Synthesis And Electrocatalytic Properties Of Ni-Based Phosphide/Nickel Foam Self-Supporting Electrode

The exhaustion problem of global fossil fuel continues to intensify.More and more investigations are focused on the efficient exploration of green and sustainable energy.As a zero-pollution energy and high energy density source,hydrogen is the most desirable substitute for fossil fuels.Among the many hydrogen production technologies,water splitting,which include two half reactions cathodic hydrogen evolution reaction（HER）and anodic oxygen evolution reaction（OER）,is one of the most promising methods to offer a zero carbon-emission,high-purity and sustainable approach to generate hydrogen.However,the high overpotential of HER and OER hinders its feasibility in water electrolysis.Generally,precious metals（Pt for HER and Ir O₂/Ru O₂ for OER）are employed to greatly reduce the overpotential and promote the smooth progress of water electrolysis,but their low-reserves and high-cost limit the large-scale application.Therefore,the preparation of an efficient and inexpensive catalyst has become a challenge.In this paper,the macro-pores of nickel foam（NF）were spatially divided into hierarchical porous structures by NF as the skeleton structure.This strategy effectively accommodated more catalyst and increased the specific surface area of the prepared self-supporting electrode.Carbon nanotubes（CNTs）were loaded with Ni-P alloy by simple palladium-free electroless plating.Then,the"interlaced network"Ni-P/CNTs was filled and anchored in the macropores of NF,forming the self-supporting electrode Ni-P/CNTs/NF.The Ni-P/CNTs/NF electrode showed excellent hydrogen evolution performance.In order to improve the catalytic performance of Ni-P/CNTs for water electrolysis,Ni-P/CNTs and melamine were mixed for heat treatment.The Ni-P alloy was transformed into N-doped nickel phosphide nanoparticles（N-Ni₃P/Ni）.And the nanoparticles were embedded in N-doped carbon nanotubes（N-CNTs）,forming a"network structure"（N-Ni₃P/Ni/N-CNTs）.Similarly,the network structure was anchored in the macropores of NF by electroplating to achieve the effect of space division（N-Ni₃P/Ni/N-CNTs/NF）.The N-Ni₃P/Ni/N-CNTs/NF electrode only needed 73 m V（HER）and 270 m V（OER）overpotential to reach 10 m A cm^-2.Moreover,a voltage of 1.57 V was required to reach 20 m A cm^-2.Highly stable Co₃O₄ was prepared as a catalyst support,which was anchored in the NF by electroplating nickel to form an electrode with high space utilization（Co₃O₄/NF）.Then,the Co₃O₄/NF surface was coated with a layer of Ni Co P alloy using palladium-free electroless plating.Finally,the self-supporting electrode with cobalt-doped nickel phosphide nanosheet（Co-Ni_xP_y@Co₃O₄/NF）was obtained through high-temperature phosphating.Due to the intense synergistic effects among different metals,regulated electronic structure,high active surface area evolved from the unique 2D flake-like nanostructure and hierarchically porous support,the resultant Co-Ni_xP_y@Co₃O₄/NF was served as excellent self-supported electrocatalysts for HER and OER.To perform overall water splitting,the coupling of Co-Ni_xP_y@Co₃O₄/NF demonstrated an excellent overall splitting activity,only a low voltage of 1.47 V was required to reach 20 m A cm^-2 without obviously activity degradation in the stability test for 36 h.