Activating nickel-based anodes for high-performance fuel cells
|Hydrogen fuel cells could play a key role in a cleaner energy future, but their widespread deployment depends on replacing expensive platinum-group metals with more abundant alternatives. Anion-exchange membrane fuel cells (AEMFCs) are particularly promising in this respect, and nickel is one of the leading candidates for catalyzing the hydrogen oxidation reaction (HOR).
However, nickel has a hidden weakness: when exposed to oxygen, its surface rapidly forms an oxide layer that effectively switches the catalyst off. Simon Amigues (ICGM – Institut Charles Gerhardt de Montpellier), Michal Ronovský (LEPMI – Laboratory of Electrochemistry and Physical-Chemistry of Materials and Interfaces, Grenoble), Tomáš Hrbek (Faculty of Mathematics and Physics at Charles University, Prague) and colleagues studied this process, showing that it can represent a critical factor in the performance and reproducibility of nickel-based AEMFCs.
Researchers investigated three representative nickel HOR catalysts using both electrochemical experiments and complete fuel cells. Using several analytical techniques, including the Electron Spectroscopy for Chemical Analysis under Environmental Conditions (EnviroEsca) instrument available at CERIC Czech Partner Facility, scientists described the electrochemical behaviour and activation of these nickel surfaces. The results demonstrate that an activation step is essential to remove or reduce the native oxide layer before hydrogen oxidation can proceed. Importantly, the team also identified an unexpected opponent: oxygen crossing through the anion-exchange membrane. Even small amounts can create sufficiently oxidizing conditions to re-passivate nickel.
The most practical solution proved to be a simple chemical activation procedure, initially feeding hydrogen to the anode and nitrogen to the cathode: in fact, once activated, nickel-based anodes delivered high power density and stable operation.
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