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Platinum-free highly active electro-catalysts

Objective

  • To increase the intrinsic Electrochemical activity of nano-structured nickel catalysts by developing of a route to create high-index facets nickel nano-particles.
  • To produce porous nickel electrodes by thermal spraying technology.
  • To investigate the stability of the catalysts in industrial conditions.

Hydrocarbon-based fuels have been the primary source of energy for mankind for centuries. However, these fuels are the primary source of greenhouse emissions which are severely affecting the global climate and jeopardizing the living environment of future generations. These issues drive a growing concern about finding suitable alternative that can successfully replace the conventional fuels used in a wide spectrum of applications from electricity generation to automotive and aerospace applications. Of the alternate fuels tested or proposed, hydrogen is a promising candidate.

Besides others ways, water electrolysis is an interesting technology for hydrogen production. To achieve maximal production rates with minimal electrical power, the used electrocatalysts have to be well designed. Platinum has, from the electrochemical point of view, the best performances among metals. However, platinum is not only very expensive, but is as well a very rare element on earth. For example, according to recent very optimistic estimations, the global platinum resources currently known about would sustain a fleet of 500 million fuel cell vehicles for just 15 years [Gordon et al.*]. There is an urgent need to develop other catalysts, not based on platinum. An interesting candidate is nickel.

*R.B. Gordon, M. Bertram, and T. E. Graedel, "Metal stocks and sustainability" Proceedings of the National Academy of Sciences of the US (2006) 103, 1209-1214

Increasing Electrochemical Activity of Nickel For The Hydrogen Evolution Reaction

There are two strategies to increase the activity of an electro-catalyst such as nickel:

  1. Increase the electro-active surface : This is for example achieved by using porous catalysts (such as Rainey nickel) or nickel in form of nano-particles or nano-wires
  2. Increase the intrinsic catalytic activity of nickel in regard to hydrogen evolution: The strategy consists in modifying the binding energy between the nickel and hydrogen by creating an alloy between nickel and a metal with high bonding energy such as Mo for example.

Both strategies were explored in the recent literature about nickel electrocatalysts for hydrogen production. However, the Electrochemical activity of a metal is as well strongly dependent on the crystalline orientation of the surface. It is known that in general surfaces with high Miller indexes have improved activity. This has as well been proven in the case of nickel. Recently, Tian* et al. published in Science a methodology to create high-index facets platinum nano-particles. The objective is to adapt this technique to nickel.

*Na Tian, Zhi-You Zhou, Shi-Gang Sun, Yong Ding, Zhong Lin Wang "Synthesis of Terahexahedral Platinum nanocrystals with High-Index facets and high electro-Oxidation Activity" Science (2007) 316, 732-735

Nano-structured Nickel Electro-Catalyst Produced By Thermal Spraying

Thermal sprays are extensively used in the aerospace, automotive, and power generation industries to provide protective coatings on engine, landing gear, and turbine components that are exposed to heat, corrosion, and wear. In a conventional thermal system such as plasma or high velocity oxygen fuel (HVOF) spray, coating particles with a size of tens of microns are fed into the spray gun where they are heated and accelerated to high velocities. Consequently, the high speed impact of molten or semi-molten particles on the surface provides enough energy for the particle to fuse with the surface.

In the past few years, there have been major efforts to utilize thermal spray systems to deposit nano-particles on a substrate because of the superior performance of nano-structured coatings. The main direction to achieve nano-structured coatings has been using liquid feedstock. The liquid suspension of dispersed nano-particles (with a size range of 30 to 200 nm) is injected into thermal spray flames. The liquid jet is first fragmented into small droplets via an atomization mechanism. Then the liquid droplets evaporate allowing the nano-particles contained in the droplets to accelerate and melt as in a conventional thermal spray process. This technology shows significant promise for coating with nano-powders using thermal spray guns, allowing us to produce thick nano-structured coatings with a moderate cost suitable for industrial applications.


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