ICMCTF 2024 Session TS1-1-MoM: Coatings for Batteries and Hydrogen Applications I

The author describes in his talk the scale up process for PEM electrolyzers regarding coating technologies. The first part of the talk shows the need for scale up in the green hydrogen market due to the huge amount of green hydrogen which has to be produced till 2030 and 2050 to reach net zero targets. For this industrial standardization of coating processes are needed as soon as possible. Here the upscale process of reproducible and reliable roll 2 roll equipment are shown and getting over the limiting factors like dimension instability of membrane materials and multi-layer coating applications of rare materials like iridium.

The second part describes the boundaries of today's coating methods describing the parameters needed to be optimized. The background on one of the standard methods today, slot die coating is described here in detail with some theoretical background on slot die coating technology and an overview on developments for intermittent slot die coatings. The third part of the talk describes a new digital fabrication method for electrolyzers and shows the opportunity for the overall green hydrogen market using digital fabrication methods, reducing the carbon footprint of coating equipment for PEM electrolyzer.

Single atom catalysts (SAC) represent an intriguing option due to their ability to unlock the latent catalytic potential in oxygen reduction reaction (ORR). Nevertheless, the endurance of individual atomic entities is confronted by numerous impediments, encompassing the dissolution of metallic species, metal agglomeration, and the deactivation of catalytically active sites. A crucial factor in enhancing stability lies in the judicious selection of a compatible support catalyst capable of fostering strong metal-support interaction (SMSI).

Carbon is widely utilized as a catalyst support material owing to its favorable electron conductivity and the ability assume diverse dimensional configurations, ranging from 0D to 3D. Additionally, the carbon support facilitates additional customization, such as the introduction of Chalcogen or Pnictogen atom groups through doping, leading to enhanced catalytic activity.

Development of efficient, cost-effective, and environmentally friendly processes for the realization of high-quality graphene on metallic substrates is highly desirable for multiple energy applications as well as next-generation graphene-based green electronics. Several polymers including those derived from natural sources represent a rich source of carbons that can be converted into graphitic carbons by energy inputs in different forms. Lasers represent a form of energy input that is direct-write type and does not need the whole substrate to be heated at high temperatures for carbonization. Herein, we examine carbonization of natural product-derived polymer(s) into graphitic (few layers graphene) carbon using CO₂ laser-assisted direct-write process. Such a process is generally termed as Laser-Induced Graphene (LIG). In particular, we demonstrate the key and interesting role played by nickel in enhancing the degree of graphitization (Ni-LIG). Indeed, the unique advantage of this nickel-catalyzed scanning laser-induced transient pyrolysis process implemented under ambient conditions is that we are able to uniformly graphitize the thermoset polymer coating that would otherwise yield hard carbons or a mixture of ordered/disordered carbon in a furnace-based pyrolysis process. It was observed that upon optimized laser processing condition, the Ni-(CH₃COO)₂. 4H₂O salt added to the polymer gets reduced to Ni (111), which in turn catalyzes the nucleation process. We note the appearance of disordered carbon chains initially, which upon interacting precisely with the nickel surface lowers the activation barrier for graphene formation by annealing the defects. Moreover, due to the very low lattice mismatch between Ni (111) and graphene, a strong interphase is formed, facilitating efficient contact and charge transfer. As the surface coating is decorated with a mixture of Ni/NiO (as confirmed by XRD and XPS), water dissociation as well as adsorption of water oxidation intermediates is promoted, leading to an impressive value of overpotential for oxygen evolution reaction (OER) at 10 mA/cm² of only 330 mV in 1M KOH. We also examined the case of urea-incorporated material to induce N-doping so as to enhance the conductivity via the incorporation of the П-conjugated system. However, the incorporated pyrrolic N defects in the carbon layer were noted to hinder the nucleation of graphitization at the Ni atom, resulting in a low I_G/I_D ratio. This material was therefore studied for charge storage property by cyclic voltammetry and galvanostatic charge-discharge (GC) measurement. It was found that N-doped N-Ni-LIG has a higher specific capacitance compared to Ni-LIG.

