Platinum nanoparticles supported on nitrobenzene-functionalised graphene nanosheets as electrocatalysts for oxygen reduction reaction in alkaline media

A systematic study on the electrocatalytic properties of Pt nanoparticles supported on nitrobenzene-modified graphene (Pt-NB/G) as catalyst for oxygen reduction reaction (ORR) in alkaline solution was performed. Graphene nanosheets were spontaneously grafted with nitrophenyl groups using 4-nitrobenzenediazonium salt. The electrocatalytic activity towards the ORR and stability of the prepared catalysts in 0.1 M KOH solution have been studied and compared with that of the commercial Pt/C catalyst. The results obtained show that the NB-modified graphene nanosheets can be good Pt catalyst support with high stability and excellent electrocatalytic properties. The specific activity of Pt-NB/G for O₂ reduction was 0.184 mA cm⁻², which is very close to that obtained for commercial 20 wt% Pt/C catalyst (0.214 mA cm⁻²) at 0.9 V vs. RHE. The Pt-NB/G hybrid material promotes a four-electron reduction of oxygen and can be used as a promising cathode catalyst in alkaline fuel cells.     

Graphene oxide decorated bimetal (MnNi) oxide nanoflakes used as an electrocatalyst for enhanced oxygen evolution reaction in alkaline media

Precious non-noble metals have been constantly attracting research attention in order to realize an inexpensive, extra active and more stable electrocatalysts in terms of various oxidation states and structures for their applications in oxidation (splitting) of water. In the present work graphene oxide incorporated, MnO₂-NiO composite metal oxide nanoflakes were synthesized on the stainless steel substrate using efficient electrodeposition route in alkaline media and drop casting method with further annealing treatment at 400 °C for 4 h. Initially MnO₂-NiO nanoflakes were deposited using different cyclic sweep rates, later graphene oxide suspension was drop casted on the MnO₂-NiO nanoflakes and subsequently subjected to annealing at 200 °C for 2 h. The prepared electrode material is denoted as GO/MnO₂-NiO/SS and used as an electrocatalyst for oxygen evolution. Field emission scanning electron microscopy, transmission electron microscopy, Energy dispersive electron spectroscopy and X-ray diffraction spectroscopy were used to study the crystalline nature and morphologies of the deposited films. The electrochemical properties of the electrode material were investigated using cyclic voltammetry and linear sweep voltammetry. The electrode exhibits low overpotential and small Tafel slope of 379 mV and 47.84 mVdec⁻¹ at the current density of 10 mA cm⁻² in alkaline (KOH) medium. In addition, the electrode shows a long time stability of 28800 s. Hence, the present study suggests that the GO incorporated Mn-Ni bimetal oxide modified electrode is suitable electrode material for oxygen evolution reaction (OER), owing to its facile preparation, inexpensive, easy handling and high active nature.     

Silver supported on Co3O4 modified carbon as electrocatalyst for oxygen reduction reaction in alkaline media

The electroreduction of oxygen was firstly studied on Ag/Co₃O₄–C in alkaline media prepared by depositing Ag on Co₃O₄ modified carbon (Co₃O₄–C). The Ag/Co₃O₄–C composite not only displayed relatively large electrochemical active surface area (ESA), high catalytic activity towards oxygen reduction reaction (ORR), but also exhibited good methanol tolerance and stability in alkaline media. Ag/Co₃O₄–C could be a valuable catalyst for ORR and be applied to alkaline fuel cells and metal–air batteries.     

碱性介质中碳纳米管FeNi复合物上电催化析氧反应(英文)

Non-noble metals such as Fe and Ni have comparable electrocatalytic activity and stability to that of Ir and Ru in an oxygen evolution reaction (OER). In this study, we synthesized carbon nanofibers with embedded FeNi composites (FeNi-CNFs) as OER electrocatalysts by a facile route comprising electrospinning and the pyrolysis of a mixture of metal precursors and a polymer solution. FeNi-CNFs demonstrated catalytic activity and stability that were better than that of 20 wt% Ir on Vulcan carbon black in oxidizing water to produce oxygen in an alkaline media. Physicochemical and electrochemical characterization revealed that Fe and Ni had synergistic roles that enhanced OER activity by the uniform formation and widening of pores in the carbon structure, while the CNF matrix also contributed to the increased stability of the catalyst.     

