Nickel Molybdenum Nitride Nanorods Grown on Ni Foam as Efficient and Stable Bifunctional Electrocatalysts for Overall Water Splitting.

Non-noble-metal electrocatalysts for water splitting hold great promises for developing sustainable and clean energy sources. Herein, a highly efficient bifunctional electrode consisting of Ni-doped molybdenum nitride nanorods on Ni foam is prepared through topotactic transformation of NiMoO4 nanorods that are in situ hydrothermally grown on Ni foam. The electrode not only contains rich, accessible, electrochemically active sites but also possesses extraordinary chemical stability. It exhibits excellent hydrogen evolution reaction and oxygen evolution reaction performance in 1.0 M KOH with low overpotentials of 15 and 218 mV, respectively, at a current density of 10 mA cm-2, superior to the commercial benchmark materials Pt/C and RuO2 under the same condition. A simple water electrolyzer using the obtained electrode as both the anode and cathode needs a very low cell potential of 1.49 V to reach a current density of 10 mA cm-2 and maintains stability for 110 h without degradation. The excellent performance of the electrode could be attributed to the formation of highly conductive, corrosion- and oxidation-resistant metal nitrides and the synergetic effect between intimately interconnected, electrochemically active nickel molybdenum nitride and Ni or NiO nanoparticles. This study shows that the use of transition metal nitrides in combination of nanostructured heterojunctions of multiple active components enables one to develop highly stable and efficient water electrolyzers without precious metals. The preparative strategy used in this work could be applied to devise new electrocatalysts.