Ahmed Zubair, Rai Ritu, Kumar Rajinder, Maruyama Takahiro, Bera Chandan, Bagchi Vivek
Institute of Nano Science and Technology (INST), Sector-81, Knowledge City, Sahibzada Ajit Singh Nagar, Punjab 140306, India.
Department of Applied Chemistry, Meijo University, 1-501 Shiogamaguchi, Tempaku, Nagoya 468-8502, Japan.
ACS Appl Mater Interfaces. 2021 Nov 24;13(46):55281-55291. doi: 10.1021/acsami.1c19536. Epub 2021 Nov 15.
One of the major objectives of using the improved Hummers' method was to exfoliate the graphene layers by oxidizing and thereafter reducing them to obtain highly conductive reduced graphene layers, which can be used in the construction of electronic devices or as a part of catalyst composites in energy conversion reactions. Herein, we have employed a similar idea to exfoliate the layered double hydroxide (LDH), which is proposed as a promising material for the oxygen evolution reaction (OER) electrocatalysis. Usually, the efficiency of these materials is largely restricted due to their sheetlike morphology, which is susceptible to stacking. In this work, NiFe-LDH sheets were fabricated on nickel foam in a one-step co-precipitation technique and their ultrathin nanosheets (∼2 nm) are obtained by oxygen-plasma-controlled exfoliation. In addition, the oxygen vacancies in exfoliated sheets were generated by a chemical reduction method that further improved the electronic conductivity and overall electrocatalytic performance of the catalyst. This approach can address the limitations of NiFe-LDH, such as poor conductivity and low stability, making it more efficient for electrocatalysis. It is also observed that the catalyst having 60 s O-plasma exposure after chemical reduction, i.e., NiFe-OOH, outperformed remaining electrocatalysts and exhibited superior OER activity with a low overpotential of 330 mV to achieve a high current density of 50 mA cm. The catalyst also displayed an ECSA-normalized OER overpotential of 288 mV at a current density of 10 mA cm and exhibited excellent long-term stability (120 h) in an alkaline electrolyte. Remarkably, ultrathin defect-rich catalyst continuously produced O, resulting in a high faradaic efficiency of 98.1% for the OER.
使用改进的Hummers法的主要目标之一是通过氧化然后还原石墨烯层来使其剥离，以获得高导电性的还原石墨烯层，其可用于构建电子器件或作为能量转换反应中催化剂复合材料的一部分。在此，我们采用了类似的思路来剥离层状双氢氧化物（LDH），其被认为是一种用于析氧反应（OER）电催化的有前景的材料。通常，这些材料的效率在很大程度上受到其片状形态的限制，这种形态容易发生堆叠。在这项工作中，通过一步共沉淀技术在泡沫镍上制备了NiFe-LDH片材，并通过氧等离子体控制的剥离获得了其超薄纳米片（约2nm）。此外，通过化学还原法在剥离的片材中产生氧空位，这进一步提高了催化剂的电子导电性和整体电催化性能。这种方法可以解决NiFe-LDH的局限性，如导电性差和稳定性低的问题，使其在电催化方面更高效。还观察到，化学还原后经过60s氧等离子体暴露的催化剂，即NiFe-OOH，性能优于其余电催化剂，表现出优异的OER活性，在低过电位330mV下可实现50mA cm的高电流密度。该催化剂在10mA cm的电流密度下还显示出288mV的ECSA归一化OER过电位，并在碱性电解质中表现出优异的长期稳定性（120h）。值得注意的是，超薄富缺陷催化剂持续产生O，导致OER的法拉第效率高达98.1%。
