Study on the HER and OER catalytic properties of NiPOH-RuO2 for alkaline water electrolysis
Electrode materials for water electrolysis play an important role in hydrogen evolution and oxygen evolution.Nickel hydroxyphosphite(Ni11(HPO3)8(OH)6,abbreviated as NiPOH)has more porous structures and abundant active sites,however,its low conductivity with a corresponding slow electron transfer rate limits its electrocatalyticproperties.The addition of highly conductive and active substances can improve the electron transmission efficiency and reaction kinetics,which is expected to enhance its catalytic activity and stability during the process of water electrolysis.In this paper,the NiPOH-x at.％RuO2 electrodes was grown in situ on the nickel foam by a hydrothermal method.X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),scanning electron microscope(SEM),linear sweep voltammetry(LSV)and Chronopotentiometry(CP)wereused to study the influence of RuO2 content on the micromorphology and electrochemical properties of the prepared electrodes.The performance ofNiPOH-x at.％RuO2 during the whole process of electrolyzing water was explored by the First-principles calculations.It's shown that the RuO2could change the morphology,and make the microspheres have a larger specific surface area.The Ni element was composed of Ni2+and Ni3+,and Ru consisted of Ru3+and Ru4+.The energy barriers for electron transfer were decreased after doping RuO2 to NiPOH,and the electron density near the Fermi level increased.When the current density was 10 mA/cm2,the hydrogen overpotential was significantly reduced with the addition of RuO2 and the hydrogen overpotential of NiPOH-3 at.％RuO2 could reach the minimum of 93 mV,while the hydrogen overpotential of the NiPOH electrode was 161 mV.The Tafel slope of the oxygen evolution of NiPOH-3 at.％RuO2 electrode could be the minimum at the same time.The hydrogen evolution process of the NiPOH-x at.％RuO2 electrode was a Volmer-Heyrovsky controlled reaction dominated by the Heyrovsky step.
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