Surface Chemistry Laboratory of Electronic Materials, Department of Chemical Engineering , Pohang University of Science and Technology (POSTECH) , Pohang 37673 , Republic of Korea.
Advanced Functional Nanomaterial Laboratory, Department of Chemical Engineering , POSTECH , Pohang 37673 , Republic of Korea.
ACS Appl Mater Interfaces. 2018 Dec 26;10(51):44518-44526. doi: 10.1021/acsami.8b16962. Epub 2018 Dec 12.
As a key half-reaction in water splitting, the oxygen evolution reaction (OER) process is kinetically sluggish. Layered double hydroxides (LDHs) are regarded as the highly promising electrocatalysts to promote the OER kinetics. However, the closely stacking layered structure of pristine bulk LDHs restricts the exposure of electrocatalytically active sites, and it remains a great challenge to find an efficient strategy to exfoliate the bulk LDHs into ultrathin and stable nanosheets with increased surface area and exposed active sites. Herein, a novel Ostwald ripening driven exfoliation (ORDE) of NiFe LDHs has been achieved in situ on the electrodes by spontaneously self-etching and redepositing via a simple hydrothermal treatment without the assistance of any exfoliating reagent or surfactant. The thermodynamically driven Ostwald ripening has been expanded to the exfoliation of two-dimensional layered materials for the first time. Compared with conventional exfoliation methods, this ORDE is a time-saving and green strategy that avoids the serious adsorption of surfactant molecules. The ORDE of NiFe LDHs is accomplished in situ on a Cu mesh electrode, which not only exhibits excellent electrical contact between LDHs catalyst and electrodes but also prevents the restacking of the exfoliated LDHs. As a result, the exfoliated ultrathin, clean, and vertically aligned NiFe nanosheets with much higher surface area and numerous exposed active edges and sites demonstrated significantly enhanced OER performances with low overpotential of 292 mV at 10 mA cm and long-term stability for more than 60 h, as well as remarkable flexibility. Additionally, bulk Ni(OH) nanosheets on Ni foams have also been exfoliated by a similar mechanism, indicating this ORDE strategy can be widely extended to other 2D layered materials for novel applications.
作为水分解的关键半反应，氧析出反应（OER）过程动力学缓慢。层状双氢氧化物（LDHs）被认为是促进 OER 动力学的极具前景的电催化剂。然而，原始块状 LDHs 的紧密堆叠层状结构限制了电催化活性位点的暴露，寻找有效的策略将块状 LDHs 剥离成具有增加的表面积和暴露的活性位点的超薄和稳定的纳米片仍然是一个巨大的挑战。在此，通过简单的水热处理，无需任何剥离试剂或表面活性剂的协助，在电极上原位实现了 NiFe LDHs 的新型奥斯特瓦尔德熟化驱动剥离（ORDE）。热力学驱动的奥斯特瓦尔德熟化首次扩展到二维层状材料的剥离。与传统的剥离方法相比，这种 ORDE 是一种节省时间和环保的策略，避免了表面活性剂分子的严重吸附。ORDE 的 NiFe LDHs 是在 Cu 网电极上原位完成的，这不仅在 LDHs 催化剂和电极之间表现出良好的电接触，而且还防止了剥离的 LDHs 的堆积。结果，剥离的超薄、清洁且垂直排列的 NiFe 纳米片具有更高的表面积和更多暴露的活性边缘和位点，表现出显著增强的 OER 性能，在 10 mA cm 时的过电位仅为 292 mV，长期稳定性超过 60 h，以及显著的灵活性。此外，Ni 泡沫上的大块 Ni(OH)纳米片也通过类似的机制被剥离，表明这种 ORDE 策略可以广泛扩展到其他二维层状材料，用于新的应用。
