One-step Na2S2O3-activation strategy on the construction of CoS–Co(OH)2 nanoflakes@Cu31S16 microrod architectures for alkaline overall water splitting

Cost-effective bifunctional electrocatalysts with excellent performance and less pollution could potentially meet the urgent needs for overall water splitting application. In the present work, a facile Na2S2O3-activation process was used to realize the one-step achievement of CoS–Co(OH)2@Cu31S16 microrod architectures from the early-formed Cu2S microrods on Cu foam (CF). The curly Co(OH)2 nanoflakes with embedded CoS nanodots of 2–3 nm as shell layer encapsulated Cu31S16 microrod core through coordination interaction of metal ions and S2O32−. On manipulating the activation time (10–240 min), a series of cobalt-dependent Co-CuxS microrod arrays were established on Cu foam without much difference in morphology, here CuxS represents the complex of Cu2S and Cu31S16. Longer activation time led to more Cu31S16 and less Cu2S in the CuxS microrod core. In an alkaline medium (1.0 mol dm−3 KOH), the Co-CuxS-Y/CF (Y = 10, 30, 60, 120, 240 min) composite arrays showed superior bifunctional electrocatalytic performances for water splitting on comparison to Cu2S/CF precursor, the OER and HER overpotentials can reach 268 mV and 143 mV at the current density of 50 mA cm−2. The optimal Co-CuxS-240 composite, namely CoS–Co(OH)2@Cu31S16, extended outstanding overall water splitting activity and good durability (50 h-performing without obvious decrease). The excellence is primarily attributed to the combined hierarchical structure of multi-dimensional components with both OER and HER active sites in one architecture. The electrocatalyst with 0–2 dimensional compositions is favorable to the transportation of oxygen species and electrons in the electrochemical process and stimulates a synergistic reaction between the multiple functional components.