Many grand challenges in energy conversion and storage need discovery of new materials. However, there are not too many reported synthesis approaches that could easily be implemented for screening and rational understanding of structure-behavior relationships. Specifically, the challenges include semiconductors for photoelectrochemical water splitting, stable electrocatalysts for oxygen evolution and reduction, and nitrogen reduction and for many heterogeneous gas-solid reactions including carbon dioxide reduction. Many of the above challenges require synthesis of multi-element alloys with composition over entire range regardless of phases present.  

Here, we report a new synthesis technique that can be used to accelerate the discovery of materials for various energy conversion and storage applications. Specifically, this technique allows a rapid and controlled synthesis of mixed metal oxide particles using plasma oxidation of liquid droplets containing mixed metal precursors. The conventional wet chemical methods for synthesis of multi-metal oxide alloys often require time-consuming high pressure and temperature processes, and so the challenge is to develop rapid and scalable techniques with precise compositional control.  The concept is demonstrated by synthesizing binary and ternary transition metal oxide alloys with control over entire composition range using metal precursor solution droplets oxidized using atmospheric oxygen plasma. The results show the selective formation of metastable spinel and the rocksalt solid solution phases with compositions over the entire range by tuning the metal precursor composition. The synthesized manganese doped nickel ferrite nanoparticles, NiMn_zFe_2-zO₄ (01), exhibits considerable electrocatalytic activity towards oxygen evolution reaction (OER), achieving an overpotential of 0.39V at a benchmarking current density of 10 mAcm^-2 for a low manganese content of z = 0.20.