This contribution reports the discovery and analysis of the first PGM-free, p-block Sn-based single metal and nitrogen-doped carbon (MNC) catalysts for the electroreduction of molecular oxygen (ORR) in acidic conditions at fuel cell cathodes. The prepared SnNC catalysts meet and exceed state of art FeNC catalysts in terms of intrinsic catalytic turn over frequency (TOF) and hydrogenair fuel cell power density. The SnNC-NH3 catalysts displayed a 40-50% higher current density than FeNC-NH3 at cell voltages below 0.7 V. Added benefits include a high favorable selectivity for the 4-electron reduction pathway and a Fenton-inactive character of Sn.A range of analytical techniques, combined with DFT calculations indicate that stannic Sn(IV)-Nx single metal sites with moderate oxygen chemisorption properties and low pyridinic N coordination numbers act as catalytic active moieties. The superior PEMFC performance of SnNC cathode catalysts under realistic, hydrogen-air fuel cell conditions, particularly after NH3 activation treatment, makes them a promising replacement of today's state-of-art Fe-based catalysts. 4Growing concerns over fossil energy and the environment are incentives to develop new energy technologies. Low-temperature hydrogen/air proton-exchange membrane fuel cell (PEMFC) is one such technology, converting hydrogen into electrical energy 1, 2 . For catalyzing the oxygen reduction reaction (ORR) and hydrogen oxidation reaction at the electrodes, PEMFCs rely however on precious, in particular platinum-based catalysts 3, 4 , a scarce and expensive metal.Research to replace precious group metals (PGMs) has led to a class of bio-inspired catalysts, labelled MNC, that involve non-precious 3d transition metal cations stabilized by nitrogen atoms (Metal-Nx moieties), themselves incorporated in conductive carbon matrices. Fe, Co and Mn are hitherto the only three metals that result in ORR-active Metal-Nx moieties in acidic reaction environments 5,6,7,8,9,10 . While the number and utilization of such moieties embedded in carbon are being improved 9 , the fundamental nature of such sites is not so new. Indeed, the large body of experimental research on pyrolyzed FeNC and CoNC materials identifies Metal-N4 motifs as the most active sites for catalyzing ORR in acid 11,12,13 . Such sites are akin to square-planar Metal-N4 sites in Fe or Co macrocycles, identified in 1964 to be ORR active 14 Here, we report the discovery of the first p-block single metal site catalyst, SnNC, exhibiting catalytic ORR reactivities in acidic environments that meet and exceed all state-of-art PGM-free catalyst concepts, while adding important benefits in terms of catalyst stability. The catalytically active single-metal SnNx moieties embedded in the surface of the SnNC catalyst were characterized by high-resolution scanning transmission electron microscopy (STEM) coupled with electron energy loss spectroscopy (EELS), extended X-ray absorption fine structure (EXAFS), Xray photoelectron spectroscopy (XPS) and 119 Sn Mössbauer spectroscopy, com...

Establishing new reactivity map descriptor of TOF–SD for PGM-free Fe–N–C catalysts ORR activity.

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A highly active NiMo electrocatalyst for HOR in alkaline media with power density at 0.5 V higher than 100 mW cm−2 (peak value of 120 mW cm−2), which is similar to palladium was synthesized and comprehensively studied.

Novel highly active electrocatalysts for hydrazine hydrate fuel cell application were developed, synthesized and integrated into an operation vehicle prototype. The materials show in both rotating disc electrode (RDE) and membrane electrode assembly (MEA) tests the world highest activity with peak current density of 16,000 A g(-1) (RDE) and 450 mW cm(-2) operated in air (MEA).

Addition of Zn to Pd changes its catalytic behavior for steam reforming of methanol. Previous work shows that improved catalytic behavior (high selectivity to CO2) is achieved by the intermetallic, tetragonal L10 phase PdZnb1, where the Pd:Zn ratio is near 1:1. The Pd-Zn phase diagram shows a number of other phases, but their steady state reactivity has not been determined due to the difficulty of precisely controlling composition and phase in supported catalysts. Hence, the role of Zn on Pd has generally been studied only on model single crystals where Zn was deposited on Pd(111) with techniques such as TPD and TPR of methanol or CO. The role of small amounts of Zn on the steady state reactivity of Pd-Zn remains unknown. Therefore, in this work, we have synthesized unsupported powders of phase pure PdZna, a solid solution of Zn in fcc Pd, using a spray-pyrolysis technique. The surface composition and chemical state were studied using Ambient Pressure XPS (AP-XPS) and were found to match the bulk composition and remain so during methanol steam reforming (MSR) (Ptot = 0.25 mbar). Unlike the PdZnb11 phase, we find that PdZna is 100% selective to CO during methanol steam reforming with TOF at 250 o C of 0.12 s-1. Steady state ambient pressure microreactor experiments and vacuum TPD of methanol and CO show that the a phase behaves much like Pd, but Zn addition to Pd improves TOF since it weakens the Pd-CO bond, eliminating the poisoning of Pd by CO during MSR over Pd. The measured selectivity for fcc PdZna therefore confirms that adding small amounts of Zn to Pd is not enough to modify the selectivity during MSR, and that the PdZnb1 tetragonal structure is essential for CO2 formation during MSR.

