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Journal articleCannon CG, Klusener PAA, Brandon NP, et al., 2024,
Electrochemical and spectroscopic characterisation of organic molecules with high positive redox potentials for energy storage in aqueous flow cells
, Energy Advances, Vol: 3, Pages: 2587-2596We show that a number of ubiquitous organic molecules used as redox mediators and chemically sensing species can be used as positive couples in electrochemical energy storage. Air and acid stable organic molecules were tested in aqueous acid electrolytes and employed as the positive electrolyte in H2-organic electrochemical cells. The dissolved organic species were characterised in-operando using UV-vis spectroscopy. N,N,N′,N′-tetramethylbenzidine was found to be a stable and reversible redox organic molecule, with a 2 e− molecule−1 capacity and a 0.83 V cell potential. N-Oxyl species were also tested in purely aqueous acidic flow battery electrolytes. A H2-violuric acid cell produced a reversible potential of 1.16 V and demonstrated promising redox flow cell cycling performance.
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Journal articleKasuk K-A, Nerut J, Grozovski V, et al., 2024,
Design and impact: navigating the electrochemical characterization methods for supported catalysts
, ACS Catalysis, Vol: 14, Pages: 11949-11966, ISSN: 2155-5435This review will investigate the impact of electrochemical characterization method design choices on intrinsic catalyst activity measurements by predominantly using the oxygen reduction reaction (ORR) on supported catalysts as a model reaction. The wider use of hydrogen for transportation or electrical grid stabilization requires improvements in proton exchange membrane fuel cell (PEMFC) performance. One of the areas for improvement is the (ORR) catalyst efficiency and durability. Research and development of the traditional platinum-based catalysts have commonly been performed using rotating disk electrodes (RDE), rotating ring disk electrodes (RRDE), and membrane electrode assemblies (MEAs). However, the mass transport conditions of RDE and RRDE limit their usefulness in characterizing supported catalysts at high current densities, and MEA characterizations can be complex, lengthy, and costly. Ultramicroelectrode with a catalyst-filled cavity addresses some of these problems, but with limited success. Due to the properties discussed in this review, the recent floating electrode (FE) and the gas diffusion electrode (GDE) methods offer additional capabilities in the electrochemical characterization process. With the FE technique, the intrinsic activity of catalysts for ORR can be investigated, leading to a better understanding of the ORR mechanism through more reliable experimental data from application-relevant high-mass transport conditions. The GDEs are helpful bridging tools between RDE and MEA experiments, simplifying the fuel cell and electrolyzer manufacturing and operating optimization process.
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Journal articleKucernak AR, Wang H, Lin X, 2024,
Avoid using phosphate buffered saline (PBS) as an electrolyte for accurate OER studies
, ACS Energy Letters, Vol: 9, Pages: 3939-3946, ISSN: 2380-8195 -
Journal articleZhang W, Liu C, Kucernak A, et al., 2024,
Synergizing single-atom and carbon-encapsulated nanoparticles of Fe for efficient oxygen reduction and durable Zn-air batteries
, ACS Applied Energy Materials, Vol: 7, Pages: 5398-5407, ISSN: 2574-0962Overcoming the sluggish kinetics of the oxygen reduction reaction (ORR) remains a critical challenge for Zn–air batteries. Fe–N/C catalysts have emerged as promising alternatives to precious Pt-based materials. Herein, we report the design and synthesis of carbon-encapsulated Fe nanoparticles decorated Fe–N/C (denoted as FeNPs@Fe–N/C) via controlled pyrolysis. The FeNPs@Fe–N/C catalyst exhibits excellent ORR performance in alkaline media with a half-wave potential (E1/2) of 0.893 VRHE. The strategic integration of carbon-encapsulated Fe nanoparticles substantially improves the catalytic activity of Fe–N/C catalysts. The FeNPs@Fe–N/C as the Zn–air battery cathode delivers an impressive peak power density of 175.7 mW cm–2 and excellent stability over 500 h, surpassing the Pt/C benchmarks. Density functional theory calculations reveal that the carbon-encapsulated Fe nanoparticles facilitate electron transfer to the catalytic site by modulating the d-band center, thereby boosting the ORR activity. This research paves the way for future design strategies integrating nanoparticles and single atoms for efficient electrocatalysis.
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Journal articleCannon CG, Klusener PAA, Petit LF, et al., 2024,
Methylene blue in a high-performance hydrogen-organic rechargeable fuel cell
, ACS Applied Energy Materials, Vol: 7, Pages: 2080-2087, ISSN: 2574-0962A hydrogen-organic hybrid flow battery (FB) has been developed using methylene blue (MB) in an aqueous acid electrolyte with a theoretical positive electrolyte energy storage capacity of 65.4 A h L–1. MB paired with the versatile H2/H+ redox couple at the negative electrode forms the H2–MB rechargeable fuel cell, with no loss in capacity (5 sig. figures) over 30 100% discharge cycles of galvanostatic cycling at 50 mA cm–2, which shows excellent stability. A peak power density of 238 mW cm–2 has also been demonstrated by utilizing 1.0 M MB electrolyte. This represents a type of scalable electrochemical energy storage system with favorable properties in terms of material cost, stability, crossover management, and energy and power density, overcoming many typical limitations of organic-based redox FBs.