Development of versatile CdMoO4/g-C3N4 nanocomposite for enhanced photoelectrochemical oxygen evolution reaction and photocatalytic dye degradation applications

Fabrication of an efficient, stable, and versatile photocatalysts for the energy and environment remediation applications is an urgent task for the current researchers. In this work, we have successfully synthesized a versatile hybrid photocatalysts, i.e.; CdMoO₄/g-C₃N₄ (CMO/CN) by a facile and simple one-pot in-situ hydrothermal method. Here CdMoO₄ (CMO) microspheres were deposited on the g-C₃N₄ (CN) sheets. Fabricated CN, CMO, and CMO/CN composite photocatalysts were analyzed with various characterization techniques like UV–visible diffuse reflectance spectra (UV–Vis DRS), photoluminescence spectroscopy (PL), time-resolved fluorescence lifetime (TRFL), electrochemical impedance spectroscopy (EIS), powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FT-IR), Scanning electron microscopy–energy-dispersive X-ray analysis (SEM-EDX), transmission electron microscope (TEM), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), and Brunauer–Emmett–Teller (BET). The results reveal that the formation of a strong heterojunction between two semiconductors leads to the formation of active photocatalyst. Furthermore, as-synthesized materials were tested for the photoelectrocatalytic (PEC) oxygen evolution reactions (OERs) in acidic medium, and photocatalytic (PC) degradation of methylene blue (MB) under light irradiation. Among all tested samples, CMO/CN-10 has shown the highest current density 52.74 mA cm^?2 at 1.95 V with lowest over potential of 0.70 mV on glassy carbon electrode for OER in acidic medium under the light irradiation. The PC degradation rate constant of CMO/CN-10 composite in MB solution is k = 2.0 × 10^?2 min^?1, whereas for the pure CMO and CN degradation rate constant is k = 5.7 × 10^?3 min^?1 and k = 1.2 × 10^?2 min^?1, respectively. This enhancement in PEC and PC properties is due to the fast migration of photo-induced electrons in the case of CMO/CN-10 nanocomposite. Trapping experiment results reveal the major reactive species for PC degradation of MB is ?OH (hydroxyl radicals) and h⁺ (holes), respectively, and suitable PC reaction mechanism also proposed for CMO/CN-10 composites. Based on the above remarkable results, it would be a potential nanocomposite for the PEC oxygen evolution and PC degradation of MB under light illumination.     

S-O bond chemically constrained NiS2/rGO nanocomposite with enhanced Na-ion storage capacity

NiS₂ has become a research hotspot of anode materials for Na-ion batteries due to its high theoretical specific capacity. However, the volume effect, the dissolution of polysulfide intermediates and the low conductivity during the charge/discharge process lead to the low specific capacity and poor cycling stability. NiS₂/rGO nanocomposite was prepared by a facile two-step process: GO was prepared by modified Hummers method, and then NiS₂/rGO nanocomposite was synthesized by l-cys assisted hydrothermal method. NiS₂/rGO nanocomposite shows excellent cycle performance and rate performance, which could be attributed to the mesoporous structure on the graphene skeleton with high conductivity. Besides, the chemical constraint of a unique SO bond on NiS₂ could inhibit the dissolution of intermediates and the loss of irreversible capacity.     

