Print light synthesis of Ni catalysts for CO2RR

EFCF 2025: Low-Temp. Fuel Cells, Electrolysers & H2 Processing 1 – 4 July 2025, Lucerne Switzerland https://doi.org/10.5281/zenodo.17244113 A0707 Page 1/6 A0707 Print light synthesis of Ni catalysts for CO2RR Wanderson Oliveira da Silva* (1), Muriel Mauron (2), Stéphane Audriaz (2), Paul Grandgeorge (2), Gioele Balestra (2), Mathieu Soutrenon (1) (1) Institute of Systems Engineering, School of Engineering, HES-SO Valais-Wallis, Rue de l’industrie 23, 1950 Sion/Switzerland; (2) Institute iPrint, HEIA-FR, HES-SO Fribourg, Route de l’Ancienne Papeterie 180, 1723 Marly/Switzerland; *Contact corresponding authors: www.EFCF.com/ContactRequest Abstract The electroreduction of CO2 into valuable chemicals provides a sustainable pathway to mitigate GHG emissions while addressing pressing energy and environmental challenges. This study focuses on a scalable and cost-effective process for fabricating cathodes with Nibased catalysts to convert CO2 into CO by reactive inkjet printing. Metal precursor-based inks were formulated for the process and printed using a custom-built inkjet printer. Postprinting using a xenon flash lamp was employed to reduce the nickel metal precursor into active catalyst structures. The full process is called print light synthesis (Figure 1). This method reduces energy consumption and production time compared to conventional hightemperature synthesis. SEM/EDX and XRD analysis confirmed uniform catalyst deposition and predominant presence of metallic Ni after the print light synthesis process. Microwave plasma atomic emission spectrometry (MP-AES) analysis evidenced a conversion rate of approximately 80% from nickel precursor into metallic Ni. Electrochemical characterizations, including cyclic voltammetry and chronoamperometry coupled to gas chromatography analysis, confirmed the efficiency of the synthesized Ni/C PLS catalyst (0.5 mgNi/cm²) for selective CO2 conversion into CO, with a faradaic efficiency of 64% at -0.75V (vs RHE). Figure 1: Schematic of the print light synthesis process. EFCF 2025: Low-Temp. Fuel Cells, Electrolysers & H2 Processing 1 – 4 July 2025, Lucerne Switzerland https://doi.org/10.5281/zenodo.17244113 A0707 Page 2/6 Introduction The electrochemical reduction of carbon dioxide (CO₂RR) is a promising strategy for addressing two of the most critical challenges nowadays: (i) climate change and (ii) the sustainable production of fuels and chemicals. CO2 recycling into valuable products through electroreduction provides a pathway to close the carbon loop, potentially achieving carbon neutrality when coupled with renewable electricity sources. Moreover, CO₂RR operates under relatively mild conditions, is compatible with existing chemical infrastructure, and supports the development of decentralized production systems, making it a scalable and economically attractive solution for a circular carbon economy. As research progresses, advancements in catalyst design and reactor engineering are required to further improve the efficiency and selectivity of CO2 electroreduction into added-value compounds/fuels. 1. Scientific Approach The electrochemical reduction of CO2 can be controlled mainly by the catalyst type and applied potential, providing selectivity to a desired added-value compound/fuel. The CO2RR can generate several products such as formic acid (HCOOH), carbon monoxide (CO), methanol (CH3OH), ethanol (C2H5OH), methane (CH4), ethylene (C2H4) and other hydrocarbons and alcohols. [1] Precious metals such as gold and silver are commonly employed as catalysts for CO2RR, however their high price and scarcity are limiting factors for applications in practical devices. In this scenario, non-noble metals such as iron (Fe), nickel (Ni), cobalt (Co), copper (Cu), etc., have gained significant attention as cost-effective and earth-abundant alternatives for CO₂RR. [2] In particular, nickel (Ni) shows to be effective for converting CO₂ to carbon monoxide (CO), which is well known as a key precursor for syngas and chemical synthesis. [3-5] However, despite their significant advantages