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Journal articleSarmah S, Kakati BK, Kucernak ARJ, et al., 2024,
Fabrication of hierarchically structured supercapacitor using N and S co‐doped activated carbons derived from Samanea saman biomass
, Energy Storage, Vol: 6, ISSN: 2578-4862Biomass-derived activated carbons have emerged as highly promising electrode materials for electrochemical supercapacitors due to their remarkable characteristics, such as high surface area, cost-effectiveness, and environmental sustainability. This study focuses on the synthesis of N and S co-doped activated carbons (NSACs) from Samanea saman (rain tree) biomass through a combined hydrothermal-chemical activation process. Leveraging the advantageous hierarchical structure inherent to biological sources, the resulting NSACs demonstrate enhanced ion transport, leading to remarkable capacity and power density. The NSACs synthesized by pyrolysis at 800°C exhibit exceptional specific capacitances of 434 and 401 Fg−1 in Na2SO4 and H2SO4 electrolytes, respectively, in a three-electrode system. The capacitance retention of the same NSAC was found to be 77.6% at a corresponding current density of 10 Ag−1 in H2SO4 electrolyte. This outstanding electrochemical performance can be attributed to the material's high specific surface area (1402 m2 g−1), well-defined hierarchical porous structure, and a substantial degree of graphitization. A symmetric supercapacitor constructed using the synthesized NSACs demonstrates notable energy densities of 14.5 and 25.0 Whkg−1, with H2SO4 and Na2SO4 electrolytes respectively. Furthermore, the symmetric supercapacitor exhibits excellent stability, retaining 91.3%–94.3% of its capacity after 5000 consecutive GCD cycles with H2SO4 and Na2SO4 electrolytes, respectively. The synergistic combination of the unique characteristics of NSACs derived from Samanea saman biomass presents a promising avenue for the development of high-performance and environment-friendly supercapacitors.
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Journal articleZhang W, Yi S, Yu Y, et al., 2024,
Fe-based dual-atom catalysts for the oxygen reduction reaction
, Journal of Materials Chemistry A, Vol: 12, Pages: 87-112, ISSN: 2050-7488The oxygen reduction reaction (ORR) is widely employed at the cathode of next-generation energy devices such as fuel cells and metal–air batteries to accommodate electrons produced by anode reactions. The development of highly efficient and durable electrocatalysts for the ORR has been constrained by the involvement of multiple oxygen-containing intermediates and their scaling relations. Recently, dual-atom catalysts (DACs) supported on carbon materials have been intensively studied as ORR electrocatalysts due to their potential to precisely tune the adsorption/reactive performance of each metal site. In particular, Fe-based DACs exhibit outstanding ORR activities, holding great promise as substitutes for state-of-the-art Pt-based catalysts. However, the adjustment of the microenvironment of metal sites, loading density, scaling relation limitation, and excessively strong adsorption energy pose limitations on the practical applications of Fe-based DACs. To promote studies of Fe-based DACs, we summarize the current research status in this review by focusing on (1) the fundamental of the ORR and effects of Fe-based DACs, (2) common synthesis strategies of Fe-based DACs, and (3) ORR performance evaluations of Fe-based DACs. Additionally, this review provides our viewpoint on future directions and possible strategies to design catalysts for further optimization of the ORR.
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Journal articleNguyen S, Anthony DB, Katafiasz T, et al., 2024,
Manufacture and characterisation of a structural supercapacitor demonstrator
, Composites Science and Technology, Vol: 245, ISSN: 0266-3538Structural power composites, a class of multifunctional materials, may facilitate lightweighting and accelerate widespread electrification of sustainable transportation. In the example considered in this paper, structural power composite fuselage components could provide power to open aircraft doors in an emergency and thus reduce or eliminate the mass and volume needed for supercapacitors currently mounted on the doors. To demonstrate this concept, an 80 cm long multifunctional composite C-section beam was designed and manufactured, which powered the opening and closing of a desktop-scale composite aircraft door. Twelve structural supercapacitor cells were made, each 30 cm × 15 cm × 0.5 mm, and two stacks of four cells were integrated into the web of the beam by interleaving and encasing them with low-temperature-cure woven carbon fibre/epoxy prepreg. This article culminates by considering the engineering challenges that need to be addressed to realise structural power composite components, particularly in an aerospace context.
