Cu-Deficient Plasmonic Cu_2-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°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. Cu_2-xS nanoplates with three different doping levels were tested for their electrocatalytic activity for the oxygen reduction reaction (ORR) in alkaline solution. Importantly, increasing the concentration of free holes in Cu_2-xS significantly enhanced the ORR catalytic activity. Furthermore, to improve the electrical conductivity, the most heavily doped Cu_2-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 Cu_2-xS catalysts can provide a four-electron reduction pathway. The ORR catalytic activity of the Cu_2-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. (Figure Presented).