The NICKEFFECT project continues its mission to revolutionise electrocatalysis by replacing scarce and costly platinum with more abundant nickel-based alloys. In the latest instalment of the Young Scientific Talk series, Parisa Molaei, a PhD researcher from the Vrije Universiteit Brussel (VUB), presented a comprehensive look at her research: “Three-Dimensional Multiscale Simulation Framework for Nickel–Tungsten (Ni-W) Electrodeposition in Porous Electrodes.”
This work, a collaboration between VUB, LCA, and CIDETEC, bridges the gap between theoretical modelling and experimental validation to improve the efficiency of catalyst development.
The Challenge: Beyond Platinum
Platinum is the gold standard for catalytic applications, but its high cost and scarcity pose significant barriers to sustainable industrial scaling. Nickel alloys serve as a promising alternative, offering excellent performance at a fraction of the cost. To optimise these materials, the NICKEFFECT team uses porous electrodes (such as carbon cloth) because their high surface area significantly enhances catalytic activity. However, coating these complex, three-dimensional structures uniformly is a significant engineering challenge.
A Multiscale Approach to Modelling
Molaei’s research utilises a multiscale simulation framework to predict how nickel and tungsten deposit onto complex surfaces. She explained that while different methods exist—from Density Functional Theory (DFT) at the atomic level to Phase Field methods for film growth—this project focuses on the Continuum Theory using the Finite Element Method (FEM).
The framework is divided into two distinct scales:
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Macroscale Model: This focuses on the entire electrochemical cell, including the anode, cathode, and electrolyte. It allows researchers to study current distribution over the electrode surface and test different cell geometries and holder materials—such as the copper frame used to ensure better electrical contact—before conducting physical experiments.
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Microscale Model: This zooms into the “fiber networks” of the porous electrode. By representing the carbon cloth as a 3D arrangement of cylinders, the model simulates how ions transport through the tiny pores via diffusion, convection, and migration.
Key Findings and Experimental Validation
The simulation framework was validated through experiments where different voltages (potentials) were applied while keeping the total transferred charge constant.
1. Surface Morphology and Uniformity
The Macroscale model predicted that lower potentials lead to a more uniform current distribution. This was confirmed by Scanning Electron Microscopy (SEM) images, which showed that high voltages resulted in coarser, larger particles, while lower voltages produced finer, more uniform coatings.
2. Ion Depletion in Deep Pores
A critical insight from the Microscale model concerned the “edge effect” and ion transport limitations. As the potential increases, the reaction rate for nickel accelerates significantly. This causes nickel ions to be consumed rapidly at the outer layers of the porous electrode, leading to a depletion of ions in the deeper regions.
3. Tungsten Composition
The research highlighted a fascinating trend in alloy composition:
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Nickel is the primary reactant with a high reaction rate.
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Tungsten is deposited via induced co-deposition, meaning it has a lower reaction rate.
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In deeper layers at high potentials, the fraction of tungsten actually increases. This isn’t because more tungsten is being deposited, but because the nickel is so depleted that the relative percentage of tungsten in the alloy becomes higher.
Improving Catalyst Efficiency
While the primary goal of the study was to validate the simulation framework, the results also yielded practical benefits for the NICKEFFECT project. The team observed that switching the substrate to carbon cloth and operating at a specific potential (5V) yielded the best catalytic performance, aligning perfectly with the model’s predictions.
This 3D multiscale framework provides a powerful tool for the NICKEFFECT consortium, allowing for the “virtual” testing of electrode designs and deposition conditions, ultimately accelerating the transition toward sustainable, nickel-based electrocatalysis.