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1. Real-time imaging of activation and degradation of carbon supported octahedral Pt–Ni alloy fuel cell catalysts at the nanoscale using in situ electrochemical liquid cell STEM

   https://doi.org/10.1039/c9ee01185d  

   Beermann, Vera ; Holtz, Megan E. ; Padgett, Elliot ; de Araujo, Jorge Ferreira ; Muller, David A. ; Strasser, Peter ( August 2019 , Energy & Environmental Science)

   Octahedrally shaped Pt–Ni alloy nanoparticles on carbon supports have demonstrated unprecedented electrocatalytic activity for the oxygen reduction reaction (ORR), sparking interest as catalysts for low-temperature fuel cell cathodes. However, deterioration of the octahedral shape that gives the catalyst its superior activity currently prohibits the use of shaped catalysts in fuel cell devices, while the structural dynamics of the overall catalyst degradation are largely unknown. We investigate the time-resolved degradation pathways of such a Pt–Ni alloy catalyst supported on carbon during cycling and startup/shutdown conditions using an in situ STEM electrochemical liquid cell, which allows us to track changes happening over seconds. Thereby we can precisely correlate the applied electrochemical potential with the microstructural response of the catalyst. We observe changes of the nanocatalysts’ structure, monitor particle motion and coalescence at potentials that corrode carbon, and investigate the dissolution and redeposition processes of the nanocatalyst under working conditions. Carbon support motion, particle motion, and particle coalescence were observed as the main microstructural responses to potential cycling and holds in regimes where carbon corrosion happens. Catalyst motion happened more severely during high potential holds and sudden potential changes than during cyclic potential sweeps, despite carbon corrosion happening during both, as suggested bymore »ex situ DEMS results. During an extremely high potential excursion, the shaped nanoparticles became mobile on the carbon support and agglomerated facet-to-facet within 10 seconds. These experiments suggest that startup/shutdown potential treatments may cause catalyst coarsening on a much shorter time scale than full collapse of the carbon support. Additionally, the varying degrees of attachment of particles on the carbon support indicates that there is a distribution of interaction strengths, which in the future should be optimized for shaped particles. We further track the dissolution of Ni nanoparticles and determine the dissolution rate as a function of time for an individual nanoparticle – which occurs over the course of a few potential cycles for each particle. This study provides new visual understanding of the fundamental structural dynamics of nanocatalysts during fuel cell operation and highlights the need for better catalyst-support anchoring and morphology for allowing these highly active shaped catalysts to become useful in PEM fuel cell applications.« less
2. Electrocatalytic Conversion of Furanic Compounds for Production of Valuable Chemicals

   Li, Wenzhen ; Chadderdon, Xiaotong ; Chadderdon, David ; Liu, Hengzhou ( August 2021 , 72nd International Society of Electrochemistry Meeting)

