Construction Of Novel Self-supporting Nickel Phosphide-based Electode And Their Properties In Hydrogen Evolution Reaction And Reduction Of Nitrate

Hydrogen energy stands out in the new energy family for its characteristics of high gravimetric energy density,clean and renewable.Compared with the industrial method that still heavily relies on high-carbon energy sources,hydrogen（H₂）generated by the cathodic hydrogen evolution reaction（HER）via water electrolysis has attracted wide attention for its merits of environment-friendly,high purity,and high energy conversion rate.The exploitation of non-precious metal catalysts with high efficiency,superior stability,favorable price and wide pH adaptability is the core measures to promote the industrial application of hydrogen generation by HER.Recent years,on-going endeavors have been devoted to the nickel phosphide-type TMPs,in sight of the merits of favorable catalytic activity,cost-effective,earth abundance;however,few of them can maintain their excellent performances in a wide pH value from 0 to 14.To offer an effective strategy for the construction of high-efficient and pH-universal nickel phosphide catalyst and the exploitation of the new application field of nickel phosphide,two nickel phosphide（Ni₂P）electrocatalysts with the boosted properties for hydrogen evolution reaction and nitrate reduction were prepared by tuning the electronic structure and morphology.The details are as follows:（1）A facile approach toward the fabrication of nickel phosphide（Ni₂P）assembled on carbon cloth（CC）was proposed via the coupling method of electroless plating and low temperature phosphorization.Through manipulating the deposition time,phosphorus content of chemical deposition process,as well as the phosphorization temperature and phosphorization ratio in the low temperature phosphorization techniques,the optimal Ni₂P/CC with the best performance can be obtained and the evolution processes of the phase and morphology of Ni₂P were studied in depth.The corresponding HER tests found that the walnut-like three-dimensional Ni₂P/CC electrode displays high electrocatalytic performances over a wide pH range,especially in an acidic medium that only requires an overpotential of 119 mV at 10 mA cm^–2.In addition,through electroreduction in the process of HER with Ni₂P/CC as the electrocatalyst,a removal efficiency of 65.3%for nitrate-containing solution can be achieved.（2）For the furtherance of performances toward HER and nitrate reduction of Ni₂P,herein,Ni₂P/NF-EHP catalyst was synthesized on the three-dimensional Ni foam（NF）substrate via the coupling methods of electroless nickel-phosphorus（Ni-P）plating,hydrothermal synthesis and low temperature phosphorization techniques.This catalyst displays a dramatically boosted HER property and a wide adaptability to pH;the overpotential at 10 mA cm^-2were 78 mV in 0.5 M H₂SO₄,125 mV in 1.0 M PBS and 101mV in 1.0 M KOH.This can be attributed to the multiple defects caused by electroless deposition Ni-P on the NF and abundant active sites present on the porous bicontinuous configuration.Moreover,the HER process of Ni₂P/NF-EHP catalyst can be competent for the nitrate reduction,a remarkable removal efficiency of 92.6%for this pollutant can be achieved;furthermore,it has an excellent recycling performance both in electrochemical hydrogen evolution and electroreduction of nitrate.This work will not only provide an effective strategy for the treatment of nitrate wastewater,but also expand the application of excellent HER catalysts in the prevention and control of water pollution,especially in the control of nitrate nutrients.