Oxygen Electrocatalysis on Mixed-Metal Oxides/Oxyhydroxides: From Fundamentals to Membrane Electrolyzer Technology
Oxygen Electrocatalysis on Mixed-Metal Oxides/Oxyhydroxides: From Fundamentals to Membrane Electrolyzer Technology
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DOI：
10.1021/accountsmr.1c00087
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发表时间：
2021-07-13
影响因子：
14.6
通讯作者：
Boettcher, Shannon W.
中科院分区：
文献类型：
--
作者：
Krivina, Raina A.;Ou, Yingqing;Boettcher, Shannon W.
综述：催化析氧反应（OER）对于关键的储能技术非常重要，特别是用于生产氢燃料的水电解和光电解。在中性到碱性条件下，第一行过渡金属氧化物/（羟基）氧化物是已知最快的OER催化剂，并且在过去十年中一直是深入研究的对象。它们高性能的关键在于有意或无意地向镍/钴氧化物中添加铁，这些氧化物在OER过程中会转变为层状（羟基）氧化物结构。然而，由于主体结构和吸附铁位点的动态变化以及这些无序活性相中局部结构的多样性，揭示铁在催化中所起的作用以及真正“活性位点”的分子特性已被证明具有挑战性。在本文中，我们重点介绍我们为理解铁在镍/钴（羟基）氧化物OER催化剂中的作用所做的工作。我们首先讨论如何通过考虑催化剂层厚度（质量负载）和电导率以及底层基底与催化剂的化学相互作用以及电解质中铁物种的存在，来表征作为薄膜的第一行过渡金属（羟基）氧化物催化剂的本征活性。我们展示了铁掺杂的镍/钴（羟基）氧化物在催化过程中如何重构、吸附/解吸铁，以及在某些情况下在电化学测试过程中如何降低或恢复其活性。我们强调了相关技术和程序，这些技术和程序使我们能够更好地理解铁在激活其他第一行过渡金属用于OER方面的作用。我们发现了铁在镍/钴（羟基）氧化物中的几种掺入模式，并展示了这些模式如何与活性和耐久性相关。我们还讨论了这种理解如何为在阴离子交换膜水电解槽（AEMWE）中纳入地球上储量丰富的过渡金属OER催化剂提供信息，该电解槽提供局部碱性阳极环境但使用纯水运行，并且相对于使用铂族金属（PGM）催化剂的更成熟的质子交换膜水电解槽（PEMWE）具有优势。我们概述了在AEMWE阳极引入铁掺杂的镍/钴（羟基）氧化物催化剂的关键问题，例如铁物种穿过聚合物膜引发的氧化过程、pH梯度对催化剂稳定性的影响以及在压缩堆叠配置中可能有限的催化剂利用率。我们还针对这些问题提出了可能的缓解策略。最后，我们总结了剩余的挑战，包括铁掺杂的镍/钴（羟基）氧化物在OER条件下的长期稳定性以及缺乏动态活性表面的准确模型，这些都阻碍了我们对这些催化剂的理解，从而影响了我们设计这些催化剂的能力。
CONSPECTUS: Catalyzing the oxygen evolution reaction (OER) is important for key energy-storage technologies, particularly water electrolysis and photoelectrolysis for hydrogen fuel production. Under neutral-to-alkaline conditions, first-row transitionmetal oxides/(oxy)hydroxides are the fastest-known OER catalysts and have been the subject of intense study for the past decade. Critical to their high performance is the intentional or accidental addition of Fe to Ni/Co oxides that convert to layered (oxy)hydroxide structures during the OER. Unraveling the role that Fe plays in the catalysis and the molecular identity of the true "active site" has proved challenging, however, due to the dynamics of the host structure and absorbed Fe sites as well as the diversity of local structures in these disordered active phases.In this Account, we highlight our work to understand the role of Fe in Ni/Co (oxy)hydroxide OER catalysts. We first discuss how we characterize the intrinsic activity of the first-row transition-metal (oxy)hydroxide catalysts as thin films by accounting for the contributions of the catalyst-layer thickness (mass loading) and electrical conductivity as well as the underlying substrate's chemical interactions with the catalyst and the presence of Fe species in the electrolyte. We show how Fe-doped Ni/Co (oxy)hydroxides restructure during catalysis, absorb/desorb Fe, and in some cases degrade or regenerate their activity during electrochemical testing. We highlight the relevant techniques and procedures that allowed us to better understand the role of Fe in activating other first-row transition metals for OER. We find several modes of Fe incorporation in Ni/Co (oxy)hydroxides and show how those modes correlate with activity and durability. We also discuss how this understanding informs the incorporation of earthabundant transition-metal OER catalysts in anion-exchange-membrane water electrolyzers (AEMWE) that provide a locally basic anode environment but run on pure water and have advantages over the more-developed proton-exchange-membrane water electrolyzers (PEMWE) that use platinum-group-metal (PGM) catalysts. We outline the key issues of introducing Fe-doped Ni/Co (oxy)hydroxide catalysts at the anode of the AEMWE, such as the oxidative processes triggered by Fe species traveling through the polymer membrane, pH-gradient effects on the catalyst stability, and possibly limited catalyst utilization in the compressed stack configuration. We also suggest possible mitigation strategies for these issues. Finally, we summarize remaining challenges including the long-term stability of Fe-doped Ni/Co (oxy)hydroxides under OER conditions and the lack of accurate models of the dynamic active surface that hinder our understanding of, and thus ability to design, these catalysts.