Dual-doped graphene/perovskite bifunctional catalysts and the oxygen reduction reaction

We report the first investigation of dual-doped graphene/perovskite mixtures as catalysts for oxygen reduction. Pairwise combinations of boron, nitrogen, phosphorus and sulfur precursors were co-reduced with graphene oxide and mixed with La_0.8Sr_0.2MnO₃ (LSM) to produce SN-Gr/LSM, PN-Gr/LSM and BN-Gr/LSM catalysts. In addition, the dual-doped graphenes, graphene, LSM, and commercial Pt/C were used as controls. The addition of LSM to the dual-doped graphenes significantly improved their catalytic performance, with optimised composition ratios enabling PN-Gr/LSM to achieve 85% of the current density of commercial Pt/C at − 0.6 V (vs. Ag/AgCl) at the same loading. The effective number of electrons increased to ca. 3.8, and kinetic analysis confirms the direct 4 electron pathway is favoured over the stepwise (2e + 2e) route: the rate of peroxide production was also found to be lowered by the addition of LSM to less than 10%.     

Constructing bifunctional Co/MoC@N-C catalyst via an in-situ encapsulation strategy for efficient oxygen electrocatalysis

The large-scale application of Zn-air battery requires the development of efficient,low-cost,and stable bifunctional electrocatalysts for the oxygen evolution r...     

Biomass-derived bifunctional electrocatalysts for oxygen reduction and evolution reaction: A review

Oxygen electrode catalysts are important as inter-conversion of O₂ and H₂O is crucial for energy technologies.However,the sluggish kinetics of oxygen reduction and evolution reactions(ORR and OER)are a hindrance to their scalable production,whereas scarce and costly Pt and Ir/Ru-based catalysts with the highest electrocatalytic activity are commercially unviable.Since good ORR catalysts are not always efficient for OER and vice versa,so bifunctional catalysts on which OER and ORR occurs on the same electrode are very desirable.Alternative catalysts based on heteroatom-doped carbon nanomaterials,though showed good electrocatalytic activity yet their high cost and complex synthesis is not viable for scalable production.To overcome these drawbacks,biomass-derived heteroatom-doped porous carbons have recently emerged as low-cost,earth-abundant,renewable and sustainable environment-friendly materials for bifunctional oxygen catalysts.The tunable morphology,mesoporous structure and high concentration of catalytic active sites of these materials due to heteroatom(N)-doping could further enhance their ORR and OER activity,along with tolerance to methanol crossover and good durability.Thus,biomassderived heteroatom-doped porous carbons with large surface area,rich edge defects,numerous micropores and thin 2 D nanoarchitecture could be suitable as efficient bifunctional oxygen catalysts.In the present article,synthesis,N-doping,ORR/OER mechanism and electrocatalytic performance of biomassderived bifunctional catalysts has been discussed.The selected biomass(chitin,eggs,euonymus japonicas,tobacco,lysine and plant residue)except wood,act as both C and N precursor,resulting in N selfdoping of porous carbons that avoids the use of toxic chemicals,thus making the synthesis a facile and environment-friendly green process.The synthetic strategy could be further optimized to develop future biomass-based N self-doped porous carbons as metal-free high performance bifunctional oxygen catalysts for commercial energy applications.Recent advances and the importance of biomass-based bifunctional oxygen catalysts in metal-air batteries and fuel cells has been highlighted.The material design,perspectives and future directions in this field are also provided.     

Characterisation of bifunctional electrocatalysts for oxygen reduction and evolution by means of SECM

Journal of Solid State Electrochemistry - Electrocatalysts that can reversibly reduce oxygen and oxidise water are of prime importance for the advancement of new emerging electrochemical energy...     

A defective iron-based perovskite cathode for high-performance IT-SOFCs: Tailoring the oxygen vacancies using Nb/Ta co-doping

The sluggish kinetics of the electrochemical oxygen reduction reaction(ORR) in intermediatetemperature solid oxide fuel cells(IT-SOFCs) greatly limits the overall cell performance. In this study,an efficient and durable cathode material for IT-SOFCs is designed based on density functional theory(DFT) calculations by co-doping with Nb and Ta the B-site of the SrFeO_3-δ perovskite oxide. The DFT calculations suggest that Nb/Ta co-doping can regulate the energy band of the parent SrFeO     

Role of rhodium doping into lanthanum cobalt oxide (LaCoO3) perovskite and the induced bifunctional activity of oxygen evolution and reduction reactions in alkaline medium