铁取代的钴-磷多酸作为酸性介质中性能增强的析氧催化剂

纯无机的非贵金属基双/三金属氢氧(氧)化物因其优异的析氧反应(OER)性能而得到广泛关注及研究.但这些催化剂的原子精度的结构表征较为困难,阻碍了人们对其构效关系的认识,从而影响了进一步对催化性能的精确调控.金属有机框架(MOFs)材料因具有明确的结构及化学组成可调等优点,可以作为一类结构确定的OER电催化剂,但是MOFs为有机配体和金属离子配位形成的框架材料,与金属氢氧(氧)化物结构类型不同.多酸是由高氧化态的Mo^Ⅵ/Ⅴ,W^Ⅵ/Ⅴ,V^Ⅴ/Ⅳ,Nb^Ⅴ和Ta^Ⅴ等组成的金属-氧簇.多酸尺寸介于分子与块体氧化物之间,可以被看作一种具有明确结构的分子氧化物.因此,多酸可用作模型体系从分子水平上探究金属氢氧(氧)化物催化剂的反应机理.此外,多酸已被证明是很有前景的非贵金属水氧化催化剂.对于OER,酸性介质更具优势,因为它与碱性介质相比具有高能效、低欧姆损耗、易于产物分离等优点.但是,非贵金属OER电催化剂在酸性介质中很难稳定且性能通常不如贵金属催化剂.制备酸性介质中高效和稳定的非贵金属OER电催化剂仍然是一大挑战.在本论文中,我们首先采用'原位同构取代'策略,将结构明确的[{Co4(OH)3PO4}4(SiW9O34)4]^32-(1)钴-磷多酸阴离子中的Co原子替换成Fe原子,合成了不同Fe含量的[{Fe2Co2(OH)3PO4}4(SiW9O34)4]^24-(2)和[{FeCo3(OH)3PO4}4(SiW9O34)4]^28-(3).然后通过离子交换,向1,2和3中引入Ba^2+,成功合成了不溶于水的多酸阴离子结构维持的多相催化剂Ba[1],Ba[2]和Ba[3].性能最好的Ba[3]在0.5 mol L^-1 H2SO4溶液中达到10 mA cm^-2的电流密度仅需要385 mV过电位(无iR校正),比相同条件下无Fe取代的Ba[1]和商业IrO2催化剂的过电位分别低66 mV和8 mV.经过2000圈的循环伏安测试和24 h的长时间电解测试,Ba[1],Ba[2]和Ba[3]均表现出较高的稳定性.另外,采用红外光谱(FT-IR)以及电感耦合等离子体质谱(ICP-MS)等多种表征测试手段进一步确认了它们的稳定性.本文采用的'原位同构取代'策略为合成更高效的结构明确的多金属催化剂提供了新思路,同时也为进一步从分子水平上探索相关催化机理提供了难得的模型.     

The nature of synergistic effects in transition metal oxides/in-situ intermediate-hydroxides for enhanced oxygen evolution reaction

Oxygen evolution reaction is highly important for hydrogen production via water splitting but requires ～0.22 V onset overpotential, resulting in at least 15% extra energy consumption even utilized with the benchmark hetero-doped transition-metal hydroxide catalysts. The lack of fundamental understanding on catalyst behaviour and on synergistic mechanisms limit the breakthrough for material design. Here, we systematically summarise a variety of investigations and arguments on the mechanism from the microscale (optimal octahedral intermediate with six M?O coordination) to atomic scale (the active site behaviour). The electron–orbital scale (e_g) is further described for the intrinsic OER activity. The synergistic effect may also lead to a short-cut pathway of lattice-oxygen-mediated mechanism to achieve a smaller overpotential. This review provides a theoretical reference for the design of advanced catalysts.     

Direct synthesis of platinum group metal-free Fe-N-C catalyst for oxygen reduction reaction in alkaline media

A direct, template-free synthesis of a novel, active Fe-N-C oxygen reduction reaction catalyst by the pyrolysis of ethylenediaminetetraacetic acid ferric sodium salt is demonstrated. Detailed physical characterization of the catalyst is carried out by surface area measurement, X-ray diffraction, Raman spectroscopy and X-ray photoelectron spectroscopy in addition to electrochemical analysis using Rotating Ring Disk Electrode measurements. We study the effects of synthesis temperature on graphitization, surface area and their concurrent effects on the catalytic performance of the final products.     

Electrocatalytic oxygen evolution reaction of hierarchical micro/nanostructured mixed transition cobalt oxide in alkaline medium

Journal of Solid State Electrochemistry - In this work, different cobalt-based mixed transition metal oxides (MTMOs) were fabricated by hydrothermal process followed by calcination. Doping Co3O4...     

