Optimizing Co Content in Intermetallic L10-FeCoPt Nanoparticles to Enhance the Electrocatalytic Performance

The L10-FeCoPt nanoparticles with ultra-small size, highly ordered structure, and various Co contents have been successfully obtained by annealing the wet-chemical synthesized nanoparticles. The addition of third-element Co into L10-FePt nanoparticles would increase the grain size, facilitate the disorder-order transition, and enhance the saturation magnetization and coercivity. The better permanent magnet properties and maximum electrocatalytic HER activity of L10-FeCoPt nanoparticles were achieved when added the moderate Co content (4.5 % and 8.5 %). The hydrogen evolution reaction (HER) kinetics and density functional theory revealed that the Co atom would promote the hybridization of Fe-3d and Pt-5d orbitals and increase the hydrogen adsorption free energy to closer to 0. Optimization of Co content to a suitable range would generate higher permanent magnetic properties and suitable surface energy, which facilitated the proton transformation and lowered the Tafel slope to follow the Volmer-Tafel process in HER. This work illustrates that optimizing third-element content in Pt-based magnetic intermetallic is a feasible strategy to operate the electrocatalytic reaction pathway and enhance the electrocatalytic performance.