Enhancement of oxygen evolution performance of water splitting at high 
current density by novel electrodeposited NiFe-LDH coatings

Simón G. Quiroz , Santiago Cartagena , Jorge A. Calderón *

Centro de Investigación, Innovación y Desarrollo de Materiales – CIDEMAT, Universidad de Antioquia, Cr. 53 No 61 – 30, Torre 2, Lab. 330, Medellín, Colombia

A R T I C L E  I N F O

Keywords:
NiFe-LDH
Oxygen evolution reaction (OER)
Water splitting
Electrocatalyst
Electrodeposition

A B S T R A C T

Efficient water splitting is a key goal in renewable hydrogen production. However, it is a high-demand energy 
process. Hence, developing highly efficient and inexpensive electrocatalysts is essential to overcoming this 
challenge. The cell voltage of the electrochemical water splitting is between 1.8 and 2 V, much higher than the 
theoretical minimum value of 1.23 V, being the oxygen evolution reaction (OER), the most kinetics limiting 
process, having overpotentials between 210–330 mV at a current density of 30 mA cm-2. This work develops low- 
cost and scalable electrodes for OER by electrodeposition of NiFe layered double hydroxide (LDH) coatings, with 
different Ni:Fe ratios in the electrodeposition bath. Coating obtained with Ni:Fe ratio of 15:1 exhibits the best 
catalytic activity for OER and shows the lowest Tafel slope of 38.5 mVdec-1 and the lowest overpotentials of only 
206 and 244 in 1 M NaOH at 30 and 100 mAcm-2, respectively, which are the most favorable kinetics parameters 
respect to those found in literature reports. Furthermore, this developed coating material shows excellent 
electrocatalytic stability for OER after 80 h of operation at a high current density of 400 mAcm-2 in an alkaline 
medium, which is a typical condition for practical operation of electrolyzers. The developed catalytic coating by 
electrodeposition technique shows high performance and stability, economical and straightforward reproduc
ibility. It also supports conformational coatings on complex three-dimensional and high-surface-area substrates, 
like nickel foam, making it a highly scalable process.

1. Introduction

Currently, the application of hydrogen as a means of energy storage 
has attracted the attention of different research institutions and in
dustries globally. This is motivated in part by developments in renew
able energy, which have resulted in a surplus of unused wind and 
photovoltaic energy [1]. The production of hydrogen from water elec
trolysis is a good option to enable the use of surplus renewable energy. 
Hydrogen can play a vital role in a zero-emission future, due to its high 
energy density (140 MJ/kg), which is more than double that of typical 
fossil fuels (50 MJ/kg). It can be used in many applications as a fuel and 
is a suitable medium for large-scale energy storage [2]. Nonetheless, for 
hydrogen to serve in addressing energy and environmental challenges, 
several problems that remain in obtaining it must be overcome. In the 
case of alkaline electrolyzers, the most mature form of technology for 
carrying out the electrolysis of water, one such challenge that has 
generated significant interest is how to achieve high energy efficiency 
[3]. The typical cell voltage when carrying out electrochemical water 
splitting is between 1.8 and 2 V, much higher than the theoretical 

minimum value of 1.23 V. Therefore, it is necessary to reduce the 
overpotentials associated with the hydrogen evolution reaction (HER) 
that takes place at the cathode and the oxygen evolution reaction (OER) 
that occurs at the anode [4–6].

Therefore, it is crucial to develop materials with high activity for 
both OER and HER to enhance the performance of alkaline electrolyzers. 
Although some noble metals, such as platinum, as well as ruthenium and 
iridium-based oxides, have been shown to serve as electrocatalytic 
materials that reduce the overpotential that needs to be applied for HER 
and OER reactions, the high cost of these precious metals limits their 
practical application [7–10]. Therefore, it is necessary to investigate 
catalytic systems that require very low content of these platinum group 
metals or that use other more abundant catalytic materials. These sys
tems need to be low cost, to allow scaling and have high catalytic ac
tivity for OER and HER reactions [11]. Developing efficient 
electrocatalysts of non-noble metals, composed of elements abundant on 
the earth, is a highly sought-after goal as it would enable the obtaining 
of cost-competitive hydrogen. However, the anodic half-cell reaction 
hinders the efficiency of water electrolysis. The overpotentials in 

* Corresponding author.
E-mail address: andres.calderon@udea.edu.co (J.A. Calderón). 

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Electrochimica Acta

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https://doi.org/10.1016/j.electacta.2025.146332
Received 30 January 2025; Received in revised form 13 April 2025; Accepted 26 April 2025  

Electrochimica Acta 528 (2025) 146332 

Available online 27 April 2025 
0013-4686/© 2025 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by- 
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alkaline water electrolysis are typically between 20–200 mV for HER 
and 220–330 mV for OER at a current density of 10mAcm-2 [12–15]. 
This is because the mechanism of OER is more complex than its coun
terpart HER. OER involves multiple steps, some of them requiring the 
transfer of a single electron, which results in slower kinetics and typi
cally demands higher overpotentials compared to the HER [16,17].

