Tracking Catalyst Redox States and Reaction Dynamics in Ni-Fe Oxyhydroxide Oxygen Evolution Reaction Electrocatalysts: The Role of Catalyst Support and Electrolyte pH
Tracking Catalyst Redox States and Reaction Dynamics in Ni-Fe Oxyhydroxide Oxygen Evolution Reaction Electrocatalysts: The Role of Catalyst Support and Electrolyte pH
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DOI：
10.1021/jacs.6b12250
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发表时间：
2017-02-08
影响因子：
15
通讯作者：
Strasser, Peter
中科院分区：
文献类型：
--
作者：
Goerlin, Mikaela;de Araujo, Jorge Ferreira;Strasser, Peter
Ni-Fe羟基氧化物是碱性电解质中用于析氧反应（OER）的最活性的已知电催化剂，因此在电化学能量转换的背景下具有重要的科学和技术重要性。在这里，我们发现，调查，并讨论以前未解决的影响导电支持和电解质pH值的Ni-Fe（OOH）催化剂的氧化还原行为和催化OER活性，结合原位紫外-可见光谱电化学，操作电化学质谱（DEMS），和原位低温X射线吸收光谱（XAS）。载体和pH > 13强烈增强Ni-Fe羟基氧化还原峰对的催化前伏安电荷，使它们更阴极化，并导致催化OER活性增加2-3倍。基于DEM的法拉第氧效率和电化学UV-vis迹线的分析一致地证实了我们的伏安法观察，证明了在较高pH下更多的阴极O-2释放和更多的阴极Ni氧化起始。使用可以原位监测氧化的Ni+3/+4的量的UV-vis，证实了在高电解质pH下氧化还原过程的较早开始，并进一步提供了混合Ni-Fe中心中Ni+3/+4的较小部分的证据，证实了未解决的矛盾，即随着Fe含量的增加，金属氧化还原活性降低。随着Fe含量的增加，氧化还原峰的非单调超能斯特pH依赖性显示Pourbaix斜率为-120 mV/pH，表明两个质子-一个电子转移。我们解释和讨论的实验pH值的影响，使用精细耦合（PCET）和去耦质子转移-电子转移（PT/ET）涉及带负电荷的配体在Fe中心产生的计划。我们共同提供了对最重要的碱性OER催化剂的催化反应动力学和相关催化剂氧化还原化学的新见解。
Ni-Fe oxyhydroxides are the most active known electrocatalysts for the oxygen evolution reaction (OER) in alkaline electrolytes and are therefore of great scientific and technological importance in the context of electrochemical energy conversion. Here we uncover, investigate, and discuss previously unaddressed effects of conductive supports and the electrolyte pH on the Ni-Fe(OOH) catalyst redox behavior and catalytic OER activity, combining in situ UV-vis spectro-electrochemistry, operando electrochemical mass spectrometry (DEMS), and in situ cryo X-ray absorption spectroscopy (XAS). Supports and pH > 13 strongly enhanced the precatalytic voltammetric charge of the Ni-Fe oxyhydroxide redox peak couple, shifted them more cathodically, and caused a 2-3-fold increase in the catalytic OER activity. Analysis of DEMS-based faradaic oxygen efficiency and electrochemical UV-vis traces consistently confirmed our voltammetric observations, evidencing both a more cathodic O-2 release and a more cathodic onset of Ni oxidation at higher pH. Using UV-vis, which can monitor the amount of oxidized Ni+3/+4 in situ, confirmed an earlier onset of the redox process at high electrolyte pH and further provided evidence of a smaller fraction of Ni+3/+4 in mixed Ni-Fe centers, confirming the unresolved paradox of a reduced metal redox activity with increasing Fe content. A nonmonotonic super-Nernstian pH dependence of the redox peaks with increasing Fe content-displaying Pourbaix slopes as steep as -120 mV/pH-suggested a two proton-one electron transfer. We explain and discuss the experimental pH effects using refined coupled (PCET) and decoupled proton transfer-electron transfer (PT/ET) schemes involving negatively charged oxygenate ligands generated at Fe centers. Together, we offer new insight into the catalytic reaction dynamics and associated catalyst redox chemistry of the most important class of alkaline OER catalysts.