Bifunctional Cu2S–Co(OH)2 nanotube array/Cu foam electrocatalyst for overall water splitting

Bifunctional electrocatalysts with excellent performances as well as low cost and simple synthesis might meet urgent needs for overall water splitting application. In the present work, Cu₂S–Co(OH)₂ nanotube array was achieved on Cu foam by using an aqueous in-situ construction method at ambient temperature. The synthetic process involves four steps of chemical reactions: sulfidation, etching, reduction and cobalt-growth. The arrays on Cu foam (CF) underwent successive unit transformations from Cu(OH)₂ nanorods to Cu₂S–Cu(OH)₂ nanorods, Cu₂S–Cu₂O nanotubes and eventually to Cu₂S–Co(OH)₂ nanotubes. The combination of Co(OH)₂ nanoflakes and Cu₂S nanotubes made the composite array/CF highly effective for OER, HER and overall water splitting applications. In an alkaline medium (1.0 mol dm⁻³ KOH), the OER and HER overpotentials are 268 and 241 mV vs. RHE at the current density of 50 mA/cm² with excellent long-term stability of 48 h. The overall water splitting examination on Cu₂S–Co(OH)₂ nanotube array/CF catalyst gives superior electrochemical activity and high stability, where the overpotential is as low as 320 mV vs. RHE at 10 mA/cm², and the current density remained unchanged for 100 h. The combined composition and morphology catalyst of Cu₂S nanotubes and Co(OH)₂ nanoflakes is promising for future practical applications.