) reveals several advantages of these SSCs: higher selectivity, less colloidal Pt formation, less alkene isomerization/hydrogenation, and better tolerance towards functional groups in substrates. Despite some leaching, our catalysts exhibit satisfactory recyclability and the single-site structure remains intact on oxide supports after reaction. Pt single-sites were proved to be the main active sites rather than colloidal Pt formed during the reaction. An induction period is observed in which Pt sites are activated by Cl detachment and replacement by reactant alkenes. The most active species likely involves temporary detachment of Pt from ligand or support. Catalytic performance of Pt SSCs is sensitive to the ligand and support choices, enabling fine tuning of Pt sites. This work highlights the application of heterogeneous SSCs created by the novel metal-ligand self-assembly strategy in an industrially-relevant reaction. It also offers a potential catalyst for future industrial hydrosilylation applications with several improvements over current commercial catalysts.  相似文献   

6.
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7.
A novel nanoparticulate catalyst of copper (Cu) and ruthenium (Ru) was designed for low-temperature ammonia oxidation at near-stoichiometric mixtures using a bottom-up approach. A synergistic effect of the two metals was found. An optimum CuRu catalyst presents a reaction rate threefold higher than that for Ru and forty-fold higher than that for Cu. X-ray absorption spectroscopy suggests that in the most active catalyst Cu forms one or two monolayer thick patches on Ru and the catalysts are less active once 3D Cu islands form. The good performance of the tuned Cu/Ru catalyst is attributed to changes in the electronic structure, and thus the altered adsorption properties of the surface Cu sites.  相似文献   

8.
    
Quantitative analysis of poisonous Pd hydroxide phase formation during methane combustion in the presence of water is performed via in situ X-ray absorption spectroscopy from 200 to 500 deg C for palladium catalysts supported on tin and aluminum oxides. Water presence inhibits oxidation of the metallic Pd; for the Pd/Al2O3 catalyst the major oxidation product is Pd(OH)2, with PdO being the dominant phase on the Pd/SnO2 system. Tin dioxide is reduced during methane oxidation in the presence of water, regardless of the excess oxygen in the feed. Temperature-programmed surface reactions at anaerobic and low-oxygen conditions revealed that the Pd/SnO2 catalyst has an inability to catalyze methane steam reforming, as opposed to Pd/Al2O3. We suggest that tin oxide extracts hydroxyls from the PdO surface, which makes the latter more active in methane combustion in the presence of water but inactive in methane steam reforming.  相似文献   

9.
    
Highly active NiFeOx electrocatalysts for the oxygen evolution reaction (OER) suffer gradual deactivation with time owing to the loss of Fe species from the active sites into solution during catalysis. The anodic deposition of a CeOx layer prevents the loss of such Fe species from the OER catalysts, achieving a highly stable performance. The CeOx layer does not affect the OER activity of the catalyst underneath but exhibits unique permselectivity, allowing the permeation of OH? and O2 through while preventing the diffusion of redox ions through the layer to function as a selective O2‐evolving electrode. The use of such a permselective protective layer provides a new strategy for improving the durability of electrocatalysts.  相似文献   

10.
    
Development of cost-effective and highly efficient oxygen evolution reaction (OER) electrocatalysts has become a vital project of renewable energy technologies. The OER is critical for a variety of electrochemical energy devices such as water electrolyzers, metal-air batteries, CO2 reduction, and electrosynthesis of ammonia. Compared to extensively studied metal oxide catalysts, graphitized carbon catalysts have been newly emerged as promising OER catalysts especially in less corrosive alkaline media, due to their low cost, high electrical conductivity, unique physicochemical properties, and excellent electrocatalytic performances. In this review, we discussed recent advances in nanostructured carbon electrocatalysts. At first, metal-free OER carbon electrocatalysts including single- and multi-heteroatom doping and edge- and defect-rich defects are introduced. Then, transition metal and heteroatom co-doped nanocarbons are summarized including Co−N−C, Ni−N−C, and Fe-N−C. In addition, carbon based hybrid electrocatalysts are highlighted, which include carbon based transition metal nitrides (TMNx), sulfides (TMSx), and selenides (TMSex), and phosphides (TMPx). Finally, current challenges and perspective for future research on carbon-based OER catalysts are outlined.  相似文献   

