Synthesis of mesoporous carbon spheres via a soft-template route for catalyst supports in PEMFC cathodes.

Synthesis of carbon spheres via a soft-template route should be further improved for industrial applications especially in terms of time, cost and scalability. The present work reports on the relatively fast production of mesoporous carbon via an ammonia-catalyzed hydrothermal soft-template one-pot route denoted as CFAH with m-aminophenol as the carbon source and triblock copolymer Pluronic® F127 as the template. For comparison, an acidic route with resol as the carbon precursor (CFRH) was evaluated as well. The best results regarding particle size and pore distribution of the as-prepared CFRH and CFAH samples were obtained in 2 M HCl and 6 M NH4OH at 120 °C for 12 h and 700 °C pyrolysis temperature, respectively. GDE with CFRH and CFAH supported platinum showed excellent ECSA retention of about 60-70% during accelerated degradation testing under half-cell conditions compared to only 13% for GDE with Pt/CVulcan reference material.

Investigation of Al(TfO)3-based deep eutectic solvent electrolytes for aluminium-ion batteries. Part I: understanding the positively charged Al complex formation.

Aluminium-ion batteries (AIB) are very attractive energy storage systems due to the high availability and theoretical energy density of metallic aluminium. However, the practical performance of AIBs in AlCl3-based electrolytes is limited by the low reversible capacity of the positive graphite electrode for large AlCl4- anions. Moreover, the use of high energy oxide-based electrodes such as MnO2 requires the presence of positively charged aluminium complexes in the electrolyte. In this work, the coordination of Al complexes in deep eutectic solvents (DESs) composed of Al triflate Al(TfO)3 as the conducting salt, urea and/or acetamide as the hydrogen bond donor and formamide and N-methylacetamide as the solvent was investigated. Both solvents were able to dissolve and dissociate Al(TfO)3 principally to a single positively charged Al complex [Al(TfO)2-solventn]+ which was confirmed by Raman and NMR spectroscopy analyses. Furthermore, the addition of urea led to further dissociation to the [AlTfO-solventn-urea2]2+ complex that can be assigned to the bidentate hydrogen bonding of urea with TfO at a specific ratio of urea/Al(TfO)3 of 4 : 1. Because of their partial miscibility with urea, other conventional solvents such as propylene carbonate and acetonitrile dissociate Al(TfO)3 only once to form [AlTfO2-solventn]+. The as-prepared formamide and N-methylacetamide-based DES electrolytes show good conductivity values of 9.65 and 2.45 mS cm-1, respectively.

Influence of Resorcinol to Sodium Carbonate Ratio on Carbon Xerogel Properties for Aluminium Ion Battery.

Carbon xerogels were synthesized using a soft-template route with resorcinol as the carbon source and sodium carbonate as the catalyst. The influence of the resorcinol to catalyst ratio in the range of 500-20,000 on pore structure, graphitic domains, and electronic conductivity of as-prepared carbon xerogels, as well as their performance in an aluminium ion battery (AIB), was investigated. After carbonization steps of the polymers up to 800 °C, all carbon samples exhibited similar specific volumes of micropores (0.7-0.8 cm³ g-1), while samples obtained from mixtures with R/C ratios lower than 2000 led to carbon xerogels with significantly higher mesopore diameters up to 6 nm. The best results, in terms of specific surface (1000 m² g-1), average pore size (6 nm) and reversible capacity in AIB cell (28 mAh g-1 @ 0.1 A g-1), were obtained with a carbon xerogel sample synthetized at a resorcinol to catalyst ratio of R/C = 500 (CXG500). Though cyclic voltammograms of carbon xerogel samples did not exhibit any sharp peaks in the applied potential window, the presence of both oxidation and a quite wide reduction peak in CXG500-2000 cyclic voltammograms indicated pseudocapacitance behaviour induced by diffusion-controlled intercalation/de-intercalation of AlCl4- ions into/from the carbon xerogel matrix. This was confirmed by shifting of the (002) peak towards lower 2θ angle values in the XRD pattern of the CXG500 electrode after the charging step in AIB, whereas the contribution of pseudocapacitance, calculated from half-cell measurements, was limited to only 6% of overall capacitance.

