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

Abstract

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.

Adjustable antiperovskite cobalt-based nitrides as efficient electrocatalysts for overall water splitting

“…S6a, b and S7a, b†) in the non-faradaic potential range. 52,53 Fig. 3c shows that CuNCo 3 /NF possesses the largest C dl value of 77.99 mF cm −2 and it is 44.01 mF cm −2 for CoN 0.73 Co 3 /NF.…”

Oxygen-Plasma-Induced Hetero-Interface NiFe2O4/NiMoO4 Catalyst for Enhanced Electrochemical Oxygen Evolution

“…Meanwhile, in the Ni 2p 1/2 , the peaks of the Ni 2+ and Ni 3+ species can be fitted at 874.0 eV and 875.2 eV, respectively. In addition, two satellite peaks for Ni can be observed at 862.8 and 880.7 eV [ 51 ]. As shown in Figure S5b , the further fitted peaks at 708.5 and 709.1 eV in the Fe 2p 3/2 are ascribed to Fe 2+ and Fe 3+ , respectively, while the peaks observed at 721.6 and 722.2 eV in the Fe 2p 1/2 are owed to the existence of Fe 2+ and Fe 3+ , respectively.…”

“…The ratio of the Fe 3+ to Fe 2+ peak areas in the Fe 2p 3/2 was calculated as 0.948. Furthermore, one satellite peak for Fe appears at 715.7 eV [ 51 ].…”

Recent Advances of Modified Ni (Co, Fe)-based LDH 2D Materials for Water Splitting

“…In general, the traditional LDHs are layered stacked structures, which not only shield a large number of catalytic active sites, but also inhibit the electron and mass transfer during electrocatalytic reactions over catalyst. Therefore, it can be stripped into ultrathin nanosheets with smaller size by exfoliation strategy to significantly enhance electrocatalytic performance [125][126][127][128][129]. The peeled single-layer ultra-thin LDHs nanosheets provide large surface area and more electrochemically active sites, thus facilitating to react with reactants.…”