Design Synthesis And Performance Study Of Electrocatalyst For Hydrogen Evolution Reaction Of Nickel Based Compounds

As clean and efficient energy,hydrogen energy will be an indispensable part of the sustainable energy structure in the future.Hydrogen production by electrolytic water is a clean and environmentally friendly technology,and it is also the most important technology for green hydrogen production.The most active catalyst for its cathodic hydrogen evolution reaction（HER）is the platinum-based noble metal catalyst.However,the high price of platinum increases the device cost and hinders large-scale application.Nickel phosphide is one of the high-active candidates to replace platinum-based catalysts.However,the activity and stability of the nickel phosphide-based HER catalysts are inferior to those of the Pt/C catalyst.Herein,we adopt a solution-based phosphidation synthetic method to optimize the HER performance of the nickel phosphide-based electrocatalysts and establish the probable correlation between structure and performance toward HER,providing a facile way for the application of noble metal-free HER electrocatalysts.The main results of the paper are described as follows:（1）A series of pure-phase Ni₂P nanoparticles（NPs）were prepared by a solution-based phosphidation synthetic method by tuning the phosphorous sources,and the interaction between precursors was proven to be the key factor that affected the phase and morphology of the products.This method avoids the production of harmful flammable PH₃gas in the classical gas-solid phosphide method and is suitable for large-scale preparation.Worm-like Ni₂P nanowire synthesized from triphenyl phosphite（TPP）has the best HER activity and stability.The overpotential of j=-10 m A·cm^-2in 0.5 mol·L^-1H₂SO₄,p H=7 PBS buffer solution,and 1 mol·L^-1KOH were 100 m V,197 m V,and 156 m V,respectively.After a 2 h stability test at the current density of-10mA·cm^-2,the overpotential values increase by 21 m V,109 m V,and 19 m V in the acidic,neutral,and alkaline electrolytes.Ex situ experiments demonstrated that the p H effect of HER performance was caused by the formation of insoluble non-active species such as phosphate,oxide,and hydroxide on the electrode surface in the neutral and alkaline conditions,while the acidic condition ensures the exposure of active Ni₂P on the surface by dissolving the inactive species.（2）Based on the solution-based synthetic method,bimetallic phosphates were prepared by doping a foreign metal（M=Fe,Cr,Mn,Co,and Zn）.HER activity was tested under 0.5 mol·L^-1H₂SO₄and 1 mol·L^-1KOH,respectively.The result shows that Co doping has a positive promoting effect.By optimizing the Ni/Co ratio,the Ni₁Co₁P/C synthesized with the Ni/Co ratio of1:1 had the best activity and stability.The overpotential of Ni₁Co₁P/C at-10m A·cm^-2in acidic and alkaline systems was 105 m V and 123 m V,respectively.The 4-hour chronopotentiometry test showed that the overpotential at-10m A·cm^-2of Ni₁Co₁P/C only increased by 9 m V and 10 m V in acidic and alkaline systems after the reaction.It is significantly lower than 31mV and 32mV of nickel phosphide,demonstrating that Co doping can improve the stability of nickel phosphide.（3）We extend the solution-based synthetic method to the nickel foam system.Dense Ni nanoparticles grow on nickel foam surfaces,and the morphology and size of nanoparticles on nickel foam surfaces can be controlled using different surfactants.The overpotential of surface-modified NP/NF-TOPO-2 decreased from 482 m V to 119 m V at-100 m A·cm^-2in acidic medium and from 410 m V to 210 m V in alkaline medium.Meanwhile,the NP/NF-TOPO-2 can be stable during a 12-hour step current test.Electrochemical analysis and characterization demonstrate that the improvement of activity was due to the increase of ECSA,and the improvement of stability was due to the improvement of corrosion resistance of the electrode materials by surface modification.