Consequently, this work focuses on developing Ni-based catalysts 
with Fe additions to enhance the kinetics of OER. Fe incorporation in Ni- 
based electrodes has received considerable attention due to its multiple 
roles in the catalytic mechanism. Additions of Fe enhances the con
ductivity of the catalytic film, optimizes bond energy for the adsorption 
of OER intermediates, suppresses unwanted metal oxidation steps, and 
facilitates the metal reduction step required for O₂ evolution [18,19]. In 
the case of nickel oxides, Fe incorporation has been demonstrated to 
significantly improve electrochemical performance in the OER [20,21]. 
Landon et al. reported the formation of a NiO/NiFe₂O₄ phase at low Fe 
concentrations, which plays a crucial role in enhancing oxygen evolu
tion activity [22]. The Ni-Fe ratio is a critical factor in catalytic per
formance, materials containing 60–90 % Ni w/w exhibit optimal activity 
for OER [23,24]. Beyond composition, the ability of Ni-Fe-based mate
rials to form amorphous structures with high electrochemically active 
surfaces is essential for achieving superior electrocatalytic activity [25,
26]. Similar to Ni-Fe oxides, Ni-Fe hydroxides also demonstrate excel
lent OER performance and are commonly found in layered structures 
[27]. Several studies have shown that Ni-Fe-based double-layer hy
droxides (NiFe-LDHs) rank among the most active OER electrocatalysts 
due to their tunable cation ratios, large surface-to-volume ratio, high 
density of adaptable catalytic sites, and a layered structure that can be 
modified through anion exchange to facilitate rapid species diffusion 
[28–31].

While previous studies have primarily explored Ni–Fe electro
catalytic coatings synthesized via traditional chemical routes, limited 
attention has been given to the scalable electrodeposition of NiFe-LDH 
catalytic coatings. Electrodeposition technique offers several key ad
vantages for the synthesis of electrocatalytic materials. This technique 
enables the direct, binder-free growth of catalysts on conductive sub
strates, resulting in excellent electrical contact and low interfacial 
resistance [32–36]. This intimate interface promotes efficient electron 
transfer and maximizes catalyst utilization. A major advantage of elec
trodeposition is its ability to synthesize a wide range of materials under 
ambient conditions, unlike many conventional physical or chemical 
methods that require elevated temperatures, high pressures, complex 
and large-time processing [37–40]. Additionally, electrodeposition 
provides precise control over coating thickness, composition, and 
morphology by tuning parameters such as applied potential, current 
density, electrolyte composition, and deposition time. It also supports 
conformal coatings on complex three-dimensional, high-surface-area 
substrates (e.g., nickel foam, carbon cloth), facilitating the fabrication of 
self-supported electrodes with enhanced mechanical robustness and 
long-term catalytic durability [32–36]. Collectively, these attributes 
make electrodeposition a scalable, cost-effective, and highly versatile 
strategy for the fabrication of high-performance electrocatalysts.

Considering that OER presents the higher kinetics limitation of the 
two reactions in alkaline water electrolysis, in this work, low-cost 
electrodes for OER are developed by novel electrodeposition of NiFe- 
LDH coatings. The method has the following advantages: 1) uses a 
scalable process with low energy requirement, compared with other 
techniques like hydrothermal, which requires the use of heat for several 
h, and microwave, which needs the use of specialized equipment. 2) 
Unlike other methods, where Fe is electrodeposited, there is no need to 
use N or Ar during the process. 3) quick production time of <1 h. 4) it is 
binder-free, as the catalyst is directly formed on the conductive sub
strate. 5) A high surface area is generated for this method in one step. 6) 
common and cheap compounds are used during the synthesis. This work 
analyzes different Ni:Fe ratios in the electrodeposition bath with the aim 
of optimizing the coating formulation and obtaining one of the most 

catalytic NiFe-LDH compound with respect to other already reported, 
and with great stability in high current densities.

2. Experimental

2.1. Materials and reagents

Commercial nickel foam (NF) with dimensions of approximately 1 
cm x 1 cm x 0.16 cm were used as the working substrate. Nickel (II) 
nitrate hexahydrate (Ni (NO3)2 ⋅6H2O was purchased from Thermo 
Scientific ≥ 98 %. Ferrous (III) nitrate nonahydrate (Fe(NO3)3 9H2O ≥
99.0 %, sodium hydroxide (NaOH) 99.0 %, potassium hydroxide (KOH) 
≥ 85.0 % were purchased from EMSURE® MERCK.

2.2. Preparation of NiFe-LDH/NF

NF was sonicated in 3 M HCl solution for 5 min to remove the NiOx 
on the surface. Then, NF was washed using deionized water. The elec
trodeposition was carried out in a standard three-electrode electro
chemical cell containing NF as the working electrode, platinum mesh as 
the counter electrode and an Ag/AgCl (3 M KCl) as the reference elec
trode. The electrolyte bath contained Ni(NO3)2 6H2O and Fe(NO3)3 
9H2O as precursors of the nickel and iron. The molar ratio of Ni:Fe in the 
electrolyte bath varied between (1:1,2:1,3:1,4:1,5:1, 10:1,12:1,15:1 and 
20:1) where differences in catalytic activity are found for the OER. The 
coatings were electrodeposited via potentiostatic deposition at − 1 V (vs 
Ag/AgCl) for 2400 s at room temperature (23 ◦C) and in an electrolyte 
bath with a pH value of 2.0.

2.3. Characterization techniques

The structure and morphology of the coated electrodes (NiFe-LDH/ 
NF) were characterized by scanning electron microscopy (SEM) and the 
chemical element analysis was performed by energy-dispersive X-ray 
spectroscopy (EDS), using a JEOL-JSM 6490LV device with accelerating 
voltage of 20 kV. The crystalline structures of the NiFe-LDH/NF elec
trode were obtained by X-ray diffraction (XRD) with Cu Kα radiation as 
the X-ray source (λ=1.54059 Å) operated with a source power of 40 kV 
and 15 mA from a 2θ from 10◦ to 80◦ Phase composition was evaluated 
through Raman spectroscopy, using a Horiba Jobin Yvon (Labram HR) 
Nikon (BX41) microscope with a CCD detector (Wright 1024 × 256 
pixels) with a laser of 625 nm.

