Binder-Free Heterostructured NiFe₂O₄/NiFe LDH Nanosheet Composite Electrocatalysts for Oxygen Evolution Reactions

Abstract

Constructing two-dimensional (2D), free-standing, nonprecious, and robust electrocatalysts for oxygen evolution reactions (OERs) is of primary importance in the commercial water-splitting technology. Herein, we have constructed a 2D heterostructured NiFe 2 O 4 /NiFe layered double hydroxides (LDH) mixed composite on a low-cost stainless-steel mesh substrate using a lowtemperature one-step wet chemical synthesis method and have also investigated the effect of starting material concentration on the formation of the NiFe 2 O 4 /NiFe LDH mixed composite. The as-prepared NiFe 2 O 4 /NiFe LDH-25 electrocatalyst drives a 100 mA/cm 2 OER with the lowest reported overpotential of 190 mV and a Tafel slope 21.5 mV/dec and drives a stable 100 mA/cm 2 OER process in 1 M KOH. These OER activities are superior to that of the state-of-the-art RuO 2 OER electrocatalyst. The excellent OER activity appears to be due to the synergetic effect of NiFe LDHs and NiFe 2 O 4 . In addition, the vertically aligned heterostructure of the NiFe 2 O 4 /NiFe LDH composite thin sheets provides a large number of active edge sites, directly attached to the highly conducting substrate, which contributes to improving the electronic conductivity of the electrocatalyst. This work provides valuable insight into the design and one-step synthesis of NiFe 2 O 4 /NiFe LDH bimetallic mixed oxide and hydroxide composite thin films with enhanced OER activity and stability as well as deciphering the origin of the OER enhancement by metal oxides and metal hydroxides.

ZIF-Derived Porous CoNi2S4 on Intercrosslinked Polypyrrole Tubes for High-Performance Asymmetric Supercapacitors

“…The NiCo-LDH@PPy displays three peaks at 24.4°, 33.5°, and 60°, corresponding to (006), (012), and (009) planes of α-Ni­(OH) 2 (JCPDS no. 14–0117) . After vulcanization, the peaks belonging to NiCo-LDH disappear, and some new reflections at 26.8°, 31.5°, 38.4°, 50.3°, and 55.1° are clearly detected in the NiCoS@PPy, which are indexed to the (220), (311), (400), (511), and (440) crystal planes of the cubic CoNi 2 S 4 (JCPDS No.…”

“…14−0117). 21 After vulcanization, the peaks belonging to NiCo-LDH disappear, and some new reflections at 26.8°, 31.5°, 38.4°, 50.3°, and 55.1°are clearly detected in the NiCoS@PPy, which are indexed to the (220), (311), (400), (511), and (440) crystal planes of the cubic CoNi 2 S 4 (JCPDS No. 24-0334).…”

Amorphous heterogeneous NiFe-LDH@Co(OH)2 supported on nickel foam as efficient OER electrocatalysts

“…OER process involves fourelectron transfers. When the first, second, and third electron transfers are rate-determining steps, the Tafel slope is estimated to be close to 120, 40, and 28 mV dec −1 [46], respectively. The Tafel slopes of all the prepared samples are calculated and displayed in Fig.…”

Two‐step electrodeposition of Hausmannite sulphur reduced graphene oxide and cobalt‐nickel layered double hydroxide heterostructure for high‐performance supercapacitor

“…LDHs, however, suffer from low electrical conductivity, low cyclic performance, aggregation, poor electrochemical stability, and poor rate capability due to slow reaction kinetics at high specific currents when performing charge‐discharge processes 18,19 . This can be alleviated by producing a highly conductive and more stable heterostructure system with spinels configuration 20 . Spinels, which possess chemical structure MM′ 2 O 4 , with M and M′ as divalent and trivalent metals respectively benefit from having high electrochemical activity due to reversible adsorption characteristics, multivalent charge transport, elevated chemical stability, and increased redox reactions, these attributes increase the theoretical specific capacity.…”

“…18,19 This can be alleviated by producing a highly conductive and more stable heterostructure system with spinels configuration. 20 Spinels, which possess chemical structure MM 0 2 O 4 , with M and M 0 as divalent and trivalent metals respectively benefit from having high electrochemical activity due to reversible adsorption characteristics, multivalent charge transport, elevated chemical stability, and increased redox reactions, these attributes increase the theoretical specific capacity. This is a result of the improvement of electron transport efficiency and ion diffusion ratio.…”