ALD/ALE 2021 Session AA1: Energy: Catalysis and Fuel Cells
AA1-1 High-crystalline RuO2based on Atomic Layer Deposition for Oxygen Evolution Catalyst
Jaehyeok Kim, Donghyun Kim, Jusang Park, Hyungjun Kim (Yonsei University, Korea)
To alternate carbon-based energy source to protect the nature, hydrogen is widely researched worldwide. Electrochemical water splitting is the promising method that produces no pollutant, only H2and O2. However, Oxygen Evolution Reaction (OER) is sluggish, which determines the overall efficiency of electrocatalyst, so that water splitting is limited in industrial field.
RuO2has been researched as efficient catalyst for oxygen evolution. The crystallinity of the RuO2affects the efficiency. Therefore, synthesis of high-crystalline RuO2is important. To enhance the efficiency of RuO2, large surface-to-volume ratio and controllability of the crystallinity are the key factors in synthesis method.
Atomic Layer Deposition (ALD) has advantages of excellent conformality, large-area uniformity, and precise controllability of the thickness. For efficient catalyst, large surface area is helpful because it is directly related to the reaction sites. ALD is suitable fabrication process for electrocatalyst.
In this report, RuO2film was synthesized based on ALD on Carbon Fiber Paper (CFP) at different growth temperature, which has large surface-to-volume ratio with high conductivity. It can be directly used for OER catalyst with enlarged active sites of OER. For the analysis, material properties of ALD RuO2 such as X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy, SiO2substrate was prepared as reference. Electrochemical properties was measured in 3-electrode system consists of working electrode, reference electrode, and counter electrode. It showed low overpotential and Tafel slope, which imposes promising candidate for OER catalyst.
Ya Yan, Bao Yu Xi, Bin Zhao, and Xin Wang, “A review on noble-metal-free bifunctional heterogeneous catalysts for overall electrochemical water splitting,” J. Mater. Chem. A, 2016, 4, 17587–17603, DOI: 10.1039/c6ta08075h
 Kelsey A. Stoerzinger, Liang Qiao, Michael D. Biegalsk, and Yang Shao-Horn “Orientation-Dependent Oxygen Evolution Activities of Rutile IrO2and RuO2, ,” J. Phys. Chem. Lett. 2014, 5, 1636−1641
AA1-2 Atomic Layer Deposition of Pt@Pd Core-Shell Structure Electrocatalyst for Carbon Dioxide Reduction
Ming Li, Ruud Kortlever, Ruud van Ommen (Delft University of Technology)
Using electrocatalysts to convert CO2 into chemicals or fuels through electrochemical reactions is an attractive approach to reduce CO2 emissions and decrease the greenhouse effect. However, existing electrocatalysts have several technological limitations, such as low selectivity, poor stability, low conversion rates of the feedstock, and high overpotential which will lead to energy losses. Most of the electrocatalyst improvement strategies focus on catalyst structure and composition optimization such as nanostructuring, doping and alloying, etc. However, the widely used catalyst fabrication methods, like impregnation, colloidal, ion-exchange methods are tough to tailor the morphology of the catalyst down to the atomic scale, let alone other delicate structures like nano-sized core-shell particles. One promising solution is to use the atomic layer deposition method to fabricate electrocatalysts with well-defined nanostructure. It is reported that Pd-Pt bimetallic catalyst can reduce CO2 toward formic acid and achieve a high faradic efficiency at room temperature and atmospheric pressure. We investigate whether the performance of this catalyst could be further improved by tuning the nanostructure of the catalyst with ALD. We studied how to use fluidized bed ALD to synthesize core-shell structure bimetallic electrocatalysts, and synthesized the Pd-Pt bimetallic catalyst with core-shell structure on carbon black substrate in this work. The metal loading of the catalyst is precisely controlled. TEM, XPS, XRD, SEM, and ICP-OES were used to characterize the catalyst structure and metal loading. Electrochemical measurements were carried out in a custom-made H-cell using a three-electrode assembly at room temperature. This gives us a better understanding of the effect of the catalyst structure on carbon dioxide reduction, helping us to come to an optimized structure and the corresponding ALD strategy to make it.
AA1-3 Understanding Metal-Support Interactions in Model Pd/ALD-Al2O3/SiO2 Catalysts
Arun Asundi, Emmett Goodman (Stanford University); Adam Hoffman (SLAC National Accelerator Laboratory); Karen Bustillo (Lawrence Berkeley Lab, University of California, Berkeley); Jonathan Stebbins (Stanford University); Simon Bare (SLAC National Accelerator Laboratory); Stacey Bent, Matteo Cargnello (Stanford University)
The synergy between coexisting metal and metal oxide phases is critical in determining the reactivity of many supported heterogeneous catalysts. The interaction between the active metal and the support is one example of this synergy and can be controlled to modulate catalyst performance. ALD offers a unique opportunity to study metal-support interactions by enabling support modification one atomic layer at a time. Metal-support interactions are readily apparent in Pd methane combustion catalysts, where support properties can affect reaction rate by several orders of magnitude. Previous work has shown that the methane combustion rate is significantly higher for Pd/Al2O3 than Pd/SiO2, but the nature of the metal-support interaction that determines this reaction rate is not well-understood. In this work, we study the effects of support chemical properties and morphology on the methane combustion reactivity of Pd supported on ALD Al2O3-modified SiO2.
