230 results found
Barrio J, Pedersen A, Sarma SC, et al., 2023, FeNC Oxygen Reduction Electrocatalyst with High Utilization Penta-Coordinated Sites., Adv Mater
Atomic Fe in N-doped carbon (FeNC) electrocatalysts for oxygen (O2 ) reduction at the cathode of proton exchange membrane fuel cells are the most promising alternative to platinum-group-metal catalysts. Despite recent progress on atomic FeNC O2 reduction, their controlled synthesis and stability for practical applications remain challenging. A two-step synthesis approach has recently led to significant advances in terms of Fe-loading and mass activity; however, the Fe utilization remains low owing to the difficulty of building scaffolds with sufficient porosity that electrochemically exposes the active sites. Herein, this issue is addressed by coordinating Fe in a highly porous nitrogen-doped carbon support (≈3295 m2 g-1 ), prepared by pyrolysis of inexpensive 2,4,6-triaminopyrimidine and a Mg2+ salt active site template and porogen. Upon Fe coordination, a high electrochemical active site density of 2.54 × 1019 sites gFeNC -1 and a record 52% FeNx electrochemical utilization based on in situ nitrite stripping are achieved. The Fe single atoms are characterized pre- and post-electrochemical accelerated stress testing by aberration-corrected high-angle annular dark field scanning transmission electron microscopy, showing no Fe clustering. Moreover, ex situ X-ray absorption spectroscopy and low-temperature Mössbauer spectroscopy suggest the presence of penta-coordinated Fe sites, which are further studied by density functional theory calculations.
Rubio-Garcia J, Kucernak A, Chakrabarti BK, et al., 2023, High Performance H<inf>2</inf>−Mn Regenerative Fuel Cells through an Improved Positive Electrode Morphology, Batteries, Vol: 9
The 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.
Ishfaq 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: 0021-9983
This 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.
Ye 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: 1433-7851
Redox 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.
Ye 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: 2041-1723
Redox 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.
Kucernak 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: 2155-5435
The 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.
Xia Y, Ouyang M, Yufit V, et al., 2022, A cost-effective alkaline polysulfide-air redox flow battery enabled by a dual-membrane cell architecture, Nature Communications, Vol: 13, Pages: 1-13, ISSN: 2041-1723
With the rapid development of renewable energy harvesting technologies, there is a significant demand for long-duration energy storage technologies that can be deployed at grid scale. In this regard, polysulfide-air redox flow batteries demonstrated great potential. However, the crossover of polysulfide is one significant challenge. Here, we report a stable and cost-effective alkaline-based hybrid polysulfide-air redox flow battery where a dual-membrane-structured flow cell design mitigates the sulfur crossover issue. Moreover, combining manganese/carbon catalysed air electrodes with sulfidised Ni foam polysulfide electrodes, the redox flow battery achieves a maximum power density of 5.8 mW cm-2 at 50% state of charge and 55 °C. An average round-trip energy efficiency of 40% is also achieved over 80 cycles at 1 mA cm-2. Based on the performance reported, techno-economic analyses suggested that energy and power costs of about 2.5 US$/kWh and 1600 US$/kW, respectively, has be achieved for this type of alkaline polysulfide-air redox flow battery, with significant scope for further reduction.
Valkova M, Anthony DB, Kucernak ARJ, et al., 2022, Predicting the mechanical behaviour of structural supercapacitor composites, Composites Part A: Applied Science and Manufacturing, Vol: 156, ISSN: 1359-835X
Multifunctional structural power composites may transform transport electrification, and other applications, but require performance and reliability improvements. Computational modelling has the potential to accelerate their development and deployment. This work addresses the lack of predictive models for the mechanical behaviour of structural supercapacitor composites exploiting carbon aerogel-modified carbon fabric electrodes. The elastic behaviour was investigated using finite element analysis of quasi-meso-scale periodic unit cell models, considering the effects of constituent properties, defects, stacking geometry, and boundary conditions. Nanoindentation was used to evaluate the Young’s modulus of carbon aerogel. Parametric modelling demonstrated a strong influence of the ply offset and matrix materials on the composite elastic properties. The initial numerical results overpredicted the actual performance measured from tensile and in-plane shear experiments in the literature. Optical, scanning electron and micro X-ray imaging revealed extensive pre-cracking and voidage in the physical laminates. Additional computational investigations showed that the pre-cracks were associated with a degradation of shear stiffness. The remaining performance gap was attributed to voidage. The present study highlights that challenges for mechanical performance and its prediction stem from the presence of processing defects and a lack of in-situ material data. Nevertheless, the models identify the potential of hierarchical laminates containing aerogels to generate sizable performance improvements, both in multifunctional and purely structural contexts.