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Journal articleJackson C, Smith G, Kucernak AR, 2024,
Deblending and purification of hydrogen from natural gas mixtures using the electrochemical hydrogen pump
, International Journal of Hydrogen Energy, Vol: 52, Pages: 816-826, ISSN: 0360-3199This work evaluates the use of Electrochemical Hydrogen Pumps (EHPs) for H2 deblending from natural gas (NG) grids for use in H2 refuelling stations which need to meet the high ISO 14687-2019-D purity standards. Concentrations of 20, 50 and 80% H2 in either CH4 or NG were tested at current densities of 0.2 and 0.3 A cm−2. Moreover, the impact of adding O2 and O2/O3 bleeds to the inlet EHP feeds were investigated for their effectiveness in mitigating poisoning of the EHP catalysts. The CH4 concentration requirement of <100 μmol mol−1 was met using NG at 0.3 A cm−2 (20–80% H2) or with 80% H2 at 0.2 A cm−2; however, the CO2 limit of <2 μmol mol−1 could not be met, due to the high permeability of CO2 in Nafion®. Moreover, the other hydrocarbon concentrations limit of <2 μmol mol−1 could be met when operating with 80% H2 in NG at 0.3 A cm−2. Additionally, the EHP demonstrated low energy consumption, particularly at 0.2 A cm−2 ranging from 3.5 to 12.5 kWh kgH2−1.
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Journal articleHardisty SS, Lin X, Kucernak ARJ, et al., 2024,
Single-atom Pt on carbon nanotubes for selective electrocatalysis
, Carbon Energy, Vol: 6, ISSN: 2637-9368Utilizing supported single atoms as catalysts presents an opportunity to reduce the usage of critical raw materials such as platinum, which are essential for electrochemical reactions such as hydrogen oxidation reaction (HOR). Herein, we describe the synthesis of a Pt single electrocatalyst inside single-walled carbon nanotubes (SWCNTs) via a redox reaction. Characterizations via electron microscopy, X-ray photoelectron microscopy, and X-ray absorption spectroscopy show the single-atom nature of the Pt. The electrochemical behavior of the sample to hydrogen and oxygen was investigated using the advanced floating electrode technique, which minimizes mass transport limitations and gives a thorough insight into the activity of the electrocatalyst. The single-atom samples showed higher HOR activity than state-of-the-art 30% Pt/C while almost no oxygen reduction reaction activity in the proton exchange membrane fuel cell operating range. The selective activity toward HOR arose as the main fingerprint of the catalyst confinement in the SWCNTs.
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Journal articleJackson C, Metaxas M, Dawson J, et al., 2023,
Nanostructured catalyst layer allowing production of ultralow loading electrodes for polymer electrolyte membrane fuel cells with superior performance
, ACS Applied Energy Materials, Vol: 6, Pages: 12296-12306, ISSN: 2574-0962This study introduces a simple method to produce ultralow loading catalyst-coated membrane electrodes, with an integrated carbon “nanoporous layer”, for use in polymer electrolyte membrane fuel cells or other electrochemical devices. This approach allows fabrication of electrodes with loadings down to 5.2 μgPt cm–2 on the anode and cathode (total 10.4 μgPt cm–2, Pt3Zn/C catalyst) in a controlled, uniform, and reproducible manner. These layers achieve high utilization of the catalyst as measured through electrochemical surface area and mass specific activities. Electrodes composed of Pt/C, PtNi/C, Pt3Co/C, and Pt3Zn/C catalysts containing 5.2–7.1 μgPt cm–2 have been fabricated and tested. These electrodes showed an impressive performance of 111 ± 8 A mgPt–1 at 0.65 V on Pt3Co/C with a power density of 31 ± 2 kW gPt,total–1, about double that of the best previous literature electrodes under the same operating conditions. The performance appears apparently mass transport free and dominated by electrokinetics over a very wide potential range, and thus, these are ideal systems to study oxygen electrokinetics within the fuel cell environment. The improved performance is associated with reduced “contact resistance” and more specifically a reduction in the resistance to lateral current flow in the catalyst layer. Analytical expressions for the effect illuminate approaches to improve electrode design for electrochemical devices in which catalyst utilization is key.
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Journal articleZhang G, Kucernak A, 2023,
Time-resolved product observation for CO2 electroreduction using synchronised electrochemistry-mass spectrometry with soft ionisation (sEC-MS-SI).
, Angewandte Chemie International Edition, Vol: 62, ISSN: 1433-7851The mechanistic understanding of electrochemical CO2 reduction reaction (CO2 RR) requires a rapid and accurate characterisation of product distribution to unravel the activity and selectivity, which is yet hampered by the lack of advanced correlative approaches. Here, we present the time-resolved identification of CO2 RR products by using the synchronised electrochemistry-mass spectrometry (sEC-MS). Transients in product formation can be readily captured in relation to electrochemical conditions. Moreover, a soft ionisation (SI) strategy is developed in MS for the direct observation of CO, immune to the interference of CO2 fragments. With the sEC-MS-SI, the kinetic information, such as Tafel slopes and onset potentials, for a myriad of CO2 RR products are revealed and we show the hysteresis seen for the evolution of some species may originate from the potential-driven changes in surface coverage of intermediates. This work provides a real-time picture of the dynamic formation of CO2 RR products.
