High-performance oxygen reduction electrocatalysis enabled by Ni _core Pd _shell nanoparticles immobilized on MoS ₂ nanosheets

The development of certain energy storage devices, such as fuel cells (FCs), as well as next-generation metal-air batteries (MABs), has increased during the first 25 years of the current century, mostly due to the startlingly rapid depletion rate of fossil fuels. The above devices operate electrochemically and commonly involve the oxygen reduction reaction (ORR). ORR mainly proceeds through a 4e^- pathway and suffers from both thermodynamic and kinetic limitations. Considering that the development of most next-generation electrocatalysts is still in its infancy, the use of noble metals is inevitable when the goal is to meet industry standards for commercially operating FCs in terms of the energy output while maintaining a low CO₂ footprint. Palladium (Pd) appears to be the most economically viable and overall balanced choice in terms of cost/activity trade-off. However, the goal of utilizing low amounts of noble metals remains crucial for the development of electrocatalysts. The approach of constructing core-shell nanoparticles appears to be an attractive strategy for achieving atom economy and limiting the use of noble metals. The core-shell strategy relies on building a non-precious metal core and then displacing surface atoms with noble metal atoms to furnish a thin coating shell. The use of two-dimensional nanomaterials with suitable intrinsic properties and chemical/physicochemical tunability could also help to improve the steps towards sustainable electrocatalysts. Transition metal dichalcogenides (TMDs), especially MoS₂, have not been explored as substrates for core-shell nanoparticles. This work focuses on immobilizing Ni_corePd_shell nanoparticles onto exfoliated semiconducting MoS₂ nanosheets to furnish a novel ORR electrocatalyst. The Ni_corePd_shell nanoparticles were stabilized with 1-pyrenebutyric acid (PBA), and subsequently, were non-covalently immobilized on the 2H-MoS₂ basal plane, to offer new ORR active sites along the pre-existing unsaturated Mo edges. The novel nanoensemble was fully characterized by spectroscopic, thermal and microscopic methods, to assess the interaction between the two moieties. Ultimately, the nanoensemble was studied as an alkaline ORR electrocatalyst through advanced electrochemical techniques, which unveiled the mechanism behind this interesting system, supporting its potential as a promising system for next-generation ORR electrocatalysts.