Promotion of Overall Water Splitting Activity Over a Wide pH Range by Interfacial Electrical Effects of Metallic NiCo-nitrides Nanoparticle/NiCo 2 O 4 Nanoflake/graphite Fibers.

Many efforts have been made to develop bifunctional electrocatalysts to facilitate overall water splitting. Here, a fibrous bifunctional 3D electrocatalyst is reported for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) with high performance. The remarkable electrochemical performance is attributed of the catalysts to a number of factors: the metallic character of the three components (i.e., Ni3 N, CoN, and NiCo2 O4 ); the electronic structure, nanoflake-nanosphere network with abundant electroactive sites, and the electric field effect at the interfaces between different components. The oxide-nitride/graphite fibers have the lowest overpotential requirements of 71 and 183 mV at 10 mA cm-2 for HER and OER in alkaline medium, respectively. These values are comparable to those of commercial Pt/C (20 wt%) and RuO2 . The electrodes also show a response to HER and OER in both neutral and acid media. Furthermore, the 3D structure can be highlighted by all-round electrodes for overall water splitting. The calculations on the changes in electrons transfer and the Femi level from oxides to oxides/nitrides reveal that the observed superb electrocatalytic performance can be attributed to the presence of Ni3 N and CoN derived from the in situ nitridation of NiCo2 O4 .