Activity of La0.75Sr0.25Cr0.5Mn0.5O3-δ , Ni3Sn2 and Gd-doped CeO2 towards the reverse water-gas shift reaction and carburisation for a high-temperature H2O/CO2 co-electrolysis.

The syngas mixture of CO and H2, e.g. from natural gas reforming, is currently an important feedstock supplier for the synthesis of numerous chemicals. In order to minimize fossil source dependency and reduce global warming, alternative processes to produce syngas, such as high-temperature co-electrolysis of H2O and CO2 via the internal reverse water-gas shift (RWGS) reaction, may be meaningful. In this study, the influence of the H2 : CO2 ratio on the activity, selectivity and stability of the as-prepared La0.75Sr0.25Cr0.5Mn0.5O3-δ (LSCrM) and Ni3Sn2 as well as commercial Ni and Gd-doped CeO2 (GDC20) powder materials for the reverse RWGS reaction was investigated in a tubular quartz glass reactor at 700 °C and 800 °C and ambient pressure. The highest conversion factor close to the maximum value of 50% for CO was yielded for the LSCrM, Ni and GDC20 samples by applying a 0.5 : 0.5 H2 : CO2 feed ratio at 800 °C. Similar activity was calculated for the Ni3Sn2 alloy after normalization to the Ni mass content. Moreover, all the investigated catalysts exhibited higher selectivity for CO and H2O products than Ni, with which CH4 molar concentrations up to 0.9% and 2.4% were collected at 800 °C and 700 °C, respectively. The influence of feed pressure on the carburisation process was inspected in a tubular Ni-Cr reactor. Under a carbon-rich gas mixture at 3 bar and 700 °C, large amounts of graphitic carbon were deposited solely on the Ni sample after 100 h of exposure time. After the exposure of the powder materials to 0.5 : 0.5 and 0.9 : 0.1 H2 : CO2 atmospheres for 300 h at 700 °C and 10 bar, traces of amorphous carbon were surprisingly detected only on Ni3Sn2 powder via Raman microscopy. Thus, because GDC20 ist not active for electrochemical H2 production, LSCrM or a mixture of both LSCrM and GDC20 materials appears to be the most promising candidate for Ni substitution in high-temperature H2O/CO2 co-electrolysis.

An Electrically Rechargeable Zinc/Air Cell with an Aqueous Choline Acetate Electrolyte.

Due to the feasibility of an electrically rechargeable zinc/air cell made of a zinc foil as active material, an aqueous choline acetate (ChAcO) mixture as an electrolyte and a spinel MnCo2O4 (MCO) and NiCo2O4 (NCO) as a bi-functional oxygen catalyst was investigated in this work. The 30 wt.% water-containing aqueous ChAcO solution showed high contact angles close to those of KOH favoring triple-phase boundary formation in the gas diffusion electrode. Conductivity and pH value of 30 wt.% H2O/ChAcO amounted to 5.9 mS cm-1 and 10.8, respectively. Best results in terms of reversible capacity and longevity of zinc/air cell were yielded during 100 h charge/discharge with the MnCo2O4 (MCO) air electrode polarization procedure at 100 µA cm-2 (2.8 mA g-1zinc). The corresponding reversible capacity amounted to 25.4 mAh (28% depth of discharge (DOD)) and the energy efficiency ranged from 29-54% during the first and seventh cycle within a 1500 h polarization period. Maximum active material utilization of zinc foil at 100 µA cm-2 was determined to 38.1 mAh (42% DOD) whereas a further charging step was not possible due to irreversible passivation of the zinc foil surface. A special side-by-side optical cell was used to identify reaction products of the zinc/air system during a single discharge step in aqueous ChAcO that were identified as Zn(OH)2 and ZnO by Raman analysis while no carbonate was detected.