Transition metal oxides, especially perovskites, have been considered effective electrocatalysts for the oxygen evolution (OER) and oxygen reduction (ORR) reactions in an alkaline solution. Here, a series of lanthanum cobalt rhodium oxide perovskites with the chemical formula LaCo_1-xRh_xO₃ (LCRO, 0.1 ≤ x ≤ 0.70) were prepared through the approach of solid-phase synthesis and their bifunctional electrocatalytic activity was assessed for both the OER and ORR. The crystallinity, morphology, surface, and electrocatalytic features of the LCRO were significantly correlated with the rhodium content. The LaCo_0.7Rh_0.3O₃ electrocatalysts with x = 0.3 showed enhanced electrocatalytic bifunctional performance with a substantially lower OER/ORR onset potential of 1.38/0.73 V vs HRE, smaller Tafel slope (116/90 mV/dec), and low charge-transfer resistance, which is the most efficient catalyst among the other studied ratios and superior to the pristine lanthanum cobalt oxide benchmark electrocatalysts. The LaCo_0.7Rh_0.3O₃ electrode exhibit good bifunctional electrocatalytic behavior and long-term durability with an OER and ORR onset potential gap (ΔE = E_OER ? E_ORR) of only 0.65 V, which could be credited to the enriched oxygen vacancies, lattice expansion and the improved electrical conductivity upon the doping of larger size of Rh ions. The LaCo_1-xRh_xO₃ catalysts are obtained from abundant materials that have the potential of highly-active bifunctional OER and ORR electrocatalysts.     

Carbon-based bifunctional electrocatalysts for oxygen reduction and oxygen evolution reactions:Optimization strategies and mechanistic analysis

Electrocatalysts are one of the essential components for the devices of high-efficiency green energy storage and conversion, such as metal-air cells, fuel cells, and water electrolysis systems. While catalysts made from noble metals possess high catalytic performance in both oxygen reduction reaction(ORR)and oxygen evolution reaction(OER), their scarcity and expensiveness significantly limit large-scale applications. In this regard, metal-free/non-noble metal carbon-based catalysts have become c...     

Rapid and durable oxygen reduction reaction enabled by a perovskite oxide with self-cleaning surface

The growth of electrochemically inert segregation layers on the surface of solid oxide fuel cell cathodes has become a bottleneck restricting the development of perovskite-structured oxygen reduction catalysts.Here,we report a new discovery in which enriched Ba and Fe ions on the near-surface of Nd_1/2Ba_1/2Co_1/3Fe_1/3Mn_1/3O_3-δ spontaneously agglomerate into dispersed Ba₅Fe₂O₈ nanoparticles and mainta...     

A promising amendment for water splitters: Boosted oxygen evolution at a platinum,titanium oxide and manganese oxide hybrid catalyst

A hybrid catalyst composed of a platinum thin layer and modified with manganese oxide (MnOx) is recommended for the oxygen evolution reaction (OER). The Pt layer of the catalyst was physically sputtered onto a TiOx-coated Si substrate (this TiOx layer was sputtered inbetween the Si substrate and Pt layer to improve their adhesion and prevent their mutual diffusion). On top of the Pt layer, another thin TiOx layer (∼60 nm) was spun before the electrochemical deposition of MnOx. The investigation focused primarily to evaluate the impact of the catalyst’s annealing in oxygen atmosphere on its catalytic activity toward OER. Interestingly, before the modification with MnOx, a large catalytic enhancement both in activity (∼228 mV negative shift at 20 mA cm⁻² if compared to conventional bare Pt catalysts) and stability was achieved at the catalyst annealed at 600 °C toward OER in 0.5 M KOH. Surprisingly, the addition of MnOx to the catalyst synergized a boosted activity amplifying the negative shift to 470 mV at the same current density. Bunch of materials and electrochemical techniques were combined to reveal important remarks about the catalyst’s morphology, structure, composition and intrinsic activity which was attributed to electronic rather than geometric factors.     

The gamma-ray induced chemisorption of oxygen on perovskite type catalysts: Determination by reduction with hydrazine sulphate/hydroxylamine hydrochloride

Chemisorbed oxygen can be determined quantitatively by the measurement of gaseous N₂/N₂O liberated by treatment with hydrazine sulphate/hydroxylamine hydrochloride. The amount of chemisorbed oxygen depends on the degree of dispersion during irradiation and also the -dose. The chemisorption is enhanced in the presence of moisture. The partial reduction of the transition metal ion favours the formation of chemisorbed oxygen.     

