The conversion of biomass into valuable carbon composites as efficient non‐precious metal oxygen‐reduction electrocatalysts is attractive for the development of commercially viable polymer electrolyte membrane fuel‐cell technology. Herein, a versatile iron–tannin‐framework ink coating strategy is developed to fabricate cellulose‐derived Fe3C/Fe‐N‐C catalysts using commercial filter paper, tissue, or cotton as a carbon source, an iron–tannin framework as an iron source, and dicyandiamide as a nitrogen source. The oxygen reduction performance of the resultant Fe3C/Fe‐N‐C catalysts shows a high onset potential (i.e. 0.98 V vs the reversible hydrogen electrode (RHE)), and large kinetic current density normalized to both geometric electrode area and mass of catalysts (6.4 mA cm?2 and 32 mA mg?1 at 0.80 V vs RHE) in alkaline condition. This method can even be used to prepare efficient catalysts using waste carbon sources, such as used polyurethane foam. 相似文献
Utilizing the projected tracking error of the redundant joint angles, we studied the calibration problem of the sensor zero
positions of a planar 2-dof parallel manipulator in this paper. Based on the study of the relationship between the projected
tracking error of the joint angles and the error of the sensor zero positions, a new error function is proposed for the calibration
of the sensor zero positions of the parallel manipulator. It is proved that the error function is robust to the measurement
error of the joint sensors, so accurate calibration results can be obtained by minimizing the error function even if the measurement
of the joint angles is not accurate. With a simple searching strategy for the minimal value of the error function, we designed
an auto-calibration procedure and verified the validity of the calibration procedure through real experiments on a real redundant
planar 2-dof parallel manipulator. 相似文献
A facile reactive seeding (RS) method was developed for the preparation of continuous MOF membranes on alumina porous supports, in which the porous support acted as the inorganic source reacting with the organic precursor to grow a seeding layer. 相似文献
Cobalt (or iron)–polyphenol coordination polymers with crystalline frameworks are synthesized for the first time. The crystalline framework is formed by the assembly of metal ions and polyphenol followed by oxidative self‐polymerization of the organic ligands (polyphenol) during hydrothermal treatment in alkaline condition. As a result, such coordination crystals are even partly stable in strong acid (such as 2 m HCl). The metal (Co or Fe)‐natural abundant polyphenol (tannin) coordination crystals are a renewable source for the fabrication of metal/carbon composites as a nonprecious‐metal catalyst, which show high catalytic performance for both oxygen reduction reaction and oxygen evolution reaction. Such excellent performance makes metal–polyphenol coordination crystals an efficient precursor to fabricate low‐cost catalysts for the large‐scale application of fuel cells and metal–air batteries. 相似文献
Cr, Fe, Ce and W doped MoVTeNbO M2 phase catalysts were synthesized and used in the selective oxidation of propylene to acrylic acid (AA). Results show that the introduction of Cr, Fe, Ce and W substantially affects the physicochemical properties and catalytic performance of MoVTeNbO-based catalysts. Un-doped catalyst consists of M2 phase and TeO2, while Cr, Fe, Ce and W-doped catalysts are mainly composed of M2 and MoO3. It is indicated that doping of Cr, Fe, Ce and W can restrain the formation of TeO2, but favour the formation of MoO3. Un-doped, Cr and W-doped catalysts display irregular-shaped particles morphology, while Fe and Ce-doped catalysts display nanosheets morphology. In addition, the valence of superficial elements of catalysts changed greatly with the doping elements. For catalytic performance, in addition to Cr, the propylene conversion of the catalyst decreases obviously with doping of other elements, probably due to the drastically reduced specific surface area with doping of Fe, Ce and W. The existence of Cr and Ce can increase the selectivity to AA at all test temperatures (360–440 ℃), while Fe and W-doped catalysts only show higher selectivity than the un-doped one at high temperature of 420 and 440 ℃. It is illustrated that the catalysts with redox ability at relatively low temperature is more favorable for the selectivity to AA. Among them, Cr-doped catalyst shows the highest selectivity (85.3%) and yield (63.5%) of AA at test temperature of 380 ℃, which are 15.3 and 7.5% higher than that of un-doped catalyst, respectively.
Graphic Abstract
The M2 phase MoVTeNbO catalysts doped with Cr, Fe, Ce and W have been synthesized. It is demonstrated that the addition of Cr improves the stability of Te4+, and Cr-doped M2 phase shows excellent catalytic performance in the selective oxidation of propylene to acrylic acid.