Hydrogen Depolarised Anode: Proof of Concept and Operational Overpotential Determination
Authors: Sacré Nicolas , Chenitz Regis , Faral Manon , Mokrini Asmae , Huot Jean-Yves , Bouchard Pierre , Bibienne Thomas , Laroche Nicolas , Magnan Jean-François , Dollé Mickael 
Published: May 2020

Lithium hydroxide world demand is growing very fast and will drastically increase in the next years. It could become a critical material in the coming years. This lightning growth is mostly due to lithium-ion batteries development. In particular, the proportion always more important of hybrid and electric cars sell worldwide. This consumer change is mainly driven by a better environmental concern. However, the battery production price and its high environmental cost are breaking the market potential.

In order to jointly decreasing these two limitations, Nemaska Lithium is developing a non conventional approach to produce battery-grade lithium hydroxide from his spodumene mine located in the north of Quebec. Its electro-membrane process mainly consumes green electricity and avoid the utilization of huge quantity of chemical products. In a constant improvement ambition, Nemaska Lithium decided to study the opportunity to use a Hydrogen Depolarized Anode (HDA) in order to save energy for the direct electro-membrane synthesis of high purity Lithium Hydroxide.

This new approach is inspired from proton exchange membrane fuel cells because the anode reaction is similar (H2 → 2H+ + 2e-). This similarity has oriented the general architecture of the electrode. Thus, it was chosen to supply with hydrogen the back of the HDA and to privilege a porous structure. The other side of the HDA is in close contact with the electrolyte composed of lithium sulfate and sulfuric acid (to enhance the conductivity). The cell porosity orients the reactant to the platinum catalytic sites where the reaction itself is taking place. From this place, produced protons must travel through the Nafion and the electrolyte while electrons circulate on the opposite way across the cell porosity. As if global operation is similar between fuel cells and HDA, a certain number of specificities that do not exist in fuel cell can influence the performance of the HDA. To name just a few main examples, the influence of a liquid phase in contact with the anode and the impact of the lithium sulfate on the kinetic reaction.

To reach a most complete possible comprehension of this new technology, a R&D equipment has been specifically developed to support the operation of a 50 cm2 cell. This study will demonstrate the ability of an HDA to oxidize efficiently hydrogen without needing an important overpotential. Two approaches will be developed to isolate the anode overpotential induced during its operation. Following that, the influence of different parameters like salt concentration and Nafion humidity will be quantified. By crossing the cell operation data with different ex-situ characterisations (pH or conductivity measurements, microscopy images, etc...), the influence of the different components will be deconvoluted, leading to a complete understanding of the HDA operation. Following this, an optimized composition will be proposed with a very competitive operational overpotential versus standard used anode.