Catalysts were prepared through a combined ALD and colloidal synthesis method. Uniform SiO2 nanospheres were modified with different thicknesses of Al2O3 films deposited by ALD. Colloidal Pd nanocrystals were then deposited on the ALD-Al2O3/SiO2 supports. This synthesis method enabled independent control over the Pd nanocrystal size, Pd loading, and chemical nature of the support. The transition of the support properties from SiO2 to Al2O3 results in two regimes of improved reactivity as a function of Al2O3 ALD cycle number: the reaction rate increases rapidly at low Al2O3 coverage and increases gradually at high Al2O3 loading. The two stages of promotion show that both surface and bulk properties of Al2O3 are important factors in controlling the reaction rate. At sub-monolayer alumina coverage, the reaction rate is determined by the number of Pd/Al interface sites. Through infrared spectroscopy we show that a monolayer of Al2O3 is deposited during the first three ALD cycles, leading to a linear increase in reaction rate as a function of ALD cycle number as the support surface transitions from SiO2 to Al2O3. At high Al2O3 loadings, bulk properties of Al2O3 such as purity and crystallinity also affect reaction rate. 27Al nuclear magnetic resonance spectroscopy reveals intermixing between Si and Al and crystallization of the Al2O3 for sufficiently thick coatings, both of which modulate the methane combustion rate. This work demonstrates the many support characteristics that influence catalyst reactivity through metal-support interactions. The controlled ALD-colloidal synthesis method used in this work can be applied to fundamental studies of metal-metal oxide interactions in many catalyst systems.
AA1-4 Size Control of Gold Nanoparticles Using Sequential Atomic Layer Deposition of Gold and Titanium Dioxide
Saeed Saedy, Rebecca Baaijens (Delft University of Technology); Eden Goodwin (Carleton University); Matthew Griffiths, Seán T. Barry (Carleton University, Canada); J. Ruud van Ommen (Delft University of Technology)
Gold nanoparticles (AuNPs) supported on metal oxides exhibit exceptional catalytic activities in several processes, especially oxidation reactions. The performance of AuNPs strongly depends on size. Large gold particles do not show notable catalytic activity; the lack of efficient synthesis and stabilization methods of AuNPs resulted in gold being considered a catalytically inactive metal for decades. Additionally, due to weak interaction with the supports, the supported GNPs usually are not stable enough and tend to agglomerate, again resulting in activity loss.
This strong dependency of catalytic activity imposes a significant obstacle in developing supported AuNPs as catalysts, especially when the AuNPs with an average size smaller than 5 nm are desired. This challenge becomes more significant when the preparation of large amounts of supported AuNPs is the final goal, which is the prerequisite of practical applications. For such applications, the supported AuNP synthesis method needs to be capable of controlling the AuNPs size, scaling to large-scale production, and reproducibility. The conventional AuNP syntheses are a variety of liquid phase methods, which have been widely studied for decades; however, they still suffer from poor size control, contamination of the final product with residual solvents/co-reactants, reproducibility issues, and high sensitivity to operating conditions.
Atomic layer deposition (ALD) has proven successful for the synthesis of supported metal NPs for various applications, especially as catalysts. ALD makes it possible to synthesize supported NPs with controlled size, shape, and morphology. Recently we reported ALD synthesis of supported AuNPs on TiO2 in a fluidized bed reactor, with the minimum average particle size of 4 nm. In this work, we report a modification to our previous synthesis, enabling us to attain Au/TiO2 with an average particle size of 2.8 nm. In this method, a sequential ALD of metallic gold (using trimethylphosphinotrimethylgold(III)), TiO2 (using isopropoxytitanium (IV)), and ozone (as an oxidizer) at 105°C were used to confine the ALD deposited AuNPs with a TiO2 over-coat. Different TiO2:Au pulse ratios from 1 to 4 were used. An analysis by inductively coupled plasma optical emission spectrometry of the resulting samples showed a gold loading of about 0.8% in samples. Transmission electron micrographs indicated a decrease of AuNP average size from 3.7 nm to 2.8 nm. Interestingly, the particle size distribution became narrower with increasing the TiO2:Au pulse ratio. The standard deviation of AuNP size decreased from 1.4 nm to 0.8 nm.View Supplemental Document (pdf)
AA1-7 Atomic Layer Deposition for Improved Biomass Conversion Catalysts
Wilson McNeary, Sean Tacey, Gabriella Lahti, Davis Conklin (National Renewable Energy Laboratory); Kinga Unocic (Oak Ridge Natinal Laboratory); Eric Tan (National Renewable Energy Laboratory); Evan Wegener (Argonne National Laboratory); Tugce Eralp Erden (Johnson Matthey); Staci Moulton, Chris Gump, Jessica Burger (Forge Nano); Michael Griffin, Carrie Farberow (National Renewable Energy Laboratory); Michael Watson, Luke Tuxworth (Johnson Matthey); Kurt van Allsburg (National Renewable Energy Laboratory); Arrelaine Dameron, Karen Buechler (Forge Nano); Derek Vardon (National Renewable Energy Laboratory)