Fast Microwave-Assisted Hydrothermal Synthesis of Pure Layered δ-MnO2 for Multivalent Ion Intercalation.

This work reports on the synthesis of layered manganese oxides (δ-MnO2) and their possible application as cathode intercalation materials in Al-ion and Zn-ion batteries. By using a one-pot microwave-assisted synthesis route in 1.6 M KOH (MnVII:MnII = 0.33), a pure layered δ-MnO2 birnessite phase without any hausmannite traces was obtained after only a 14 h reaction time period at 110 °C. Attempts to enhance crystallinity level of as-prepared birnessite through increasing of reaction time up to 96 h in 1.6 M KOH failed and led to decreases in crystallinity and the emergence of an additional hausmannite phase. The influence of MnII:OH- ratio (1:2 to 1:10) on phase crystallinity and hausmannite phase formation for 96 h reaction time was investigated as well. By increasing alkalinity of the reaction mixture up to 2.5 M KOH, a slight increase in crystallinity of birnessite phase was achieved, but hausmannite formation couldn't be inhibited as hoped. The as-prepared layered δ-MnO2 powder material was spray-coated on a carbon paper and tested in laboratory cells with Al or Zn as active materials. The Al-ion tests were carried out in EMIMCl/AlCl3 while the Zn-Ion experiments were performed in water containing choline acetate (ChAcO) or a ZnSO4 solution. Best performance in terms of capacity was yielded in the Zn-ion cell (200 mWh g-1 for 20 cycles) compared to about 3 mAh g-1 for the Al-ion cell. The poor activity of the latter system was attributed to low dissociation rate of tetrachloroaluminate ions (AlCl4-) in the EMIMCl/AlCl3 mixture into positive Al complexes which are needed for charge compensation of the oxide-based cathode during the discharge step.

Environmental Screening of Electrode Materials for a Rechargeable Aluminum Battery with an AlCl3/EMIMCl Electrolyte.

Recently, rechargeable aluminum batteries have received much attention due to their low cost, easy operation, and high safety. As the research into rechargeable aluminum batteries with a room-temperature ionic liquid electrolyte is relatively new, research efforts have focused on finding suitable electrode materials. An understanding of the environmental aspects of electrode materials is essential to make informed and conscious decisions in aluminum battery development. The purpose of this study was to evaluate and compare the relative environmental performance of electrode material candidates for rechargeable aluminum batteries with an AlCl3/EMIMCl (1-ethyl-3-methylimidazolium chloride) room-temperature ionic liquid electrolyte. To this end, we used a lifecycle environmental screening framework to evaluate 12 candidate electrode materials. We found that all of the studied materials are associated with one or more drawbacks and therefore do not represent a "silver bullet" for the aluminum battery. Even so, some materials appeared more promising than others did. We also found that aluminum battery technology is likely to face some of the same environmental challenges as Li-ion technology but also offers an opportunity to avoid others. The insights provided here can aid aluminum battery development in an environmentally sustainable direction.

An Overview and Future Perspectives of Aluminum Batteries.

A critical overview of the latest developments in the aluminum battery technologies is reported. The substitution of lithium with alternative metal anodes characterized by lower cost and higher abundance is nowadays one of the most widely explored paths to reduce the cost of electrochemical storage systems and enable long-term sustainability. Aluminum based secondary batteries could be a viable alternative to the present Li-ion technology because of their high volumetric capacity (8040 mAh cm(-3) for Al vs 2046 mAh cm(-3) for Li). Additionally, the low cost aluminum makes these batteries appealing for large-scale electrical energy storage. Here, we describe the evolution of the various aluminum systems, starting from those based on aqueous electrolytes to, in more details, those based on non-aqueous electrolytes. Particular attention has been dedicated to the latest development of electrolytic media characterized by low reactivity towards other cell components. The attention is then focused on electrode materials enabling the reversible aluminum intercalation-deintercalation process. Finally, we touch on the topic of high-capacity aluminum-sulfur batteries, attempting to forecast their chances to reach the status of practical energy storage systems.