Iron-tuned super nickel phosphide microstructures with high activity for electrochemical overall water splitting

Large-scale hydrogen production by electrolytic splitting of water is mainly governed by high-efficient yet cheap electrocatalysts that could be capable of accelerating the sluggish hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Herein, we report Fe-tuned Ni2P electrocatalysts with controllable morphology and structure by regulating atomic ratio of Ni/Fe, and reveal the Fe species-modulated electronic state behaviors and -boosted catalytic activity for water splitting. The electrocatalytic activity of Fe-tuned Ni2P nanosheets for both HER and OER can be further enhanced by assembling the nanosheets vertically on conductive 2D carbon fiber (CF) matrix to make hierarchical monolithic 3D electrode (Ni1.5Fe0.5P/CF), which features more accessible active sites and open structure that helps to speed up both the HER and OER. The improved electrocatalytic activity of Ni1.5Fe0.5P/CF is due to the combined synergistic effects of the high conductivity of CF matrix and the strong interaction between active species and the CF support, as evidenced by a low overpotential of 293 mV to achieve a high current density of 100 mA cm−2 with superior long-term stability for OER. When the monolithic 3D Ni1.5Fe0.5P/CF electrodes were used as both anode and cathode for overall water splitting, a current density of 10 mA cm−2 is generated at a low potential of 1.589 V, while at 20 mA cm−2, the potential is only 1.635 V. It has been demonstrated that modulating metal catalysts (nanosized nickel phosphide) with iron atoms is powerful, and may open up avenues to the design and fabrication of highly efficient catalysts for energy storage and conversion.