2.4. Electrochemical measurements

OER tests were performed in a AUTOLAB PGSTAT302F potentiostat/ 
galvanostat using a standard three-electrode electrochemical cell at 
room temperature (~23 ◦C). The as-prepared electrodes were employed 
as the working electrodes, a graphite rod electrode was used as counter 
electrode and Hg/HgO as reference electrode. All measurements were 
performed using NaOH 1 M electrolyte, except for comparative stability 
which was performed with KOH 1 M.

The OER performance of the obtained NiFe-LDH/NF electrocatalyst 
were evaluated using linear sweep voltammetry (LSV) in NaOH (1 M) 
aqueous electrolyte with a scan rate of 1 mVs-1 from 0.3 to 1.10 V. Tafel 
slopes were obtained from potentiodynamic measurements with a scan 
rate of 80µVs-1. The electrochemical double-layer capacitances (Cdll) 
were estimated from cyclic voltammetry (CV) measurement in a non- 
Faradaic region under different scan rates (10, 20, 30, 40, 60, 80, 100 
and 120 mV.s-1). The potential window selected, where no faradaic 
processes were observed, was from 0.015 to 0.115 V vs Hg/HgO, so that 
the measured currents only considered the charging of the double layer. 
A linear fitting of the capacitive current (j) vs. scan rate curve was 
performed to obtain the double layer capacitance, determined as the 
slope of the line [41,42]. To study the behavior of the 
electrode-electrolyte interface, electrochemical impedance spectroscopy 

S.G. Quiroz et al.                                                                                                                                                                                                                               Electrochimica Acta 528 (2025) 146332 

2 



(EIS) was performed using a Zhaner IM6E potentiostat at a potential 
polarization of 0.525 V vs Hg/HgO in a frequency range from 100 KHz to 
10 mHz with 10 mV of amplitude perturbance. The stability of the 
developed electrodes is evaluated by chronopotentiometries at a high 
current density of |400|mAcm-2 for 25 h.

All potentials reported in this work were converted to a reversible 
hydrogen electrode (RHE) using the following equation. ERHE = EHg/HgO 
+ 0.098+ 0.059pH. The voltage data were corrected by i-R compen
sation using the following equation Ec = Em − IRS. The overpotential (η) 
for OER was obtained as follow: η = ERHE − 1.23 V. Where EHg/HgO is the 
measured potential corrected, I is the response current of the measure
ment at the working electrode and Rs was the ohmic resistance of the 
solution obtained with current interrupt measurements and EIS.

3. Results and discussion

3.1. Structural and elemental characterization

SEM micrographs at different magnifications of the surface 
morphology of electrodeposited NiFe-LDH/NF are shown in Fig. 1. The 
formation of sheets that cover a large part of the surface of the nickel 
foam is observed for the higher Ni:Fe ratios in the electrodeposition 
bath. In addition, on these sheets, the formation of other species can be 
observed, associated with Ni-Fe oxyhydroxides, which provide an 
increased number of catalytic sites, favoring the performance of the 
material for OER [43–49]. Fig. 1a shows the substrate NF. It is possible 
to observe that, for the 2:1 ratio shown in Fig. 1b, there is no presence of 
the characteristic sheets of NiFe-LDH [50,51]. In that case, only a change 
on the substrate surface is observed, without any presence of the Ni-Fe 
coating. This is further confirmed by the EDS, which shows only the 
presence of nickel, as shown in the data in

Table 1. In the case of the 5:1 (Ni:Fe) ratio shown in Fig. 1c, the 
sheets are present on the surface of the foam, but they do not cover a 
large amount of the surface of the substrate, which is also shown to be 
the case for the 4:1 and 3:1 coatings. Those coatings are shown in 
Figure S1 in the supplementary material, where it is possible to observe 
that the coating is not present homogeneously on the entire surface of 
the substrate. More homogeneous coatings were obtained with the 10:1 
and 15:1 ratios (Fig. 1d-e). These were the coatings with the best results, 
as will be discussed later. In the case of 20:1 ratio, some areas are not 
totally covered by the deposited material or where the coating begins to 

detach from the substrate, see Fig. 1f. Therefore, lower performance for 
the OER is expected in this case. Also, it can be observed that the 
presence of the NiFe-LDH coating on NF generates a rougher surface as 
Ni:Fe ratio increases. Therefore, the electroactive surface area of the 
electrode is also expected to increase.

Table 1 shows the results of the EDS elemental analysis. As can be 
seen, the coatings contain Ni, Fe, and O, as expected for the material. It is 
confirmed that, for low ratio coatings, there is no presence of elements 
other than nickel (1:1 and 2:1). In addition,

Table 1 shows that the intermediate Ni:Fe ratios used in the elec
trolytic bath produce deposits with higher content of Fe than Ni in the 
coating. This indicates a preference for the deposition of Fe over Ni, even 
though iron is the less noble metal of the two. This phenomenon, called 
“anomalous co-deposition”, is consistent with literature reports, which 
describe the preferential deposition of the less noble metal with respect 
to the more noble one [52–54]. The literature mentions several possible 
mechanisms that could explain this behavior, but one of the most 
accepted is that the inhibition of Ni deposition in the presence of Fe is 
due to the preferential adsorption of intermediate iron species on the 
electrode surface [55–59].

