ABSTRACT
CuCo2S4 is an important mixed-metal spinel-type sulfide that is typically synthesized using high-temperature solid-state reactions, which produce agglomerated particles with low surface areas that are not optimal for applications such as heterogeneous catalysis. Here, we show that highly crystalline and nonagglomerated colloidal CuCo2S4 nanoparticles can be synthesized in solution at 200 °C, which is significantly lower than previously reported methods. The CuCo2S4 nanoparticles were found to be highly active electrocatalysts for the oxygen evolution reaction (OER) under strongly alkaline conditions (1.0 M KOH, pH 14), requiring an OER overpotential of 395 mV to produce a current density of 10 mA cm(-2). X-ray photoelectron spectroscopy (XPS) studies showed evidence of oxide formation, suggesting, in conjunction with the observed electrocatalytic properties, that the mixed-metal sulfides may serve as precursors to oxides and/or hydroxides, which are likely to be the catalytically active species.
ABSTRACT
Nanoparticles of nickel phosphide (Ni2P) have been investigated for electrocatalytic activity and stability for the hydrogen evolution reaction (HER) in acidic solutions, under which proton exchange membrane-based electrolysis is operational. The catalytically active Ni2P nanoparticles were hollow and faceted to expose a high density of the Ni2P(001) surface, which has previously been predicted based on theory to be an active HER catalyst. The Ni2P nanoparticles had among the highest HER activity of any non-noble metal electrocatalyst reported to date, producing H2(g) with nearly quantitative faradaic yield, while also affording stability in aqueous acidic media.