Electrochemical Performances Of Fe-based Alloy And Oxide Nanoparticles Modified Ordered Mesoporous Carbon

Since1999, ordered mesoporous carbons (OMCs) have been paid more and more attention due to varity of characteristics, such as a novel structure, large special surface area, uniform and controllable pore size, high pore volume, well electroconductivity and stability. They have been widely used in catalysis, adsorption, electrochemical, sensor, energy storage, biology, and so on. But, single ordered mesoporous carbon is difficult to satisfy people’s various performance requirement. Therefore, it is an urgent need to solve the above problem at present that various functionalized composites are prepared by incorporation of the metal or metal oxide nanoparticles in ordered mesoporous carbon for improving the performance of OMC and expanding its application field. In this paper, Fe based alloy and related oxide incorporated OMC nanocomposites are prepared, the performances of the OMC based nanocomposites direct methanol fuel cell, electrochemical hydrogen storage, electrochemical biosensor, and supercapacitor are investigated. Material design, preparation, physic and electrochemical performances and related mechanism are studied. The main contents are summaried as following:(1) Ordered mesoporous carbon (OMC) supported well-dispersed PtFex nanoparticles with a controllable size distribution was prepared via a modified polyol synthesis route, using hexachloroplatinic acid and ferric chloride as Pt and Fe source, and ethylene glycol as a reducing agent. The catalytic activities relevant to direct methanol fuel cell of the PtFex/OMC composites were investigated using cyclic voltammetry, single-cell proton exchange membrane fuel cell (PEMFC) test and electrochemical impedance spectroscopy (EIS) technique. Due to the existence of more Pt0species and Fe ion corrosion caused by the formation of the alloyed PtFex catalyst, Pt0can provide the more active sites for methanol oxidation reaction, and the methanol oxidation activity of the PtFex/OMC electrode is evidenced to be enhanced by the increased anodic peak current with increasing the incorporation content of Fe. The oxygen reduction reaction (ORR) current density of0.662A/cm2and power density of237.2mW/cm2generated by the PtFe3/OMC sample are more than two times the values of0.32A/cm2and102.6mW/cm2by the Pt/OMC sample. The PtFe3/OMC catalyst in0.5M H2SO4+1M CH3OH displays the highest specific catalytic activity of100.6mA/m2, which is almost3times lower than that of283.7mA/m2in0.5M H2SO4. The enhanced higher activity for the PtFe3/OMC sample can be firstly attributed to a highly homogeneous dispersion of the PtFe3nanoparticles on the mesoporous channels within OMC, such PtFe3nanoparticles with a diameter of3.3nm can accelerate the formation of Pt-OH groups. Meanwhile, the alloyed PtFe3nanoparticles can provide a lower onset potential for the electrooxidation of CO/H2than that of pure Pt, and would contribute more to the promotion of C-H breaking and COaad tolerance. Furthermore, the larger surface area, the favorable pore structure and the structural integrity between the PtFe3nanoparticles and the OMC matrix, electrochemical reactions can effectively facilitate the transportation of reactants and products in liquid medium.(2) Well-dispersed NiFex nanopartiles doped OMC for hydrogen storage were prepared by wet impregnation and H2reduction techniques. NiFex doped OMC is of structurally well ordered two-dimensional hexagonal structure. NiFe2alloyed nanoparticles with an average diameter of4.7nm are well decorated homogeneously both on the exterior surfaces and interior canals of the OMC matrix. The adsorption isotherms of nitrogen suggest of the NiFe2nanoalloys doped OMC possessed a high surface area of1209m2/g, a pore size of4.29nm, and a pore volume of1.35cm3/g. The electrochemical hydrogen storage capacities of OMC and NiFex/OMC are comparatively investigated using electrochemical impedance spectroscopy technique, potentiodynamic polarization, cyclic voltammetry, galvanostatic charge-discharge techniques. The mechanism of hydrogen storage of NiFex/OMC can be explained by atomic hydrogen spillover from a supported catalyst. Results show that the Ni and Fe alloyed nanoparticles act as active hydrogen adsorption sites and thus increase the Had coverage degree, which is in favor of increasing the redox reaction of hydrogen absorption-desorption processes. With the molar ratio of nickel and iron decreasing, the discharge capacity and the cycle performance have a notable improvement due to its better dispersion, higher surface area, larger mesopore volume, smaller charge-transfer resistance, and stronger anti-corrosion ability. There appears a relatively stable discharge platform at about0.8-0.9V, almost corresponding with hydrogen oxidation reaction process (hydrogen desorption). The discharge capacity of NiFe2/OMC reaches a maximum of418mAh/g, which is about four times higher than that of pure OMC electrode.(3) The electrode materials of NiFex/OMC+Nafion+GC and enzymatic GOX+NiFex/OMC+Nafion+GC electrochemical biosensor were fabricated by wet impregnation and hydrogen reduction process. It shows that NiFex/OMC as electrochemical biosensor electrode material has a batter quasi-reversible reaction. The electrochemical performances of nanocomposite as nonenzynatic or enzymatic sensor in different pH value of phosphate buffer solution are investigated. The results show that NiFe2/OMC+Nafion+GC electrode has good electrochemical performance toward H2O2, with a detection range of6.2～42710μM, the sensitivity of4.29μA/mM cm2, and a detection limit of0.24μM. The NiFe2/OMC+Nafion+GC electrode displays a high selectivity and stability on H2O2. The GOX+NiFe2/OMC+Nafion+GC electrode has better electrochemical performance on glucose, with a detection range of48.6～7500μM, the sensitivity of6.9μA/mM cm2, and a detection limit of2.7μM. The GOX+NiFe2/OMC+Nafion+GC electrode has a higher selectivity and stability on glucose. A reduction reaction of H2O2is generated by medium NiFex/OMC for electronic sensing effect. Glucose oxidase (GOX) immobilized on the mediator NiFex/OMC can prompte the oxidation reaction of glucose on GOX+NiFe2/OMC+Nafion+GC electrode. NiFe2/OMC composite has better electrochemical biosensor performance.(4) The RuO2/OMC and RuO2-Fe2O3/OMC electrode materials were sythetized by impregnation and in situ heating method. The nanoparticles size of RuO2and RuO2-Fe2O3is1.86and2.23nm, respectively. The fine nanoparticles can be easily deposited and embedded in the pore wall of OMC without blocking the mesoporous channel. The hybrid with RuO2-Fe2O3nanoparticles dispersed evenly in pore wall of two-dimensional mesoporous carbon has a higher specific surface area of768m2/g, larger pore volume of1.01cm3/g, and proper pore size of4.3nm. These characteristics such as suitable pore channel, large surface area, small charge transfer impedance value are helpful for ion and electron transmition. The maximum electrochemical capacity tested in acid electrolyte is265F/g. Meanwhile, RuO2-Fe2O3/OMC supercapacitor shows high electrochemical stability and reversibility. It shows a higher electrochemical stability (>900cycles), higher energy density (21.3Wh/kg) and power density (4000W/kg). RuO2-Fe2O3/OMC electrode is an ideal electrode material for supercapacitors, which combines a double-layer capacitance with pseudo-capacitance.