Ultrathin layered double hydroxide nanosheets with Ni(III) active species obtained by exfoliation for highly efficient ethanol electrooxidation

Abstract

The development of non-precious metal electrocatalysts for renewable energy conversion and storage is compelling but greatly challenging due to low activity of the existing catalysts. Herein, the ultrathin NiAl-layered double hydroxide nanosheets (NiAl-LDH-NSs) are prepared by simple liquid-exfoliation of bulk NiAl-LDHs and first used as ethanol electrooxidation catalysts. The ultrathin two-dimensional (2D) structure ensures that the LDH nanosheets expose a greater number of active sites. More importantly, much Ni(III) active species (NiOOH) in the ultrathin nanosheets are formed by the exfoliation process, which play an authentic catalytic role in the ethanol oxidation reaction (EOR). The presence of NiOOH remarkably improves the reactivity and electrical conductivity of LDH nanosheets. These synergistic effects lead to strikingly more than 30 times enhanced EOR activity of NiAl-LDH-NSs compared to bulk NiAl-LDHs. The obtained electrocatalytic activity is also much better than those of most Ni- and LDH-based EOR catalysts reported to date. In addition, the ultrathin NiAl-LDH-NS electrocatalyst also exhibits good long-term stability (maintain 81.8% of the original value after 10000 s). This study not only provides a highly competitive EOR catalyst, but also opens new avenues toward the design of highly efficient electrode materials that have various potential applications in supercapacitor, Ni-MH battery and other electrocatalytic systems.

Effects of Incorporated Iron or Cobalt on the Ethanol Oxidation Activity of Nickel (Oxy)Hydroxides in Alkaline Media

“…Nickel-based materials have been employed for the electrocatalytic ethanol oxidation [6][7][8][9] due to their low cost and high stability in alkaline media. Some strategies to enhance the overall catalytic activity for alcohol oxidation involve the exfoliation of the nickel layered hydroxide [6] in order to generate more reactive sites and expose a higher number of them to the solution, the synthesis of nanostructured materials with controlled shape [10,11] or the use of effective catalyst supports such as carbon nanoflakes [12,13] or nanofibers [14]. The incorporation of other metal atoms to the nickel (oxy)hydroxide (NiO x H y ) structure is also a known method to change the catalytic properties of the material [15].…”

Advanced Exfoliation Strategies for Layered Double Hydroxides and Applications in Energy Conversion and Storage

“…The plate‐like bulk NiAl‐LDHs exhibited a thickness of ≈20 nm, after exfoliation, the obtained nanosheets presented a thickness range of 0.75–0.88 nm displayed in the AFM height profiles (Figure 2d,e). The successful exfoliation was also confirmed by the obvious Tyndall phenomenon and the absence of characteristic peaks in the XRD pattern 19. The exfoliation process of LDHs can be facilitated by the ultrasonic treatment and the suspension of nanosheets with a concentration up to 40 g L −1 could be obtained 20.…”

“…d) AFM image and e) corresponding height profiles for NiAl‐LDH nanosheets. Reproduced with permission 19. Copyright 2017, Elsevier Ltd.…”

Recent advance in ultrathin/ultrasmall layered double hydroxides

“…XRD是多晶材料结构研究的重要手段, 用XRD对 LDHs进行结构分析最早报道于1967年 [52] , 通过LDHs 的XRD分析, 可以得到其晶相结构、晶胞参数等信息. (e) 在微乳液中生成最终的水滑石产品 (d) the LDH phase starts to crystallize; (e) the final product in a "water pool" [40] LDHs纳米材料成功合成的重要判据 [49,53,54] . 2014年, O'Hare课题组 [32,33] 采用AMOST法对ZnAl-LDH进行处 理, XRD图中(00l)峰的消失说明成功制备了剥离程度…”

“…早期, 人们利用SEM对不同方法制备的LDHs的粒径分布、 形貌特点等做了深入系统研究 [55] . HRTEM可给出 AFM常被用于研究LDHs材料的厚度 [44,54] . 2019年 Song课题组 [56] 合成了单原子Ru负载的NiFe-LDH, 由 AFM可知, 这种超薄超小的水滑石厚度为~1 nm, 证明 成功合成了单层水滑石.…”