Effect of graphene surface functionalization on the oxygen reduction reaction in alkaline media

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无模板合成微米管状Co3O4基复合材料高效催化电解水析氧反应

电解水制氢因具有清洁高效的优点而被认为是大规模生产氢能最有希望的技术之一.然而,电解水半反应之一的析氧反应(OER)需经历复杂且动力学缓慢的4电子转移过程.加之热力学上的阻碍,OER实际需要的电位远大于1.23 V的理论值,导致其能耗高,限制了电解水的效率和商业化应用.因此,亟待开发高效的OER电催化剂.管状结构具有较高的比表面积、充分暴露的活性位点和丰富的短路径扩散通道,是一种理想的电催化结构.同时,Co3O4基材料因其制备容易、成本低和OER电催化学活性较高等特点,成为近年来电催化材料的研究热点.此外,非金属元素P的掺杂条件温和,并且可以有效改变过渡金属电子结构.因此,本文通过合理设计管状的Co3O4基电催化剂并进行P掺杂,尝试将形貌调控和元素改性的优势发挥到最大.为了解析影响生成管状结构的因素,本文通过控制变量法系统地研究了管状Ni/Co3O4的制备条件,包括阳离子种类和含量、添加剂种类和含量、阴离子种类等对催化剂形貌和性能的影响.表征结果表明,初始的乙酸钴镍氢氧化物棱柱对反应环境较为敏感,从而成为直接影响最终微米管状结构的关键因素.此外,对Ni/Co3O4微米管进行适量的P掺杂,能提高材料的电子传输性能和优化材料的电子结构;而且P的掺杂直接提高了样品中的M3+/M2+比例(M代表Co和Ni),而M3+是M基电催化材料的活性位点,这进一步增加了OER的活性位点进而提高其催化活性.总之,通过结构和成分的优化,得到了OER催化性能显著提高的微米管状P-Ni/Co3O4,其性能甚至超过了商业化RuO2电催化剂.     

Bimetallic carbide nanocomposite enhanced Pt catalyst with high activity and stability for the oxygen reduction reaction

Nanocomposites consisting of the bimetallic carbide Co(6)Mo(6)C(2) supported on graphitic carbon ((g)C) were synthesized in situ by an anion-exchange method for the first time. The Co(6)Mo(6)C(2)/(g)C nanocomposites were not only chemically stable but also electrochemically stable. The catalyst prepared by loading Pt nanoparticles onto Co(6)Mo(6)C(2)/(g)C was evaluated for the oxygen reduction reaction in acidic solution and showed superior activity and stability in comparison with commercial Pt/C. The higher mass activity of the Pt-Co(6)Mo(6)C(2)/(g)C catalyst indicated that less Pt would be required for the same performance, which in turn would reduce the cost of the fuel cell electrocatalyst. The method reported here will promote broader interest in the further development of other nanostructured materials for real-world applications.     

Investigations of the catalytic properties of manganese oxides for the oxygen reduction reaction in alkaline media

The oxygen reduction reaction (ORR) was studied in KOH electrolyte on different manganese oxides, dispersed on a carbon powder (MnO_x/C). The oxides were prepared by different methods, for producing MnO, Mn₃O₄ and MnO₂ as major phases dispersed on the Vulcan XC-72 carbon. The oxides were characterized by XRD (X-ray diffraction) and in situ XANES (X-ray absorption near edge structure). The electrochemical measurements were made using cyclic voltammetry and steady state polarization curves carried out in an ultra-thin layer rotating ring/disk electrode. The results have shown lower activity for the ORR on the MnO_x/C species compared to that on Pt/C, but higher activity compared to that of pure Vulcan carbon. Formation of involving 2e⁻ per O₂ molecule is the main path of the ORR in the studied MnO_x/C catalysts but, at low overpotentials and rotation rates the number of electrons is raised to 4 due to the occurrence of a disproportionation reaction. Large differences of electrocatalytic activity were seen for the different oxide species, and these were related to the presence of a Mn(IV) phase and the occurrence of a mediation processes involving the reduction of Mn(IV) to Mn(III), followed by the electron transfer of Mn(III) to oxygen.     