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Journal articleSarma SC, Barrio J, Bagger A, et al., 2023,
Reaching the fundamental limitation in CO2 reduction to CO with single atom catalysts
, Advanced Functional Materials, Vol: 33, ISSN: 1616-301XThe electrochemical CO2 reduction reaction (CO2RR) to value-added chemicals with renewable electricity is a promising method to decarbonize parts of the chemical industry. Recently, single metal atoms in nitrogen-doped carbon (MNC) have emerged as potential electrocatalysts for CO2RR to CO with high activity and faradaic efficiency, although the reaction limitation for CO2RR to CO is unclear. To understand the comparison of intrinsic activity of different MNCs, two catalysts are synthesized through a decoupled two-step synthesis approach of high temperature pyrolysis and low temperature metalation (Fe or Ni). The highly meso-porous structure results in the highest reported electrochemical active site utilization based on in situ nitrite stripping; up to 59±6% for NiNC. Ex situ X-ray absorption spectroscopy (XAS) confirms the penta-coordinated nature of the active sites. The catalysts are amongst the most active in the literature for CO2 reduction to CO. The density functional theory calculations (DFT) show that their binding to the reaction intermediates approximates to that of Au surfaces. However, it is found that the turnover frequencies (TOFs) of the most active catalysts for CO evolution converge, suggesting a fundamental ceiling to the catalytic rates.
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Journal articleCannon CG, Klusener PAA, Brandon NP, et al., 2023,
Aqueous redox flow batteries: small organic molecules for the positive electrolyte species
, ChemSusChem: chemistry and sustainability, energy and materials, Vol: 16, ISSN: 1864-5631There are a number of critical requirements for electrolytes in aqueous redox flow batteries. This paper reviews organic molecules that have been used as the redox-active electrolyte for the positive cell reaction in aqueous redox flow batteries. These organic compounds are centred around different organic redox active moieties such as the aminoxyl radical (TEMPO and N-hydroxyphthalimide), carbonyl (quinones and biphenols), amine (e.g indigo carmine), ether and thioether (e.g. thianthrene) groups. We consider the key metrics that can be used to assess their performance: redox potential, solubility, redox kinetics, diffusivity, operating pH, stability, and cost. We develop a new figure of merit - the theoretical intrinsic power density - which combines the first four of the aforementioned metrics to allow ranking of different redox couples on just one side of the battery. The organic electrolytes show theoretical intrinsic power densities which are 2-100 times larger than that of the VO2+/VO2+ couple, with TEMPO-derivatives showing the highest performance. Finally, we survey organic positive electrolytes in the literature on the basis of their redox-active moieties and the aforementioned figure of merit.
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Journal articleSarma SC, Barrio J, Gong M, et al., 2023,
Atomically dispersed Fe in a C2N-derived matrix for the reduction of CO2 to CO
, Electrochimica Acta, Vol: 463, ISSN: 0013-4686Carbon-supported single metal atoms coordinated to nitrogen have recently emerged as efficient electrocatalysts for the electrochemical CO2 reduction reaction (CO2RR) to CO; although the presence of aggregated metallic species can decrease Faradaic efficiency, catalyst utilization and promote the hydrogen evolution reaction. In this work, we employ our recent synthetic protocol for producing single and dual Fe atoms in a high surface area C2N-derived nitrogen-doped carbon and test the catalysts for CO2 reduction. The higher resolution of the X-ray absorption spectroscopy that we employed herein, relative to our previous report, allowed us to more accurately pinpoint the dominant site as pentacoordinated Fe single atoms. The material displays high active site utilization of 25.1 ± 1.2% (based on in situ nitrite stripping experiments). Additionally, a Faradaic efficiency of 98% for the CO2RR to CO was obtained, with a turnover frequency of 2.5 e− site−1 s−1, at -0.56 V vs a reversible hydrogen electrode (RHE); on par with state-of-the-art Au catalysts.
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Journal articleShi Z, Zhang X, Lin X, et al., 2023,
Phase-dependent growth of Pt on MoS2 for highly efficient H2 evolution
, Nature, Vol: 621, Pages: 300-305, ISSN: 0028-0836Crystal phase is a key factor determining the properties, and hence functions, of two-dimensional transition-metal dichalcogenides (TMDs)1,2. The TMD materials, explored for diverse applications3-8, commonly serve as templates for constructing nanomaterials3,9 and supported metal catalysts4,6-8. However, how the TMD crystal phase affects the growth of the secondary material is poorly understood, although relevant, particularly for catalyst development. In the case of Pt nanoparticles on two-dimensional MoS2 nanosheets used as electrocatalysts for the hydrogen evolution reaction7, only about two thirds of Pt nanoparticles were epitaxially grown on the MoS2 template composed of the metallic/semimetallic 1T/1T' phase but with thermodynamically stable and poorly conducting 2H phase mixed in. Here we report the production of MoS2 nanosheets with high phase purity and show that the 2H-phase templates facilitate the epitaxial growth of Pt nanoparticles, whereas the 1T' phase supports single-atomically dispersed Pt (s-Pt) atoms with Pt loading up to 10 wt%. We find that the Pt atoms in this s-Pt/1T'-MoS2 system occupy three distinct sites, with density functional theory calculations indicating for Pt atoms located atop of Mo atoms a hydrogen adsorption free energy of close to zero. This probably contributes to efficient electrocatalytic H2 evolution in acidic media, where we measure for s-Pt/1T'-MoS2 a mass activity of 85 ± 23 A [Formula: see text] at the overpotential of -50 mV and a mass-normalized exchange current density of 127 A [Formula: see text] and we see stable performance in an H-type cell and prototype proton exchange membrane electrolyser operated at room temperature. Although phase stability limitations prevent operation at high temperatures, we anticipate that 1T'-TMDs will also be effective supports for other catalysts targeting other important reactions.
