胺和水插层磷酸锰仿生模拟氢键网络用于电催化水氧化

Biomimicking Hydrogen-Bonding Network by Ammoniated and Hydrated Manganese(Ⅱ)Phosphate for Electrocatalytic Water Oxidation

自然界光合作用的析氧催化剂为不对称锰簇结构。催化中心除了自身特殊的结构外,还与周围氨基酸残基和水分子通过氢键来连接以提供高速的质子电子迁移通道。这些迁移通道对人工锰基析氧催化剂的开发和研究具有重要的启发意义,但却较少受到关注。本文通过简单的共沉淀法制备了一种夹有乙二胺离子和水分子的磷酸锰纳米片,磷酸锰与层间分子通过氢键连接,形成了氢键网络,一定程度上模拟了自然界析氧中心的外围结构。与氢键网络被破坏的磷酸锰纳米片相比,这种含有丰富、广泛和连续氢键网络的磷酸锰纳米片在中性条件下具有较高的催化析氧性能。磷酸锰纳米片中的氢键网络具有与光系统Ⅱ中氢键网络类似的功能,它加快了质子的转移速率,从而促进电催化水氧化。

Asymmetric manganese cluster,the active center of photosystemⅡ(PSⅡ)in nature,is hydrogen-bonded to surrounding amino acid residues and water molecules.This phenomenon is of great inspiration significance for developing and studying artificial Mn-based oxygen evolution reaction(OER)catalysts.Herein,we prepared manganese phosphate nanosheets through intercalation of ethylenediamine ions and water molecules((EDAI)(H2O)MnPi)using a simple coprecipitation method.(EDAI)(H2O)MnPi is also hydrogen-bonded to interlayer ethylenediamine ions and water molecules,forming a hydrogen-bonding network.The morphology of the(EDAI)(H2O)MnPi sample was characterized by scanning electron microscopy(SEM)and transmission electron microscopy.The thickness of(EDAI)(H2O)MnPi was characterized by atomic force microscopy.The composition and structure of(EDAI)(H2O)MnPi were characterized by X-ray diffraction(XRD)and energy dispersive X-ray spectroscopy.For control studies,manganese phosphate(EDAI)MnPi and(H2O)MnPi samples were also synthesized.The structure and morphology of(EDAI)MnPi and(H2O)MnPi samples were characterized by XRD and SEM.The difference between(EDAI)(H2O)MnPi,(EDAI)MnPi,and(H2O)MnPi were further characterized by thermal gravimetric analysis and derivative thermogravimetric analysis.Electrocatalytic properties of the(EDAI)(H2O)MnPi,(EDAI)MnPi,and(H2O)MnPi for OER were studied in 0.05 mol·L-1 pH=7 phosphate buffered saline solution,through linear sweep voltammetry,electrochemical impedance spectroscopy,and controlled potential electrolysis(CPE)test.The electrochemical surface area(ECSA)analyses of(EDAI)(H2O)MnPi,(EDAI)MnPi,and(H2O)MnPi samples were recorded by charging currents in the non-Faradaic potential region at different scan rates.Considering the different ECSAs of different materials,the water oxidation activities of three materials were normalized by ECSA.Compared with counterparts of(EDAI)MnPi(610 m V)and(H2O)MnPi(580 m V),manganese phosphate nanosheets(EDAI)(H2O)MnPi exhibited a lower overpotential of 520 m V when driving a current density of 1 m A·cm-2 in neutral conditions.The CPE experiment revealed that(EDAI)(H2O)MnPi remained active for at least 10 h.Manganese phosphate nanosheets containing a rich,extensive,and continuous hydrogen bond network exhibited improved OER performance in neutral conditions.The hydrogen-bonding network in manganese phosphate nanosheets has similar functions to the hydrogen-bonding network in PSⅡ,which could accelerate the transfer rate of protons and facilitate electrocatalytic water oxidation.This study may provide guidance for the design of water oxidation catalysts with rich hydrogen bond network.