Pernice MF, Qi G, Senokos E, et al., 2022, Mechanical, electrochemical and multifunctional performance of a CFRP/carbon aerogel structural supercapacitor and its corresponding monofunctional equivalents, Multifunctional Material, Vol: 5
Mehmood A, Gong M, jaouen F, et al., 2022, High loading of single atomic iron sites in Fe-NC oxygen reduction catalysts for proton exchange membrane fuel cells, Nature Materials, Vol: 5, Pages: 311-323, ISSN: 1476-1122
Non-precious iron-based catalysts (Fe-NCs) require high active site density (SD) to meet the performance targets as cathode catalysts in proton exchange membrane fuel cells (PEMFCs). SD is generally limited to that achieved at 1-3 wt%(Fe) loading due to the undesired formation of iron-containing nanoparticles at higher loadings. Here we show that by pre-forming a carbon-nitrogen matrix using a sacrificial metal (Zn) in the initial synthesis step and then exchanging iron into this preformed matrix we achieve 7 wt% iron coordinated solely as single atom Fe-N4 sites as identified by 57Fe cryo Mössbauer spectroscopy and X-ray absorption spectroscopy. SD values measured by in situ nitrite stripping and ex situ CO chemisorption methods are 4.7x1019 and 7.8x1019 sitesg-1, with a turnover frequency of 5.4 electrons̭sites-1s-1 at 0.80 V in 0.5M H2SO4 electrolyte. The catalyst delivers excellent PEMFC performance with current densities of 41.3 mAcm-2 at 0.90 ViR-free using H2-O2 (10.6 Ag-1) and 145 mA cm-2 at 0.80 V (199 mAcm-2 at 0.80 ViR-free) using H2-air.
Gong M, Guo Y, Malko D, et al., 2022, Using molecular oxygen and Fe-N/C heterogeneous catalysts to achieve Mukaiyama epoxidations via in situ produced organic peroxy acids and acylperoxy radicals, Catalysis Science & Technology, Vol: 12, Pages: 2978-2989, ISSN: 2044-4753
Under mild conditions of room temperature and pressure, and using either pure oxygen or air, aldehydes are converted using a heterogeneous Fe–N/C catalyst to produce the corresponding organic peroxy acid and acylperoxy radicals, which forms the epoxide from cyclohexene with high yield (91% for isobutyraldehyde in O2). Real-time monitoring of the rate of oxygen consumption and the electrochemical potential of the Fe–N/C catalyst has been used to study the formation of the peroxy acid and subsequent catalytic epoxidation of cyclohexene. Using isobutyraldehyde, it is shown that the aldehyde and the iron-based carbon catalyst (Fe–N/C) are involved in the rate determining step. Addition of a radical scavenger increases the induction time showing that radicals are initiated by the reaction between the aldehyde and the catalyst. Furthermore, UV-vis spectroscopy with 2,2′-azino-di-(3-ethylbenzthiazoline sulfonic acid) (ABTS) proved the in situ formation of peroxy acid. In the presence of cyclohexene, the peroxy acid leads to the corresponding epoxide with high yield. Monitoring the open circuit potential (OCP) and oxygen flow concurrently follows the production of the peroxy acid. The epoxidation reaction can take place only when the increase in open circuit potential is greater than 0.14 V, suggesting an in situ direct link between the relative oxidative strength of the peroxy acid and the likelihood of epoxidation.