Novel highly active electrocatalysts for hydrazine hydrate fuel cell application were developed, synthesized and integrated into an operation vehicle prototype. The materials show in both rotating disc electrode (RDE) and membrane electrode assembly (MEA) tests the world highest activity with peak current density of 16 000 A g À1 (RDE) and 450 mW cm À2 operated in air (MEA).The automotive world will be changed in 2015, when leading manufacturers will publicly introduce their first generation of commercial fuel cell vehicles. It should be noticed, however, that these automobiles were developed with proton exchange membrane (PEM) technology and membrane electrode assemblies (MEAs) in fuel stacks containing platinum catalysts for both hydrogen oxidation and oxygen reduction.There are several drawbacks of PEM-based technology, including: the high cost of fuel cell membranes, the extremely high cost of platinum, and the absence of a developed hydrogen infrastructure. Further, the use of hydrogen requires a high-pressure tank, which requires a full redesign of the automobile frame. These factors result in a high-cost commercial vehicle with a low driving range and safety issues.In contrast to PEM hydrogen fueled vehicles development, researchers from Daihatsu Motor Co. have introduced the idea of anion-exchange membrane fuel cell with liquid fuels. [1][2][3][4][5][6][7][8][9][10][11] Switching from acidic proton exchange to alkaline, anion-exchange membranes has many benefits, including: 1) fast fuel oxidation and oxygen reduction and 2) possible use of cheaper non-platinum group metal catalysts as anode and cathode material for both sides of the MEA. The liquid fuel of choice was hydrazine hydrate, which has no carbon atoms and thus will not contribute to increased CO 2 levels, the theoretical electromotive force is 1.56 Vand it can be oxidized by number of cheap catalysts. [12] To meet the power output requirements of a stack with limited size, the anode material should provide the highest power density, be stable, and selective toward the production of water and nitrogen with no ammonia (NH 3 ) generation. Up to now, catalysts reported had a low activity with operation in air (real vehicles operation conditions).Herein we report the synthesis of novel Ni-based supported catalysts by a completely solvent-free method. The method is based on a mechanochemical approach and is scalable to hundreds of kilograms of catalyst and can be considered a "green" synthesis method compared with conventional synthesis, which requires the use of solvents. These catalysts show high activity in both rotating disc electrode (RDE) and MEA tests, with real vehicles operation conditions. The effects of catalysts loading and carbon addition on hydrazine electrooxidation were studied on nickel-based materials for the first time.These electrocatalysts for hydrazine electrooxidation were synthesized by solvent-free impregnation of nickel and zinc precursors by using a high-energy mechanochemical approach. The synthesized materials were compreh...

a b s t r a c tNanostructured palladium-copper electrocatalysts with Pd:Cu ratios of 1:3, 1:1, and 3:1 were synthesized using a Sacrificial Support Method (SSM) in combination with the thermal reduction of metal precursors. The materials were comprehensively characterized by X-ray diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), Scanning and Transmission Electron Microscopy (SEM and TEM), surface area measurements (Brunauer-Emmett-Teller, BET) and Differential Electrochemical Mass Spectroscopy (DEMS). The SSM method enables the preparation of nano-sized unsupported Pd-Cu catalysts with uniformlydistributed particles and high surface area, in the range of 40 m 2 g catalyst −1 . Their catalytic activity for the electrooxidation of several alcohols (methanol, ethanol, ethylene glycol and glycerol) was investigated in alkaline media. In situ Infrared Reflection Adsorption Spectroscopy (IRRAS) and Density Functional Theory (DFT) calculations were used in order to understand the mechanism of the various alcohols electrooxidation reactions.