摘要
Hematite(α-Fe_(2)O_(3))constitutes one of the most promising photoanode materials for oxygen evolution reaction(OER).Recent research on Fe_(2)O_(3)have found a fast OER rate dependence on surface hole density,suggesting a multisite reaction pathway.However,the effect of heteroatom in Fe_(2)O_(3)on the multisite mechanism is still poorly understood.Herein we synthesized Fe_(2)O_(3)on Ti substrates(Fe_(2)O_(3)/Ti)to study the oxygen intermediates of OER by light-dark electrochemical scans.We identified the Fe-OH species disappeared and Ti-OH intermediates appeared on Fe_(2)O_(3)/Ti when pH=11‒14,which significantly improved the OER performance of Fe_(2)O_(3)/Ti.Combined with the density functional theory calculations,we propose that Ti atom acts as cocatalyst site and captures proton from neighboring Fe-OH species under highly alkaline condition,thereby promoting the coupling of Fe=O and reducing the energy barrier of the non-electrochemical step.Our work provides a new insight into the role of heteroatom in OER multisite mechanism based on clarifying the reaction intermediates.
赤铁矿(Fe_(2)O_(3))是光电催化析氧反应(OER)中极具潜力的半导体光阳极材料之一,其性能的提升一直是研究热点.近期研究表明,在碱性环境中,Fe_(2)O_(3)光阳极的OER反应速率与其表面空穴密度之间存在幂律依赖性.与单位点质子耦合电子转移(PCET)机制(^(*)OH→^(*)O→*OOH→O_(2))不同,Fe_(2)O_(3)上的OER遵循多位点反应机制,即表面羟基(^(*)OH)通过空穴的氧化积累转化为氧基(^(*)O),随后在相邻活性位点间发生O-O耦合.钛(Ti)掺杂是提升Fe_(2)O_(3)上OER性能的重要手段之一,但Ti等异质原子在多位点反应机制中的具体作用(是活性位点还是助催化位点)尚不明晰.为探明Ti等异质原子的具体作用,本文利用电化学光-暗态扫描方法识别碱性环境中OER反应中间态,并结合密度泛函理论(DFT)计算,考察了异质Ti原子在赤铁矿OER多位点反应路径中的作用机制.首先,通过水热法将Fe_(2)O_(3)纳米棒分别生长在金属Ti基底及氟掺杂二氧化锡(FTO)导电基底上,构建了Fe_(2)O_(3)/Ti和Fe_(2)O_(3)/FTO两种复合材料体系.实验发现,Fe_(2)O_(3)/Ti体系的最佳退火温度为550℃.在此条件下,X射线衍射分析不仅展现了α-Fe_(2)O_(3)衍射峰,还检测到了金红石TiO_(2)(110)晶面的衍射峰.侧面高分辨球差电镜测试结果表明,Fe_(2)O_(3)/Ti表面覆盖有一层约120 nm厚的Fe_(2)O_(3)层;而在Ti基底与Fe_(2)O_(3)之间,则存在厚度约为100 nm的Ti氧化层.值得注意的是,尽管在Fe_(2)O_(3)体相内并未观察到明显的Ti原子掺杂现象,但推测在高温退火条件下,可能有少量Ti原子会扩散到Fe_(2)O_(3)界面.X射线光电子能谱测试表明,Fe_(2)O_(3)/Ti复合材料界面处Fe与Ti元素间存在显著的相互作用,其中Fe位点作为电子给体,Ti位点则作为电子受体.为了深入理解这一相互作用对OER的影响,进行了不同pH环境下的电化学光-暗态扫描研究.结果发现,在pH 7-10的范围内,Fe_(2)O_(3)/Ti和Fe_(2)O_(3)/F
基金
中央高校基础研究基金(2022CDJQY-007,2022CDJJCLK001,2023CDJXY-046).
