Preparation Of Three-dimensional Electrode Materials And The Electrochemical Performance Towards For Hydrogen Evolution And Oxygen Evolution Reaction

Electrolytic water splitting has been considered as a clean,effective and promising method for hydrogen evolution and oxygen evolution reaction.At present,most of the widely studied electrochemical catalysts for water splitting are often prepared in the form of powders.They are necessary to add adhesive to fix the catalyst on the glassy carbon electrode to study the performance of the catalyst.This process usually results in an increase of the contact resistance between catalyst and electrolyte,and unavoidable powder agglomeration,which deteriorate the catalytic performance of the catalysts.In addition,the bubbles release during the electrochemical test are liable to cause the peel-off of the catalyst from the electrode,resulting in the instability issues.In contrast,three-dimensional?3D?electrode,which can offer large catalyst/electrode contact area,avoid to use organic adhesives,thus resulting in much reduced contact resistance and enhanced HER catalytic activity.In addition,the porous structure could facilitate the bubbles release,and enhance the robust stability.It has been known that efficient and stable electrolytic water catalysts can be obtained by in-situ synthesis of catalysts on three-dimensional conductive substrates such as copper foam,nickel foam.Inspired by this,3D electrodes were fabricated and the electrochemical performances towards hydrogen evolution reaction and oxygen evolution reaction are examined,as shown below:?1?In-situ growth of Mo_xC nanoflower and nanobelt catalysts on copper foam were successfully achieved by a two-step method:hydrothermal preparation of molybdenum precursors,followed by pyrolysis at controlled temperatures.Mo_xC/Cu showed excellent performance for HER in both alkaline and acidic media,with a low overpotential of 169 mV to reach the current density of 200 mA cm^–2 in 1 M KOH,and 194 mV in 0.5 M H₂SO₄,and a corresponding Tafel slope of 98 and 74 mV dec^–1,respectively.X-ray photoelectron spectroscopy and electrochemical tests were applied to study the mechanism of MoxC/Cu for HER.The electrocatalytic activity is also found to vary with the Mo²⁺/Mo³⁺and N contents in the samples that impact the electrical conductivity and electron-transfer kinetics of the hydrogen evolution reaction.?2?Ni₂P/NF nanoneedle and Ni₂P-Ni₁₂P₅/NF nanoparticle catalysts were prepared by a simple hydrothermal method in two different reaction solutions.The obtained catalysts were used for HER,in 0.5 M H₂SO₄,with low overpotential of 227 and 170 mV at 200 mA cm^–2,and small Tafel slope(82.7 and 58.9 mV dec^–1),respectively.The long-term CV cycle tests shows that Ni₂P-Ni₁₂P₅/NF had excellent stability in the acidic solutions.The synergistic effect of Ni₂P and Ni₁₂P₅ can improve the HER performance of the catalyst.Ni₂P/NF and Ni₂P-Ni₁₂P₅/NF exhibit excellent OER activity and stability in 1 M KOH,with overpotential of 257and 375 mV at 200 mA cm^–2,and small Tafel slope(69.4 and 83.6 mV dec^–1),respectively.Nickel foam has a high specific surface area and pore structure which promotes the release of bubbles.High-conductivity Ni₂P/NF nanoneedle facilitate the transfer of effective electrons from the catalyst to the electrode,and the synergistic effect of N doping can improve the OER performance of the catalyst.