Enhanced oxygen and hydrogen evolution performance by carbon-coated CoS₂-FeS₂ nanosheets

It is vital to tailor the surface structure and composition of nanocatalysts, which greatly affect the catalytic activity through the exposure of specific atom coordination environment. To date, less progress has been made in tuning the interface structures of pyrite for promoting the catalytic activity towards overall water splitting. Herein, we developed a facile one-spot strategy to make carbon-layer-coated CoS2-FeS2 heterojunction nanosheets. The carbon layer and interface structures between Co-S and Fe-S were characterized via high resolution transmission electron microscopy. It exhibited a high OER activity with 1.47 V at 10 mA cm-2, which was superior to that of the commercial RuO2. Meanwhile, the carbon-layer-coated CoS2-FeS2 heterojunction nanosheets with the overpotential of 210 mV at 10 mA cm-2 was more active than FeS2 nanosheets with 240 mV in the hydrogen evolution reaction. Notably, it enhanced the catalytic activity towards the overall water splitting with the voltage of 1.66 V at 10 mA cm-2 using a two-electrode system. The remarkable long-term stability was verified by a slight change in the current density of 6 mA cm-2 for 26 h. The prominent catalytic activity could be related to the exposure of the carbon layer and interface structures. This work demonstrates that engineering the interface structure is essential for boosting the overall water splitting activity.