   Biomass is abundant, inexpensive and renewable, therefore, it is highly expected to play a significant role in our future energy and chemical landscapes. The US DOE has identified furanic compounds (furfural and 5-(hydroxymethyl)furfural (HMF)) as the top platform building-block chemicals that can be readily derived from biomass sources [1]. Electrocatalytic conversion of these furanic compounds is an emerging route for the sustainable production of valuable chemicals [2, 3]. In my presentation, I will first present our recent mechanistic study of electrochemical reduction of furfural through a combination of voltammetry, preparative electrolysis, thiol-electrode modifications, and kinetic isotope studies [4]. It is demonstrated that two distinct mechanisms are operable on metallic Cu electrodes in acidic electrolytes: (i) electrocatalytic hydrogenation (ECH) and (ii) direct electroreduction. The contributions of each mechanism to the observed product distribution are clarified by evaluating the requirement for direct chemical interactions with the electrode surface and the role of adsorbed hydrogen. Further analysis reveals that hydrogenation and hydrogenolysis products are generated by parallel ECH pathways. Understanding the underlying mechanisms enables the manipulation of furfural reduction by rationally tuning the electrode potential, electrolyte pH, and furfural concentration to promote selective formation of important bio-based polymer precursors and fuels. Next, Imore »will present electrocatalytic conversion of HMF to two biobased monomers in an H-type electrochemical cell [5]. HMF reduction (hydrogenation) to 2,5-bis(hydroxymethyl)furan (BHMF) was achieved under mild electrolyte conditions and ambient temperature using a Ag/C cathode. Meanwhile, HMF oxidation to 2,5-furandicarboxylic acid (FDCA) with ~100% efficiency was facilitated under the same conditions by a homogeneous nitroxyl radical redox mediator, together with an inexpensive carbon felt anode. The selectivity and efficiency for Ag-catalyzed BHMF formation were sensitive to cathode potential, owing to competition from HMF hydrodimerization reactions and water reduction (hydrogen evolution). Moreover, the carbon support of Ag/C was active for HMF reduction and contributed to undesired dimer/oligomer formation at strongly cathodic potentials. As a result, high BHMF selectivity and efficiency were only achieved within a narrow potential range near –1.3 V. Fortunately, the selectivity of redox-mediated HMF oxidation was insensitive to anode potential, thus allowing HMF hydrogenation and oxidation half reactions to be performed together in a single cathode-potential-controlled cell. Electrocatalytic HMF conversion in a paired cell achieved high molar yields of BHMF and FDCA, and nearly doubled electron efficiency compared to the unpaired cell. Finally, I will briefly introduce our recent work on the development of a three-electrode flow cell with an oxide-derived Ag (OD-Ag) cathode and catbon felt anode for paring elecatalytic oxidation and reduction of HMF. The flow cell has a remarkable cell voltage reduction from ~7.5 V to ~2.0 V by transferring the electrolysis from the H-type cell to the flow cell [6]. This represents a more than fourfold increase in the energy efficiency at the 10 mA operation. A combined faradaic efficiency of 163% was obtained to BHMF and FDCA. Alternatively, the anodic hydrogen oxidation reaction on platinum further reduced the cell voltage to only ~0.85 V at 10 mA operation. These paired processes have shown potential for integrating renewable electricity and carbon for distributed chemical manufacturing in the future.« less
3. Improved cell performance and sulphur tolerance using A-site substituted Sr2Fe1.4Ni0.1Mo0.5O6–δ anodes for solid-oxide fuel cells

   https://doi.org/10.1093/ce/zkac089  

   Li, Haixia ; Wang, Wanhua ; Lin, Jie ; Park, Ka-Young ; Lee, Taehee ; Heyden, Andreas ; Ding, Dong ; Chen, Fanglin ( March 2023 , Clean Energy)

   Solid-oxide fuel cells (SOFCs) offer great promise for producing electricity using a wide variety of fuels such as natural gas, coal gas and gasified carbonaceous solids; however, conventional nickel-based anodes face great challenges due to contaminants in readily available fuels, especially sulphur-containing compounds. Thus, the development of new anode materials that can suppress sulphur poisoning is crucial to the realization of fuel-flexible and cost-effective SOFCs. In this work, La0.1Sr1.9Fe1.4Ni0.1Mo0.5O6–δ (LSFNM) and Pr0.1Sr1.9Fe1.4Ni0.1Mo0.5O6–δ (PSFNM) materials have been synthesized using a sol-gel method in air and investigated as anode materials for SOFCs. Metallic nanoparticle-decorated ceramic anodes were obtained by the reduction of LSFNM and PSFNM in H2 at 850°C, forming a Ruddlesden–Popper oxide with exsolved FeNi3 bimetallic nanoparticles. The electrochemical performance of the Sr2Fe1.4Ni0.1Mo0.5O6–δ ceramic anode was greatly enhanced by La doping of A-sites, resulting in a 44% decrease in the polarization resistance in reducing atmosphere. The maximum power densities of Sr- and Mg-doped LaGaO3 (LSGM) (300 μm) electrolyte-supported single cells with LSFNM as the anode reached 1.371 W cm −2 in H2 and 1.306 W cm–2 in 50 ppm H2S–H2 at 850°C. Meanwhile, PSFNM showed improved sulphur tolerance, which could be fully recovered after six cycles from H2 to 50 ppmmore »H2S–H2 operation. This study indicates that LSFNM and PSFNM are promising high-performance anodes for SOFCs.

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4. Remarkably improved electrochemical hydrogen storage by multi-walled carbon nanotubes decorated with nanoporous bimetallic Fe–Ag/TiO ₂ nanoparticles

   https://doi.org/10.1039/C8DT03897J  

   Akbarzadeh, Raziyeh ; Ghaedi, Mehrorang ; Nasiri Kokhdan, Syamak ; Vashaee, Daryoosh ( January 2019 , Dalton Transactions)