Lin R, Kang L, Zhao T, et al., 2022, Identification and manipulation of dynamic active site deficiency-induced competing reactions in electrocatalytic oxidation processes, Energy and Environmental Science, Vol: 15, Pages: 2386-2396, ISSN: 1754-5692
Electrocatalytic organic compound oxidation reactions (OCORs) have been intensively studied for energy and environmentally benign applications. However, relatively little effort has been devoted to developing a fundamental understanding of OCORs, including the detailed competition with side reactions and activity limitations, thus inhibiting the rational design of high-performance electrocatalysts. Herein, by taking the NiWO4-catalysed urea oxidation reaction (UOR) in aqueous media as an example, the competition between the OCOR and the oxygen evolution reaction (OER) within a wide potential range is examined. It is shown that the root of the competition can be ascribed to insufficient surface concentration of dynamic Ni3+, an active site shared by both the UOR and OER. A similar phenomenon is observed in other OCOR electrocatalysts and systems. To address the issue, a “controllable reconstruction of pseudo-crystalline bimetal oxides” design strategy is proposed to maximise the dynamic Ni3+ population and manipulate the competition between the UOR and the OER. The optimised electrocatalyst delivers best-in-class performance and an ∼10-fold increase in current density at 1.6 V versus the reversible hydrogen electrode for alkaline urea electrolysis compared to those of the pristine materials.
Ye M, Sharp P, Brandon N, et al., 2022, System-level comparison of ammonia, compressed and liquid hydrogen as fuels for polymer electrolyte fuel cell powered shipping, International Journal of Hydrogen Energy, Vol: 47, Pages: 8565-8584, ISSN: 0360-3199
With the aim to reduce emissions from marine transport, electric propulsion systems for a water taxi and container ship powered by a hydrogen polymer electrolyte membrane fuel cell system are designed and analyzed compared to the current fuel-oil engine systems in terms of system energy and exergy efficiency, fuel consumption, mass and volume, environmental impacts and cost. Hydrogen is stored either as a compressed gas (GH2), cryogenic liquid (LH2) or produced from liquid ammonia (LNH3) and can deliver 91%,91% and 88% greenhouse gas reductions, respectively. All hydrogen sources fit within ship volume and mass constraints apart from GH2 in the cargo ship. In the absence of carbon policy measures, the costs over a 25-year system life are 108% (GH2), 112% (LH2), 116% (LNH3) greater for the container ship and 43% (GH2), 105% (LNH3) greater for the water taxi. A carbon tax of £75-191/tonne CO2eq would allow the low carbon options to become cost competitive.
Parra-Puerto A, Rubio-Garcia J, Markiewicz M, et al., 2022, Carbon aerogel based thin electrodes for zero-gap all vanadium redox flow batteries - quantifying the factors leading to optimum performance, ChemElectroChem, Vol: 9, ISSN: 2196-0216
Direct growth of resorcinol−formaldehyde carbon aerogels (CAGs) on carbon paper electrodes was achieved using a new approach. Materials with variations in density, mesoporosity and microporosity were prepared. Microstructural properties of the resultant thin electrodes are shown to directly influence performance in zero-gap redox flow battery (RFB). BET analysis shows a total surface area between 643 to 931 m2 g−1. Deposition of only ≈15 wt.% CAG on the carbon electrode leads to a 320-fold increase in electrochemical surface area. Analysis of the results saw a strong positive correlation of RFB performance with surface area. The best performing electrodes had a good balance between microporous and external surface area, and on the macroscopic scale had sufficiently large pores to allow efficient electrolyte permeation. The poorest performing electrodes which had the highest surface area, also had poor macroscopic porosity leading to large mass transport and solution resistance losses. The best performing electrodes were tested in a zero-gap setup using polarization curves, showing a 25 % increase in power density at 100 mA cm−2 and a peak power density of 706 mW cm−2 at 1 V using thin electrodes
Simon BA, Gayon-Lombardo A, Pino-Muñoz CA, et al., 2022, Combining electrochemical and imaging analyses to understand the effect of electrode microstructure and electrolyte properties on redox flow batteries, Applied Energy, Vol: 306, Pages: 1-22, ISSN: 0306-2619
