The carbon-supported Pt nanoclusters (20 wt% metal) electrodes have been tested as oxygen reduction catalysts in 0.1M KOH solutions. The novel non-conventional microporous-mesoporous carbide derived carbon powder, synthesized from molybdenum carbide (Mo 2 C) at 750 • C using the high-temperature chlorination method, has been used as an electrocatalyst support for oxygen electroreduction. For comparison, the corresponding parameters for commercially available VulcanXC72 and (20 wt%) Pt-VulcanXC72 have been obtained. Results of the X-ray diffraction analysis show that the Pt nanoclusters have been deposited mainly as the face-centered cubic (fcc) crystals at both carbon supports. The Pt particles were distributed uniformly on the porous carbon supports, and the average particle size of the Pt nanoclusters at (20 wt%) Pt-C(Mo 2 C) and at (20 wt%) Pt-VulcanXC72 were 42 and 57 Å, respectively. The (20 wt%) Pt-C(Mo 2 C) catalyst demonstrated higher activity (calculated effective electrochemical surface area A eff = 0.485 cm 2 ) with high specific surface area S BET = 1600 m 2 g −1 toward the oxygen electroreduction reaction at room temperature compared with that for the (20 wt%) Pt-VulcanXC72 (A eff = 0.320 cm 2 ) with S BET = 180 m 2 g −1 . The four-electron oxygen reduction mechanism has been established for both, i.e., the (20 wt%) Pt-C(Mo 2 C) and (20 wt%) Pt-VulcanXC72 catalysts based electrodes.
Two different Fe-N/C(SiC) catalysts (Fe + Bipyr/C(SiC) and Fe + Phen/C(SiC)) for oxygen reduction based on silicon carbide derived carbon were synthesized and investigated in 0.1 M KOH aqueous solution by rotating disc electrode method. It was found that the electrocatalytic activity and stability are significantly influenced by the change of the nitrogen ligand in the catalyst. Comparable current density values obtained for 20%Pt-Vulcan electrode could be achieved for Fe + Bipyr/C(SiC) and Fe + Phen/C(SiC) catalysts in alkaline media. The durability tests (~150 h) showed that the decrease of the activity for Fe + Bipyr/C(SiC) and Fe + Phen/C(SiC) is only 0.5 mV h − 1 and 0.17 mV h − 1 , respectively. The Fe + Bipyr/C(SiC) catalyst demonstrated higher activity in the RDE measurements, but during the long-term test the Fe + Phen/C(SiC) catalyst prove to be more stable than Fe + Bipyr/C(SiC).
The oxygen reduction reaction (ORR) kinetics was studied on catalysts with a very low Pt loading (3.5, 8.3 and 12.4 wt%) and small Pt nanoparticles (from 2.0 to 3.9 nm) deposited onto the molybdenum carbide derived carbon. Three different platinum catalysts were synthesized and characterized by the high resolution transmission electronmicroscopy, in situ atomic force microscopy, inductively coupled plasma mass spectrometry, X-ray diffraction and nitrogen sorption analysis. The electrocatalytic activity toward ORR was analyzed with rotating disk electrode and cyclic voltammetry methods in 0.1 M KOH, 0.05 M H 2 SO 4 and 0.1 M HClO 4 aqueous solutions. The Pt mass corrected current (j Pt ) values depend on the Pt loading and at fixed Pt weight percent in the catalyst j Pt increases in the sequence: 0.1 M KOH < 0.05 M H 2 SO 4 < 0.1 M HClO 4 . The catalyst containing 8.3 wt% platinum with the mean particle size of 3.3 nm is found to be optimum for ORR in various electrolyte solutions. The physical and electrochemical methods have been used for estimation of the electrochemically active surface area of the Pt catalysts.
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