Factorial Analysis to Optimize the Trimetallic Conife-LDH/Graphene Composites for the Oxygen Evolution Reaction
Authors: Alves Daniele , Dempsey Eithne , Breslin Carmel B 
Published: December 2024

For many decades, fossil fuels, including gas, oil, and coal, have acted as the primary contributors to electricity generation [1]. Nevertheless, the combustion of carbon-based fuels causes substantial emissions of greenhouse gases, notably carbon dioxide (CO2), thereby precipitating climate change and adversely affecting human well-being and the environment [2]. Consequently, there is an endeavour to innovate and develop efficient and environmentally acceptable energy sources. The oxygen evolution reaction (OER) constitutes a pivotal half-reaction within diverse renewable energy technologies. Despite its significance, the OER is intrinsically sluggish and energy-intensive, necessitating the advancement of electrocatalysts that are both efficient and stable to facilitate this reaction [3]. In recent years, layered double hydroxides (LDH) have emerged as potential candidates for OERs due to their cost-effectiveness, versatile composition, and favourable electrocatalytic properties [4]. Ni-based LDHs, particularly NiFe-LDH, have been extensively investigated and proven to be effective OER electrocatalysts in alkaline environments [5]. However, its limited electrical conductivity hinders further enhancement of its OER catalytic activity. Meanwhile, Co-based LDHs, such as NiCo-LDH and CoFe-LDH have been proven to have excellent electrocatalytic activity [6]. In contrast to binary LDHs, the ternary LDHs, incorporating diverse transition elements can exhibit higher capacitance and contain more abundant active sites [7]. However, the utilization of LDH electrode materials is limited by their low conductivity and tendency for agglomeration. Graphene serves as an excellent substrate for catalyst immobilisation in electrocatalysis, owing to its superior electrical conductivity, high surface areas, and impressive stability [8]. Therefore, the combination of ternary LDHs, characterised by reversible redox activity, and conductive graphene is expected to represent an efficient approach for fabricating hybrid materials with enhanced oxygen evolution reaction (OER) activity, facilitated by the advantageous interplay between LDHs and graphene.

Accordingly, in this study, trimetallic CoNiFe-LDHs were designed and grown on graphene (G) through a one-step hydrothermal approach to obtain a structure that promotes efficient charge transfer, optimizing the OER kinetics. A 2-level full-factorial model was used to determine the effect of Co (1.5, 3 and 4.5 mmol) and graphene (10, 30 and 50 mg) concentrations on the OER onset potential, which was the chosen response parameter. The independent and dependent variables were fitted to the linear model equation, using ANOVA analysis. The F-values, the ratio of noise to response, confirmed that the model is significant (p<0.05). The p-values less than 0.05 indicate the model terms, such as cobalt and graphene concentrations and their interaction, are significant, implying that the OER onset potential is strongly correlated to these parameters. The polarization curves of CoNiFe-LDH/G composites for OER are shown in Figure 1. The OER was run in triplicate using the Co3Ni3Fe3-LDH/G30 (central point) to estimate the variability (0.58%). The comparison study showed that a low onset potential (1.54 V) and overpotential at 10 mA cm-2 (1.58 V) was achieved for Co1.5Ni3Fe3-LDH/G10, demonstrating that a low concentration of cobalt and graphene could make for an ideal electrocatalyst in practical applications.

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Figure 1