Engineering topics
Serov, Alexey
Publications and source records attributed to Serov, Alexey.
Fabrication, morphology, and performance of fiber mat cathode MEAs with a MOF-based PGM-free catalyst
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Machine learning-guided design of direct methanol fuel cells with a platinum group metal-free cathode
Direct methanol fuel cells (DMFCs) offer a promising solution for clean electricity generation, particularly in small electronics and remote auxiliary power units. However, optimizing their efficiency and performance is challenging due to the complex interactions between various factors. Here, we present a novel approach that integrates experiments with machine learning to model and predict the performance of these fuel cells using atomically dispersed platinum group metal (PGM)-free catalysts at the cathode. Further, our machine learning models, trained on diverse input parameters, allow for the comprehensive optimization of DMFC performance prior to fabrication and testing. Through extensive experimental validation, we demonstrate that this data-driven approach accurately predicts key performance metrics, such as maximum power output and polarization curves. By combining our models with interpretable game-theory methods, we provide deep insights into the factors governing fuel cell performance, ultimately paving the way for the design of scalable and efficient DMFC technologies.
In-situ polarization modulation IRRAS investigation of ammonia electrooxidation on Pt-Ir and Pt-Ru nanoparticles prepared on engineered catalyst supports
The catalytic activity and surface reactivity of monometallic Pt and bimetallic Pt-Ir and Pt-Ru nanoparticles, supported on two distinct Engineered Catalyst Supports (ECSs), were investigated for the Ammonia Electrooxidation Reaction (AmER) in alkaline media. XRD measurements confirmed alloy formation between Pt-Ir and Pt-Ru nanoparticles, as indicated by the shift of the (111) reflection to higher 2θ values. Cyclic voltammetry, linear sweep voltammetry, and chronoamperometry experiments were conducted to assess the catalytic activity of the Pt, Pt-Ir, and Pt-Ru electrocatalysts. All bimetallic catalysts exhibited lower onset potentials compared to Pt. The differing Tafel slopes between Pt (74 mV dec⁻¹), Pt-Ir (152 mV dec⁻¹), and Pt-Ru (118–197 mV dec⁻¹) suggest that alloying Pt with Ir or Ru alters the reaction mechanisms. Furthermore, the bimetallic Pt-Ir and Pt-Ru catalysts demonstrated greater tolerance for concentrated ammonia solutions relative to Pt. In-situ Polarization Modulation Infrared Reflection Absorption Spectroscopy (PM-IRRAS) provided insights into the formation of N-H species, azide anions (N₃⁻), and N-O compounds. For the Pt-Ru catalyst, an additional peak around ~3600 cm⁻¹ was observed, corresponding to OH⁻ species. The PM-IRRAS results align with the Gerischer–Mauerer mechanism, indicating that partially dehydrogenated ammonia adsorbates act as active intermediates in the oxidation of ammonia over Pt-Ir and Pt-Ru catalysts.
Is Pt dissolution a concern from the counter electrode in electrochemical oxygen evolution reaction?
The Pt metal and its oxides dissolution from the counter electrode (CE, in hydrogen evolution reaction (HER)) has been suspected to affect the non-noble metal catalysts toward oxygen evolution reaction (OER). However, little effort has been devoted to this concern, and this work aims to determine the effect. The influence of electrolytes (H 2 SO 4 and NaOH) and Pt CE (acid-treated and pristine) on the Pt dissolution and membrane separations (Nafion and PiperION) on preventing Pt species migration were evaluated. Here, the results indicate only 11.2 ppb Pt from the cathodic electrolyte with Nafion 211 and 5 M NaOH electrolyte is observed, and no Pt is found from all other samples with acid-treated Pt CE. Regarding pristine Pt CE, 0.4 and 4.4 ppb Pt are observed from 0.5 M H 2 SO 4 and 5 M NaOH electrolytes, respectively. The findings in this work include: (1) Nafion membrane can effectively prevent the migration of Pt species from the cathode to the anode side; (2) a simple acid treatment of Pt could minimize the Pt dissolution into the acid electrolyte while showing an opposite role in the alkaline electrolyte; (3) the Pt dissolution from all experiments is minor, indicating Pt is a suitable CE for OER.