Reducing the cost of redox flow batteries (RFBs) is critical to achieving broad commercial deployment of largescale energy storage systems. This can be addressed in a variety of ways, such as reducing component costs orimproving electrode design. The aim of this work is to better understand the relationship between electrodemicrostructure and performance. Four different commercially available carbon electrodes were examined – twocloths and two papers (from AvCarb® and Freudenberg Performance Materials) – and a comprehensive study ofthe different pore-scale and mass-transport processes is presented to elucidate their effect on the overall cellperformance. Electrochemical measurements were carried out in a non-aqueous organic flow-through RFB withthese different electrodes, using two supporting solvents (propylene carbonate and acetonitrile) and at a varietyof flow rates. Electrode samples were scanned using X-ray computed tomography, and a customised segmentation technique was employed to extract several microstructural parameters. A pore network model was used tocalculate the pressure drops and permeabilities, which were found to be within 1.26 × 10− 11 and 1.65 × 10− 11m2 for the papers and between 8.61 × 10− 11 and 10.6 × 10− 11 m2 for the cloths. A one-dimensional model wasdeveloped and fit to polarisation measurements to obtain mass-transfer coefficients, km, which were found to bebetween 1.01 × 10− 6 and 5.97 × 10− 4 m s− 1 with a subsequent discussion on Reynolds and Sherwood numbercorrelations. This work suggests that, for these fibrous materials, permeability correlates best with electrochemical cell performance. Consequently, the carbon cloths with the highest permeability and highest masstransfer coefficients, displayed better performances.
Jackson C, Lin X, Levecque P, et al., 2021, Toward understanding the utilization of oxygen reduction electrocatalysts under high mass transport conditions and high overpotentials, ACS Catalysis, Vol: 12, Pages: 200-211, ISSN: 2155-5435
There is currently a disconnect between the high electrocatalyst oxygen reduction reaction (ORR) performance measured ex situ, using the rotating disc electrode (RDE), and the in situ membrane electrode assembly (MEA) performance. The disconnect in the electrocatalyst performance raises questions both about the pitfalls of the RDE technique at extrapolating the performance to higher overpotentials and how to improve the in situ catalyst layer performance to meet ambitious fuel cell targets. This work aims to bridge the gap by measuring the ORR ex situ performance under high mass transport conditions, at high overpotentials, using the floating electrode (FE) technique. Here, we determine the performance of three Pt/C electrocatalysts using the FE in 1 M HClO4 and 1 M H2SO4 to show that the MEA activities measured at 80 °C, 150 kPag were substantially lower than the room temperature and pressure performance of the same catalyst in 1 M HClO4 using the RDE and FE methods and also lower than the FE in 1 M H2SO4, implying MEA limitations are not purely due to sulfonate adsorption from the Nafion. Finally, FE and MEA data was modeled which obtained jo values on the FE (oxide free conditions) which were 4–6× larger, at 11–26 μA cm–2, than those measured on the MEA. The difference is interpreted as due to better water removal in the FE system. This work shows that MEA catalyst layers are vastly underutilized, due to poor water transport, and current densities equivalent to 10–16 A cm–2 at 0.65 V for 400 μgPt cm–2 (25–40 A mg–1) are achievable, whereas the current mass activity of MEAs is <40% of this value at 25 and 80 °C, 150 kPag.
Karadotcheva E, Nguyen SN, Greenhalgh ES, et al., 2021, Structural Power Performance Targets for Future Electric Aircraft, Energies, Vol: 14, Pages: 6006-6006
The development of commercial aviation is being driven by the need to improve efficiency and thereby lower emissions. All-electric aircraft present a route to eliminating direct fuel burning emissions, but their development is stifled by the limitations of current battery energy and power densities. Multifunctional structural power composites, which combine load-bearing and energy-storing functions, offer an alternative to higher-energy-density batteries and will potentially enable lighter and safer electric aircraft. This study investigated the feasibility of integrating structural power composites into future electric aircraft and assessed the impact on emissions. Using the Airbus A320 as a platform, three different electric aircraft configurations were designed conceptually, incorporating structural power composites, slender wings and distributed propulsion. The specific energy and power required for the structural power composites were estimated by determining the aircraft mission performance requirements and weight. Compared to a conventional A320, a parallel hybrid-electric A320 with structural power composites >200 Wh/kg could potentially increase fuel efficiency by 15% for a 1500 km mission. For an all-electric A320, structural power composites >400 Wh/kg could halve the specific energy or mass of batteries needed to power a 1000 km flight.
