Interface‐Engineered Ni(OH)₂/β‐like FeOOH Electrocatalysts for Highly Efficient and Stable Oxygen Evolution Reaction

Abstract

Iron-based (oxy)hydroxides are especially attractive electrocatalysts for the oxygen evolution reaction (OER) owing to their earth abundance, low cost, and nontoxicity. However, poor OER kinetics on the surface restricts the performance of the FeOOH electrocatalyst. Herein, a highly efficient and stable Ni(OH) /β-like FeOOH electrocatalyst is obtained by facile electroactivation treatment. The activated Ni(OH) /β-like FeOOH sample indicates an overpotential of 300 mV at 10 mA cm for the OER, and no clear current decay after 50 h of testing; this is comparable to the most efficient nickel- and cobalt-based electrocatalysts on planar substrates. Furthermore, studies suggest that β-like FeOOH plays a key role in remarkably enhancing the performance during the electroactivation process owing to its metastable tunnel structure with a lower barrier for interface diffusion of Ni ions between the bilayer electrocatalyst. This study develops a new strategy to explore efficient and low-cost electrocatalysts and deepens understanding of bilayer electrocatalysts for the OER.

Reversible Charge Transfer and Adjustable Potential Window in Semiconductor/Faradaic Layer/Liquid Junctions

“…To further reveal the Ni(OH) 2 distributions, the XPS depth profile was used to analyze the samples by Ar + etching and the results are indicated in Figures 2F-2H. The binding energy at 856.3 eV with a satellite peak at 862.1 eV on the surfaces of the two samples by CBD and PED is assigned to Ni 2p (Ji et al, 2013;Zhu et al, 2017aZhu et al, , 2017b. A new peak at 853.1 eV appears at different depths of the two samples owing to the reduction of Ni 2+ into metallic Ni by Ar + etching (Kim and Winograd, 1974).…”

“…As a reference sample, Ni(OH) 2 was first directly deposited on an FTO substrate by CBD method. In the dark, the colorless Ni(OH) 2 on FTO substrate becomes black after being oxidized into NiOOH at the potential of 1.46 V versus reversible hydrogen electrode (RHE) (see Figure 3A) (Zhu et al, 2017a(Zhu et al, , 2017b. The C-Fe 2 O 3 /Ni(OH) 2 becomes dark red from red at the same potential in the dark (see Figure 3B).…”

Electrochemical Cathodic Treatment of Mild Steel as a Host for Ni(OH)2 Catalyst for Oxygen Evolution Reaction in Alkaline Media

“…During OER, at the applied anodic potential, catalytically active sites of Ni(OH) 2 /NiOOH phase interact with Fe(OH) 2 /FeOOH . The mixture of Fe(OH) 2 /FeOOH and Ni(OH) 2 /NiOOH turn to higher catalytically active phase and improve the conductivity resulting in low charge transfer resistance as evidenced in the EIS studies . In view of the fact, Ni acts as catalyst centre via formation of Ni 2+ /Ni 3+ (Ni−O, NiOO) whereas Fe act as Lewis acid and promote as well as stabilize the neighbouring Ni oxidation state under the OER conditions .…”

“…[45] The mixture of Fe(OH) 2 /FeOOH and Ni(OH) 2 /NiOOH turn to higher catalytically active phase and improve the conductivity resulting in low charge transfer resistance as evidenced in the EIS studies. [8,46] In view of the fact, Ni acts as catalyst centre via formation of Ni 2 + /Ni 3 + (NiÀ O, NiOO) whereas Fe act as Lewis acid and promote as well as stabilize the neighbouring Ni oxidation state under the OER conditions. [8,37] In the long term operation, affordable catalytic activity even at low Ni(OH) 2 content is due to interaction of Ni with the Fe(OH) 2 /FeOOH like layered double hydroxide.…”

Insight into the Degradation Mechanisms of Atomic Layer Deposited TiO2 as Photoanode Protective Layer

“…The nickel-iron catalyst is necessary for efficient charge injection into the electrolyte 28, [68][69][70][71] , and if it is not present, no oxidative current is obtained in the studied range of potentials (dotted line in Figure 3b). In fact, Ni(Fe)OOH is the real catalytic phase obtained after cycling in alkaline electrolytes such as standard KOH solutions, one of the earth-abundant OER catalyst with lower overpotentials 38,[72][73][74][75][76][77][78][79][80][81] In Figure 4, we present the topography and conductivity atomic force microscopy maps (c-AFM) of ALD-TiO2 samples grown on degenerately doped p + -Si substrates at 150 ºC and 300 ºC with 5 nm NiFe thermally evaporated on top. Measurements of TiO2/NiFe layers were performed at +1 V, simulating the electron flow from the tip to the substrate across the layer, like in OER anodic conditions.…”