   Nanoporous bimetallic Fe–Ag nanoparticles (NPs) were synthesized using a facile chemical reduction method and used to decorate the surface of multi-walled carbon nanotubes (MWCNTs) for hydrogen sorption and storage. The effect of TiO 2 nanoparticles on the hydrogen storage properties of Fe–Ag/CNTs was further studied in detail. For this purpose, several nanocomposites of nanoporous bimetallic Fe–Ag/TiO 2 nanoparticles with different amounts of bimetallic Fe–Ag NPs were prepared via a hydrothermal method. The hydrogen storage capacity of the as-prepared nanocomposites was studied using electrochemical methods. The Fe–Ag/TiO 2 /CNT nanocomposite with 0.04 M bimetallic Fe–Ag NPs showed the highest capacity for hydrogen storage, which was ∼5× higher than that of pristine MWCNTs. The maximum discharge capacity was 2931 mA h g −1 , corresponding to a 10.94 wt% hydrogen storage capacity. Furthermore, a 379% increase in discharge capacity was measured after 20 cycles. These results show that Fe–Ag/TiO 2 /CNT electrodes display superior cycling stability and high reversible capacity, which is attractive for battery applications.
5. Electrocatalytic Hydrogenation of Furanic Compounds: From Mechanism Study to Paired Electrolyzer Design

   Li, Wenzhen ; Liu, Hengzhou ; Chadderdon, Xiaotong ; Chadderdon, David ; Lee, Ting-Han ; Cochran, Eric ( August 2021 , 262nd ACS National Meeting)

   Biomass is abundant, inexpensive and renewable, therefore, it is highly expected to play a significant role in our future energy and chemical landscapes. The US DOE has identified furanic compounds (furfural and 5-(hydroxymethyl)furfural (HMF)) as the top platform building-block chemicals that can be readily derived from biomass sources [1]. Electrocatalytic conversion of these furanic compounds is an emerging route for the sustainable production of valuable chemicals [2, 3]. In my presentation, I will first present our recent mechanistic study of electrocatlytic hydrogenation (ECH) of furfural through a combination of voltammetry, preparative electrolysis, thiol-electrode modifications, and kinetic isotope studies [4]. It is demonstrated that two distinct mechanisms are operable on metallic Cu electrodes in acidic electrolytes: (i) electrocatalytic hydrogenation (ECH) and (ii) direct electroreduction. The contributions of each mechanism to the observed product distribution are clarified by evaluating the requirement for direct chemical interactions with the electrode surface and the role of adsorbed hydrogen. Further analysis reveals that hydrogenation and hydrogenolysis products are generated by parallel ECH pathways. Understanding the underlying mechanisms enables the manipulation of furfural reduction by rationally tuning the electrode potential, electrolyte pH, and furfural concentration to promote selective formation of important bio-based polymer precursors and fuels Wemore »further studied the mechanisms on the Pb electrode, based on the potential regulated ECH and ER products. Isotopic incorporation studies and electrokinetics have confirmed ECH process to alcohol and alkyl product followed different pathways: alcohol was generated from Langmuir Hinshelwood step through surface-bound furfural and hydrogen, which is sensitive to surface structures. In contrast, alkyl product was formed through an Eley–Rideal step via surface-bound furfural and the inner-sphere protons. By modifying the electrode/electrolyte interface, we have elucidated H2O and H3O+ matters in forming alcohol and alkyl products, respectively. Dynamic oscillation studies and electron paramagnetic resonance (EPR) finally confirmed that the alcohol and dimer products shared the same intermediate. The dimer was formed through the intermediate desorption from the surface to form radicals and the self-coupling of two radicals at the bulk electrolyte. Next, I will present electrocatalytic conversion of HMF to two biobased monomers in an H-type electrochemical cell [5]. HMF reduction (hydrogenation) to 2,5-bis(hydroxymethyl)furan (BHMF) was achieved under mild electrolyte conditions and ambient temperature using a Ag/C cathode. Meanwhile, HMF oxidation to 2,5-furandicarboxylic acid (FDCA) with ~100% efficiency was facilitated under the same conditions by a homogeneous nitroxyl radical redox mediator. We recently developed a three-electrode flow cell with an oxide-derived Ag (OD-Ag) cathode and catbon felt anode for paring elecatalytic oxidation and reduction of HMF [6]. The flow cell has a remarkably low cell voltage: from ~7.5 V to ~2.0 V by transferring the electrolysis from the H-type cell to the flow cell. This represents a more than fourfold increase in the energy efficiency at the 10 mA operation. A combined faradaic efficiency of 163% was obtained to BHMF and FDCA. Alternatively, the anodic hydrogen oxidation reaction on platinum further reduced the cell voltage to only ~0.85 V at 10 mA operation. These paired processes have shown potential for integrating renewable electricity and carbon for distributed chemical manufacturing in the future.« less