Cu-Deficient Plasmonic Cu2-xS Nanoplate Electrocatalysts for Oxygen Reduction

Cation deficient transition metal sulfides have attracted increased attention due to their unique properties that arise from degenerate p-doping, particularly their localized surface plasmon resonance (LSPR) and related optical properties. Here, we present the first study of their electrocatalytic activity. We developed a facile one-pot method to prepare p-doped copper sulfide nanoplates with tunable LSPR at moderate temperature (below 100 degrees C) without any hot injection or rapid mixing step. The doping level was controlled by varying the concentration of cation precursor (Cu2+) to finely tune the LSPR wavelength without changing the nanoplate size or morphology. Cu2-xS nanoplates with three different doping levels were tested for their electrocatalytic activity for the oxygen reduction reaction (ORB.) in alkaline solution. Importantly, increasing the concentration of free holes in Cu2-xS significantly enhanced the ORR catalytic activity. Furthermore, to improve the electrical conductivity, the most heavily doped Cu2-xS nanoplates were deposited on carbon black (Vulcan XC-72) and reduced graphene oxide (rGO), thereby leading to substantial enhancement of ORR steady-state current in both electrochemical and mass-transfer controlled potential regions. A calculation of average electron transfer number along with the measured peroxide yield indicated that both carbon black and rGO supported Cu2-xS catalysts can provide a four-electron reduction pathway. The ORR catalytic activity of the Cu2-xS nanoplates does not yet match that of state-of-the-art Pt/C catalysts. However, this work opens up new opportunities to apply p-doped copper chalcogenides as electrocatalysts for the ORR beyond conventional nonprecious metal catalysts based upon Fe, Co, N, and C.