Fig. 2 shows the X-ray diffraction (XRD) patterns of NiFe-LDH 
coatings electrodeposited from baths with different Ni:Fe ratios. No 
diffraction peaks corresponding to the characteristic crystalline phase of 
NiFe-LDH were observed below of 2θ = 35◦. However, the characteristic 
morphology in plates and further Raman spectroscopy analysis (next 
section) demonstrate the existence of NiFe-LDH compound on the cat
alytic coating. The XRD result indicates that an amorphous structure of 
NiFe-LDH is achieved. This observation is consistent with previous 

Fig. 1. SEM micrographs for different Ni:Fe ratios at of x100 and x6000 magnifications. a) NF. b) Ni:Fe 2:1. c) Ni:Fe 5:1. d) Ni:Fe 10:1. e) Ni:Fe 15:1. f) Ni:Fe 20:1.

Table 1 
EDS analysis for NiFe coatings.

Sample Ni (at.%) Fe(at.%) O(at.%)

1:1 100 – –
2:1 100 – –
3:1 81.06 1.52 17.42
4:1 8.85 19.52 71.63
5:1 14.16 34.62 51.22
10:1 9.67 33.06 57.27
12:1 11.15 23.93 64.92
15:1 9.83 28.07 62.10
20:1 11.14 20.02 68.83

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3 



literature reports indicating that NiFe-LDH compounds synthesized by 
electrodeposition commonly exhibit an amorphous structure [60–62]. 
Moreover, it has been widely reported that amorphous NiFe-LDHs 

display superior catalytic activity toward the oxygen evolution reac
tion (OER) compared to their crystalline counterparts. This enhance
ment is attributed to lattice distortions at the surface of the amorphous 

Fig. 2. XRD patterns for different Ni:Fe ratios.

Fig. 3. Raman spectra obtained for the different NiFe-LDH coatings.

S.G. Quiroz et al.                                                                                                                                                                                                                               Electrochimica Acta 528 (2025) 146332 

4 



metal or metal oxide, which lead to the formation of abundant active 
sites, thereby resulting in higher OER activity compared to crystalline 
hydroxides [63–68]. The diffractogram for the ratio of 3:1 shows peaks 
at 2θ associated exclusively with the substrate (Ni foam) at 45.38◦, 
52.6◦, and 77.05◦ [27,69]. A similar result is observed for the 5:1, 4:1, 
2:1, and 1:1 ratios, as shown in Figure S2. In the case of coatings with 
high Ni: Fe ratios in the bath (10:1, 12:1, 15:1, and 20:1), additional 

peaks at 37.88◦ and 44.12◦ appear, which suggests the presence of the 
NiFe2O4 phase [45,70]. The integration of the NiFe2O4 phase into 
NiFe-LDH materials significantly enhances the catalytic activity of the 
surface to the OER reaction, as well as improving mass transport and 
charge transfer at the electrode [45,71].

Raman spectroscopy measurements were performed to determine 
the main compounds formed after the electrodeposition of coatings on 

Fig. 4. OER Performance of Ni-Fe samples in 1 M NaOH. a) Anodic evaluation LSV for OER. b) Anodic overpotential obtained for OER (at 30, 50, and 100 mAcm-2).

S.G. Quiroz et al.                                                                                                                                                                                                                               Electrochimica Acta 528 (2025) 146332 

5 



the nickel foam substrate. Fig. 3 shows the Raman spectra of the coatings 
obtained for different Ni:Fe ratios. Bands observed at 211.1, 279.6, and 
684.6 cm-1 are associated with the binary oxide NiFe2O4 [70,72]. This 
result agrees with the findings obtained with the diffractograms. These 
vibration modes correspond to the asymmetrical and symmetrical 
bending of the oxygen atom in the Fe-O bond and the symmetrical 
stretching of the Fe-O, respectively [71]. The bands located at 472.8 and 
552.5 cm-1 are attributed to the stretching vibrations of Ni-O of the 
NiFe-LDH [27,73–76]. Raman spectroscopy technique reveals the for
mation of NiFe-LDH compound during the electrodeposition of the 
coating.

3.2. OER test performance

The OER performance of the developed electrocatalytic coatings was 
evaluated in an alkaline medium (1 M NaOH) through linear sweep 
voltammetry, as shown in Fig. 4a. The effect of varying the Ni:Fe ratio in 
the electrodeposition bath on the catalytic performance of the coatings 
for the OER is evident by the leftward displacement of the curves. The 
results indicate that, as the Ni:Fe ratio increases, there is a decrease in 
the overpotential of OER, resulting in a higher current density with a 
lower overpotential applied to the electrode for the OER reaction. These 
results confirmed the benefit of Fe addition on catalytic performance of 
the Ni coatings.

Fig. 4b shows the overpotential behavior as the Ni:Fe ratio varies, 
revealing a minimum value at a ratio of 15:1. This trend is replicated for 
different current densities (30, 50, and 100 mAcm-2). It can be observed 
that, beyond the 15:1 ratio, the overpotential required for the OER in
creases once again. The electrocatalytic material exhibiting the best 
performance is the one obtained with an Ni:Fe ratio of 15:1, achieving 
overpotentials of 206.86, 223.89, and 244.13 mV for current densities of 
30, 50, and 100 mAcm-2, respectively. In contrast, for the uncoated 
substrate, overpotentials of 353.28, 365.53, and 384.24 mV are 
observed at current densities of 30, 50, and 100 mAcm-2. These values 
are significantly higher than those obtained with any of the electrodes 
evaluated with the NiFe-LDH coatings, demonstrating that the devel
oped material coating enhances the catalytic activity of the electrode in 
the OER.

