A Low-Temperature Molecular Precursor Approach to Copper-Based Nano-Sized Digenite Mineral for Efficient Electrocatalytic Oxygen Evolution Reaction

In the urge of designing noble metal-free and sustainable electrocatalysts for oxygen evolution reaction (OER), herein, a mineral Digenite Cu$_{9}$S$_{5}$ has been prepared from a molecular copper(I) precursor, [{(PyHS) $_{2}$Cu$^{l}$ (PyHS)} $_{2}$] (OTf)$_{2}$ (1), and utilized as an anode material in electrocatalytic OER for the first time. A hot injection of 1 yielded a pure phase and highly crystalline Cu$_{9}$S$_{5}$, which was then electrophoretically deposited (EPD) on a highly conducting nickel foam (NF) substrate. When assessed as an electrode for OER, the Cu$_{9}$S$_{5}$/NF displayed an overpotential of merely 298±3 mV at a current density of 10 mAcm$^{-2}$ in alkaline media. The overpotential recorded here supersedes the value obtained for the best reported Cu-based as well as the benchmark precious-metal-based RuO$_{2}$ and IrO$_{2}$ electrocatalysts. In addition, the choronoamperometric OER indicated the superior stability of Cu$_{9}$S$_{5}$/NF, rendering its suitability as the sustainable anode material for practical feasibility. The excellent catalytic activity of Cu$_{9}$S$_{5}$ can be attributed to the formation of a crystalline CuO overlayer on the conductive Cu$_{9}$S$_{5}$ that behaves as active species to facilitate OER. This study delivers a distinct molecular precursor approach to produce highly active copper-based catalysts that could be used as an efficient and durable OER electro(pre)catalysts relying on non-precious metals