Boldrin P, Malko D, Mehmood A, et al., 2021, Deactivation, reactivation and super-activation of Fe-N/C oxygen reduction electrocatalysts: gas sorption, physical and electrochemical investigation using NO and O2, Applied Catalysis B: Environmental, Vol: 292, Pages: 1-12, ISSN: 0926-3373
We show that gaseous nitric oxide (NO) and oxygen (O2) are useful molecular probes to uncover complex surface processes in Fe-N/C catalysts. We unravel the difference between using gaseous NO in a temperature programmed desorption experiment and using NO (and progenitors) in an electrochemical experiment. Gas phase O2 adsorption is almost exclusively desorbed as CO2, and continued exposure to oxygen increases the amount of chemisorbed oxygen species on the surface. The oxidation state of the carbon surface is an important activity determining factor, and under normal “electrochemical” conditions many of the active sites are blocked. Only by treatment at 600 °C in Ar can we free those sites for oxygen adsorption, however under atmospheric storage, and especially during the oxygen reduction reaction (ORR), the surface quickly becomes deactivated with chemisorbed oxygen species and water. We demonstrate that the material can be super-activated by reductive electrochemical treatment, both in an electrochemical three electrode cell and in a fuel cell. The energy gained following the treatment is significantly larger than the energetic cost.
Qi G, Nguyen S, Anthony DB, et al., 2021, The influence of fabrication parameters on the electrochemical performance of multifunctional structural supercapacitors, Multifunctional Materials, Vol: 4, ISSN: 2399-7532
Multifunctional structural supercapacitors based on carbon fibre electrodes (CF) and structural electrolytes (SEs) can realise multifunctionality by simultaneously bearing load and providing electrochemical energy storage. Structural supercapacitor constituents (i.e. electrodes and electrolytes) have undergone significant development to enhance their electrochemical and mechanical properties. However, the fabrication of fully functional devices presents a number of practical challenges to achieve optimal multifunctional properties, particularly those associated with assembly and lamination. This work investigated the effect of separator selection and processing parameters on the electrochemical performance of structural supercapacitors, as well as evaluating the repeatability of the SE filming process. Two layers of glass fibre fabrics were the most effective separator for preventing short-circuiting of the structural supercapacitors. The weight fraction of the SE matrix had a significant effect on the capacitance, energy and power of the structural supercapacitors. By addressing such fabrication challenges, high performance structural supercapacitors can be manufactured with greater reproducibility and at larger scales such that they are suitable for integration in industrial applications.
Mehmood A, Ali B, Gong M, et al., 2021, Development of a highly active Fe-N-C catalyst with the preferential formation of atomic iron sites for oxygen reduction in alkaline and acidic electrolytes, Journal of Colloid and Interface Science, Vol: 596, Pages: 148-157, ISSN: 0021-9797
Nitrogen-doped porous carbons containing atomically dispersed iron are prime candidates for substituting platinum-based catalysts for oxygen reduction reaction (ORR) in fuel cells. These carbon catalysts are classically synthesized via complicated routes involving multiple heat-treatment steps to form the desired Fe-Nx sites. We herein developed a highly active Fesingle bondNsingle bondC catalyst comprising of exclusive Fe-Nx sites by a simplified solid-state synthesis protocol involving only a single heat-treatment. Imidazole is pyrolyzed in the presence of an inorganic salt-melt resulting in highly porous carbon sheets decorated with abundant Fe-Nx centers, which yielded a high density of electrochemically accessible active sites (1.36 × 1019 sites g−1) as determined by the in situ nitrite stripping technique. The optimized catalyst delivered a remarkable ORR activity with a half-wave potential (E1/2) of 0.905 VRHE in alkaline electrolyte surpassing the benchmark Pt catalyst by 55 mV. In acidic electrolyte, an E1/2 of 0.760 VRHE is achieved at a low loading level (0.29 mg cm−2). In PEMFC tests, a current density of 2.3 mA cm−2 is achieved at 0.90 ViR-free under H2–O2 conditions, reflecting high kinetic activity of the optimized catalyst.