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Journal articleLiu Z, Peng C, Wu J, et al., 2023,
Regulating electron distribution of P2-type layered oxide cathodes for practical sodium-ion batteries
, Materials Today, Vol: 68, Pages: 22-33, ISSN: 1369-7021For transition metal oxide materials, high Ni content is an effective method to obtain a high specific capacity. However, the theoretical capacity is determined due to the certain amount of variable charges of transition metal ions. The increased capacity in specific voltage window may attribute to the easier transport of alkali ions, instead of more active elements. Borrowing the theory of Ni-rich materials in LIB, excess Ni elements were added into P2-type layered oxide material to form the Jahn-Teller active Ni3+ ions. About 25%-61% Ni3+ ions can effectively promote de-/intercalation of Na+ ions due to the decreased diffusion energy barrier and increased adsorption energy of Na+. The preferred “Ni-rich” material Na0.67Mn0.45Ni0.22Co0.33O2 (Ni-R1) shows a reversible specific capacity of 114 mA h g−1 in the voltage range of 2.0–4.25 V. In addition, it shows an excellent cycle stability, the capacity retention ration is 80% after 1000 cycles at a current density of 1 A g−1. The in-depth study proves that, Jahn-Teller active Ni3+ ions can effectively regulate the valence electron distribution of surrounding ions in synthesis stage. However, it will promote Jahn-Teller distortion when the Ni3+ content is increased to 74%, which makes the rate performance deteriorate dramatically. The present work provides a simple and efficient way to increase the capacity in suitable voltage range for application.
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Journal articleTan R, Wang A, Ye C, et al., 2023,
Thin film composite membranes with regulated crossover and water migration for long-life aqueous redox flow batteries.
, Advanced Science, Vol: 10, Pages: 1-11, ISSN: 2198-3844Redox flow batteries (RFBs) are promising for large-scale long-duration energy storage owing to their inherent safety, decoupled power and energy, high efficiency, and longevity. Membranes constitute an important component that affects mass transport processes in RFBs, including ion transport, redox-species crossover, and the net volumetric transfer of supporting electrolytes. Hydrophilic microporous polymers, such as polymers of intrinsic microporosity (PIM), are demonstrated as next-generation ion-selective membranes in RFBs. However, the crossover of redox species and water migration through membranes are remaining challenges for battery longevity. Here, a facile strategy is reported for regulating mass transport and enhancing battery cycling stability by employing thin film composite (TFC) membranes prepared from a PIM polymer with optimized selective-layer thickness. Integration of these PIM-based TFC membranes with a variety of redox chemistries allows for the screening of suitable RFB systems that display high compatibility between membrane and redox couples, affording long-life operation with minimal capacity fade. Thickness optimization of TFC membranes further improves cycling performance and significantly restricts water transfer in selected RFB systems.
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Journal articleAsfaw HD, Kucernak A, Greenhalgh ES, et al., 2023,
Electrochemical performance of supercapacitor electrodes based on carbon aerogel-reinforced spread tow carbon fiber fabrics
, Composites Science and Technology, Vol: 238, ISSN: 0266-3538Fabric-based supercapacitor electrodes were fabricated by embedding spread tow carbon fiber fabrics, in monolithic, bicontinuous carbon aerogels (CAG). The incorporation of CAG, at less than 30 wt%, increased the specific surface area of the CAG-CF fabric to above 230 m2 g−1 and the pore volume to about 0.35 cm3 g−1, orders of magnitude higher than that for the as-received carbon fibres. The presence of the CAG not only improves the electrochemical performance of the composite electrodes but may enhance the mechanical response due to the high stiffness of the aerogel structure. Cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance measurements were performed on symmetric supercapacitor cells consisting of two CAG-reinforced fabrics in an ionic liquid electrolyte. The specific capacitance of the symmetric supercapacitor was determined to be in the range 3–5 F g−1, considerably higher than that for the plain carbon fibers. Since optimum structural electrolytes are not yet available, this value was normalized to the total mass of both electrodes to place an upper bound on future structural supercapacitors using this spread tow CAG-CF system. The maximum specific energy and specific power, normalized to the total mass of the electrodes, were around 2.64 W h kg−1 and 0.44 kW kg−1, respectively. These performance metrics demonstrate that the thin CAG-modified spread tow fabrics are promising electrodes for future use in structural supercapacitors. In principle, in future devices, the reduced ply thickness offers both improved mechanical properties and shorter ion diffusion distance, as well as opportunities to fabricate higher voltage multicell assemblies within a given component geometry.
