Porous Ni Foams Filled by N-Doped Carbon Nanotubes Coated with N-Doped Ni₃P and Ni Nanoparticles for Catalytic Water Splitting

The development of bifunctional catalysts possessing high efficiency and excellent stability was still a challenge as regards overall water splitting. Herein, a reasonable space division strategy of Ni foam (NF) was proposed to design a bifunctional catalyst. Ni-P alloy was loaded on carbon nanotubes (CNTs) through Pd-free electroless plating (Ni-P/CNTs). Subsequently, the Ni-P/CNT catalysts mixed with melamine were annealed for N doping. The N-doped CNTs coated with N-doped Ni3P and Ni nanoparticles (N-Ni3P-Ni/N-CNTs) were obtained. Finally, the N-Ni3P-Ni/N-CNTs were used as a filler to divide the pore size of NF by electroplating Ni, obtaining a network-like hierarchical porous electrode (N-Ni3P-Ni/N-CNTs/NF). This hierarchical porous structure exposed abundant catalytically active sites, facilitated the mass transfer, and prevented the catalyst agglomeration and corrosion that promote electrolyte contact and favor facile electron transfer kinetics. On the basis of the rational design, a self-supported N-Ni3P-Ni/N-CNTs/NF electrode showed a high specific surface area and exhibited superior electrocatalytic performances. The electrode achieved low overpotential of 73 and 270 mV at 10 mA cm–2 for the hydrogen and oxygen evolution reaction, respectively. Besides, it required a cell voltage of only 1.57 V to achieve 20 mA cm–2 when assembled in a 1 M KOH electrolyte for overall water splitting. Hence, this study represented a rational design of self-supported bifunctional electrode for overall water splitting.