Development of PGM-Free Catalysts for Fuel Cells Using Advanced Polymerization Techniques

Platinum Group Metal Free (PGM-Free) catalysts present a promising opportunity to make hydrogen fuel cells more affordable, however, issues with stability and electrochemical activity continue to hinder their application. Recent studies point to the availability of nitrogen and a well-defined pore structure as avenues of improvement. To address this need, copolymer templated nitrogen-enriched carbon (CTNC) was used as precursor to prepare PGM-free catalysts for oxygen reduction reaction. By employing its rich nitrogen content and interconnected, controlled porous structure, a significant amount of Fe-N-C active sites were formed by co-annealing CTNC with an iron source. The formed N/Fe co-doped nanocarbon (CTNC-Fe) catalyst exhibits high electrochemical activity in oxygen reduction reaction (ORR) under acidic conditions and can function remarkably well as a catalyst in fuel cell under standard procedures. FeNx active sites were detected and the nanostructure of CTNC was retained despite the various processing steps involved during synthesis.

The use of CTNC allows for control of the pore morphology of the catalyst using controlled/ “living” radical polymerization to synthesize the block copolymer (BCP) precursor. This allowed a greater level of control in tuning the formation of active sites, their energy activation barrier and therefore the electrochemical activity of the catalyst. The interaction between pore morphology and formation of active sites remains unclear, even though the produced catalysts were confirmed to be influenced significantly by the composition and degree of polymerization of the BCP precursors.

This work describes a novel and revolutionary method of PGM-free catalyst synthesis using advanced polymerization techniques. Much work remains to be done in improving andoptimizing the methods of synthesis of the catalyst. This includes improving the Fe-doping process either by use of standard procedures with transition metal salt precursors or by a newly developed method presented in this work using poly(vinyl ferrocene), an iron containing metallopolymer. In addition, further experimentation with different CTNCs made by varying the composition and degree of polymerization. At any rate, the catalyst presented here has already reached a level of electrochemical activity competitive with other PGM-free catalysts (half-wave potential of 0.8 V vs NHE) and presents a new approach to the development and scalability of affordable fuel cells as a sustainable clean energy alternative.