Mazzucato M, Daniel G, Mehmood A, et al., 2021, Effects of the induced micro- and meso-porosity on the single site density and turn over frequency of Fe-N-C carbon electrodes for the oxygen reduction reaction, Applied Catalysis B: Environmental, Vol: 291, Pages: 1-14, ISSN: 0926-3373
Fe-N-C have emerged as one of the best non-PGM alternatives to Pt/C catalysts for the electrochemical reduction of O2 in fuel cells. In this work, we explore the effect of steam and CO2 treatments at high temperatures on the nanometric porous structure of a commercial carbon black. Using those support materials, we synthesize different Fe-N-C catalysts to achieve a better understanding on the role of micro- and mesopores of the support towards catalytic site formation and site activity. Different time and temperature of treatments result in an almost linear increment of surface area and microporous volume, which allows better nitrogen functionalization. Site density evaluation, performed using a recently described NO-stripping technique, showed an increase in site density and TOF which correlates well with the morphology variation. The percentage of active iron increases from 2.65 % to 14.74 % in activated catalysts confirming a better access of electrolyte to the iron sites.
Kucernak A, Wu J, Mehmood A, et al., 2021, Highly selective O2 reduction to H2O2 catalyzed by cobalt nanoparticles supported on nitrogen-doped carbon in alkaline solution, ACS Catalysis, Vol: 11, Pages: 5035-5046, ISSN: 2155-5435
We report the synthesis of cobalt nanoparticles supported on nitrogen-doped carbon (CoNPs@N/C), which can reduce O2 into H2O2 with high selectivity (up to 93%) in 0.1 M KOH electrolyte and retains >90% activity even after 10 h polarization. The catalyst achieves a current density of 1 mA cm–2 at 0.76 V(RHE) and a peroxide production rate of ∼3.8molH2O2 gCo–1 h–1 over a 10 h period. Our study also highlights the requirement for good peroxide production catalysts to be poor hydrogen peroxide disproportionation catalysts. We show how the high activity of the CoNPs@N/C catalyst is correlated with low activity toward the peroxide disproportionation reaction.
Nguyen S, Millereux A, Pouyat A, et al., 2021, Conceptual multifunctional design, feasibility and requirements for structural power in aircraft cabins, Journal of Aircraft: devoted to aeronautical science and technology, Vol: 58, Pages: 677-687, ISSN: 0021-8669
This paper presents a theoretical investigation into the potential use of structural power composites in regional aircraft passenger cabins and the corresponding challenges to widespread use, including fire-resistance, long-term cycling performance, and cost. This study focusses on adapting sandwich floor panels with structural power composite face sheets, designed to power the in-flight entertainment system. Using a simple mechanical model to define the structural requirements, based on state-of-the-art laminated structural power composites, a series of electrochemical energy storage performance targets were calculated: a specific energy > 144 Wh/kg, a specific power > 0.29 kW/kg, an in-plane elastic modulus > 28 GPa and in-plane tensile and compressive strengths > 219 MPa. Significantly, the use of a distributed energy storage system offered a significant range of other mass and cost savings, associated with a simplified power system, and the use of ground-generated electrical energy. For an Airbus A220-100, the analysis predicted potential mass and volume savings of approximately 260 kg and 510 land annual reductions in CO2and NOx emissions of approximately 280 tonnes and 1.2 tonnes respectively. This extended design analysis of a specific component highlights both the far-reaching implications of implementing structural power materials and the potential extensive systemic benefits.