The mechanism of selective NOx reduction by hydrocarbons in excess oxygen on oxide catalysts: V. Adsorption properties of a commercial Ni-Cr oxide catalyst

According to X-ray diffraction analysis data, the test catalyst was a Ni-Cr spinel with an impurity of NiO. With the use of in situ IR spectroscopy, it was found that nitrite, nitrate, and acetate surface complexes occurred under the reaction conditions of the selective catalytic reduction of nitrogen oxides by propane in the presence of oxygen on the nickel-chromium catalyst. As the temperature was increased, the nitrite complexes were converted into nitrate species. The molar absorption coefficient of surface nitrate complexes was determined. According to IR-spectroscopic and TPD data, the nitrate complexes were bound relatively weakly to the surface. The temperature region of their existence was 50–200°C. The temperature region of existence of the surface acetate complexes was 200–400°C. The individual adsorption of oxygen was not observed; however, oxygen-containing surface sites (Cr⁵⁺=O) participated in the formation of the surface complexes of reactants.     

Mechanism of alkene isomerization by bifunctional ruthenium catalyst: A theoretical study

The molecular mechanism of the isomerization of 1-pentene to form (E)-2-pentene catalyzed by the bifunctional ruthenium catalyst has been investigated using density functional theory calculations. The reaction is likely to proceed through the following steps: 1) the β-H elimination to generate the ruthenium hydride intermediate; 2) the reductive elimination of the hydride intermediate to generate the nitrogen-protonated allyl intermediate; 3) the transportation of the hydrogen by the dihedral rotation with Ru–P bond acting as axis; 4) the oxidative addition to afford another hydride complex; 5) the reductive elimination of the hydride intermediate to form the C₂-C₃ π-coordinated agostic intermediate; 6) the coordination of the nitrogen to the ruthenium center to give the final product. The rate-determining step is the oxidative addition step (the process of the hydrogen moves to ruthenium center from the nitrogen atom) with the free energy of 31.2 kcal/mol in the acetone solvent. And the N-heterocyclic ligand in the catalyst mainly functions in the two aspects: affords an important internal-basic center (nitrogen atom) and works as a transporter of hydrogen. Our results would be helpful for experimentalists to design more effective bifunctional catalysts for isomerization of a variety of heterofunctionalized alkene derivatives.     

Study on the catalytic reduction mechanism of SO2 by CO over doped copper perovskite catalyst in presence of oxygen

Summary The reduction mechanism of SO₂ by CO using LaCoO₃ and doped copper as catalysts was investigated. The activity, selectivity of sulfur and the COS amount under various reaction conditions were tested. The results showed that the Cu doped catalysts were better than the undoped catalyst and 10% copper-doping gave the optimum catalyst.     

SC-IrO2NR-carbon hybrid: A catalyst with high electrochemical stability for oxygen reduction

The enhanced electrochemical stability of the synthesized hybrid catalyst has been demonstrated by the introduction of the synergistic effect between carbon powder additive and the prepared catalyst.Single crystal IrO 2 nanorod (SC-IrO 2 NR) catalyst was prepared by a sol-gel method.The structure and performance of the catalyst sample were characterized by X-ray diffraction spectroscopy (XRD),scanning electron microscope (SEM),transmission electron microscope (TEM),rotating disk electrode (RDE) and cyclic voltammetry (CV) measurements.XRD patterns and TEM images indicate that the catalyst sample has a rutile IrO 2 single crystal nanorod structure.The onset potential for oxygen reduction reaction (ORR) of the SC-IrO 2 NR-carbon hybrid catalyst specimen is 0.75 V (vs.RHE) in RDE measurement.CV and RDE test results show that the SC-IrO 2 NR-carbon hybrid catalyst has a better electrochemical stability in comparison with the commercial Pt/C catalyst,with attenuation ratios of 17.67% and 44.60% for the SC-IrO 2 NR-carbon hybrid catalyst and the commercial Pt/C catalyst after 1500 cycles,respectively.Therefore,in terms of stability,the SC-IrO 2 NR-carbon hybrid catalyst has a promising potential in the application of the proton exchange membrane fuel cell.     

Confinement of sulfur-doped NiO nanoparticles into N-doped carbon nanotube/nanofiber-coupled hierarchical branched superstructures:Electronic modulation by anion doping boosts oxygen evolution electrocatalysis

The search for non-precious and efficient electrocatalysts towards the oxygen evolution reaction (OER) is of vital importance for the future advancement of mult...     

Dopant substitution and oxygen migration in the complex perovskite oxide Ba3CaNb2O9: A computational study

Atomistic simulation methods have been used to study the defect chemistry of the complex perovskite oxide Ba₃CaNb₂O₉. Calculations were carried out for the hexagonal (P-3m1) phase and the cubic (Fm-3m) phase. The hexagonal structure is predicted to be energetically more stable at room temperature. In both structures the most favourable dopant for Nb⁵⁺ is found to be Ca²⁺ rather than Mg²⁺, in contrast to the generally accepted rule that size similarities govern such processes. The diffusion of oxygen vacancies in the hexagonal and cubic phases occurs within different networks of corner-sharing NbO₆ and CaO₆ octahedra. Irrespective of the arrangement of octahedra, however, migration of oxygen vacancies around NbO₆ octahedra takes place with lower activation energies than around the CaO₆ octahedra.     