Table 2 compares the performance of similar NiFe-LDH catalytic 
materials reported in the literature with the current coating material 

developed by the electrodeposition method in this work. The literature 
reports indicate several different methods of synthesis of the NiFe-LDH 
compound, such as hydrothermal, PLAL (pulsed laser ablation in liquid), 
solvothermal, and microwave. While sol-gel synthesis involves multiple 
stages, including gelation, drying, and thermal treatments that can take 
several hours to days and require high temperatures, leading to high 
energy consumption, and typically necessitates the use of binders to 
adhere the material to the substrate, introducing additional ohmic 
resistance [39,77,78]. Hydrothermal synthesis also requires long reac
tion times under elevated temperature and pressure conditions, often 
necessitating the use of autoclaves and, in some cases, post-synthesis 
thermal treatments [37,38,79]. In contrast, electrodeposition is per
formed under ambient temperature and pressure conditions, simplifying 
the process, reducing energy demands, and improving safety. It enables 
direct, in situ synthesis of catalytic materials on conductive substrates 
without binders, improving mechanical adhesion and reducing interfa
cial resistance, thus enhancing charge transfer efficiency and catalyst 
utilization. Additionally, electrodeposition allows precise control over 
key parameters such as composition, thickness, and morphology of the 
coating by adjusting applied potential, current density, electrolyte 
composition, and deposition time [32–36]. The process is also notably 
faster, taking only a few minutes compared to the several hours required 
by sol-gel or hydrothermal methods. These features make electrodepo
sition a versatile, scalable, and cost-effective technique for fabricating 
high-performance, self-supported electrodes. Table 2 shows that the 
catalytic performance in OER of the material developed in this work is 
better than that of other NiFe-LDH developed. The NiFe-LDH material 
with the best performance of those developed (Ni: Fe 15:1) exhibits 
excellent OER activity with low overpotentials compared to other 
NiFe-LDH materials at different current densities (30, 50, and 100 
mAcm-2). Additionally, the NiFe-LDH material (15:1) shows lower 
overpotentials than NiFe-LDH materials doped with Zn or Co, as well as 
other modified materials such as sulfated NiFe-LDH and 
RuO2/NiFe-LDH/NF.

3.3. Kinetics study of OER

Fig. 5 shows the Tafel slopes of the NiFe-LDH coating material, used 
to study the kinetics of the OER. Two Tafel slopes were observed, one for 
low overpotentials and the other for high overpotentials. The presence 

Table 2 
Comparison of the OER performance of various NiFe -based electrocatalysts reported in literature and in this work.

Material Method Syntesis Electrolyte Overpotential  
(mV)

Current density  
(mAcm-2)

Reference

Ni6Fe4LDH grinding 1 M KOH 280 10 [80]
NiFe@LDH Hydrothermal 1 M KOH 260 10 [40]
v-l-LDH/NF drip method 1 M KOH 230 100 [81]
NiFe-LDH@NF Hydrothermal 1 M KOH 210 10 [82]
Ni2Fe1-LDH Hydrothermal 1 M KOH 245 10 [83]
Ni2Fe1-LDH Hydrothermal 1 M KOH 295 30 [83]
Zn-NiFe-LDH Hydrothermal 1 M KOH 218 10 [84]
Co1.98–NiFe LDH Solvothermal 1 M KOH 266 50 [85]
Co1.98–NiFe LDH Solvothermal 1 M KOH 290 100 [85]
NiFe-LDH Hydrothermal 1 M KOH 270 80 [86]
Ni/Fe3O4 / NiFe LDH Hydrothermal 1 M KOH 275 20 [87]
NiO/NiFe LDH PLAL* 1 M KOH 205 30 [43]
NiFeZn LDH Hydrothermal 1 M KOH 204 10 [88]
NiFeZn LDH/NF Hydrothermal 1 M KOH 323 100 [89]
Sulfated NiFe LDH Microwave 1 M KOH 288 50 [90]
Sulfated NiFe LDH Microwave 1 M KOH 339 100 [90]
RuO2/NiFe-LDH/NF Hydrothermal 1 M KOH 226 10 [91]
RuO2/NiFe-LDH/NF Hydrothermal 1 M KOH 319 50 [91]
PR-NiFe-LDH Hydrothermal 1 M KOH 278 10 [92]
NiFe-LDH/CNTs Hydrothermal 1 M KOH 269 20 [93]
NiFe-LDH 15:1 Electrodeposition 1 M NaOH 206 30 This Work
NiFe-LDH 15:1 Electrodeposition 1 M NaOH 223 50 This Work
NiFe-LDH 15:1 Electrodeposition 1 M NaOH 244 100 This Work

* PLAL(Pulsed Laser Ablation in Liquid).

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6 



of two slopes in the polarization curves suggests that it is likely that two 
different electrochemical processes are occurring due to the formation of 
different species and kinetics steps that limit the reaction during anodic 
polarization at low and high overpotentials [94,95].

Table 3 summarizes the Tafel slope values for NiFe-LDH coating 
materials. Notably, a Ni:Fe ratio of 15:1 yields the lowest Tafel slopes, of 
56.7 mVdec-1 and 38.5 mV dec‑1 for low and high overpotentials, 
respectively. It is important to highlight that the lowest Tafel slope value 
of 38.5 mV dec‑1 is obtained at high polarization, which is the most 
common condition in which electrolyzers are operated. This indicates 
favorable kinetics conditions for the performance of water electrolysis at 
high current densities and high polarization. Comparing these Tafel 
slope values with those reported in the literature for NiFe-LDH, which 
typically range between 40–50 mVdec-1, it can be stated that the 
developed material with an Ni:Fe ratio of 15:1 exhibits significant cat
alytic activity, better than that previously reported for OER [71,90,96,
97].

