Unraveling a Graphene Exfoliation Technique Analogy in the Making of Ultrathin Nickel-Iron Oxyhydroxides@Nickel Foam to Promote the OER.

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 in situ 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-OOHOV, 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-2. The catalyst also displayed an ECSA-normalized OER overpotential of 288 mV at a current density of 10 mA cm-2 and exhibited excellent long-term stability (120 h) in an alkaline electrolyte. Remarkably, ultrathin defect-rich catalyst continuously produced O2, resulting in a high faradaic efficiency of 98.1% for the OER.