Report

Teaser, summary, work performed and final results

Periodic Reporting for period 2 - IL-E-CAT (Enhancing electrocatalysis in low temperature fuel cells by ionic liquid modification)

Teaser

The transition towards renewable energy is especially driven by sustainable electrical energy. This makes a demand for highly efficient electrochemical conversion processes within the energy and also chemical production section. Key component of these electrochemical...

Summary

The transition towards renewable energy is especially driven by sustainable electrical energy. This makes a demand for highly efficient electrochemical conversion processes within the energy and also chemical production section. Key component of these electrochemical conversion processes are electrocatalysts. Especially for the oxygen reduction reaction highly active catalysts are needed to push the commercialization e.g. of the low temperature polymer electrolyte fuel cell (PEM-FC).
Recently it was shown that the activity of state of the art platinum catalysts can be boosted, if they are modified with a tiny amount of ionic liquid (IL). Despite this impressive effect, the origin of the boosting is unclear. Objectives of IL-E-CAT are the full scientific exploration of the remarkable activation and stabilization effects. Structure property relationships for IL, active metal and support should be deduced and be applied to increase the activity even further. Additionally, the general applicability of this concept should be demonstrated by transferring it to other electrocatalysed reactions.

Work performed

Despite of the high complexity of the IL, active metal and support interaction the methodology of the project allowed to deduce first fundamental structure-performance relationships, which are summarized subsequently:

1) An IL with higher hydrophobicity can more efficiently reduce the coverage/blockage of Pt by non-reactive oxygenated species and can result in a more pronounced boosting effect on activity. As a generalization, the IL modification seems to be effective in reactions where water product is produced.

2) ILs with too long hydrocarbon side chains (e.g. above 6 C-atoms) can hinder surface accessibility of active sites, probably arising from the spontaneous self-assembly of IL molecules with long non-polar side chains and the consequent formation of lipid-like structure on Pt surfaces. This effect leads to reduced activity of the Pt catalyst despite the increase in hydrophobicity of long chain ILs.

3) The IL can suppress Pt dissolution which acts as a major mechanism for the degradation of Pt catalysts.

Final results

The IL modification boosting effect, known for Pt based catalysts, could be transferred to non-noble metal catalytic materials. The mechanism for the boosting seems to differ and interestingly, the electrochemical accessible surface area, based on capacitance measurements, can be increased by the IL modification.