The general mechanism of the OER reaction in an alkaline environ
ment is typically described by Eqs. (1)–4, with the corresponding and 
indicated Tafel slopes [98–100]. 

M + OH− ↔ MOH + e− , b = 120 mVdec− 1 (1) 

MOH + OH− ↔ MO− + H2O, b = 60 mVdec− 1 (2) 

MO− →MO + e− , b = 45 mVdec− 1 (3) 

2MO→2M + O2, b = 19 mVdec− 1 (4) 

Each of these reactions has an associated Tafel slope, providing in
sights into the limiting step of the OER reaction. In the case of the Ni-Fe 
15:1 material, which demonstrated the best performance of the devel
oped electrocatalytic materials, a slope close to 60 mVdec-1 is observed 
for low overpotentials. This suggests that the rate-determining step 
(RDS) at low overpotentials is associated with reaction (2), specifically 

related to the adsorption of an intermediate species during the OER. 
Conversely, at elevated overpotentials where Tafel slopes below 60 mV 
dec⁻¹ are recorded, the reduction in the Tafel slope indicates a shift in the 
rate-determining step (RDS) toward reaction (3), suggesting that the 
electrochemical oxidation of adsorbed MO⁻ intermediates become the 
dominant pathway.

Commonly, a higher electrochemically active surface area (ECSA) is 
associated with more active sites at the solid-liquid interface [83]. A 
direct evaluation of the relative ECSA of electrocatalysts by cyclic vol
tammetry (CV) can be done by estimating the electrochemical double 
layer capacitance (Cdl) [101]. To obtain the electrochemical double 
layer capacitance for the electrodes developed with the NiFe-LDH 
coating, the procedure already mentioned in the experimental meth
odology is followed. Here, different cyclic voltammetry measurements 
were performed at the non-faradaic region with scanning rates between 
10 – 120 mVs-1. It should be clarified that this procedure was only fol
lowed for samples where the presence of the electrocatalytic material 
was shown. The CV plots of the evaluated materials are shown in 
Figure S3 in the supplementary material. The results obtained for the 
double-layer capacitance using this method are shown in Fig. 6.

To determine the electrochemical active surface area (ECSA), the 
slopes obtained by plotting the capacitive current against the scan rate 
(Fig. 6) were used. This slope represents the electrochemical double 
layer capacitance (Cdl). The ECSA values were calculated using the ECSA 
= Cdl/Cs relationship, where Cs is the specific capacitance [102]. Cs 
represents the capacitance of an electrode with a flat surface of the 
electrocatalytic material. For Ni-Fe materials, Cs conventionally has an 
average value of 40 μFcm-2 in an alkaline media [42,69,102,103]. 
Values of ECSA for NiFe-LDH coating materials were calculated as 7.35, 
9.12, 8.91, 10.58, and 10.01 cm2 for coatings with Ni:Fe ratios of 3:1, 
5:1, 10:1, 15:1, and 20:1, respectively. Considering the results obtained, 
the highest ECSA value was that exhibited by the electrocatalytic coating 
with Ni:Fe ratio equal to 15:1. This coating material also exhibited the 
best performance for OER and the lowest Tafel slopes. However, the 
values of ECSA obtained in the current work are lower than those found 
in other works, where ECSA values between 50 – 500 cm2 have been 
reported [91,96,104,105]. For this reason, we believe that the 
outstanding performance of the developed catalytic NiFe-LDH coatings 
is due to the improvement of the catalytic activity of the material, as 
indicated by its low anodic overpotentials and low Tafel slopes.

To study the phenomena that occur at the electrode/electrolyte 
interface and to gain information about the kinetics of charge transfer 
during the OER on electrocatalytic coatings, electrochemical impedance 
spectroscopy (EIS) tests were performed for NiFe-LDH systems devel
oped with Ni:Fe ratios of 10:1, 12:1, 15:1 and 20:1. The Nyquist 

Fig. 5. Tafel plots of the OER of NiFe-LDH/NF electrocatalytic coating in 1 M NaOH. a) OER Tafel plots for NiFe-LDH/NF. b) Variation of Tafel slopes to low and high 
overpotentials.

Table 3 
Tafel Slopes for low and high overpotentials.

Tafel Slope  
Low Overpotential

Tafel Slope  
High Overpotential

Sample Slope(mVdec-1) Sample Slope (mVdec-1)
3:1 143.3 3:1 46.4
5:1 91.9 5:1 48.8
10:1 72.7 10:1 53.4
15:1 56.7 15:1 38.5
20:1 148.6 20:1 57.7

S.G. Quiroz et al.                                                                                                                                                                                                                               Electrochimica Acta 528 (2025) 146332 

7 



diagrams are represented by the equivalent electrical circuit shown in 
Fig. 7 where Rs is the ohmic resistance, Rt is the charge transfer across 
the electrode/electrolyte interface and CPEdl is the constant phase 
element that represents the double-layer capacitance. Ra and CPEa are 
the resistance and constant phase element related to adsorption limita
tions, desorption, and mass transfer of the adsorbed species on the 
working electrode [94,106,107]. Fig. 7 shows the Nyquist diagrams of 

EIS for the different NiFe-LDH coating materials evaluated at anodic 
potential of 0.525 V vs Hg/HgO (180 mV of overpotential). This anodic 
polarization potential was chosen to carry out EIS measurements 
because no oxide transformation reaction occurs in an appreciable form 
at this potential, and the most important anodic reaction that takes place 
is the OER, as can be seen in the LSV curves already shown in Fig. 4a.

