Catalyst In Alkaline Electrolyte Research Articles

Enhanced Catalytic Activities of NiPt Truncated Octahedral Nanoparticles toward Ethylene Glycol Oxidation and Oxygen Reduction in Alkaline Electrolyte

The high cost and poor durability of Pt nanoparticles (NPs) are great limits for the proton exchange membrane fuel cells (PEMFCs) from being scaled-up for commercial applications. Pt-based bimetallic NPs together with a uniform distribution can effectively reduce the usage of expensive Pt while increasing poison resistance of intermediates. In this work, a simple one-pot method was used to successfully synthesize ultrafine (about 7.5 nm) uniform NiPt truncated octahedral nanoparticles (TONPs) in dimethylformamid (DMF) without any seeds or templates. The as-prepared NiPt TONPs with Pt-rich surfaces exhibit greatly improved catalytic activities together with good tolerance and better stability for ethylene glycol oxidation reaction (EGOR) and oxygen reduction reaction (ORR) in comparison with NiPt NPs and commercial Pt/C catalysts in alkaline electrolyte. For example, the value of mass and specific activities for EGOR are 23.2 and 17.6 times higher comparing with those of commercial Pt/C, respectively. Our results demonstrate that the dramatic enhancement is mainly attributed to Pt-rich surface, larger specific surface area, together with coupling between Ni and Pt atoms. This developed method provides a promising pathway for simple preparation of highly efficient electrocatalysts for PEMFCs in the near future.

Ordered Mesoporous Nickel Sphere Arrays for Highly Efficient Electrocatalytic Water Oxidation

We report the preparation and use of the three-dimensionally ordered mesoporous Ni sphere arrays (3D-OMNiSA) as a highly effective OER catalyst in alkaline electrolyte. The 3D-OMNiSA is fabricated through lyotropic liquid crystal templating within a polymer inverse opal. The prepared 3D-OMNiSA catalyst exhibits a low overpotential of 254 mV at 10 mA cm–2 and a small Tafel slope of 39 mV decade–1, better than the commercial precious RuO2 catalyst. The mass activity (166.5 A g–1) and turnover frequency (0.0281 s–1) of 3D-OMNiSA are about 4.3 and 2.2 times that of RuO2, respectively. Additionally, this 3D-OMNiSA catalyst shows a high durability under harsh water oxidation cycling test. The outstanding OER performance of the 3D-OMNiSA could be attributed to the large surface area, efficient mass and charge transport, and high structural stability arising from the unique 3D hierarchical porous structure of the 3D-OMNiSA consisting of ordered close-packed mesoporous spheres.

Pyrolysis of Animal Bones with Vitamin B12: A Facile Route to Efficient Transition Metal–Nitrogen–Carbon (TM‐N‐C) Electrocatalysts for Oxygen Reduction

By pyrolyzing cattle bones, hierarchical porous carbon (HPC) networks with a high surface area (2520 m(2) g(-1) ) and connected pores were prepared at a low cost and large scale. Subsequent co-pyrolysis of HPC with vitamin B12 resulted in the formation of three-dimensional (3D) hierarchically structured porous cobalt-nitrogen-carbon (Co-N-HPC) electrocatalysts with a surface area as high as 859 m(2) g(-1) as well as a higher oxygen reduction reaction (ORR) electrocatalytic activity, better operation stability, and higher tolerance to methanol than the commercial Pt/C catalyst in alkaline electrolyte.

Nickel supported on nitrogen-doped carbon nanotubes as hydrogen oxidation reaction catalyst in alkaline electrolyte.

The development of a low-cost, high-performance platinum-group-metal-free hydroxide exchange membrane fuel cell is hindered by the lack of a hydrogen oxidation reaction catalyst at the anode. Here we report that a composite catalyst, nickel nanoparticles supported on nitrogen-doped carbon nanotubes, has hydrogen oxidation activity similar to platinum-group metals in alkaline electrolyte. Although nitrogen-doped carbon nanotubes are a very poor hydrogen oxidation catalyst, as a support, it increases the catalytic performance of nickel nanoparticles by a factor of 33 (mass activity) or 21 (exchange current density) relative to unsupported nickel nanoparticles. Density functional theory calculations indicate that the nitrogen-doped support stabilizes the nanoparticle against reconstruction, while nitrogen located at the edge of the nanoparticle tunes local adsorption sites by affecting the d-orbitals of nickel. Owing to its high activity and low cost, our catalyst shows significant potential for use in low-cost, high-performance fuel cells.

Identification of highly active Fe sites in (Ni,Fe)OOH for electrocatalytic water splitting.

Highly active catalysts for the oxygen evolution reaction (OER) are required for the development of photoelectrochemical devices that generate hydrogen efficiently from water using solar energy. Here, we identify the origin of a 500-fold OER activity enhancement that can be achieved with mixed (Ni,Fe)oxyhydroxides (Ni(1-x)Fe(x)OOH) over their pure Ni and Fe parent compounds, resulting in one of the most active currently known OER catalysts in alkaline electrolyte. Operando X-ray absorption spectroscopy (XAS) using high energy resolution fluorescence detection (HERFD) reveals that Fe(3+) in Ni(1-x)Fe(x)OOH occupies octahedral sites with unusually short Fe-O bond distances, induced by edge-sharing with surrounding [NiO6] octahedra. Using computational methods, we establish that this structural motif results in near optimal adsorption energies of OER intermediates and low overpotentials at Fe sites. By contrast, Ni sites in Ni(1-x)Fe(x)OOH are not active sites for the oxidation of water.