Second Target Station Project: STS Cross-Directorate Workshop on Hydrogen Fuel
Hydrogen, particularly green hydrogen produced through electrolysis using renewable energy, is poised to play a critical role in decarbonizing the global economy. Its ability to address the intermittency of renewable energy sources and decarbonize hard-to-electrify sectors positions it as a vital component of a sustainable energy future. Interest in hydrogen as a clean energy carrier is in a decade of unprecedented growth, with dozens of countries having released national hydrogen strategies contributing to a global hydrogen economy. In 2021, the Department of Energy (DOE) announced the Hydrogen Shot, the first of the Energy Earthshot Initiatives, which aims to lower the cost of clean hydrogen to $\$$1/kg by 2031. This initiative was followed by a considerable increase in funding for hydrogen technologies through the Bipartisan Infrastructure Law (BIL), with $\$$18 billion recently announced for regional demonstration projects (Hydrogen Hubs) and another $\$$11.5 billion aimed at research and development of electrolyzers, fuel cells, manufacturing, and recycling. The 2023 U.S. National Clean Hydrogen Strategy and Roadmap identifies the cost of clean hydrogen as a critical challenge for achieving economic scale. This includes the cost of hydrogen production by electrolysis, delivery and dispensing, onboard storage, and end-use technologies like fuel cells. Fundamental research and development into catalysts, component architectures, and material durability are critical to lower the costs of these vital technologies aimed at achieving a net-zero carbon emission economy by 2050.
H2NEW: Hydrogen (H2) from Next-Generation Electrolyzers of Water LTE Task 9: Liquid Alkaline
This presentation summarizes H2NEW consortium research on liquid alkaline electrolysis (Task 9).
H2NEW: Hydrogen (H2) from Next-generation Electrolyzers of Water - H2NEW LTE: Manufacturing, Scale-Up, and Integration
Summarizes H2NEWs research in Tasks 3a and 3b.
LTE-P-13 3-Electrode Cell for Screening OER/HER Electrocatalyst Activity
Procedure for screening HER/OER electrocatalysts using fully immersed electrodes covered with electrocatalyst. Optimized for usage in alkaline solutions with high loading of electrocatalysts up to 4 mg/cm2. Can be used for both PGM and PGM-free catalysts.
Directing CO 2 electroreduction pathways for selective C 2 product formation using single-site doped copper catalysts
Manipulating the selectivity-determining step in post-C–C coupling is crucial for enhancing C 2 product specificity during electrocatalytic CO 2 reduction, complementing efforts to boost rate-determining step kinetics. Here we highlight the role of single-site noble metal dopants on Cu surfaces in influencing C–O bond dissociation in an oxygen-bound selectivity-determining intermediate, steering post-C–C coupling toward ethylene versus ethanol. Integrating theoretical and experimental analyses, we demonstrate that the oxygen binding strength of the Cu surface controls the favorability of C–O bond scission, thus tuning the selectivity ratio of ethylene-to-ethanol. The Rh-doped Cu catalyst with optimal oxygen binding energy achieves a Faradaic efficiency toward ethylene of 61.2% and an ethylene-to-ethanol Faradaic efficiency ratio of 4.51 at –0.66 V versus RHE (reversible hydrogen electrode). Integrating control of both rate-determining and selectivity-determining steps further raises ethylene Faradaic efficiency to 68.8% at 1.47 A cm -2 in a tandem electrode. Our insights guide the rational design of Cu-based catalysts for selective CO 2 electroreduction to a single C 2 product.
Spectroscopic Characterization of Highly Active Fe–N–C Oxygen Reduction Catalysts and Discovery of Strong Interaction with Nafion Ionomer
Scaling up clean-energy applications necessitates the development of platinum group metal (PGM)-free fuel cell electrocatalysts with high activity, stability, and low cost. Here, X-ray absorption (XAS) at the Fe K-edge and Fe K β X-ray emission (XES) spectroscopies were used to study the electronic structure of Fe centers in highly active Fe–N–C oxygen reduction catalysts with significant commercial potential. X-ray absorption near-edge structure (XANES) analysis has shown that the majority (>95%) of Fe centers are in the Fe 3+ oxidation state, while extended X-ray absorption fine structure (EXAFS) detected a mixture of single site Fe–N 4 centers (>95%) and centers with short (~2.5 Å) Fe–Fe interactions of Fe metal and/or Fe-carbide nanoparticles (<5%) featuring the Fe o oxidation state. Surprisingly, addition of Nafion, the most widely used ionomer, resulted in pronounced changes in the XAS spectra, consistent with a strong catalyst–ionomer interaction where long Fe–Fe interactions at ~3.1 Å were shown to be a feature of Fe 3+ ions bound with the Nafion. We conclude that exposure to Nafion during the device formulation has a different effect from the aggressive acid leaching typically used in the preparation of Fe–N–C catalysts. Furthermore, it was hypothesized that the polymer interacts with single sites’ Fe 3+ centers, as well as with graphene layers protecting the Fe o nanoparticles, and extracts some Fe ions into the Nafion matrix.
Comparative techno-economic and life-cycle analysis of precious versus non-precious metal electrocatalysts: the case of PEM fuel cell cathodes
Fe–N–C catalyst production outperforms Pt/C from an enviro-economic viewpoint, but further Fe–N–C activity development is required before deployment in PEMFCs.
