NiCo nitride/carbon nanoflakes as low-cost bifunctional electrocatalysts for carbohydrate-assisted electrolytic H2 generation

Abstract

The sluggish anodic oxygen evolution reaction (OER) still remains the major bottleneck for the electrochemical water splitting to produce hydrogen. Replacing OER with the more thermodynamically favorable carbohydrate oxidation reaction (COR) offers a viable strategy for energy-saving hydrogen production. Herein, we design and fabricate the carbon-coated loose nickel-cobalt nitride nanoflakes (NiCoNx@C) on deliberately coarsened nickel foam (Ni/NF) support through a successive electrodeposition and annealing process, the thus obtained NiCoNx@C/Ni/NF electrocatalyst with hierarchical porous architecture exhibits excellent bifunctional electrocatalytic performance toward both the acidic hydrogen evolution reaction (HER) and the representative alkaline COR. The NiCoNx@C/Ni/NF achieves an ultralow working potential of 1.26 V at 50 mA cm−2 in 1 M KOH with 0.5 M fructose for COR and a small overpotential of 78 mV at 10 mA cm−2 in 0.5 M H2SO4 for HER. We further design an asymmetric-electrolyte electrolyzer, using the bifunctional NiCoNx@C/Ni/NF as both the cathode and anode, which can deliver a current density of 10 mA cm−2 for electrolytic hydrogen production with a rather low applied voltage of 0.67 V and faradaic efficiency approaching 100%, showing great potential to use waste carbohydrates to producing hydrogen energy efficiently.