Noble-metal-free electrocatalysts with enhanced ORR performance by task-specific functionalization of carbon using ionic liquid precursor systems.

The synthesis and characterization of functionalized carbon using variable doping profiles are presented. The hybrids were obtained from nitrile-functionalized ionic precursors and a ferric chloride mediator. This way, novel nitrogen doped and nitrogen-sulfur, nitrogen-phosphorus, and nitrogen-boron codoped carbon hybrids with a morphology containing microporous nanometer-sized particles were obtained. As-prepared heteroatom doped carbons exhibited superior electrocatalytic activity toward the oxygen reduction reaction (ORR) in alkaline and acid electrolytes. In particular, both the heteroatom type and iron were found to play crucial roles in improving the catalytic activity of functionalized carbon. It is worth noting that sulfur-nitrogen codoped functionalized materials synthesized in the presence of ferric chloride showed higher activity and stability in comparison to those of the commercial state-of-the-art Pt catalyst in alkaline electrolyte. Moreover, in acid electrolyte, sulfur-nitrogen codoped catalyst rivaled the activity of Pt with a stability outperforming that of Pt. Our X-ray photoelectron spectroscopy (XPS) investigation revealed a distinctive atomic structure in nitrogen-sulfur codoped material in comparison to other codoped catalysts, most likely explaining its superior electrocatalytic activity. This work presents a novel toolbox for designing advanced carbon hybrids with variable heteroatom doping profiles which presents tunable and enhanced ORR performance.

Electrooxidation of ethanol on Pt-based and Pd-based catalysts in alkaline electrolyte under fuel cell relevant reaction and transport conditions

Aiming at a detailed kinetic understanding under fuel cell relevant, but nevertheless well-defined reaction and transport conditions, the electrooxidation of ethanol on Pt-based (Pt/C, PtRu black) and Pd-based (Pd/C, Pd/CeO2/C) catalysts in alkaline solution was investigated at temperatures up to 100°C and at controlled electrolyte flow in a high temperature/high pressure thin-layer flow cell. Most important, the data reveal drastic effects of the reaction temperature. The apparent activation energies for ethanol oxidation on the different catalysts were determined and found to vary significantly with potential and the catalyst used. The addition of Ru to Pt and CeO2 to Pd/C improves the tolerance toward catalyst poisoning at low potentials, while for higher potentials and especially at higher temperatures the activity of the monometallic catalysts is higher. For reaction at 0.5V and 80°C, the Pd/C catalyst exhibits the highest activity, both in terms of metal mass specific and active surface area normalized rates; the addition of an oxophilic component is beneficial only for lower potentials. Overall, the results illustrate the need for model studies under close to realistic reaction conditions for the understanding of reactions in fuel cells.

Significantly enhanced electrocatalytic activity for methanol electro-oxidation on Ag oxide-promoted PtAg/C catalysts in alkaline electrolyte

Alloyed PtmAg nanostructures (m being the atomic Pt/Ag ratio, m=0.03–1.0) supported on carbon black were prepared and comprehensively characterized by ultraviolet–visible spectroscopy, X-ray diffraction, and transmission electron microscopy techniques. Cyclic voltammetry (CV) and chronoamperometry studies of methanol electro-oxidation reaction (MOR) in alkaline electrolyte indicated that the catalytic activity and CO tolerance of Pt were improved remarkably by the co-presence of Ag. A volcano relationship between the activity and m was found for the PtmAg/C catalysts, and both the highest mass-specific activity and the highest intrinsic activity of Pt were reached at m=0.5. Interestingly, we also found that the catalytic activity of the PtmAg/C catalysts strongly depended on the high-potential limit of CV. When the PtmAg/C catalysts were cycled up to 0.5V (vs. saturated calomel electrode), which induced a significant redox process of Ag, they showed ca. 50 times higher catalytic activity than those not subjected to the Ag redox process (up to 0.1V). Our study clearly demonstrated that the Ag oxide played a crucial role in promoting the catalytic role of Pt for MOR in alkaline electrolyte.

Recent Advances in Nonprecious Metal Catalysts for Oxygen Reduction Reaction in Fuel Cells

Non-precious metal catalysts (NPMCs) are developed for oxygen reduction in alkaline fuel cell (AFC). The performance of the catalyst in alkaline electrolyte is studied by rotating disk electrode (RDE). The NPMC prepared with carbon-supported metal-nitrogen composite precursor and subjected to heat-treatment shows comparable activity for oxygen reduction when compared with Pt/C catalyst. The fuel cell performance of the catalyst was studied using anion exchange membrane (AEM) from Tokuyama Corporation. The NPMC exhibits an open circuit potential (OCP) of 0.97 V and a maximum power density of 177 mW cm -2 at 50 °C.

Preparation of Ag/C catalysts for the O 2 electrode by the Ag(I) SCRM

Ag/C catalysts with different Ag particle-size distribution were prepared by Ag(I) single crystal reduction method (Ag(I) SCRM) and physically characterized. Their electrochemical performances were investigated by using Ag/C as O 2 reduction catalysts in alkaline electrolyte. The results showed that the electrocatalytic activity of Ag/C catalysts prepared by the Ag(I) SCRM was significantly enhanced compared with that of Ag/C catalysts prepared by Ag 2O reduction method (Ag 2O RM) under the same content of Ag. The cyclic voltammetry indicate that the larger Ag particles are favourable to the four-electron reduction of O 2, the finer Ag particles are favourable to the two-electron reduction of O 2; the overpotential of four-electron reduction is higher, the overpotential of two-electron reduction is lower.