Hollow Cobalt Sulfide Nanoparticles: A Robust and Low-Cost pH-Universal Oxygen Evolution Electrocatalyst

The development of a less expensive yet outstanding electrocatalyst in terms of activity and stability for the oxygen evolution reaction (OER) working in a universal pH range still remains challenging. Most of the highly active expensive electrocatalyts work in a single pH. Therefore, the development of a low cost electrocatalyst, which fulfils the above-mentioned requirements, is highly needed. Here, we report the development of Co3S4 hollow nanoparticles using a one-step hot injection method, and we modified them for superior electrocatalytic OER activity and stability in the entire pH range (alkaline, neutral, and acidic). Activated carbon supported Co3S4 hollow nanoparticles exhibit remarkable OER activity (overpotential, η = 0.27 V in 1.0 M KOH; 0.33 V in 0.5 M H2SO4; 0.37 V in 1.0 M phosphate buffer) and offer maximal cycling stability for more than 24–48 h (>10 000 cycles) with no loss in the magnitude of current density (10 mA/cm2). High spin states of Co2+ and Co3+ and their large spin–orbit interactions (as indicated by XPS and EPR studies) related to oxygen surface exchange mechanism are proposed to account for the observed high electrocatalytic activity at all pH levels.