there are still several challenges in terms of improving their selectivity, activity, and long-term durability for CO2RR. Therefore, continued advancements in material design, such as nanostructures, nitrogen-doping, and support engineering, are key to improve the performance of the non-noble catalysts for practical CO2 electroreduction applications. [6-9] The conventional methods to synthesize active catalysts for CO2 are still complex and challenging since multiple steps are required, for example M-N-C from single-atom catalysts (M = non-noble metals), requires not only a long time for the complete synthesis but also additional cleaning steps with strong acids, toxic solvents, and many steps of heating at high temperatures at 700-1000°C (reactors, oven, dryers, etc.), which makes challenging the scale up of the CO2 electrolyzer technology. In this context, a new approach recently introduced using a flash light irradiation from a powerful xenon flash lamp could be a promising alternative, since it can drive thermal processes reaching high temperatures (up to 2850 ºC) during a very short residence time (microto milliseconds), [10] which can likely minimize the catalyst nanoparticle growth/agglomeration and likely maximize the singleatom catalyst sites as recently illustrated by few works. [11-14] These findings evidence the potential of this technology for catalyst synthesis that could be potentially applied for several applications such as fabrication of active and selective cathodes for CO2 electrolyzers. Therefore, this study aims to introduce a new process for fabrication of cathodes for CO2RR, ideally from non-noble metals, directly from commercially available gas diffusion layers (containing MPL with porous carbon) using a new approach called print light synthesis. EFCF 2025: Low-Temp. Fuel Cells, Electrolysers & H2 Processing 1 – 4 July 2025, Lucerne Switzerland https://doi.org/10.5281/zenodo.17244113 A0707 Page 3/6 2. Experiments The employed approach involves formulating an inkjet ink from nickel nitrate (25mgNi/mL) from water and ethanol-based formulation, which was printed onto a commercial gas diffusion layer, a carbon cloth substrate coated with a microporous layer (thickness 400µm, carbon black loading 2.5 mg/cm2, PTFE 20-30wt%), using an industrial printhead (Epson S3200) to create a metal precursor layer of 0.5mgNi/cm2. This layer was then exposed to flash light irradiation (under Argon atmosphere) from a 16kW xenon flash lamp (Excelitas NobleLight, Germany) for 150 ms with a total energy density of 400 J/cm2, inducing the reduction of the nickel salt into small metal nickel nanoparticles. This entire process was denoted Print Light Synthesis (PLS) and the synthesized catalyst as Ni/C PLS. [13] The gas diffusion electrode containing Ni nanoparticles were characterized by XRD and SEM/EDX. The Ni loadings before and after the flash light irradiation process were quantified by Microwave plasma atomic emission spectrometry (MP-AES). The catalytic performance for CO2 reduction reaction (CO2RR) was evaluated using standard electrochemical techniques, in a gas-tight two-compartment cell separated by a Nafion 211 membrane in a 0.5 M KHCO3 electrolyte with CO2-saturated in the cathode side, combined with gas chromatography analysis to quantify the products from CO2RR. 3. Results The synthesized Ni/C PLS electrode was initially cleaned several times with water to dissolve/remove possible remaining nickel nitrate salt, afterwards MP-AES analysis was performed and evidenced a conversion rate of approximately 80% into metallic Ni, the estimated conversion rate was calculated from a triplicate of Ni electrodes with and without post-treatment by flash light irradiation. Figure 2 shows SEM/EDX images of the Ni/C PLS synthesized by print light synthesis. The images show a uniform Ni dispersion over the microporous carbon layer with small Ni nanoparticle sizes with almost no large agglomerations. XRD diffractograms of the Ni/C PLS and Bare GDL presented in Figure 3 show typical crystallography diffraction peaks at 44.6, 51.9, 76.46 attributed to the Ni (111), (200) and (220) planes, respectively, (PDF #04-0850), which is attributed to the metallic Ni.