Robinson J, Xi K, Kumar RV, et al., 2021, 2021 roadmap on lithium sulfur batteries, Journal of Physics: Energy, Vol: 3, ISSN: 2515-7655
Batteries that extend performance beyond the intrinsic limits of Li-ion batteries are among the most important developments required to continue the revolution promised by electrochemical devices. Of these next-generation batteries, lithium sulfur (Li–S) chemistry is among the most commercially mature, with cells offering a substantial increase in gravimetric energy density, reduced costs and improved safety prospects. However, there remain outstanding issues to advance the commercial prospects of the technology and benefit from the economies of scale felt by Li-ion cells, including improving both the rate performance and longevity of cells. To address these challenges, the Faraday Institution, the UK's independent institute for electrochemical energy storage science and technology, launched the Lithium Sulfur Technology Accelerator (LiSTAR) programme in October 2019. This Roadmap, authored by researchers and partners of the LiSTAR programme, is intended to highlight the outstanding issues that must be addressed and provide an insight into the pathways towards solving them adopted by the LiSTAR consortium. In compiling this Roadmap we hope to aid the development of the wider Li–S research community, providing a guide for academia, industry, government and funding agencies in this important and rapidly developing research space.
Riedel R, Seel AG, Malko D, et al., 2021, Superalkali-alkalide interactions and ion pairing in low-polarity solvents, Journal of the American Chemical Society, Vol: 143, Pages: 3934-3943, ISSN: 0002-7863
The nature of anionic alkali metals in solution is traditionally thought to be “gaslike” and unperturbed. In contrast to this noninteracting picture, we present experimental and computational data herein that support ion pairing in alkalide solutions. Concentration dependent ionic conductivity, dielectric spectroscopy, and neutron scattering results are consistent with the presence of superalkali–alkalide ion pairs in solution, whose stability and properties have been further investigated by DFT calculations. Our temperature dependent alkali metal NMR measurements reveal that the dynamics of the alkalide species is both reversible and thermally activated suggesting a complicated exchange process for the ion paired species. The results of this study go beyond a picture of alkalides being a “gaslike” anion in solution and highlight the significance of the interaction of the alkalide with its complex countercation (superalkali).
Lin X, Zalitis CM, Sharman J, et al., 2020, Correction to "Electrocatalyst Performance at the Gas/Electrolyte Interface under High Mass Transport Conditions: Optimization of the 'Floating Electrode'Method", ACS Applied Materials and Interfaces, Vol: 12, Pages: 57667-57667, ISSN: 1944-8244
Due to a production error, an incorrect Supporting Information file was published with this paper. The correct version is included here and has been replaced in the original article.
Chakrabarti BK, Feng J, Kalamaras E, et al., 2020, Hybrid redox flow cells with enhanced electrochemical performance via binderless and electrophoretically deposited nitrogen-doped graphene on carbon paper electrodes., ACS Applied Materials and Interfaces, Vol: 12, Pages: 53869-53878, ISSN: 1944-8244
Hybrid redox flow cells (HRFC) are key enablers for the development of reliable large-scale energy storage systems; however, their high cost, limited cycle performance, and incompatibilities associated with the commonly used carbon-based electrodes undermine HRFC's commercial viability. While this is often linked to lack of suitable electrocatalytic materials capable of coping with HRFC electrode processes, the combinatory use of nanocarbon additives and carbon paper electrodes holds new promise. Here, by coupling electrophoretically deposited nitrogen-doped graphene (N-G) with carbon electrodes, their surprisingly beneficial effects on three types of HRFCs, namely, hydrogen/vanadium (RHVFC), hydrogen/manganese (RHMnFC), and polysulfide/air (S-Air), are revealed. RHVFCs offer efficiencies over 70% at a current density of 150 mA cm-2 and an energy density of 45 Wh L-1 at 50 mA cm-2, while RHMnFCs achieve a 30% increase in energy efficiency (at 100 mA cm-2). The S-Air cell records an exchange current density of 4.4 × 10-2 mA cm-2, a 3-fold improvement of kinetics compared to the bare carbon paper electrode. We also present cost of storage at system level compared to the standard all-vanadium redox flow batteries. These figures-of-merit can incentivize the design, optimization, and adoption of high-performance HRFCs for successful grid-scale or renewable energy storage market penetration.