The values of the electrical parameters extracted from the fit of EIS 

Fig. 6. Capacitive current density vs. scan rate plot to obtain double-layer capacitance for NiFe-LDH/NF materials.

Fig. 7. Nyquist diagrams of EIS measurement for Ni-Fe coatings performed at an anodic potential of 0.525 V vs Hg/HgO. Dots are experimental measurements; lines 
are fit data with the equivalent electrical circuit (inset).

S.G. Quiroz et al.                                                                                                                                                                                                                               Electrochimica Acta 528 (2025) 146332 

8 



measurements with the equivalent electrical circuit model are presented 
in Table 4. The coating with Ni:Fe ratio of 15:1 exhibits the lowest 
charge transfer resistance, so the rate at which charge transfer occurs for 
OER is expected to be faster [96]. This coating exhibits higher catalytic 
activity than the other coatings developed. This is consistent with the 
results obtained in the different electrochemical tests performed. In 
addition, the effective double-layer capacitance estimated by EIS for the 
NiFe 15:1 material is the highest of all the coatings, which is consistent 
with that obtained by the cyclic voltammetry method.

3.4. OER stability test

The stability of the coating materials developed for OER was eval
uated by chronopotentiometry under operating conditions of a con
ventional electrolyzer, applying an anodic current density of |400| 
mAcm-2 for 25 h. Potentiometric curves of the electrocatalytic coatings 
are shown in Fig. 8. The material that presented the best performance in 
the stability test for 25 h was the electrode prepared with a Ni:Fe ratio of 
15:1. The overpotential of that electrode stayed between 300–320 mV 
throughout the test. This electrocatalytic coating also showed the best 
results in the anodic evaluation by LSV, the lowest Tafel slope of the 
materials evaluated, and the highest catalytic surface according to the 
ECSA results. All these results agree with what was obtained in the 
stability test. In general, the results of the coating materials (10:1, 12:1, 
and 15:1) show that, after 5 h of high current density application, a 
stable value is reached over time because the overpotential varies only 
between approximately 10 – 20 mV during the following 20 hours. 
However, for the catalytic coating prepared with an NiFe ratio of 20:1 
there is a greater increase in overpotential during the test, reaching up to 
350 mV at the end of the test. This is because there are areas that are not 
totally covered by the deposited material, or where the coating begins to 
detach from the substrate, causing it to have a lower performance for 
OER.

It is important to highlight that all the electrocatalytic coatings 
showed better performance for OER after anodic polarization (|400| 
mAcm-2) for 25 h. This was evidenced by comparing the LSV curves 
performed at 0 h and after 25 h of polarization, as shown in Figure S4. It 
can be seen that after 25 h of polarization at high anodic current density, 
there is a reduction of approximately 10 mV in the anodic overpotential 
during OER for all prepared electrocatalytic coatings. This result is 
associated with the morphological and structural changes of the surface 
of the coating due to anodic polarization, since additional catalytic 
species can be formed [47–49]. This was confirmed by SEM analysis 
performed on the samples after chronopotentiometry measurements, see 
Figure S5 in the supporting information. It can be observed that there is 
a change in the surface morphology of the coating, which can be asso
ciated with the appearance of Ni-Fe oxyhydroxide species formed during 
polarization [27,108,109]. This was further confirmed by the Raman 
spectra of the electroactive coating (Ni:Fe ratio of 15:1) taken after 80 h 
of anodic polarization at 400 mAcm-2, see Fig. 9. Raman spectra show 
two bands at 467 and 544 cm-1, corresponding to the formation of nickel 
oxyhydroxides [73,110,111]. These results demonstrate the formation 
of a stable catalytic phase of nickel oxyhydroxides, which explains the 
good electrochemical performance of the coating material, even after 80 
h of continuous high polarization in an alkaline environment.

The elemental surface chemical composition of the materials after 
the stability test was obtained by EDS analysis, shown in Table S1 in the 
supporting information. The coatings are mainly composed of Ni, Fe, 
and O. The corresponding EDS spectra are shown in Figure S6, next to 
the SEM image of the corresponding area where the information is ob
tained. Based on the results presented, the long-term stability of the 
electrocatalytic coatings is primarily attributed to an activation process 
driven by electrochemically induced surface restructuring, rather than 
to passivation caused by Fe leaching. After 25 h of anodic polarization at 
a high current density (400 mA cm⁻²), all coatings exhibited an 
improvement in electrocatalytic activity, evidenced by a reduction of 
approximately 10 mV in the overpotential observed in the LSV curves. 
This behavior indicates a progressive enhancement of the active surface, 
which is characteristic of activation processes. Furthermore, post- 
electrochemical SEM analysis revealed significant morphological 
changes on the coating surfaces, consistent with surface restructuring. 
This transformation was associated with the formation of Ni–Fe oxy
hydroxide species, as confirmed by Raman spectra showing character
istic bands at 467 and 544 cm⁻¹, corresponding to catalytically active 
NiOOH phases. The presence of these active phases, along with the 
coating’s ability to maintain high performance even after 80 h of 
continuous operation, suggests that a stable catalytic phase formed 
during anodic polarization. This rules out a passivation mechanism 
linked to Fe leaching, which would typically be associated with a pro
gressive decline in catalytic activity.

