Oxygen Reduction at Shape-Controlled Platinum Nanoparticles and Composite Catalysts Based on (100)Pt Nanocubes on Microporous–Mesoporous Carbon Supports Vitali Grozovski, [a, b] Heili Kasuk, [a] Jaak Nerut, [a] Eneli Härk, [a, c] Rutha Jäger, [a] Indrek Tallo, [a] and Enn Lust* [a] 1. Introduction The electrochemical oxygen reduction reaction (ORR) is a catho- dic process that occurs in many energy-storage and -conver- sion devices, and its importance is recognized in many indus- trial applications including fuel cells, low-temperature electro- lyzers, metal–air batteries, electrosynthesis reactors, and so forth. [1–9] Depending on the electrode material, pH value, and chemical composition of an electrolyte solution, the ORR pro- ceeds through either a two-electron or “direct” four-electron pathway, [3–8] which is favorable for polymer electrolyte mem- brane fuel cells (PEMFCs), solid oxide fuel cells (SOFCs), and other fuel cells. [6–17] Different types of carbon have been studied as catalyst sup- ports (glassy carbons, amorphous, pyrolytic and highly orient- ed pyrolytic graphite, as well as nanotubes) [18] and the influ- ence of the carbon support porosity and crystallinity on the ORR has been demonstrated. [1–7, 9–16, 18] However, there are only limited data addressing the ORR at the well-defined pristine carbons with narrow micropore–mesopore size distributions, such as carbide-derived carbons (CDC) and microporous–meso- porous carbons modified with Pt nanoclusters [10–17] or Pt-metal alloy nanoparticles. [8] In our recent papers, [10–17, 19–22] novel carbon supports synthesized from Mo 2 C at different tempera- tures from 600 to 1000 8C with variable specific surface area (S BET ) values, microporosity and mesoporosity, electrical con- ductivity, and corrosion stability were activated with deposited Pt nanoclusters, [10, 11, 13, 16, 19–22] which were studied for better per- formance and long-lasting durability of the PEMFC. Systematic studies of cathode catalyst materials for PEMFCs and electrical double-layer supercapacitors [10–17] show that the ORR activity crucially depends on the precursor carbide and the carbon synthesis conditions, which influence the properties of the carbon support in terms of crystallinity, porosity, S BET , micropore and mesopore area, pore volume, and pore size distribution. The main aim of this work was to study the activity of the shape-controlled (100)Pt nanoparticles [(100)Pt NPs] deposited onto/into novel C(Mo 2 C) for the ORR. Cubical (100)Pt NPs were synthesized by using the colloid chemistry method, which were subsequently deposited onto/into C(Mo 2 C) as well as on Vulcan XC72 carbon powder for comparison. The ORR data were measured in a three-electrode system for bare (100)Pt NPs, C(Mo 2 C)-supported (100)Pt–C(Mo 2 C), as well as for (100)Pt–Vulcan in 0.5 m H 2 SO 4 aqueous electrolyte solution at 22  1 8C by using cyclic voltammetry (CV) and rotating-disk- electrode (RDE) methods. 2. Results and Discussion 2.1. Pt Nanoparticle Characterization A typical TEM image of the cubic (100)Pt NPs prepared through colloid chemistry is shown in Figure 1 A. A preferential cubic shape is obtained, which suggests the presence of a pre- dominant (100) preferential surface structure. The average par- The electrochemical oxygen reduction reaction (ORR) on bare (100)Pt nanoparticles supported by molybdenum-carbide-de- rived carbon [(100)Pt–C(Mo 2 C)] with high specific surface area and controlled microporosity–mesoporosity, pore size distribu- tion, electrical conductivity, and corrosion stability was studied in 0.5 m H 2 SO 4 solution by using rotating-disk-electrode and cyclic voltammetry methods. The C(Mo 2 C) powder was pre- pared from Mo 2 C at a fixed chlorination temperature (750 8C). Pt nanoparticles were prepared through colloid chemistry and deposited onto/into C(Mo 2 C) and Vulcan XC72 carbon supports for comparison. The ORR cathodic current densities and half- wave potentials strongly depend on the characteristics of the carbon material used as the support. High values for the ORR current density were calculated for (100)Pt–C(Mo 2 C) and the half-wave potential is nearly 80 mV more positive compared with that for the (100)Pt–Vulcan XC72 catalyst with a similar catalyst loading. [a] Dr. V. Grozovski, Dr. H. Kasuk, Dr. J. Nerut, Dr. E. Härk, Dr. R. Jäger, I.Tallo, Prof. E. Lust Institute of Chemistry, University of Tartu Ravila Street 14A, 50411 Tartu (Estonia) enn.lust.ut.ee [b] Dr. V. Grozovski Department of Chemistry and Biochemistry, University of Bern Freistrasse 3, CH-3012 Bern (Switzerland) [c] Dr. E. Härk Soft Matter and Functional Materials, Helmholtz Zentrum Berlin Hahn-Meitner-Platz 1, 14109 Berlin (Germany) ChemElectroChem 0000, 00,0–0 # 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 1 & These are not the final page numbers! ÞÞ These are not the final page numbers! ÞÞ Articles DOI: 10.1002/celc.201500021