用于高效电催化析氧反应的锰掺杂镍铁双金属氢氧化物催化剂

Manganese-doped nickel-iron bimetallic hydroxide catalyst for efficient electrocatalytic oxygen evolution reaction

随着国内能源需求不断增加以及温室气体排放持续增长,寻求高效、清洁、可持续的能源成为目前亟待解决的问题.廉价、高效和稳定的氧析出反应(oxygen evolution reaction,OER)催化剂在电解水制氢领域具有广泛的应用前景.镍铁层状双金属氢氧化物(NiFe-layered double hydroxides,NiFe-LDHs)被认为是一种潜在、理想的析氧反应电催化剂.然而,对于NiFe-LDHs层板,普遍认为其边缘金属位点相较于内部金属位点具有更高的催化活性,这就导致其层板内部的金属位点无法充分利用,降低对OER反应的催化效率.因此,为了充分提升NiFe-LDHs的层板利用率,本研究将具有变价特征的锰离子引入NiFe-LDHs层板(Mn doped NiFe-layered double hydroxides,Mn-NiFeLDHs)中,利用锰离子的变价特征,充分提升层板载流子迁移率,促进层板内电子转移,同时,由于锰离子的电负性特征,部分电子将从镍位点附近转移到锰位点的周围,导致镍位点表现出缺电子特征,从而作为“电子饥饿”位点,提升层板整体对于具有富电子含氧官能团的捕获,进而有效地增强OER催化活性.催化反应结果表明,Mn-NiFeLDHs电极在电流密度10 mA/cm^(2)时表现出过电位仅为332 mV,低于初始NiFe-LDHs的384 mV.锰离子的合理掺杂有效地调整Ni^(2+)位点活性,增强其电催化活性,并为更进一步地阐明掺杂对LDHs层板活性的影响提供了实验事实支持.

Hydrogen energy has many advantages such as wide source,high calorific value,clean and renewable energy,which is considered ideal secondary energy.Under the background of“carbon peak”and“carbon neutral”,the development of hydrogen energy has become the strategic deployment of all countries in the world.Renewable energy is converted into electric energy,and hydrogen production from water electrolysis is further realized through electric energy,which is currently considered as one of the safe and green way of hydrogen production.However,in the actual process of hydrogen production by electrolysis of water,there are problems such as high reaction overpotential and low energy conversion efficiency,which seriously restrict the cost of hydrogen production.During water electrolysis,hydrogen evolution reaction(HER)and oxygen evolution reaction(OER)occur at negative and positive electrodes respectively.Compared with the HER process of the two-electron reaction,the four-electron OER process requires a higher overpotential.Therefore,the four-electron OER process becomes the decisive step of the reaction.In order to achieve high efficiency and low energy consumption of hydrogen production process,it is urgent to use cheap,efficient and stable OER catalyst.At present,the search for efficient and low-cost OER catalyst is still the“holy grail”of water splitting.Among many non-noble metal catalysts,NiFe-layered double hydroxides(NiFe-LDHs)are considered as an ideal OER electrocatalyst in alkaline conditions due to their low raw material cost and adjustable structure.However,for NiFe-LDHs laminates,it is generally believed that the edge metal sites have higher catalytic activity than the internal metal sites,which leads to the insufficient utilization of the metal sites inside the laminates and reduces the catalytic activity of the OER reaction.In order to solve the above problems,based on the microstructural regulation of NiFe-LDHs,some methods have been used to improve its catalytic activity and stability in the OER process.Heterogeneous element doping is considered to be an effective method to regulate the electronic structure and electrochemical activity of catalysts.Metal ion doping(Cr,Cu,V,etc.)can optimize the electronic structure of nickel metal active site,reduce reaction overpotential,and improve catalytic efficiency.However,the high biotoxicity of traditional transition metals(Cr,V,Cu,etc.)limits their industrial application.Mn(Mn^(2+)⇌Mn^(3+)⇌Mn^(4+))with rich variation characteristics has a potential role in regulating lamellar charge characteristics.Herein,in order to fully improve the utilization of NiFe-LDHs laminates,this study introduces manganese ions with variable valence characteristics into NiFe-LDHs laminates(Mn-NiFe-LDHs),and utilizes the variable valence characteristics of manganese ions to fully enhance the carrier mobility and promote electron transfer in the laminate.At the same time,due to the electronegativity characteristics of manganese ions,part of the electrons will be transferred from the vicinity of the nickel site to the vicinity of the manganese site,causing the nickel site to exhibit electron-deficient characteristics,which enhance the overall capture of the electron-rich oxygen-containing functional groups of the laminate,thereby effectively enhancing the OER catalytic activity.According to the results of the catalytic reaction,the Mn-NiFeLDHs electrode exhibits an overpotential of only 332 mVat a current density of 10 mA/cm^(2),which is lower than the initial NiFe-LDHs of 384 mV.The reasonable doping of manganese ions can effectively adjust the Ni2+site activity and enhance its electrocatalytic activity.And to further clarify the effect of doping on the activity of LDHs laminates to provide experimental facts support.