Recent Advances in Self-Supported Layered Double Hydroxides for Oxygen Evolution Reaction

Abstract

Electrochemical water splitting driven by clean and sustainable energy sources to produce hydrogen is an efficient and environmentally friendly energy conversion technology. Water splitting involves hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), in which OER is the limiting factor and has attracted extensive research interest in the past few years. Conventional noble-metal-based OER electrocatalysts like IrO₂ and RuO₂ suffer from the limitations of high cost and scarce availability. Developing innovative alternative nonnoble metal electrocatalysts with high catalytic activity and long-term durability to boost the OER process remains a significant challenge. Among all of the candidates for OER catalysis, self-supported layered double hydroxides (LDHs) have emerged as one of the most promising types of electrocatalysts due to their unique layered structures and high electrocatalytic activity. In this review, we summarize the recent progress on self-supported LDHs and highlight their electrochemical catalytic performance. Specifically, synthesis methods, structural and compositional parameters, and influential factors for optimizing OER performance are discussed in detail. Finally, the remaining challenges facing the development of self-supported LDHs are discussed and perspectives on their potential for use in industrial hydrogen production through water splitting are provided to suggest future research directions.

Figure 1

(a) Schematic illustration of NiFe LDH nanoplates grown on NF, (b) SEM image of pure NF, (c) crystal structure of NiFe LDH, (d) polarization curves of different electrocatalysts, and (e) Tafel plots of NiFe LDH/NF (black), Ni(OH)₂/NF (red), and 20 wt% Ir/C (blue) catalysts in a 1 M KOH solution [47]. Copyright 2014, the Royal Society of Chemistry. (f) High-resolution SEM image of 3D amorphous NiFe LDH/NF (scale bar: 200 nm) and (g) TEM image of NiFe LDH nanosheets scratched off from the NiFe LDH/NF and (inset) corresponding selected area diffraction pattern (scale bar: 10 nm) [49]. Copyright 2015, Nature Publishing Group. (h) TEM line scan and (inset) TEM image of gradient NiFe LDH (scale bar: 100 nm), (i) SEM line scan and (inset) SEM image of gradient NiFe LDH (scale bar: 500 nm), (j) EELS spectra of the Fe edge and Ni edge in gradient NiFe LDH, and (k) illustration of gradient NiFe LDH prepared by the hydrothermal method [51]. Copyright 2019, Elsevier Ltd.

Figure 2

(a) Schematic illustration of the fabrication process for the self-supported 3D core-shell Cu@NiFe LDH electrocatalysts (RT: room temperature), (b) SEM images of Cu nanowires, (c) TEM image of Cu@NiFe LDH, (d) EDS line scan spectrum of Cu@NiFe LDH, (e) polarization curves of Cu@NiFe LDH measured in 1 M KOH, and (f) chronopotentiometry curves of Cu@NiFe LDH at constant current densities of 10 and 100 mA cm⁻² [35]. Copyright 2018, the Royal Society of Chemistry. (g) Low-magnification FESEM image and (h) elemental mapping images of NiFe₂O₄ nanoparticles/NiFe LDH [59]. Copyright 2018, American Chemical Society. (i) SEM image of NiFe LDH@NiCoP/NF and (inset) high-resolution image of its NiFe LDH@NiCoP nanowires and (j) TEM image and (k) EDS mapping of a specific NiFe LDH@NiCoP nanowire [60]. Copyright 2018, Wiley-VCH.

Figure 3

(a) Optical and (b-d) SEM images of NiCo LDH nanosheet arrays on NF [62]. Copyright 2015, Elsevier Ltd. (e) SEM and (inset) corresponding TEM images of CCF LDH, (f) TEM image of CCF LDH at medium magnification, and (g) HRTEM image of CCF LDH showing the layered structure of CoFe LDH and (inset) structure model of CoFe LDH [36]. Copyright 2017, Elsevier Ltd. (h) Schematic illustration of the synthetic route to MFe LDH (M = Co, Ni, or Li) nanoarrays, (i) photographs of MFe LDH nanoarrays growing on Ni foam before and after self-oxidation in air, (j) XRD patterns of MFe LDH, and (k) linear sweep voltammetry (LSV) curves and (l) overpotentials (at 10 and 100 mA cm⁻² in 1 M KOH) of MFe LDH in comparison with the benchmark Ir/C electrocatalyst [69]. Copyright 2015, the Royal Society of Chemistry.

Figure 4

(a) Schematic illustration of the fabrication route to NiCoFe LDHs/NF via a two-step hydrothermal reaction, (b, c) SEM images of the hierarchical NiCoFe LDH nanoarrays at different magnifications, (d) polarization curves of different hierarchical LDH electrocatalysts (0.5, 1, and 2 indicate the amount of Fe(NO₃)₃·9H₂O in reactants in mmol), and (e) stability testing of the H-LDH-1 sample under constant potential in a 1 M KOH solution and (inset) SEM image of H-LDH-1 after stability testing [38]. Copyright 2014, the Royal Society of Chemistry. (f) SEM images of NiCoFe LDHs/CFC; (g) HAADF-STEM image of a typical NiCoFe LDH nanosheet and the corresponding STEM-EDS elemental mapping images of (h) Co, (i) Fe, and (j) Ni; and (k) polarization curves and (l) corresponding Tafel curves of NiCoFe LDHs/CFC, NiFe DHNAs/CFC, CoFe DHNAs/CFC, NiCo DHNAs/CFC, Ni SHNAs/CFC, Co SHNAs/CFC, and Fe SHNAs/CFC, where DHNAs and SHNAs are double- and single-hydroxide nanosheet arrays in a 1 M KOH solution, respectively [72]. Copyright 2016, American Chemical Society.

Figure 5

(a) Schematic illustration of the preparation of Ni₃FeAl_x LDH nanosheets via Al doping and selective etching, (b) SEM image of Ni₃FeAl_0.91 LDHs/NF, and (c) iR-corrected OER polarization curves and (d) Tafel plots of Ni₃FeAl_x LDH nanosheets recorded at a scan rate of 10 mV S⁻¹ in a 1 M KOH solution [75]. Copyright 2017, Elsevier Ltd. (e) Schematic illustration of the NiFeCr LDH crystal structure with intercalated water and carbonate ions, (f) XRD patterns of as-prepared LDH samples, and (g) SEM image of NiFeCr-6 : 2 : 1-F [77]. Copyright 2018, Wiley-VCH.