摘要
自然界水氧化中心Mn_(4)CaO_(5)团簇中的配位水被认为在促进水氧化方面起着重要作用.许多报道模拟了Mn_(4)CaO_(5)结构并研究了其析氧反应(OER)过程,但配位水结构难以模拟,在OER过程中的具体功能尚不明确.目前,揭示配位水在OER中的具体作用存在以下挑战.首先,大多数锰基材料的配位结构,特别是表面结构是模糊的,导致结构-性能相关性难以确定.其次,在Mn位点上引入配位水时,往往不可避免地会改变Mn中心的核心结构,甚至改变Mn的化合价,这些干扰因素可能严重混淆配位水对OER的影响,不利于探究OER过程中配位水分子的作用.因此,构建一个理想的催化剂平台用于研究配位水分子在水氧化过程中的作用具有重要意义.本文提出了一种研究OER过程中配位水分子作用的有效方法,并阐明了OER过程中源于锰中心配位水分子结构-活性关系.采用水热法合成了一种结晶型焦磷酸锰(crystalline MnPi).在相同起始物料比、不同反应条件下,采用共沉淀法制备了分子式相同的非晶型焦磷酸锰(amorphous MnPi).通过X射线衍射、红外光谱、拉曼光谱、热重分析和理论模拟,确定了MnPi催化剂的晶体结构(Mn_(2)P_(2)O_(7)·3H_(2)O).在0.05 mol L^(-1)pH=7.0的磷酸盐缓冲溶液中,crystalline MnPi催化剂比amorphous MnPi催化剂表现出更好的OER活性.晶体结构研究结果表明,crystalline MnPi催化剂暴露的Mn位点上含有四个配位水分子,并且相邻Mn位点通过氢键相互连接形成连续的氢键网络结构.连续的氢键网络使氧原子的电荷中和水平更高,使得crystalline MnPi催化剂中Mn^(Ⅱ/Ⅲ)转换更容易,进一步揭示了配位水在水氧化机理中扮演的重要角色.详细的电化学动力学研究、原位/非原位表面表征和理论计算结果表明,crystalline MnPi催化剂的Mn^(Ⅱ/Ⅲ)氧化过程在动力学和热力学上都比amorphous MnPi催化剂容易发生.同时,crystalline MnPi催化剂
The coordinated water in the Mn_(4)CaO_(5)clusters in natural water oxidation center is believed to play an important role in promoting water oxidation.However,its specific role is unclear.In this work,based on a new manganese phosphate(Mn_(2)P_(2)O_(7)·3H_(2)O)with well-defined crystal surfaces(crystalline MnPi)and its amorphous counterpart(amorphous MnPi),the effects of coordinated water molecules on water oxidation have been systematically investigated.There are four coordinated water molecules on one Mn site,which is very rare and valuable to study relevant effects from water coordination.Unusually,the crystalline MnPi outperformed the amorphous MnPi in electrocatalysis.The exposed well-defined surface of the crystalline MnPi contains continuous Mn sites with multiple coordinated water molecules.The kinetics and thermodynamics of surface oxidation have been quantitatively studied based on the appealing catalyst platform.The interaction between adjacent Mn sites leads to a 3H^(+)/2e dual site oxidation in crystalline MnPi,while this process is 2H^(+)/1e single site conversion in amorphous MnPi.The higher level of charge neutralization of oxygen atoms from continuous H-bond network in crystalline MnPi is helpful for the MnII/III oxidation,which subsequently promotes water oxidation.This study provides valuable insight into the role of coordinated water molecules in initiating water oxidation in Mn-based catalytic systems.
作者
杨树姣
江鹏飞
岳楷航
郭凯
杨璐娜
韩金秀
彭欣阳
张学鹏
郑浩铨
杨韬
曹睿
严雅
张伟
Shujiao Yang;Pengfei Jiang;Kaihang Yue;Kai Guo;Luna Yang;Jinxiu Han;Xinyang Peng;Xuepeng Zhang;Haoquan Zheng;Tao Yang;Rui Cao;Ya Yan;Wei Zhang(Key Laboratory of Applied Surface and Colloid Chemistry,Ministry of Education,School of Chemistry and Chemical Engineering,Shaanxi Normal University,Xi’an 710119,Shaanxi,China;College of Chemistry and Chemical Engineering,Chongqing University,Chongqing 401331,China;Shanghai Institute of Ceramics,Chinese Academy of Sciences(SICCAS),Shanghai 200050,China)
基金
陕西师范大学启动研究基金
国家自然科学基金(22379088)
陕西师范大学优秀研究生培养计划(LHRCYB23005).
关键词
水氧化
结构
电催化
配位水
磷酸锰
Water oxidation
Structure
Electrocatalysis
Coordinated water molecules
Manganese phosphate
