Cobalt-Iron (Oxy)hydroxide Oxygen Evolution Electrocatalysts: The Role of Structure and Composition on Activity, Stability, and Mechanism
Cobalt-Iron (Oxy)hydroxide Oxygen Evolution Electrocatalysts: The Role of Structure and Composition on Activity, Stability, and Mechanism
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DOI：
10.1021/jacs.5b00281
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发表时间：
2015-03-18
影响因子：
15
通讯作者：
Boettcher, Shannon W.
中科院分区：
文献类型：
--
作者：
Burke, Michaela S.;Kast, Matthew G.;Boettcher, Shannon W.
钴的氧化物和氢氧化物作为析氧反应的电催化剂已被广泛研究。对于相关的Ni基材料，Fe的添加显著提高了OER活性。铁在钴基材料中的作用没有很好的记录。我们发现，固有的OER活动的Co 1-xFex（OOH）是类似的100倍高x接近0.6-0.7比x = 0的每金属周转频率的基础上。如果电解质未严格纯化，则不含Fe的CoOOH从电解质杂质中吸收Fe。Fe的掺入和活性的增加与名义上的Co2+/3+氧化还原波的阳极位移相关，表明两种元素之间的强电子相互作用和Fe对Co的可能替代掺杂。原位电测量表明Co 1-xFex（OOH）在OER条件下是导电的（在类似于300 mV的过电位下类似于0.7-4 mS cm（-1）），但是FeOOH是仅在>400 mV的高过电位下具有可测量电导率（2.2 x 10（-2）mS cm（-1））的绝缘体。因此，FeOOH的表观OER活性受到低电导率的限制。微量天平测量显示x >= 0.54的膜（即，富Fe）在OER条件下溶解在1 M KOH电解质中。对于x < 0.54，膜表现出化学稳定性，但OER活性在2小时内降低了16-62%，这可能是由于转化成更致密的氧化物样相。因此，我们假设Fe是催化剂中最具活性的位点，而CoOOH主要提供导电的、高表面积的、化学稳定的主体。这些结果是重要的，因为含Fe的Co-和Ni-（氧）氢氧化物是已知的最快OER催化剂。
Cobalt oxides and (oxy)hydroxides have been widely studied as electrocatalysts for the oxygen evolution reaction (OER). For related Ni-based materials, the addition of Fe dramatically enhances OER activity. The role of Fe in Co-based materials is not well-documented. We show that the intrinsic OER activity of Co1-xFex(OOH) is similar to 100-fold higher for x approximate to 0.6-0.7 than for x = 0 on a per-metal turnover frequency basis. Fe-free CoOOH absorbs Fe from electrolyte impurities if the electrolyte is not rigorously purified. Fe incorporation and increased activity correlate with an anodic shift in the nominally Co2+/3+ redox wave, indicating strong electronic interactions between the two elements and likely substitutional doping of Fe for Co. In situ electrical measurements show that Co1-xFex(OOH) is conductive under OER conditions (similar to 0.7-4 mS cm(-1) at similar to 300 mV overpotential), but that FeOOH is an insulator with measurable conductivity (2.2 x 10(-2) mS cm(-1)) only at high overpotentials >400 mV. The apparent OER activity of FeOOH is thus limited by low conductivity. Microbalance measurements show that films with x >= 0.54 (i.e., Fe-rich) dissolve in 1 M KOH electrolyte under OER conditions. For x < 0.54, the films appear chemically stable, but the OER activity decreases by 16-62% over 2 h, likely due to conversion into denser, oxide-like phases. We thus hypothesize that Fe is the most-active site in the catalyst, while CoOOH primarily provides a conductive, high-surface area, chemically stabilizing host. These results are important as Fe-containing Co- and Ni-(oxy)hydroxides are the fastest OER catalysts known.