Solution Phase Synthesis of Structurally Ordered PtMg Alloy Electrocatalysts with Extra High Durability in Hydrogen Fuel Cells

Fuel cells are promising clean energy technology that converts chemical energy from a fuel (hydrogen gas) into electricity by utilizing electrons released to do external work. They are seen as sustainable alternatives to the existing combustion-based engines, offering exceptional promise towards clean energy with the potential to reduce reliance on fossil fuels. Alloys of platinum with transition metals exhibit excellent activity toward oxygen reduction reaction, but their poor stability in practical fuel cells retards their commercial utilization. On the other hand, platinum-alkaline-earth metal alloys promise to be active and stable due to their high alloy formation energies, yet their synthesis in nanoparticle form remains a challenge. Herein, we report a strategy that overcomes this challenge by preparing platinum-magnesium (PtMg) alloy nanoparticles in the solution phase for the first time. The PtMg nanoparticles exhibit a distinctive structure with a structurally ordered intermetallic core and a Pt-rich shell, showcasing remarkable features in the realm of other similar alloys. The PtMg/C as a cathode catalyst in a hydrogen-oxygen fuel cell exhibits a mass activity of 0.50 A mg_Pt^-1 at 0.9 V with a marginal decrease to 0.48 A mg_Pt^-1 after 30,000 cycles, exceeding the US Department of Energy 2025 beginning-of-life and end-of-life mass activity targets, respectively. Theoretical studies show that the activity stems from a combination of ligand and strain effects between the intermetallic core and the Pt-rich shell, while the stability originates from the high vacancy formation energy of Mg in the alloy.