Intercalated Graphite between Ni Foam and Ni3S2 Nanocrystals for the Activity Promotion in Overall Water Splitting

Herein, a novel 3D free-standing electrode is synthesized, consisting of Ni3S2 supported on a Ni foam (NF) with a graphite foam (GF) intercalated between them (Ni3S2@GF@NF). The hydrothermally synthesized Ni3S2 has a hierarchical structure with abundant active sites exposed, and intimate interfacial contact can be formed during the in situ synthesis process. Moreover, the intercalated GF has a large surface area and good electric conductivity, which can create a new short route to facilitate electron transfer onto the active surface of Ni3S2. The Ni3S2@GF@NF electrode exhibits an excellent hydrogen evolution reaction performance with an early overpotential of 99 mV vs reversible hydrogen electrode at 10 mA cm(-2) and a small Tafel slope of 98.2 mV dec(-1) in alkaline solutions. However, the overpotential at 10 mA cm(-2) and Tafel slope for the oxygen evolution reaction are 240 mV and 62.4 mV dec(-1) in alkaline solutions. Using Ni3S2@GF@NF as both anode and cathode, only a small cell voltage of 1.63 V is needed to obtain 10 mA cm(-2) for overall water splitting, comparable with the best free-standing materials. Moreover, it exhibits a good stability due to the protection of GF. The free-standing Ni3S2@GF@NF electrode contains no noble metals and should have a great potential in electrochemical water splitting.