In order to address the growing energy crisis and environmental concerns, the development of hydrogen energy through electrochemical water splitting into hydrogen represents a viable solution. The hydrogen evolution reaction (HER) during water splitting is multi-electron transfer process that requires catalysts to proceed at appreciable rates. Noble metals have been widely used for water splitting due to their low Gibbs free energy; however, their high cost limits their availability and hinders commercialization. To address this challenge, we conducted a study on HER in alkaline electrolytes with the aim of developing highly efficient and durable electrocatalysts. The efficiency of HER in an alkaline environment is determined by a delicate balance among three crucial factors: the energy required to dissociate water molecules, hydrogen adsorption (H_ad) on the catalyst’s surface, and the prevention of hydroxyl adsorption (OH_ad), often referred to as the poisoning of active sites.

Graphitic carbon nitride (g-C₃N₄) has been extensively studied due to its two-dimensional layered structure and high nitrogen content. However, its poor conductivity limits its application in the field of HER. Therefore, we modified transition metal phosphide on g-C₃N₄ to enhance its conductivity and increase the number of active sites. Additionally, it has been mentioned in previous studies that nickel and cobalt atoms can promote the reaction kinetics of HER in the first and second steps, respectively, thus improving the efficiency of HER in an alkaline electrolyte. Therefore, we synthesized NiCoP/g-C₃N₄ composites in different weight percent to replace the platinum electrode in a 1.0 M KOH electrolyte.

Hybrid ZnS-ethylenediamine nanomaterials (ZnS(en)_0.5) were produced in a mixed solvent of water, butanol, and ethylenediamine by solvothermal and precipitation methods. The effect of different molar ratios H₂O/Zn²⁺ between 15 and 91 have been investigated by diverse techniques; TG-DSC analysis, X-ray Diffraction, Scanning Electron Microscopy, Infrared, and Diffuse Reflectance spectroscopy. The material was then exfoliated using a combined sonication-illumination process to obtain stacked 2D ZnS nanolayers intercalated with the organic material. After optimization, the as-prepared and exfoliated ZnS(en)_0.5 nanosheets were prepared as films by spin coating to evaluate the photocatalytic H₂ production reaction. The H₂ evolution reaction was performed in a homemade glass photoreactor containing 30 mL of ethanol-water solution (50:50 vol. %). Eight films were fixed around the internal walls of the glass reactor. The solution was magnetically stirred (at 600 rpm), irradiated with UV light provided by a Hg lamp Pen-ray (of λ=254 nm and I₀ = 4.4 mWcm^-2), and placed in the center of the solution into the quartz tube. The system was bubbled with N₂ (to reduce the O₂ pressure), then it was sealed, and the lamp was turned on. The quantity of H₂ was measured using a Shimadzu GC-2014 gas chromatograph and N₂ as the carrier gas. The photocatalytic activity of all the as-prepared and sonicated-irradiated ZnS(en)_0.5 samples was evaluated by 6 h and 6 cycles. The results showed an enhancement of 7 to 22 times in the H₂ production rate as a function of the synthesis and exfoliation conditions. Intrinsic hydrogen evolution rates up to 76 mmolg^-1h^-1 were achieved using the optimized exfoliated ZnS(en)_0.5 hybrid material. This value constitutes a record in the community, which is more significant when the lamp's low power is considered. The increased photoactivity was correlated to the degree of exfoliation and the number of stacked ZnS layers in the structure.

Urea oxidation reaction (UOR) is a promising energy-saving avenue for sustainable hydrogen production. However, the 6-electron transfer reaction lead the sluggish kinetic. In this work, an ultrafast, one-step method has been used to synthesize novel NiFeCo(OH)_x@FeOOH@(NiFeCo)S_x heterostructure supported on Ni foam as electrocatalyst toward UOR. We demonstrate that the NiFeCo(OH)_x@FeOOH@(NiFeCo)S_x exhibits outstanding UOR performance with a low potential of 1.36 V versus reversible hydrogen electrode at a current density of 100 mA cm^-2. The catalyst also shows great durability for 50 hours at 10 mA cm^-2. The outstanding electrochemical performance is attributed to the high surface area, the faster electron transfer, free of binder, and the synergistic effects of among metallic components.