IrO2-SiO2 binary oxide films: Preparation, physiochemical characterization and their electrochemical properties

Mixed IrO₂-SiO₂ oxide films were prepared on titanium substrate by the thermo-decomposition of hexachloroiridate (H₂IrCl₆) and tetraethoxysilane (TEOS) mixed precursors in organic solvents. The solution chemistry and thermal decomposition kinetics of the mixed precursors were investigated by ultra violet/visible (UV/vis) spectroscopy and thermogravimetry (TGA) and differential thermal analysis (DTA), respectively. The physiochemical characterization of the resulting materials was conducted by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical measurements. It is shown from the UV/vis spectra that the electronic absorption intensity of IrCl₆²⁻ complexes in the precursors decreases in the presence of TEOS, indicating the interaction between these two components. Thermal analysis shows the decomposition reaction of H₂IrCl₆ is inhibited by TEOS in the low temperature range, but the further oxidation reaction at high temperatures of formed intermediates is independent of the presence of silane component. Physical measurements show a restriction effect of silica on the crystallization and crystal growth processes of IrO₂, leading to the formation of finer oxide particles and the porous morphology of the binary oxide films. The porous composite films exhibit high apparent electrocatalytic activity toward the oxygen evolution reaction. In addition, the long-term stability of Ti-supported IrO₂ electrodes is found to apparently improve with appropriate amount of SiO₂ incorporation, as tested under galvanostatic electrolysis.     

亚胺COFs在电催化领域的应用研究进展

亚胺共价有机框架材料(COFs)作为一种新兴的多孔晶体聚合物,具有规整的孔结构、高的比表面积、可调的抗衡离子、丰富的活性位点等.在燃料电池中,亚胺COFs对于制备高效电催化剂和促进能量转换至关重要.首先介绍了亚胺COFs基电催化剂的优势;然后综述了其作为电催化剂在还原CO2、析氧反应、析氢反应、氧还原反应等领域的应用;最后讨论了亚胺COFs高性能电催化剂当前的挑战和未来前景.     

Spinel CoFe2O4 /carbon nanotube composites as efficient bifunctional electrocatalysts for oxygen reduction and oxygen evolution reaction

In the development of fuel cells, it is the key to large-scale commercialization of fuel cells to rationally design and synthesize efficient and non-noble metals-based bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). In this paper, spinel CoFe₂O₄/carbon nanotube composites (CoFe₂O₄/CNTs/FA) were synthesized by solvothermal and calcination method. XRD, TEM, XPS and BET characterizations indicate that the addition of complexing agent fumaric acid can improve the crystal growth kinetics and morphology of CoFe₂O₄/CNTs nanohybirds. The as-synthesized CoFe₂O₄/CNTs/FA pyrolyzed at 500 °C have an outstanding bifunctional catalytic activity for ORR and OER with the potential of 1.62V (vs. RHE) at a current density of 10 mA/cm² and half-wave potential E_1/2 = 0.808V (vs. RHE) in alkaline electrolyte, respectively. It is obviously better than unloaded CoFe₂O₄ nanoparticles and commercial CNTs. CoFe₂O₄/CNTs/FA also exhibit better methanol tolerance ability and durability than commercial Pt/C and RuO₂ catalyst. This investigation broadens an idea of simple compounding of spinel with carbon-based materials to improve electrochemical properties.     

Pt-WC/C as a cathode electrocatalyst for hydrogen production by methanol electrolysis

A novel tungsten carbide promoted Pt/C (Pt-WC/C) was prepared by an intermittent microwave heating (IMH) method and used for the cathode electrocatalyst in an electrolyser for hydrogen production by methanol electrolysis. The electrolyser showed better performance for hydrogen production using the Pt-WC/C cathode electrocatalyst than using a commercial Pt/C cathode electrocatalyst. The single cell electrolyser gave reasonable current at voltages lower than 0.4 V. The novelty of this technique is the inherent simplicity and substantially lowered cost.     

A novel CO-tolerant PtRu core-shell structured electrocatalyst with Ru rich in core and Pt rich in shell for hydrogen oxidation reaction and its implication in proton exchange membrane fuel cell

A novel PtRu catalyst consisting of a Ru-rich core and a Pt-rich shell was synthesized using a two-step microwave irradiation technique. The synthesized PtRu/C catalysts were characterized by X-ray diffraction (XRD), extended X-ray absorption finestructure (EXAFS), transmission electron microscopy (TEM) as well as energy dispersive X-ray spectrometry (EDXS). The produced PtRu/C catalysts showed identical crystalline structure and diffraction peaks to Pt itself, but with negligible higher 2 shift degrees, indicating the formation of a specific composite structure rather than alloy formation. This novel structure of PtRu/C catalyst was also further verified via X-ray absorption spectroscopy. The particle size of PtRu catalysts identified by TEM was less than 5 nm. In order to investigate the CO tolerance in the hydrogen oxidation reaction (HOR), H₂ streams with six different concentrations of CO (0, 10, 50, 100, 300, and 500 ppm) were used. The electrocatalytic activity thus obtained was not only better than that of Pt/C catalyst in HOR, but also showed a better CO tolerance in various CO concentrations.     