The electrolyte change affects the performance of the electrode and 
the overall electrolysis reaction [15]. For alkaline water electrolysis, the 
most used electrolyte is a potassium hydroxide solution with a typical 
concentration between 20–30 wt% due to its high specific conductivity 
under the typical operating conditions of an alkaline electrolyzer [112]. 
However, a cheaper alternative is sodium hydroxide, an electrolyte with 
a lower specific conductivity than KOH [113]. A long-term stability test 
was then performed for the catalytic coating that showed the best per
formance (Ni:Fe 15:1), comparing the electrolyte change from 1 M 
NaOH to 1 M KOH. The results of this test are shown in Fig. 10, where it 
is possible to observe the effect of the conductivity of the electrolyte on 
the overpotential value. A more conductive electrolyte is expected to 
facilitate the mobility of charged species to the electrode/electrolyte 
interface, thus improving the OER. In addition, other studies mention 
that there is a direct influence of alkali metal cations on the OER, 
concluding that larger cations with lower hydration energy can generate 
greater access of the reactants to the active sites, improving the kinetics 
of the OER by favorably altering the adsorption energy and improving 
the rate of formation of key intermediates of the reaction [114–117]. 
When using 1 M KOH as the electrolyte, the NiFe electrode can achieve a 
lower overpotential compared to 1 M NaOH electrolyte at 400 mAcm-2. 
The electrode in the 1 M KOH electrolyte produced overpotentials 
ranging from 250–270 mV, while the electrode in the 1 M NaOH elec
trolyte yielded overpotentials ranging from 300–320 mV. Therefore, 
there is a difference in overpotential of around 50 mV between the two 
electrolytes. In addition, when the electrodes are evaluated by LSV 
before and after polarization at high current density for 80 hours in each 
electrolyte, there is no evidence of loss of catalytic activity of the coat
ings, and the electrochemical performance for OER is similarly pre
served in both electrolytes, as shown in Figure S7 in the supporting 
information.

4. Conclusions

In this work NiFe-LDH electrocatalysts were obtained on nickel foam 
by means of a simple electrodeposition method, varying the ratio be
tween nickel and iron present in the bath. The best performing Ni-Fe 
coating material developed was obtained with a 15:1 ratio in the bath. 
This catalytic coating showed overpotentials of only 206, 223 and 244 
mV for OER, for current densities of 30, 50 and 100 mAcm-2, respec
tively, which is a significantly better performance compared to similar 

Table 4 
Results obtained from the equivalent circuit for the adjustment of the Nyquist 
diagram for the different ratios.

Sample Rs  
(Ω.cm2)

Rt 
(Ω.cm2)

Ra 
(Ω.cm2)

Ca 
(mF.cm-2)

Cdl 
(mF.cm-2)

10:1 0.68 3.640 4.75 33.395 406.761
12:1 0.74 1.918 6.99 38.946 343.882
15:1 0.72 0.975 4.22 53.212 1528.564
20:1 0.74 2.036 6.50 40.371 387.566

S.G. Quiroz et al.                                                                                                                                                                                                                               Electrochimica Acta 528 (2025) 146332 

9 



catalytic materials reported in the literature. This material showed low 
Tafel slopes of 56.7 mVdec-1 and 38.5 mVdec-1 for low and high anodic 
polarizations, the ECSA was 10.58 which is lower than other materials 
reported in the literature, so the high catalytic activity is result of the 

intrinsic activity of the material and not for the surface area. In addition, 
the stability test at high current density of |400| mAcm-2 for 80 hours in 
1 M NaOH and 1 M KOH revealed that the coating material maintains 
excellent catalytic activity and stability in alkaline environments. These 

Fig. 8. Chronopotentiometry of NiFe-LDH/NF materials at |400| mAcm-2 in 1 M NaOH.

Fig. 9. Raman spectra of electroactive coating (Ni:Fe 15:1) obtained after 80 h of anodic polarization at 400 mAcm-2.

S.G. Quiroz et al.                                                                                                                                                                                                                               Electrochimica Acta 528 (2025) 146332 

10 



findings highlight the potential applicability of the NiFe-LDH electro
catalysts in real electrolyzer applications, providing a viable and effi
cient solution for sustainable hydrogen production.

Associated Content in Supporting Information

Figures S1-S7: SEM images for different Ni:Fe ratio, XRD patterns, CV 
curves, LSV curves for 0 and 25 hours, SEM images of anodic polariza
tion, EDS spectra, LSV curves for 0 and 80. TableS1: EDS analysis.

CRediT authorship contribution statement

Simón G. Quiroz: Writing – original draft, Methodology, Investi
gation. Santiago Cartagena: Writing – review & editing, Supervision, 
Methodology, Investigation, Conceptualization. Jorge A. Calderón: 
Writing – review & editing, Project administration, Methodology, 
Funding acquisition, Formal analysis, Conceptualization.

Declaration of competing interest

The authors declare that they have no known competing financial 
interests or personal relationships that could have appeared to influence 
the work reported in this paper.

Data availability statement

Data will be made available on request from the interested.

Acknowledgements

The authors thank “Ministerio de Ciencia Tecnología e Innovacion - 
Minciencias” and “Sistema General de Regalías” for the financial support 
provided by the project Contract No BPIN 2022000100089.

Supplementary materials

Supplementary material associated with this article can be found, in 
the online version, at doi:10.1016/j.electacta.2025.146332.

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	Enhancement of oxygen evolution performance of water splitting at high current density by novel electrodeposited NiFe-LDH c ...
	1 Introduction
	2 Experimental
	2.1 Materials and reagents
	2.2 Preparation of NiFe-LDH/NF
	2.3 Characterization techniques
	2.4 Electrochemical measurements

	3 Results and discussion
	3.1 Structural and elemental characterization
	3.2 OER test performance
	3.3 Kinetics study of OER
	3.4 OER stability test

	4 Conclusions
	Associated Content in Supporting Information
	CRediT authorship contribution statement
	Declaration of competing interest
	Data availability statement
	Acknowledgements
	Supplementary materials
	References