Progress towards lower-cost proton exchange membrane fuel cells

The scientific community is continuously seeking for improvements in energy conversion and storage technologies to move away from fossil fuels. Proton exchange membrane (PEM) fuel cells are promising in this respect, since the only byproduct of the reaction is water vapor. However, the technology remains limited by high costs associated with the use of platinum group metals (PGMs) in cathode and anode electrodes.

In a research update, Mølmen et al. summarized the latest strategies to reduce the amount of PGMs at the cathode where oxygen reduction takes place. Because it is a very active field, the review focused only on publications released within the last two years. The authors conclude the most promising approaches thus far involve the combination of different methods, such as alloying platinum with a transition metal or the synthesis of hollow nanoparticles.

The review divides the recent advances in catalyst materials into two categories: PGM-based catalysts and PGM-free catalysts. PGM-based catalysts can involve the alloying of platinum or another PGM with transition metals, such as iron, cobalt, nickel, or copper. Other approaches focus on the optimization of pure platinum catalysts or the supporting layer. Lastly, the protection of the PGM catalyst in a carbon-based matrix limits degradation and increases durability.

Early PGM-free catalysts included carbon doped with elements like nitrogen, sulfur, and phosphorous, which demonstrated feasibility in half cell and PEM fuel cell experiments. The field soon moved into co-doping carbon with nitrogen and a transition metal to form single-atom catalysts, which is the current focus of most PGM-free research. PGM-free catalysts can significantly reduce costs of PEM fuel cells but currently suffer from degradation and insufficient durability.

Source: “Recent advances in catalyst materials for proton exchange membrane fuel cells,” by Live Mølmen, Konrad Eiler, Lars Fast, Peter Leisner, and Eva Pellicer, APL Materials (2021). The article can be accessed at http://doi.org/10.1063/5.0045801 .