Investigation of carbon supported Au-Ni bimetallic nanoparticles as electrocatalyst for direct borohydride fuel cell

The carbon supported Au₈₀Ni₂₀, Au₅₈Ni₄₂ and Au₄₁Ni₅₉ nanoparticles for the application of direct borohydride-hydrogen peroxide fuel cell (DBHFC) are synthesized in a sodium bis(2-ethylhexyl) sulfosuccinate (AOT) reverse micelle system. The physical and electrochemical properties are investigated by transmission electron microscopy (TEM), cyclic voltammetry, chronoamperometry, chronopotentiometry and fuel cell test. The TEM results reveal that the Au-Ni bimetallic particles are uniformly dispersed on carbon with narrow size distribution and regular spherical shape. The average size of the particles is about 3 nm. The electrochemical measurements show that Au-Ni bimetallic particles can apparently promote the electrode kinetics of BH₄⁻ oxidation. The DBHFCs using carbon supported Au-Ni bimetallic particles as anode electrocatalysts are fabricated. The results show that the performance of DBHFC using Au₅₈Ni₄₂/C as anode electrocatalyst excels markedly to the others, and the maximum power density of 45.74 mW cm⁻² is obtained at 20 °C.     

Carbon supported Pt-Y electrocatalysts for the oxygen reduction reaction

Carbon supported Pt₃Y (Pt₃Y/C) and PtY (PtY/C) were investigated as oxygen reduction reaction (ORR) catalysts. After synthesis via reduction by NaBH₄, the alloy catalysts exhibited 10-20% higher mass activity (mA mg_Pt⁻¹) than comparably synthesized Pt/C catalyst. The specific activity (μA cm_Pt⁻²) was 23 and 65% higher for the Pt₃Y/C and PtY/C catalysts, respectively, compared to Pt/C. After annealing at 900 °C under a reducing atmosphere, Pt₃Y/C-900 and PtY/C-900 catalysts showed improved ORR activity; the Pt/C and Pt/C-900 (Pt/C catalyst annealed at 900 °C) catalysts exhibited specific activities of 334 and 393 μA cm_Pt⁻², respectively, while those of the Pt₃Y/C-900 and PtY/C-900 catalysts were 492 and 1050 μA cm_Pt⁻², respectively. X-ray diffraction results revealed that both the Pt₃Y/C and PtY/C catalysts have a fcc Pt structure with slight Y doping. After annealing, XRD showed that more Y was incorporated into the Pt structure in the Pt₃Y/C-900 catalyst, while the PtY/C-900 catalyst remained unchanged. Although these results suggested that the high ORR activity of the PtY/C-900 catalyst did not originate from Pt-Y alloy formation, it is clear that the Pt-Y system is a promising ORR catalyst which merits further investigation.     

Ethanol oxidation reaction activity of highly dispersed Pt/SnO2 double nanoparticles on carbon black

Highly dispersed Pt and SnO₂ double nanoparticles containing different Pt/Sn ratios (denoted as Pt/SnO₂/CB) were prepared on carbon black (CB) by the modified Bönnemann method. The average size of Pt and SnO₂ nanoparticles was 3.1 ± 0.5 nm and 2.5 ± 0.3 nm, respectively, in Pt/SnO₂(3:1)/CB, 3.0 ± 0.5 nm and 2.6 ± 0.3 nm, respectively, in Pt/SnO₂(1:1)/CB, and 2.8 ± 0.5 nm and 2.5 ± 0.3 nm, respectively, in Pt/SnO₂(1:3)/CB. The Pt/SnO₂(3:1)/CB electrode showed the highest specific activity and lowest overpotential for ethanol oxidation reaction (EOR), and was superior to a Pt/CB electrode. Current density for EOR at 0.40 and 0.60 V vs. reversible hydrogen electrode for the Pt/SnO₂(3:1)/CB electrode decayed more slowly than that for the Pt/CB electrode because of a synergistic effect between Pt and SnO₂ nanoparticles. The predominant reaction product was acetic acid, and its current efficiency was about 70%, while that for CO₂ production was about 30%.     

Tungsten carbide nanofibers prepared by electrospinning with high electrocatalytic activity for oxygen reduction

Tungsten carbide (WC) nanofibers with ultrafine diameters were synthesized by carbonizing the as-spun ammonium metatungstate (AMT) and polyvinyl pyrrolidone (PVP) composite fiber precursors. The morphologies of the WC nanofiber products were closely related to the electrospinning concentrations of AMT and PVP. Raman spectra and high resolution TEM (HR-TEM) testified that the surface of the WC nanofibers was coated by a carbon layer with a thickness of several nanometers, which could be removed to a great degree by NH₃ etching at high temperature. Cyclic voltammetry (CV) and rotating disk electrode (RDE) test results showed that the carbon-coated WC nanofibers had good electrocatalytic activities and stabilities during oxygen reduction reaction (ORR), both of which could be further improved by NH₃ post-treatment at high temperature. The catalytic roles of the WC nanofiber samples for ORR probably originated from the WC sites, but not excluding some contributions of the surface carbon species.     

Roles of organic acids during exectrooxidation reaction over Pt-supported carbon electrodes in direct methanol fuel cells

A comprehensive study has been made to explore the role of organic acids on electrocatalytic performances of platinum (Pt) nanoparticles supported on carbon porous materials (CPMs) in proton exchange membrane fuel cells (PEMFCs). In particular, the effects of carboxylic acids (R–COOH), viz. formic acid, acetic acid, propionic acid, and butyric acid on catalytic activity, stability, and durability of anodic Pt/CPM electrocatalyst in direct methanol fuel cells (DMFCs) were investigated. In the presence of doped carboxylic acids, the electrooxidative activity of Pt/CPM follows the trend: HCOOH < CH₃COOH < C₂H₅COOH < C₃H₇COOH, revealing a consistent increase in the severity of catalyst deactivation with the number of carbons on the alkyl chain of the dopant. The Pt/CPM was found to exhibit electrocatalytic performances and tolerance for poisoning than a commercial Pt/XC-72 catalyst with a similar Pt loading (20 wt%). Moreover, a notable increase in mass activity up to ca. 150% over the spent Pt/CPM catalyst was observed up on removing the organic acid in the feed stream, indicating that catalyst poisoning by deactivation may be revived, even to its “intrinsic” activity.