Iron phthalocyanine coated on single-walled carbon nanotubes composite for the oxygen reduction reaction in alkaline media

Iron (II) phthalocyanine coated on single-walled carbon nanotubes was synthesized as a non-noble electrocatalyst for the oxygen reduction reaction (ORR). The composite exhibited higher activity than the commercial Pt/C catalyst, and excellent anti-crossover effect for methanol oxidation in the ORR.     

Electrocatalysis of oxygen reduction on multi-walled carbon nanotube supported copper and manganese phthalocyanines in alkaline media

Manganese phthalocyanine (MnPc) and copper phthalocyanine (CuPc)-modified electrodes were prepared using multi-walled carbon nanotubes (MWCNTs) as a support material. The catalyst materials were heat treated at four different temperatures to investigate the effect of pyrolysis on the oxygen reduction reaction (ORR) activity of these electrocatalysts. The MWCNT to metal phthalocyanine ratio was varied. Scanning electron microscopy (SEM) was employed to visualise the surface morphology of the electrodes and the x-ray photoelectron spectroscopic (XPS) study was carried out to analyse the surface composition of the most active catalyst materials. The ORR was studied in 0.1 M KOH solution employing the rotating disk electrode (RDE) method. Glassy carbon (GC) electrodes were modified with carbon nanotube-supported metal phthalocyanine catalysts using Tokuyama AS-4 ionomer. The RDE results revealed that the highest electrocatalytic activity for ORR was achieved upon heat treatment at 800 °C. CuPc-derived catalyst demonstrated lower catalytic activity as compared to the MnPc-derived counterpart, which is in good agreement with previous literature, whereas the activity of MnPc-based catalyst was higher than that reported earlier.     

Novel lanthanum sulfide–decorated zirconia nanohybrid for enhanced electrochemical oxygen evolution reaction

Journal of Solid State Electrochemistry - Metal sulfide and oxides have drawn interest as economical substitutes to noble metal catalysts due to their ability for oxygen evolution reaction (OER)...     

Moderate heat treatment of CoFe Prussian blue analogues for enhanced oxygen evolution reaction performance

Prussian blue analogues(PBAs) with inherent ordered structures and abundant metal ion sites are widely explored as precursors for various electrochemical applications,including oxygen evolution reaction(OER).Using a range of characterization techniques including Fourier-transform infrared spectroscopy(FT-IR),X-ray photoelectron spectroscopy(XPS),X-ray diffraction(XRD) and energy dispersive spectroscopy(EDS),this work discloses the process of replacement of K⁺ by NH₄⁺     

Highly exposed NiFeOx nanoclusters supported on boron doped carbon nanotubes for electrocatalytic oxygen evolution reaction

The development of efficient and cost-effective electrocatalysts for oxygen evolution reaction (OER) is crucial for the overall water splitting. Herein, we prepared a highly exposed NiFeO_x ultra-small nanoclusters supported on boron-doped carbon nonotubes catalyst, which achieves a 10 mA/cm² anodic current density at a low overpotential of 213 mV and the Tafel slope of 52 mV/dec in 1.0 mol/L KOH, superior to the pristine NiFeO_x-CNTs and other state-of-the-art OER catalysts in alkaline media. A combination study (XPS, sXAS and XAFS) verifies that the local atomic structure of Ni and Fe atoms in the nanoclusters are similar to NiO and Fe₂O₃, respectively, and the B atoms which are doped into the crystal lattice of CNTs leads to the optimization of Ni 3d e_g orbitals. Furthermore, in-situ X-ray absorption spectroscopies reveal that the high valence state of Ni atoms are served as the real active sites. This work highlights that the precise control of highly exposed multicomponent nanocluster catalysts paves a new way for designing highly efficient catalysts at the atomic scale.     

Progress on the mechanisms of Ru-based electrocatalysts for the oxygen evolution reaction in acidic media

Water electrolysis using proton-exchange membranes is one of the most promising technologies for carbon-neutral and sustainable energy production. Generally, the overall efficiency of water splitting is limited by the oxygen evolution reaction(OER). Nevertheless, a trade-off between activity and stability exists for most electrocatalytic materials in strong acids and oxidizing media, and the development of efficient and stable catalytic materials has been an important focus of research. In this ...