11.
龙金林  顾泉  张子重  王绪绪 《化学进展》2011,23(12):2417-2441
表面金属有机化学是设计制备组成和结构明确的表面金属物种的一条有效途径。同步辐射X射线吸收精细结构光谱技术(XAFS)是当前表征固体催化剂活性中心结构的有力工具。二者结合为在分子水平上设计构筑催化中心提供了一条可借鉴的分子研究途径和方法,已发展成为催化基础研究的重要方向之一。本文综述了过去十年内,我们研究组在利用表面金属有机化学方法在沸石分子筛孔道表面分子构筑单分散金属氧活性单元和XAFS在表征多相催化材料活性位结构方面取得的一些进展。简要介绍了XAFS技术的基本物理原理、实验方法、数据分析及在表征催化材料方面的优缺点,并回顾了固体表面金属有机化学的化学基础。借助表面金属有机化学的理论和方法实现了在沸石分子筛表面分子构筑“单点”单核或“单点”多核金属钛、铜和铁催化活性中心。通过对其微观结构的详细表征,并结合其催化性能的研究建立起活性与组成、结构三者之间的关联,阐明了这些金属物种化学态与其催化活性之间的本质联系。研究结果从分子层面揭示了MCM-41表面Cu 2的热解化学机制,给出了具有明确组成和微观结构的CuO、Cu2O和Cu(0)/MCM-41材料的新制备途径, 并阐明了含铜介孔分子筛催化苯酚羟基化反应中Cu活性中心的作用本质以及铁核性相关的苯酚羟化机制;基于分子构筑的、结构和组成明确的双核二铁 簇,发现并提出了铁催化HC-NO选择性催化还原反应新途径;借助X射线精细结构分析光谱技术鉴别了含铁、钛沸石分子筛光催化剂和N掺杂二氧化钛可见光催化剂的光活性物种及局域结构,提出了“表面激发光催化作用模型”新概念。  相似文献   

12.
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13.
An aerosol‐spray‐assisted approach (ASAA) is proposed and confirmed as a precisely controllable and continuous method to fabricate amorphous mixed metal oxides for electrochemical water splitting. The proportion of metal elements can be accurately controlled to within (5±5) %. The products can be sustainably obtained, which is highly suitable for industrial applications. ASAA was used to show that Fe6Ni10Ox is the best catalyst among the investigated Fe‐Ni‐Ox series with an overpotential of as low as 0.286 V (10 mA cm?2) and a Tafel slope of 48 mV/decade for the electrochemical oxygen evolution reaction. Therefore, this work contributes a versatile, continuous, and reliable way to produce and optimize amorphous metal oxide catalysts.  相似文献   

14.
    
Using cobalt sulfate and nickel sulfate as main electrolytes, ammonium sulfate as an auxiliary electrolyte and buffer agent, and cheap iron pieces (FP) as the substrates, nickel and/or cobalt phosphide/metal heterogeneous catalytic electrode (M2P/M/FP) was grown on the substrate in situ by electrodeposition followed by low temperature phosphating. M2P/M/FP functioned as a good bifunctional electrode for HER and OER in 1 mol/L KOH, where Co2P/Co/FP needed an overpotential of 52 and 288 mV, and (NC)2P/(NC)/FP required that of 75 mV and 293 mV to afford 10 mA/cm2. Previous similar studies often ignored the role of metal and only considered the water electrolysis catalysis of metal phosphide. In this research, it was clarified that for water electrolysis, the essence of high catalysis activity of the M2P/M/FP electrode was the electronic interaction between metal and metal phosphide.  相似文献   

15.
    
An environmentally benign approach towards synthesis of a non-noble metal and/or metal oxide doped incorporated in nitrogen containing carbon matrix (Cu−Fe2O3/NC) is premeditated in this study. In-situ incorporation of Cu, Fe2O3 as well as nitrogen into the carbon matrix using a single gel precursor simplified the synthetic route and divulged bifunctional activity assisting chlorine evolution at anode and oxygen reduction reaction at cathodic counterpart during HCl electrolysis. As a result of synergy between Cu and Fe2O3 in N- doped carbon matrix, enhanced activity and stability is stimulated. Catalyst optimization was executed by varying the weight percentage of metal reactants added during precursor synthesis (2, 5 and 10 wt. %), which rendered different composition of Cu, Fe2O3 and N in the composite with flake-like morphology at same thermal treatment conditions. Electrochemical studies were performed in 0.4 M HCl analogous to industrial waste HCl, to investigate the bifunctional activity of catalyst where Cu−Fe2O3 (5 %)/NC came out to be the most active and exhibited long term stability for 24 hours at onset potential of chlorine evolution. It offered a higher current density of 92.1 mA cm−2 at 1.7 V vs. RHE during chlorine evolution and comparable activity to that of benchmark noble metal based catalyst along with more positive onset potential and high diffusion limiting current density of 0.78 V vs. RHE and 6 mA cm−2 during oxygen reduction respectively.  相似文献   

16.
    