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Journal articleWu J, Gong M, Zhang W, et al., 2023,
Simultaneously incorporating atomically dispersed Co-Nx sites with graphitic carbon layer-wrapped Co9S8 nanoparticles for oxygen reduction in acidic electrolyte
, ChemElectroChem, Vol: 10, ISSN: 2196-0216A facile yet robust synthesis is reported herein to simultaneously incorporate atomically dispersed Co-Nx sites with graphitic layer-protected Co9S8 nanoparticles (denoted as Co SACs+Co9S8) as an efficient electrocatalyst for oxygen reduction in acidic solution. The Co SACs+Co9S8 catalyst shows low H2O2 selectivity (∼5 %) with high half-wave potential (E1/2) of ∼0.78 VRHE in 0.5 M H2SO4. The atomic sites of the catalyst were quantified by a nitrite stripping method and the corresponding site density of the catalyst is calculated to be 3.2×1018 sites g−1. Besides, we also found the presence of a reasonable amount of Co9S8 nanoparticles is beneficial for the oxygen electrocatalysis. Finally, the catalyst was assembled into a membrane electrode assembly (MEA) for evaluating its performance under more practical conditions in proton exchange membrane fuel cell (PEMFC) system.
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Journal articleGong M, Mehmood A, Ali B, et al., 2023,
Oxygen reduction reaction activity in non-precious single-atom (M–N/C ) catalysts-contribution of metal and carbon/nitrogen framework-based sites.
, ACS Catalysis, Vol: 13, Pages: 6661-6674, ISSN: 2155-5435We examine the performance of a number of single-atom M-N/C electrocatalysts with a common structure in order to deconvolute the activity of the framework N/C support from the metal M-N4 sites in M-N/Cs. The formation of the N/C framework with coordinating nitrogen sites is performed using zinc as a templating agent. After the formation of the electrically conducting carbon-nitrogen metal-coordinating network, we (trans)metalate with different metals producing a range of different catalysts (Fe-N/C, Co-N/C, Ni-N/C, Sn-N/C, Sb-N/C, and Bi-N/C) without the formation of any metal particles. In these materials, the structure of the carbon/nitrogen framework remains unchanged-only the coordinated metal is substituted. We assess the performance of the subsequent catalysts in acid, near-neutral, and alkaline environments toward the oxygen reduction reaction (ORR) and ascribe and quantify the performance to a combination of metal site activity and activity of the carbon/nitrogen framework. The ORR activity of the carbon/nitrogen framework is about 1000-fold higher in alkaline than it is in acid, suggesting a change in mechanism. At 0.80 VRHE, only Fe and Co contribute ORR activity significantly beyond that provided by the carbon/nitrogen framework at all pH values studied. In acid and near-neutral pH values (pH 0.3 and 5.2, respectively), Fe shows a 30-fold improvement and Co shows a 5-fold improvement, whereas in alkaline pH (pH 13), both Fe and Co show a 7-fold improvement beyond the baseline framework activity. The site density of the single metal atom sites is estimated using the nitrite adsorption and stripping method. This method allows us to deconvolute the framework sites and metal-based active sites. The framework site density of catalysts is estimated as 7.8 × 1018 sites g-1. The metal M-N4 site densities in Fe-N/C and Co-N/C are 9.4 × 1018 sites-1 and 4.8 × 1018 sites g-1, respectively.
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Journal articleValkova M, Nguyen S, Senokos E, et al., 2023,
Current collector design strategies: The route to realising scale-up of structural power composites
, Composites Science and Technology, Vol: 236, Pages: 1-9, ISSN: 0266-3538Multifunctional structural power composites, which combine mechanical load-bearing and electrochemical energy storage, will transform electric vehicle design. This work focuses on structural supercapacitors, based on carbon aerogel-modified carbon fibre electrodes with copper current collectors. In common with many structural power embodiments, scale-up of these devices is currently limited by large internal resistances and the mass associated with current collection. There is a trade-off between the overall resistive power loss and the additional mass for the current collector material. However, in these devices, mechanical integrity is provided by the structural electrodes, allowing a range of collector designs to be considered. Using finite element simulations, these current collection strategies are explored quantitatively across a range of design space variables. The key conductivity parameters were measured experimentally, using the best existing materials, to inform direct current conduction simulations of the electrode/current collector assembly. For the present device configuration, the performance trade-off is governed by the area of the current collector. The most effective near-term strategy for power loss mitigation lies in reducing the contact resistance; however, improvements can also be obtained by modifying the collector geometry. The findings of this paper can be generalised to other structural power composites and monofunctional energy storage devices, which are relevant in many mass-sensitive electrochemical applications.
