Abstract
Both high activity and mass production potential are important for bifunctional electrocatalysts for overall water splitting. Catalytic activity enhancement was demonstrated through the formation of CoS2 nanoparticles with mono-phase and extremely porous structures. To fabricate porous structures at the nanometer scale, Co-based metal-organic frameworks (MOFs), namely a cobalt Prussian blue analogue (Co-PBA, Co3[Co(CN)6]2), was used as a porous template for the CoS2. Then, controlled sulfurization annealing converted the Co-PBA to mono-phase CoS2 nanoparticles with ~ 4 nm pores, resulting in a large surface area of 915.6 m2 g−1. The electrocatalysts had high activity for overall water splitting, and the overpotentials of the oxygen evolution reaction and hydrogen evolution reaction under the operating conditions were 298 mV and −196 mV, respectively, at 10 mA cm−2.
Highlights
Electrochemical water splitting consists of two half reactions, namely the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER)
Such Metal-organic frameworks (MOFs)-driven CoS2 nanoparticles still preserve the nonporous structure in the starting MOFs, so high electrocatalytic activities are achieved
The amount of sulfur was controlled through the thermodynamic prediction, and the sulfurization of the cobalt Prussian blue analogue (Co-PBA) was conducted under each condition using a thermal treatment
Summary
Electrochemical water splitting consists of two half reactions, namely the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER). Noble metal electrocatalysts, such as Pt (for HER) and Ru- or Ir-based materials (for OER), show excellent catalytic performance, they are difficult to apply on a large scale because of cost issues. Cobalt disulfide (CoS2) has been reported to exhibit high electrical conductivity[31] and excellent activity for both the OER and the HER9,26,32. We fabricated mono-phase CoS2 with ~ 4 nanometer-scale pores as bifunctional water splitting electrical catalysts. Thermodynamic calculations control the sulfur vapor pressure depending on the amount of cobalt-based starting materials before sulfurization. Such MOF-driven CoS2 nanoparticles still preserve the nonporous structure in the starting MOFs, so high electrocatalytic activities are achieved
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