Water electrolysis has been considered a promising avenue for ultrapure hydrogen production. However, the energy efficiency of conventional water electrolysis technologies is severely hampered by the kinetic limitations of the anodic oxygen evolution reaction (OER). Over the past decade, an innovative hybrid water electrolysis strategy of replacing the OER with more facile oxidation reactions and coupling with the cathodic hydrogen evolution reaction (HER) has been developed and demonstrated its utility of addressing the critical challenges in conventional water electrolysis. In this Review, we summarize the recent progress concerning electrochemical hydrogen production from water through hybrid water electrolysis technology, with special emphasis on the selection of electrocatalysts and alternative anodic oxidation reactions as well as the related mechanisms involving in electrochemical reactions. Finally, the current challenges and some perspectives are also discussed for the future development of hybrid water electrolysis technology.  相似文献   

17.
An iridium oxide nanoparticle electrocatalyst under oxygen evolution reaction conditions was probed in situ by ambient‐pressure X‐ray photoelectron spectroscopy. Under OER conditions, iridium undergoes a change in oxidation state from IrIV to IrV that takes place predominantly at the surface of the catalyst. The chemical change in iridium is coupled to a decrease in surface hydroxide, providing experimental evidence which strongly suggests that the oxygen evolution reaction on iridium oxide occurs through an OOH‐mediated deprotonation mechanism.  相似文献   

18.
    
Supported atomically distributed metal species are extensively applied as catalysts to exceed the properties of their bulk analogues. Their electronic structures can be easily tuned by neighboring support atoms or ligands to control their activities for different reactions. The high accessibility and therefore almost 100 % reactivity of the highly distributed active sites provide new opportunities for electrochemical applications that were previously only suitable for noble metals. Although a lot of work has been done in this area, the demand for large-scale applications and, therefore, also large-scale production is still far from sufficient. In this Review, we selected some recent publications to show the current state of applications of dispersed single-atom catalysts in the oxygen reduction/evolution reaction and hydrogen evolution reaction, with a focus on their mechanisms in reactions, the underlying challenges, and synthesis methods. A further discussion on how the electrocatalytic performance of the supported single atom catalysts can be tailored to meet the requirements of large-scale applications is also proposed.  相似文献   

19.
    
Nickel-based oxide catalysts are widely used for the oxygen evolution reaction (OER) in alkaline water electrolysis because of their low cost and high activity. In particular, the LiNiO2 catalyst shows high activity. Therefore, to elucidate the fundamental relationship between the local structure, catalyst activity, and stability of LiNiO2, we investigated the cation mixing effect by mixing sites of lithium and nickel ions in the LiNiO2-based catalysts. Lower degrees of cation mixing lead to higher intrinsic OER activity but lower long-term stability. The X-ray absorption spectra (XAS) displayed a strong hybridization state of the Ni 3d and O 2p orbitals, which is the origin of the different catalytic activity behaviors. Meanwhile, operando XAS studies combined with potentiostatic stability tests and inductively coupled plasma optical emission spectrometry (ICP-OES) demonstrated the Li ion loss during the OER process. Thus, the instability of LiNiO2 originates from de-intercalation of Li ions and this irreversible structure change deteriorates the performance. Hindering the lithium diffusion path by cation mixing is a useful strategy for maintaining performance. This strategy could provide a novel design principle for compatible high activity and long-lasting catalysts by reasonable structure mediation.  相似文献   

20.
    
Chemical and structural changes preceding electrocatalysis obfuscate the nature of the active state of electrocatalysts for the oxygen evolution reaction (OER), which calls for model systems to gain systematic insight. We investigated the effect of bulk oxidation on the overpotential of ink-casted LiMn2O4 electrodes by a rotating ring-disk electrode (RRDE) setup and X-ray absorption spectroscopy (XAS) at the K shell core level of manganese ions (Mn−K edge). The cyclic voltammogram of the RRDE disk shows pronounced redox peaks in lithium hydroxide electrolytes with pH between 12 and 13.5, which we assign to bulk manganese redox based on XAS. The onset of the OER is pH-dependent on the scale of the reversible hydrogen electrode (RHE) with a Nernst slope of −40(4) mV/pH at −5 μA monitored at the RRDE ring. To connect this trend to catalyst changes, we develop a simple model for delithiation of LiMn2O4 in LiOH electrolytes, which gives the same Nernst slope of delithiation as our experimental data, i. e., 116(25) mV/pH. From this data, we construct an ERHE-pH diagram that illustrates robustness of LiMn2O4 against oxidation above pH 13.5 as also verified by XAS. We conclude that manganese oxidation is the origin of the increase of the OER overpotential at pH lower than 14 and also of the pH dependence on the RHE scale. Our work highlights that vulnerability to transition metal redox may lead to increased overpotentials, which is important for the design of stable electrocatalysts.  相似文献   

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