Significance of slight ambient temperature variation on the electrocatalyst performance toward oxygen evolution reaction
Hundreds of oxygen evolution reaction (OER) electrocatalysts have been developed over the past few decades, and their performances are evaluated and compared at ambient temperature. However, the effect of ambient temperature variation on OER electrocatalyst performance has received less attention, which may play a remarkable role in the electrocatalytic activity. In this work, we systematically investigated the influence of ambient temperature variation on electrocatalyst performance toward OER. The results show that the slight ambient temperature variation has a significant effect on OER catalyst performance based on the changes of overpotential (10mAcm -2 ) and Tafel slope. Both remarkable chances are observed on transition metal (Ni) and noble metal (IrO 2 ) electrocatalysts, and the overpotentials decrease around 81 mV with a temperature increase by 20°C (from 10° to 30°C) for both Ni and IrO 2 electrocatalysts with the Tafel slope drops of 36.9 and 29.5 mV dec -1 , respectively. Further, a similar trend is also found in the electrochemically active surface (ECSA) normalized performance and the charge transfer resistance. This study demonstrates that reporting the actual operating temperature for OER is not only recommended but also necessary to evaluate and compare electrocatalyst activities from different materials systems properly, and neglecting the ambient temperature variation effect can highly mislead conclusions.
Highly durable platinum group metal-free catalyst fiber cathode MEAs for proton exchange membrane fuel cells
For this work, Fe-based platinum group metal (PGM)-free catalysts were incorporated into electrospun fiber mat or powder cathode membrane-electrode-assemblies (MEAs) with a Nafion 211 membrane and a Pt/C powder anode. Fabrication and characterization tests were performed on MEAs with: (1) a conventional powder cathode with a neat Nafion binder, (2) a fiber mat cathode with a Nafion/polyethylene oxide (PEO) binder, where PEO was extracted before MEA testing, (3) a powder cathode with a blended binder of Nafion and polyvinylidene fluoride (PVDF), and (4) a series of fiber mat cathodes with different Nafion/PVDF binder weight ratios. Cathode degradation occurred, with a loss in power output, in MEAs with a neat Nafion powder cathode or with a Nafion fiber cathode. In contrast, little or no power loss was observed for powder or fiber cathodes when the binder was a blend of Nafion and PVDF. The presence of hydrophobic PVDF drove water and electrogenerated peroxide out of the cathode, away from catalyst particles, which improved cathode durability, but PVDF also decreased the binder conductivity and slowed oxygen reduction kinetics, resulting in lower power densities. A 75:25 w:w Nafion:PVDF fiber cathode MEA was the best compromise for maximizing power and minimizing catalyst degradation. For such a cathode, with a PGM-free cathode catalyst loading of 3.0 mg cm –2 , a power density of 88 mW cm –2 at 0.5 V, 80 °C, and 200 kPa abs pressure was maintained for 80 h of continuous operation.
Probing individual single atom electrocatalyst sites by advanced analytical scanning transmission electron microscopy
Single atom electrocatalysts (SAEs) are promising next-generation materials for promoting a variety of important reactions, such as the oxygen reduction, nitrogen reduction, and CO 2 reduction reactions. While bulk characterization techniques such as X-ray absorption spectroscopy and Mössbauer spectroscopy have significantly enhanced our understanding of these catalysts, direct probing of individual single metal atom sites at the atomic scale is necessary to understand local variations in the properties of these sites and accelerate design and synthesis of improved SAEs. Aberration-corrected scanning transmission electron microscopy (STEM) has become a powerful tool for providing this type of atomic-scale information about SAE metal sites. These sites are typically unstable under the electron beam, however, which, in combination with conventional acquisition methods and detectors, has limited the type and quantity of information obtainable by spectroscopic STEM techniques. Here, we map multiple individual SAE metal sites in a nitrogen-doped carbon containing atomically dispersed Fe and Re (FeReNC) at the atomic scale by direct electron detection electron energy-loss spectroscopy (EELS). Direct electron detection provides an improved signal-to-noise ratio over conventional scintillator-based detectors and enables detection and real space localization of weak signals. In addition, we demonstrate an automated method for identification of metal atom positions, placement of the probe on these sites, and simultaneous EELS and energy dispersive X-ray spectroscopic (EDS) signal acquisition. This simultaneous acquisition of EELS and EDS provides access to the composition and bonding of a wide range of SAE metal sites. In this study, focusing the probe directly on the metal sites also increases the relevant data acquisition rate by more than an order of magnitude over two-dimensional mapping, enabling improved statistical measurements of site properties. The versatility, sensitivity, and speed that these techniques provide enhances our ability to probe the local elemental and chemical environment of a large number of individual SAE metal site structures at the atomic scale, enabling an improved understanding of the variations in the local properties of these electrocatalysts to be gained. As a result, significantly increased information about individual metal sites will be available to future electrochemical studies through these techniques, accelerating the development of advanced SAEs.