(Invited) Microplasma-Deposited Ni-Fe and Co Oxides for Oer and Supercapacitors

Abstract

Microplasma-based spray deposition was used to create high surface area Ni-Fe and Co oxide nanostructures on a variety of substrates (e.g., ITO, lithographic patterns, fibers) for electrocatalysis and supercapacitor applications. NiO, Fe-doped (rocksalt) NiO, NiFe2O4, and CoxOy films were deposited at 10-100 torr using a flow through, hollow cathode supersonic jet plasma with organometallic precursors. The resulting films were subsequently evaluated for their oxygen evolution reaction (OER) activity and potential use as Faradaic supercapacitors. OER overpotentials were compared for the various Ni-Fe oxides, and Fe-doping of the rocksalt NiO structure at the few % level was seen to lower overpotentials to ~0.3 V at 10 mA/cm2, which compare well with those obtained with more expensive Ru and Ir oxides. Turnover frequency increased to 0.5 1/s with Fe loading at 350 mV overpotential; morphology and surface composition (SEM, XPS) before and after electrochemical testing showed slight restructuring of the catalyst surface and an increase in Ni(OH)2. Electrochemical activity and overpotentials were also very stable, as evidenced by extended chronoamperometry and CV testing. For supercapacitor applications, NiO and CoxOy were directly spray deposited on carbon cloth at room temperature; double layer and Faradaic pseudo-capacitance ranged from 100-300 F/g at 10 mV/s scan rates, with faster plasma jet rastering rates yielding higher surface area and effective capacitance. The talk will highlight the microplasma deposition method and discuss the aforementioned electrochemical results in detail.