Modification of spinel MnCo2O4 nanowire with NiFe-layered double hydroxide nanoflakes for stable seawater oxidation

Currently, direct electrolysis of seawater-based electrolytes rather than fresh water based ones for hydro-gen production is gaining more and more attentions for creating a sustainable society. However, using sea-water remains more challenges owing to the existence of competitive reactions between chlorine evolution reaction (ClER) or hypochlorite generation reaction and oxygen evolution reaction (OER) and electrode erosion. In this study, a MnCo2O4 nanowire coated with NiFe-Layered Double Hydroxide (NiFe-LDH) layer (MnCo2O4@NiFe-LDH) composite electrocatalyst prepared by a simple two-step hydrothermal method was applied for the seawater electrolysis, which exhibited low overpotentials of 219 and 245 mV at a relatively high current density of 100 mA cm-2 in alkaline simulated and natural sea -waters, respectively, as the anode electrocatalyst. It is found that the NiFe-LDH layer on the MnCo2O4 nanowire can serve as Cl- protective layer to hinder the ClER and anode erosion and simultaneously improve the active surface area and intrinsic properties of MnCo2O4 nanowires, allowing for faster kinet-ics. While, the high valence states of Mn3+ , Co3+ , Ni3+and Fe3+ played a vital role for OER. In addition, when it was used as the bifunctional electrocatalyst for the overall real seawater splitting, the cell composed of MnCo2O4@NiFe-LDH (-) || MnCo2O4@NiFe-LDH (+) pair only required a low voltage of 1.56 V@10 mA cm-2 and simultaneously maintained excellent stability at a high current density of 100 mA cm-2. Such an elec-trocatalyst could be a promising candidate for long-term seawater splitting. (c) 2022 Elsevier Inc. All rights reserved.

Automated summary

Currently, electrolysis of seawater-based electrolytes for hydrogen production is gaining attention. A composite electrocatalyst, MnCo2O4@NiFe-LDH, was developed for seawater electrolysis, which exhibited low overpotentials and improved stability. The NiFe-LDH layer acted as a protective layer and improved the active surface area of MnCo2O4 nanowires. Additionally, high valence states of Mn3+, Co3+, Ni3+, and Fe3+ played a vital role in the oxygen evolution reaction. This composite electrocatalyst shows promise for long-term seawater splitting.