Development of palladium catalysts modified by ruthenium and molybdenum as anode in direct ethanol fuel cell

Abstract

Physical and electrochemical properties of Pd catalysts combined with Ru and Mo on carbon support were investigated. To this end, Pd, Pd1.3Ru1.0, Pd3.2Ru1.3Mo1.0 and Pd1.5Ru0.8Mo1.0 were synthesized on Carbon Vulcan XC72 support by the method of thermal decomposition of polymeric precursors and then physically and electrochemically characterized. The highest reaction yields are obtained for Pd3.2Ru1.3Mo1.0/C and Pd1.5Ru0.8Mo1.0/C and, as demonstrated by thermal analysis, they also show the smallest metal/carbon ratio compared the other catalysts. XRD (X-ray Diffraction) and Raman analyses show the presence of PdO and RuO2 for the Pd/C and the Pd1.3Ru1.0/C catalysts, respectively, a fact not observed for the Pd3.2Ru1.3 Mo1.0 /C and the Pd1.5Ru0.8Mo1.0/C catalysts. The catalytic activities were tested for the ethanol oxidation in alkaline medium. Cyclic voltammetry (CV) shows Pd1.3Ru1.0/C exhibiting the highest peak of current density, followed by Pd3.2Ru1.3Mo1.0/C, Pd1.5Ru0.8Mo1.0/C and Pd/C. From, chronoamperometry (CA), it is possible to observe the lowest rate of poisoning for the Pd1.3Ru1.0/C, followed by Pd3.2Ru1.3Mo1.0/C, Pd1.5Ru0.8Mo1.0/C and Pd/C. These results suggested that catalytic activity of the binary and the ternary catalysts are improved in comparison with Pd/C. The presence of RuO2 activated the bifunctional mechanism and improved the catalytic activity in the Pd1.3Ru1.0/C catalyst. The addition of Mo in the catalysts enhanced the catalytic activity by the intrinsic mechanism, suggesting a synergistic effect between metals. In summary, we suggest that it is possible to synthesize ternary PdRuMo catalysts supported on Carbon Vulcan XC72, resulting in materials with lower poisoning rates and lower costs than Pd/C. Graphic abstract

PdAg/C Electrocatalysts Synthesized by Thermal Decomposition of Polymeric Precursors Improve Catalytic Activity for Ethanol Oxidation Reaction

“…The addition of metals with an atomic radius greater than Pd (1.28 Å ) to its structure, as for Ag (1.34 Å ), increases the values of the lattice parameters, indicating an expansion of the crystalline lattice of Pd. Similar results are observed for other alloyed metals to Pd, such as Mo (1.29 Å ), Au (1.34 Å ), and Sn (1.40 Å ) [23,33], whereas, the crystallite size decreases with the addition of alloyed metal atoms of larger atomic radii. This behavior is consistent with previous reports in the literature [10,16,17,23].…”

“…Similar results are observed for other alloyed metals to Pd, such as Mo (1.29 Å ), Au (1.34 Å ), and Sn (1.40 Å ) [23,33], whereas, the crystallite size decreases with the addition of alloyed metal atoms of larger atomic radii. This behavior is consistent with previous reports in the literature [10,16,17,23]. Yin et al evaluated the influence of Ag concentration on the particle size and particle size distribution of Pd and observed decreasing crystallite size with increasing content of Ag [34] (see Table S1 in the Supplementary Materials), an observation in agreement with our results.…”

“…Esterification, polymerization, and calcination of percussion salts from ethylene glycol and citric acid Easy handling, low cost, and insensitivity to the presence of water Forms large and usually agglomerated particles [23] Hydrogen Reduction of metal salts using hydrogen as reducing agent Simple, cheap, fast, and clean method Flammable, explosive, and hydrogen is an expensive and difficult gas to transport. [24] Ascorbic acid Ascorbic acid is used to reduce metal salts at temperatures of 80 • C…”

“…200), (220), and (222), respectively (JCPDS 05-0681) [10,16]. Interestingly, the pristine Pd electrocatalyst also presented peaks associated with the tetragonal structure of PdO that allowed the inference of a partial Pd oxidation calcination process at 573 K. The characteristic peaks of PdO observed at 2θ of 33.5 • , 41.5 • , 54.3 • , 59.9 • , 60.5 • , and 81.8 • correspond to the planes (101), (110), (112), (103), (220), and (222), respectively (JCPDS 41-1107) [23], presenting 60% peaks of this oxide and consequently a relative proportion of 1.5 in relation to the Pd peaks.…”

“…Yin et al evaluated the influence of Ag concentration on the particle size and particle size distribution of Pd and observed decreasing crystallite size with increasing content of Ag [34] (see Table S1 in the Supplementary Materials), an observation in agreement with our results. The TG/DTG analyses of Figure 2 were performed in the temperature range 273-1200 K. The loss of mass observed is associated with the oxidation of carbon that occurs in the temperature range 600-900 K, which then allows estimation of the amount of metal, based on the remaining mass of the samples [10,23,35]. The mass percentage, in combination with the EDX results, provides an accurate value of the content of Pd and Ag mass that will be used in the discussion of electrochemical properties [23].…”