Superior methanol electrooxidation performance of (110)-faceted nickel polyhedral nanocrystals

We present the synthesis of (110)-faceted nickel polyhedral nanocrystals (NCs) and their characterization as electrocatalysts for the methanol oxidation reaction (MOR). Ni NCs were produced at 180 °C through the reduction in solution of a Ni salt. They were combined with carbon black and Nafion and deposited over glassy carbon to study their electrocatalytic properties. Electrodes based on (110)-faceted Ni NCs displayed a first order reaction with KOH in the concentration range from 0.1 M to 1.0 M. These electrodes were characterized by higher coverages of active species, but lower diffusion coefficients of the species limiting the reaction rate when compared with electrodes prepared from spherical Ni NCs. Overall, electrodes based on faceted Ni NCs displayed excellent performance with very high current densities, up to 61 mA cm-2, and unprecedented mass activities, up to 2 A mg-1, at 0.6 V vs. Hg/HgO in 1.0 M KOH containing 1.0 M methanol. These electrodes also displayed a notable stability. While they suffered an activity loss of ca. 30% during the first 10 000 s of operation, afterward activity stabilized at very high current densities, ~35 mA cm-2, and mass activities, ~1.2 A mg-1, with only a 0.5% decrease during operation from 20 000 to 30 000 s.Peer ReviewedPostprint (author's final draft

Co–Sn nanocrystalline solid solutions as anode materials in lithium-ion batteries with high pseudocapacitive contribution

Co–Sn solid-solution nanoparticles with Sn crystal structure and tuned metal ratios were synthesized by a facile one pot solution-based procedure involving the initial reduction of a Sn precursor followed by incorporation of Co within the Sn lattice. These nanoparticles were used as anode materials for Li-ion batteries. Among the different compositions tested, Co0.7Sn and Co0.9Sn electrodes provided the highest capacities with values above 1500 mAh¿g-1 at a current density of 0.2 A¿g-1 after 220 cycles, and up to 800 mAh¿g-1 at 1.0 A¿g-1 after 400 cycles. Up to 81¿% pseudocapacitance contribution was measured for these electrodes at a sweep rate of 1.0 mV¿s-1, thereby indicating fast kinetics and long durability. The excellent performance of Co–Sn nanoparticle alloy-based electrodes was attributed to both the small size of the crystal domains and their suitable composition, which buffered volume changes of Sn and contributed to a suitable electrode restructuration.Postprint (author's final draft

Co–Sn nanocrystalline solid solutions as anode materials in lithium-ion batteries with high pseudocapacitive contribution

Co–Sn solid-solution nanoparticles with Sn crystal structure and tuned metal ratios were synthesized by a facile one pot solution-based procedure involving the initial reduction of a Sn precursor followed by incorporation of Co within the Sn lattice. These nanoparticles were used as anode materials for Li-ion batteries. Among the different compositions tested, Co0.7Sn and Co0.9Sn electrodes provided the highest capacities with values above 1500 mAh¿g-1 at a current density of 0.2 A¿g-1 after 220 cycles, and up to 800 mAh¿g-1 at 1.0 A¿g-1 after 400 cycles. Up to 81¿% pseudocapacitance contribution was measured for these electrodes at a sweep rate of 1.0 mV¿s-1, thereby indicating fast kinetics and long durability. The excellent performance of Co–Sn nanoparticle alloy-based electrodes was attributed to both the small size of the crystal domains and their suitable composition, which buffered volume changes of Sn and contributed to a suitable electrode restructuration

Colloidal Ni-Co-Sn nanoparticles as efficient electrocatalysts for the methanol oxidation reaction

The deployment of direct methanol fuel cells requires engineering cost-effective and durable electrocatalysts for the methanol oxidation reaction (MOR). As an alternative to noble metals, Ni-based alloys have shown excellent performance and good stability toward the MOR. Herein, we present a series of Ni3-xCoxSn2 colloidal nanoparticles (NPs) with composition tuned over the entire Ni/Co range (0 = x = 3). We demonstrate electrodes based on these ternary NPs to provide improved catalytic performance toward the MOR in an alkaline medium when compared with binary Ni3Sn2 NPs. A preliminary composition optimization resulted in Ni2.5Co0.5Sn2 NP-based electrodes exhibiting extraordinary mass current densities, up to 1050 mA mg-1, at 0.6 V vs. Hg/HgO in 1.0 M KOH containing 1.0 M methanol. This current density was about two-fold higher than that of Ni3Sn2 electrodes (563 mA mg-1). The excellent performance obtained with the substitution of small amounts of Ni by Co was concomitant with an increase of the surface coverage of active species and an enhancement of the diffusivity of the reaction limiting species. Additionally, saturation of the catalytic activity at higher methanol concentrations was measured for Ni3-xCoxSn2 NP-based electrodes containing a small amount of Co when compared with binary Ni3Sn2 NPs. While the electrode stability was improved with respect to elemental Ni NP-based electrodes, the introduction of small amounts of Co slightly decreased the cycling performance. Additionally, Sn, a key element to improve stability with respect to elemental Ni NPs, was observed to slowly dissolve in the presence of KOH. Density functional theory calculations on metal alloy surfaces showed the incorporation of Co within the Ni3Sn2 structure to provide more effective sites for CO and CH3OH adsorption. However, the relatively lower stability could not be related to CO or CH3OH poisoning.Peer ReviewedPostprint (author's final draft

Colloidal Ni-Co-Sn nanoparticles as efficient electrocatalysts for the methanol oxidation reaction

The deployment of direct methanol fuel cells requires engineering cost-effective and durable electrocatalysts for the methanol oxidation reaction (MOR). As an alternative to noble metals, Ni-based alloys have shown excellent performance and good stability toward the MOR. Herein, we present a series of Ni3-xCoxSn2 colloidal nanoparticles (NPs) with composition tuned over the entire Ni/Co range (0 = x = 3). We demonstrate electrodes based on these ternary NPs to provide improved catalytic performance toward the MOR in an alkaline medium when compared with binary Ni3Sn2 NPs. A preliminary composition optimization resulted in Ni2.5Co0.5Sn2 NP-based electrodes exhibiting extraordinary mass current densities, up to 1050 mA mg-1, at 0.6 V vs. Hg/HgO in 1.0 M KOH containing 1.0 M methanol. This current density was about two-fold higher than that of Ni3Sn2 electrodes (563 mA mg-1). The excellent performance obtained with the substitution of small amounts of Ni by Co was concomitant with an increase of the surface coverage of active species and an enhancement of the diffusivity of the reaction limiting species. Additionally, saturation of the catalytic activity at higher methanol concentrations was measured for Ni3-xCoxSn2 NP-based electrodes containing a small amount of Co when compared with binary Ni3Sn2 NPs. While the electrode stability was improved with respect to elemental Ni NP-based electrodes, the introduction of small amounts of Co slightly decreased the cycling performance. Additionally, Sn, a key element to improve stability with respect to elemental Ni NPs, was observed to slowly dissolve in the presence of KOH. Density functional theory calculations on metal alloy surfaces showed the incorporation of Co within the Ni3Sn2 structure to provide more effective sites for CO and CH3OH adsorption. However, the relatively lower stability could not be related to CO or CH3OH poisoning.Peer Reviewe