The influence of the type of N dopping on the performance of bifunctional N-doped ordered mesoporous carbon electrocatalysts in oxygen reduction and evolution reaction

To develop more ideal bifunctional heteroatom-doped carbon electrocatalysts toward the oxygen reduction reaction(ORR) and oxygen evolution reaction(OER) for regenerative fuel cells and rechargeable metal–air batteries, herein, tobacco-derived N-containing ordered mesoporous carbon(N-OMC) electrocatalysts with different N species distributions are designed. Results indicate that the as-prepared N-OMC with more pyrrolic and pyridinic Ns exhibits much higher activities for the ORR and OER than N-OMC with more graphitic N in both acidic and alkaline media, suggesting that the increase of pyrrolic and pyridinic Ns favors the improvement of ORR and OER activities of the N-containing carbon catalysts, and showing a great potential for the designing of more effective, lower-cost ORR and OER bifunctional electrocatalysts for future regenerative fuel cells and rechargeable metal–air batteries.     

商用氧化铟锡玻璃:室温高效还原氮气的催化剂电极

NH₃作为一种必需的活化氮源,在化肥、染料、爆炸物和药物等的制造中起到了关键作用;同时,它也是一种在交通运输领域具有吸引力的无碳能源载体.工业上生产氨气使用典型的哈伯-博世工艺,但是此工艺涉及大量的能源消耗和碳排放,给环境带来巨大的压力.电化学氮还原反应(NRR)能够在温和环境下实现环境友好、节能的氨合成,但此过程需要高效的电催化剂.高效的NRR催化剂(Au、Ag、Pd和Ru)储量少、成本高,阻碍了它的实际应用.因此,设计和开发由地球上丰富的元素制成的具有成本效益的催化剂来代替NRR催化剂意义重大.本课题组最近的研究(Chem.Commun.,2018,54,12966-12969)表明,SnO2在环境条件下具有电催化氧化活性,但其低电导率限制了其性能,可通过氟掺杂或石墨烯杂化予以解决.氧化铟锡(ITO)作为一种含SnO2的材料,导电性好,可望用于NRR的高效电催化剂中.因此,本文采用商用氧化铟锡玻璃(ITO/G)作为催化剂电极,在温和环境条件下进行N₂-NH₃的电化学转化,并呈现出对生成氨气有较高的选择性.XRD和XPS结果表示,商用ITO/G中存在In,Sn和O元素;SEM显示ITO/G具有清晰的纳米薄膜结构和267 nm的截面厚度;相应的EDX谱图显示In,Sn和O元素分布均匀,且原子比为32.11:3.16:64.74.采用紫外-可见光谱及线性扫描伏安和恒电位极化等电化学测试研究了商用ITO/G的NRR活性.在0.5 M LiClO4电解液中测试时,于-0.40 V vs.RHE条件下,ITO/G的NH₃产率为1.06×10^-10 mol s^-1 cm^-2,其法拉第效率为6.17%.15N同位素标记实验证实了所测到的NH₃是由ITO/G催化的N₂电还原反应生成的.利用第一性原理计算探讨了在ITO催化剂上可能的NRR反应机理,确定了ITO催化剂的NRR活性位点、N₂化学吸附活性位点以及NRR的反应途径.此外,24 h恒电位(-0.40 V vs.RHE)极化测试和2 h恒电位极化(-0.40 V vs.RHE)测试后的XRD和SEM结果表明,该催化剂具有较高的电化学稳定性.综上所述,商用ITO/G用作在环境条件下将N₂转化为NH₃的有效催化剂电极,将为开发人工固定氮气的ITO基纳米结构提供一种研究途径.     

Palladium oxide nanoparticles supported on graphene oxide: A convenient heterogeneous catalyst for reduction of various carbonyl compounds using triethylsilane

Palladium oxide nanoparticles supported on graphene oxide ‐ triethylsilane was found to be an effective reductive system for a broad range of reduction processes, including the reduction of various carbonyl compounds such as aromatic aldehydes to their corresponding alcohols or methyl arene compounds, aromatic ketones to their respective alcohols or saturated compounds, aromatic acyl chlorides to their reduced compounds. The desired products were obtained in good to excellent yields under mild conditions. The heterogeneous environmentally friendly catalyst can be easily separated from the reaction mixture through a simple filtration, facilitating purification of the prepared compounds.