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Journal articleBarrio J, Pedersen A, Sarma SC, et al., 2023,
FeNC Oxygen Reduction Electrocatalyst with High Utilization Penta-Coordinated Sites
, ADVANCED MATERIALS, Vol: 35, ISSN: 0935-9648- Author Web Link
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Journal articleGreenhalgh ES, Nguyen S, Valkova M, et al., 2023,
A critical review of structural supercapacitors and outlook on future research challenges
, Composites Science and Technology, Vol: 235, Pages: 1-19, ISSN: 0266-3538Structural composites and electrochemical energy storage underpin electrification of transportation, but advances in electric vehicles are shackled by parasitic battery mass. The emergence of structural power composites, multifunctional materials that simultaneously carry structural loads whilst storing electrical energy, promises dramatic improvements in effective performance Here, we assess the literature on structural supercapacitors, not only providing a comprehensive and critical review of the constituent (i.e., structural electrode, structural electrolyte and structural separator) developments, but also considering manufacture, characterisation, scale-up, modelling and design/demonstration. We provide a rigorous analysis of the multifunctional performance data reported in the literature, providing the reader with a detailed comparison between the different structural supercapacitor developments. We conclude with insights into the future research and adoption challenges for structural supercapacitors. There are several significant hurdles which must be addressed to mature this technology. These include development of a processable structural electrolyte; optimisation of current collection to facilitate device scale-up; identification of load-transmitting encapsulation solutions; standard protocols for characterisation and ranking of structural supercapacitors and; predictive multiphysics models for structural supercapacitors. Through addressing such issues, these emerging multifunctional materials will deliver a novel lightweighting strategy that can contribute to managing the ongoing climate crisis.
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Journal articleWang A, Tan R, Liu D, et al., 2023,
Ion-selective microporous polymer membranes with hydrogen-bond and salt-bridge networks for aqueous organic redox flow batteries
, Advanced Materials, Vol: 35, Pages: 1-12, ISSN: 0935-9648Redox flow batteries (RFBs) have great potential for long-duration grid-scale energy storage. Ion conducting membranes are a crucial component in RFBs, allowing charge-carrying ions to transport while preventing the cross-mixing of redox couples. Commercial Nafion membranes are widely used in RFBs, but their unsatisfactory ionic and molecular selectivity as well as high costs limit the performance and the widespread deployment of this technology. To extend the longevity and reduce the cost of RFB systems, inexpensive ion-selective membranes are highly desired that concurrently deliver low ionic resistance and high selectivity towards redox-active species. In this work, high-performance RFB membranes are fabricated from blends of carboxylate- and amidoxime-functionalized polymers of intrinsic microporosity (PIMs) that exploit the beneficial properties of both polymers. The enthalpy-driven formation of cohesive interchain interactions, including hydrogen bonds and salt bridges, facilitates the microscopic miscibility of the blends, while ionizable functional groups within the sub-nanometer pores allow optimization of membrane ion transport functions. The resulting microporous membranes demonstrate fast cation conduction with low crossover of redox-active molecular species, enabling improved power ratings and reduced capacity fade in aqueous RFBs using anthraquinone and ferrocyanide as redox couples. This article is protected by copyright. All rights reserved.
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Journal articleRubio-Garcia J, Kucernak A, Chakrabarti BK, et al., 2023,
High performance H2-Mn regenerative fuel cells through an improved positive electrode morphology
, Batteries, Vol: 9, ISSN: 2313-0105The effective scaling-up of redox flow batteries (RFBs) can be facilitated upon lowering the capital costs. The application of ubiquitous manganese along with hydrogen (known as H2−Mn regenerative fuel cells (RFC)) is seen as an effective solution for this purpose. Here, we aim to evaluate different positive electrodes so as to improve the key performance metrics of the H2/Mn RFC, namely electrolyte utilization, energy efficiency, and peak power densities. Commercially available carbon paper and graphite felt are used to show that the latter provides better key performance indicators (KPIs), which is consistent with the results reported for standard all-vanadium RFBs in the literature. Even better KPIs are obtained when an in-house carbon catalyst layer (CCL) is employed in combination with graphite felt electrodes (e.g., more than 80% energy efficiency, >0.5 W cm−2 peak power density and electrolyte utilization of 20 Ah L−1 for felt and carbon metal fabric (CMF), prepared by means of electrospinning and carbonization, in comparison with about 75% energy efficiency 0.45 W cm−2 peak power density and 11 Ah L−1 electrolyte utilization for felt on its own). It is envisaged that if the electrochemical performance of CCLs can be optimized then it could open up new opportunities for the commercial exploitation of H2−Mn systems.