Heterogeneous catalysts are a key enabler of the transition towards a sustainable, bio-based economy for fuels and chemicals. However, the harsh conditions in many biomass conversion processes lead to nanoparticle sintering, support collapse, and metal leaching in conventional PGM catalysts. Next-generation catalysts must be developed to address these stability challenges. This presentation will discuss ongoing work between the Catalytic Carbon Transformation and Scale-Up Center at NREL and various industrial partners to develop scalable and cost-effective atomic layer deposition (ALD) coatings for improving the performance of biomass conversion catalysts.The substantial focus will be devoted to the benefits of TiO2 ALD coatings on supported Pd hydrogenation catalysts. Ten cycles of TiO2 ALD were found to dramatically improve the activity of a conventional Pd/Al2O3 catalyst towards aromatic hydrogenation, despite partial coverage of the Pd sites by the ALD layer. Subsequent advanced characterization and atomic-scale computational modeling revealed that the ALD coating weakened the adsorption strength of hydrogenation surface intermediates, leading to higher reaction rates. Reaction testing after exposure to sulfur impurities, high temperature oxidation, and hydrothermal treatment demonstrated the improved stability of the ALD-coated catalyst. Additionally, the ALD synthesis process was found to be scalable over two orders of magnitude with minimal deviation in synthesized catalyst properties. These results were contextualized with cost models of industrial ALD coating and aromatic hydrogenation processes to further refine the value proposition of ALD coatings. Given the demonstrated improvements in hydrogenation, TiO2 ALD coatings have also been applied to supported Pt catalysts for use in other biomass conversion reactions, such as hydrodeoxygenation for the production of sustainable aviation fuel (SAF) and the oxidation of glucose to bio-derived gluconic acid. Recent findings from these experimental campaigns will also be shared. ALD technology holds great potential in the development of next-generation catalysts for biofuels and bioproducts, and this work constitutes an important examination of the impact of ALD coatings in a variety of reaction environments.
AA1-10 Electrochemical Activation of Atomic Layer Deposited Cobalt Phosphate Electrocatalysts for Water Oxidation
Gerben van Straaten, Ruoyu Zhang, Valerio DiPalma (Eindhoven University of Technology); Georgios Zafeiropoulos (Dutch Institute For Fundamental Energy Research); Erwin Kessels (Eindhoven University of Technology); Richard van de Sanden, Michael Tsampas (Dutch Institute For Fundamental Energy Research); Adriana Creatore (Eindhoven University of Technology)
Storage of electricity into chemicals is the most viable answer to the intermittency of renewable sources and the most investigated example this is water splitting. For the O2 evolution half reaction (OER), cobalt phosphate-based electrocatalysts (CoPi) are interesting as they are made of earth-abundant elements and their catalytic activity scales with film thickness. In parallel with others, we have demonstrated synthesis of amorphous CoPi films by ALD . CoPi is prepared by combining ALD of CoOx from cobaltocene (CoCp2) and O2 plasma, with cycles of TMP ((CH3O)3PO) and O2 plasma, according to an ABCD recipe scheme [2,3]. We have also shown that tuning the Co-to-P ratio, by combining this recipe with extra cycles of CoOx, enhances the OER performance , beyond that achieved by traditional electro-deposited films.
In the present contribution we focus on the mechanism behind the enhancement of the catalytic activity of CoPi when tuning the Co-to-P ratio. We show that ALD CoPi thin films undergo activation with increasing number of cyclic voltammetry (CV) cycles. During this activation process, the current density increases in parallel with a progressive leaching of phosphorous out of the electrocatalyst and the shift of the oxidation state of Co from Co2+ to a mixture of Co2+ and Co3+ . This induce structural changes in the electrocatalyst: CV combined with Rutherford backscattering indicate that after activation, for the best performing CoPi film, as much as 22% of all Co atoms become accessible to the electrolyte. Measurements of the electrochemical surface area (ECSA) reveal that during activation, the ECSA of this film increases by a factor 30. However, this increase in ECSA is strongly dependent on the initial composition of the CoPi films. While the aforementioned increase holds for CoPi films with a Co-to-P ratio of 1.6, for films with a Co-to-P ratio of 1.9 the ECSA only increases by a factor 3.6. We find that for all investigated Co-to-P ratios, after activation the electrochemical activity scales linearly with ECSA. Thus, the initial composition affects the activity of the catalyst indirectly by guiding the restructuring of the catalyst during potential cycling and the ECSA is a critical parameter in determining the activity of CoPi-based and related electrocatalysts. Thus, next to the well-established control over film properties ALD of CoPi enables to disclose the mechanisms behind its electrochemical activation.
 J. Ronge et al., Nanoscale Adv. 1, 4166 (2019).
V. Di Palma et al., Electrochem. Commun. 98, 73 (2019).
 V. Di Palma et al., J. Vac. Sci. Technol. 38,022416 (2020).
 R. Zhang et al., ACS Catal.11, 2774 (2021)View Supplemental Document (pdf)