Wu J, Li P, Parra-Puerto A, et al., 2020, Controllable heteroatom doping effects of CrxCo2-xP Nanoparticles: A Robust Electrocatalyst for Overall Water Splitting in Alkaline Solutions., ACS Applied Materials and Interfaces, Vol: 12, Pages: 47397-47407, ISSN: 1944-8244
The effect of doping Cr on the electrocatalytic activity of supported Co2P for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline solution was investigated. A beneficial improvement in the performance of Co2P supported on carbon black (CrxCo2-xP/CB) towards HER and OER was discovered. For the HER at -200 mV overpotential the turnover frequency (TOF) increases almost six-fold from 0.26 to 1.52 electrons siteCo-1 s-1 when Co2P/CB has a small amount of Cr added to form Cr0.2Co1.8P/CB. Similarly, we estimate an increase from 0.205 to 0.585 electrons siteCo-1 s-1 for the OER at 1.6V for the same change in composition. With 10at% Cr doping, the Cr0.2Co1.8P/CB catalyst needed 226 mV overpotential to produce a cathodic current density of -100 A g_Co^(-1) and 380 mV overpotential to produce an anodic current density of 100 A g_Co^(-1). Based on both experimental results and theoretical calculations, the activity improvement results from optimization of electronic properties of Co2P after Cr doping.
Rubio-Garcia J, Cui J, Parra-Puerto A, et al., 2020, High energy density hydrogen/vanadium hybrid redox flow battery utilizing HCl as a supporting electrolyte for large scale energy storage applications, Energy Storage Materials, Vol: 31, Pages: 1-10, ISSN: 2405-8297
A high energy density Hydrogen/Vanadium (6 M HCl) system is demonstrated with increased vanadium concentration (2.5 M vs. 1 M), and standard cell potential (1.167 vs. 1.000 V) and high theoretical storage capacity (65 Wh L−1) compared to previous vanadium systems. The system is enabled through the development and use of HER/HOR catalysts with improved chemical stability towards the halogen-containing electrolyte within which the usual catalyst (Pt/C) is shown to quickly degrade during potential hold experiments. The implementation of an Ir/C catalyst at the negative side enables a system with high achievable energy density of 45 W h L−1 at 75 mA cm−2 associated with 67% electrolyte utilization. Based on such a promising performance, the system here presented could be a suitable solution for medium and large-scale energy storage with lower cost and volume footprint than existing batteries, particularly all-vanadium RFBs.
Lin X, Zalitis CM, Sharman J, et al., 2020, Electrocatalyst performance at the gas/electrolyte interface under high mass transport conditions: optimization of the "floating electrode" method., ACS Applied Materials and Interfaces, Vol: 12, Pages: 47467-47481, ISSN: 1944-8244
The thin-film rotating disk electrode (TF-RDE) is a well-developed, conventional ex-situ electrochemical method which is limited by poor mass transport in the dissolved phase and hence can only measure the kinetic response for Pt-based catalysts in a narrow overpotential range. Thus, the applicability of TF-RDE results in assessing how catalysts perform in fuel cells has been questioned. To address this problem, we use the floating electrode (FE) technique which can facilitate high mass transport to a catalyst layer composed of an ultra-low loading of catalyst (1-15 μgPt cmgeo-2) at the gas/electrolyte interface. In this paper, the aspects which have critical effects on the performance of the FE system are measured and parameterised. We find that in order to obtain reproducible results with high performance the following factors need to be taken into account: system cleanliness, break-in procedure, hydrophobic agent, ionomer type and the measurements of catalyst surface area and loading. For some of these parameters, we examined a range of different approaches/materials and determined the optimum configuration. We find that the gas permeability of the hydrophobic agent is an important factor for improving the hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR) performance. We provide evidence that the suppression of the HOR and ORR introduced by the Nafion ionomers is more than a local mass transport barrier but that a mechanism involving the adsorption of the sulfonate on Pt also plays a significant role. The work provides intriguing insights into how to manufacture and optimize electrocatalyst systems which must function at the gas/electrolyte interface.
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