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Journal articleIshfaq A, Nguyen S, Greenhalgh ES, et al., 2022,
Multifunctional design, feasibility and requirements for structural power composites in future electric air taxis
, Journal of Composite Materials, Vol: 57, Pages: 817-828, ISSN: 0021-9983This study investigates the viability of implementing multifunctional structural power composites in a four-seater air taxi, the CityAirbus. For a given specific energy of the power source, the cruise endurance can be approximately doubled by using structural power composites as opposed to conventional batteries. Replacing all the eligible composite mass and batteries with structural power composites can reduce the CityAirbus weight by 25%. To achieve the current design performance, the minimum required elastic modulus, strength, specific energy and power for the structural power composite are 54 GPa, 203 MPa, 74 Wh/kg and 376 W/kg, respectively: current state-of-the-art structural power composites are now approaching this level of performance. Hence, structural power composites are considered feasible for adoption in the urban air mobility sector and have the potential to improve endurance and facilitate commercialization. This paper also discusses several key challenges that must be addressed to realize the adoption of structural power composites in future electric air taxis.
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Journal articleYe C, Tan R, Wang A, et al., 2022,
Long-life aqueous organic redox flow batteries enabled by amidoxime-functionalized ion-selective polymer membranes
, Angewandte Chemie International Edition, Vol: 61, ISSN: 1433-7851Redox flow batteries (RFBs) based on aqueous organic electrolytes are a promising technology for safe and cost-effective large-scale electrical energy storage. Membrane separators are a key component in RFBs, allowing fast conduction of charge-carrier ions but minimizing the cross-over of redox-active species. Here, we report the molecular engineering of amidoxime-functionalized polymers of intrinsic microporosity (AO-PIMs) by tuning their polymer chain topology and pore architecture to optimize membrane ion transport selectivity. AO-PIM membranes are integrated with three emerging aqueous organic flow battery chemistries, and the synergetic integration of ion-selective membranes with molecular engineered organic molecules in neutral-pH electrolytes leads to significantly enhanced cycling stability.
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Journal articleYe C, Wang A, Breakwell C, et al., 2022,
Development of efficient aqueous organic redox flow batteries using ion-sieving sulfonated polymer membranes
, Nature Communications, Vol: 13, ISSN: 2041-1723Redox flow batteries using aqueous organic-based electrolytes are promising candidates for developing cost-effective grid-scale energy storage devices. However, a significant drawback of these batteries is the cross-mixing of active species through the membrane, which causes battery performance degradation. To overcome this issue, here we report size-selective ion-exchange membranes prepared by sulfonation of a spirobifluorene-based microporous polymer and demonstrate their efficient ion sieving functions in flow batteries. The spirobifluorene unit allows control over the degree of sulfonation to optimize the transport of cations, whilst the microporous structure inhibits the crossover of organic molecules via molecular sieving. Furthermore, the enhanced membrane selectivity mitigates the crossover-induced capacity decay whilst maintaining good ionic conductivity for aqueous electrolyte solution at pH 9, where the redox-active organic molecules show long-term stability. We also prove the boosting effect of the membranes on the energy efficiency and peak power density of the aqueous redox flow battery, which shows stable operation for about 120 h (i.e., 2100 charge-discharge cycles at 100 mA cm−2) in a laboratory-scale cell.
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Journal articleKucernak A, Zhang G, cui Y, 2022,
Real-time in situ monitoring of CO2 electroreduction in the liquid and gas phases by coupled mass spectrometry and localized electrochemistry
, ACS Catalysis, Vol: 12, Pages: 6180-6190, ISSN: 2155-5435The mechanism and dynamics of the CO2 reduction reaction (CO2RR) remain poorly understood, which is largely caused by mass transport limitations and lack of time-correlated product analysis tools. In this work, a custom-built gas accessible membrane electrode (GAME) system is used to comparatively assess the CO2RR behavior of Au and Au−Cu catalysts. The platform achieves high reduction currents (∼ – 50 mA cm–2 at 1.1 V vs RHE) by creating a three-phase boundary interface equipped with an efficient gas-circulation pathway, facilitating rapid mass transport of CO2. The GAME system can also be easily coupled with many other analytical techniques as exemplified by mass spectrometry (MS) and localized ultramicroelectrode (UME) voltammetry to enable real-time and in situ product characterization in the gas and liquid phases, respectively. The gaseous product distribution is explicitly and quantitatively elucidated with high time resolution (on the scale of seconds), allowing for the independent assessment of Tafel slope estimates for the hydrogen (159/168 mV decade–1), ethene (160/170 mV decade–1), and methane (96/100 mV decade–1) evolution reactions. Moreover, the UME is used to simultaneously measure the local pH shift during CO2RR and assess the production of liquid phase species including formate. A positive shift of 0.8 pH unit is observed at a current density of −11 mA cm–2 during the CO2RR.
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Contact Details
Prof. Anthony Kucernak
G22B
Molecular Sciences Research Hub (MSRH)
Imperial College London
White City Campus
London
W12 0BZ
United Kingdom
Phone: +44 (0)20 7594 5831
Fax: +44 (0)20 7594 5804
Email: anthony@imperial.ac.uk