[15] In addition, the absence of XRD peaks from nickel oxide, nickel nitrite, nickel carbide and/or unconverted nickel nitrate salt, suggests the majority formation of metallic nickel by using the PLS approach. Therefore, print light synthesis is a promising approach that successfully synthetized Ni nanoparticles directly on a gas diffusion layer (GDL). Figure 2: SEM/EDX images of the Ni/C PLS synthesized by print light synthesis. EFCF 2025: Low-Temp. Fuel Cells, Electrolysers & H2 Processing 1 – 4 July 2025, Lucerne Switzerland https://doi.org/10.5281/zenodo.17244113 A0707 Page 4/6 Figure 3: X-ray diffractograms of the Ni/C PLS and Bare GDL. The catalytic performance of the synthesized Ni/C PLS was initially investigated by cyclic voltammetry (CV), using a standard three electrode electrochemical cell, in KOH 1 M electrolyte saturated with argon at a scan rate of 5 mV s−1 as shown in Figure 4a. The CV profile presents typical Ni redox peaks at 1.2-1.45V (vs RHE), the anodic peak shows the Ni oxidation state from Ni(II) to Ni(III), where b-Ni(OH)2 is oxidized to b-NiOOH and the cathodic peak shows the reduction process, this evidence the formation of active Ni catalyst sites by using PLS method. The catalytic performance of Ni/C PLS for CO2 electroreduction was evaluated by linear sweep voltammetry (LSV). The LSV curves presented in Figure 4b showed higher current density at more positive onset potential for CO2-saturated electrolyte compared to Argon, which evidences the occurrence of CO2 electroreduction. Gas chromatography analysis coupled with electrochemical tests at constant potential electrolysis were performed at different potentials for 30 min to quantify the products from CO2RR.[16] As illustrated by Figure 4c the CO2 conversion into CO starts at -0.6V (vs RHE) and shows a maximum faradaic efficiency of CO at -0.75V (vs RHE) with 64% and current density of 6mA cm-2 (Figure 4d), at more cathodic potentials and current densities H2 production is likely favored due to the CO2 mass transport limitations, however the FECO could be further improved by using a flow cell configuration. Overall, Ni/C PLS catalyst demonstrated a promising activity and selectivity for CO2RR to CO, however, further PLS improvements will continue to be explored in order to achieve a higher faradaic selectivity for CO (>90%) as already reported by previous works,[3,5] that typically apply nickel singleatom catalysts (Ni SACs) supported on nitrogen-doped carbon (NC) materials, however from complex and time consuming synthesis protocols, on the other hand PLS has the advantage to be a faster and simple approach. Therefore, this innovative approach (print light synthesis) can manufacture active gas diffusion electrodes (potentially from different metals, alloys and/or SACs) for electrochemical CO2 reduction, paving the way for more sustainable and efficient methods to address global carbon emissions and create value-added products. EFCF 2025: Low-Temp. Fuel Cells, Electrolysers & H2 Processing 1 – 4 July 2025, Lucerne Switzerland https://doi.org/10.5281/zenodo.17244113 A0707 Page 5/6 Figure 4: (a) Cyclic voltammetry of Ni/C PLS in KOH 1M saturated with Argon at scan rate of 5 mV s-1. (b) Linear sweep voltammetry of Ni/C PLS in KHCO3 0.5M saturated with Argon and CO2 at scan rate of 5 mV s-1. (c) Faradaic efficiency of CO and H2 from CO2RR catalyzed by Ni/C PLS at different potentials after 30 minutes of electrolysis in CO2saturated KHCO3 0.5M aqueous solution and (d) Faradaic efficiency of CO from CO2RR catalyzed by Ni/C PLS at different current densities after 30 minutes of electrolysis in CO2saturated KHCO3 0.5M aqueous solution. Acknowledgements The authors thank the HES-SO University of Applied Sciences and Arts Western Switzerland for supporting the project P2-RIPCO2-129765. The authors wish to thank Prof. Hubert H. Girault from EPFL for his support. References [1] S. Nitopi, E. Bertheussen, S.B. Scott, X. Liu, A.K. 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