Enhanced HER and OER performance via CoS2-NiS2 heterostructures on N-doped carbon nanotube frameworks

The development of highly efficient electrocatalysts is of utmost importance for advancing electrochemical energy conversion technologies. Transition metal sulfide heterostructure electrocatalysts have been widely studied and applied in electrocatalysis due to their highly inherent activity in the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) at the interface. We prepared NiS₂/CoS₂ nanoparticle heterostructures doped with nitrogen-carbon nanotubes (CoS₂/NiS₂@N-CNTs) to induce the formation of bifunctional reaction sites. This design contributes to the excellent catalytic activity for electrocatalytic water splitting. The CoS₂/NiS₂@N-CNTs electrocatalyst exhibits prominent catalytic activities toward HER and OER, which required low overpotentials of 126 and 205 mV to yield the current density of 10 mA cm⁻² in 1 M KOH. The prepared electrocatalysts exhibit fast reaction kinetics with tafel slopes of 71 and 82 mV dec⁻¹ in HER and OER, respectively. The catalyst has a larger electrochemically active surface area (ECSA) of 1030 cm⁻² and a strong electron transfer capability with an electrochemical impedance of 41 Ω. These properties are mainly attributed to the unique heterogeneous structure of the catalyst. In addition, CoS₂/NiS₂@N-CNTs catalyst is used as both the cathode and anode to fabricate a two-electrode system in a 1.0 M KOH solution measured at 1.53 V. Meanwhile, the stability measurement maintains for 23 h at a current density of 10 mA cm⁻² with negligible degradation. This work has successfully developed an approach for rational design and novel synthesis of metal sulfide hybrids as bifunctional electrocatalysts with high activity and stability for overall water splitting.